Replace JSR305 null-safe annotations by SpotBugs annotations

Reason is that JSR305 annotations cannot be used in a modular environment due to split package issues.

acme4j-client/src/main/java/org/shredzone/acme4j/Account.java

@@ -26,9 +26,7 @@ import java.util.List;
 import java.util.Objects;
 import java.util.Optional;
 
-import javax.annotation.CheckForNull;
+import edu.umd.cs.findbugs.annotations.Nullable;
-import javax.annotation.ParametersAreNonnullByDefault;
-
 import org.shredzone.acme4j.connector.Connection;
 import org.shredzone.acme4j.connector.Resource;
 import org.shredzone.acme4j.connector.ResourceIterator;
@@ -46,7 +44,6 @@ import org.slf4j.LoggerFactory;
 /**
  * Represents an account at the ACME server.
  */
-@ParametersAreNonnullByDefault
 public class Account extends AcmeJsonResource {
     private static final long serialVersionUID = 7042863483428051319L;
     private static final Logger LOG = LoggerFactory.getLogger(Account.class);
@@ -67,7 +64,7 @@ public class Account extends AcmeJsonResource {
      * @return {@code true} if the user agreed to the terms of service. May be
      *         {@code null} if the server did not provide such an information.
      */
-    @CheckForNull
+    @Nullable
     public Boolean getTermsOfServiceAgreed() {
         return getJSON().get(KEY_TOS_AGREED).map(Value::asBoolean).orElse(null);
     }
@@ -108,7 +105,7 @@ public class Account extends AcmeJsonResource {
      *
      * @since 2.8
      */
-    @CheckForNull
+    @Nullable
     public String getKeyIdentifier() {
         return getJSON().get(KEY_EXTERNAL_ACCOUNT_BINDING)
                 .optional().map(Value::asObject)
@@ -277,7 +274,6 @@ public class Account extends AcmeJsonResource {
     /**
      * Editable {@link Account}.
      */
-    @ParametersAreNonnullByDefault
     public class EditableAccount {
         private final List<URI> editContacts = new ArrayList<>();
 

acme4j-client/src/main/java/org/shredzone/acme4j/AccountBuilder.java

@@ -21,10 +21,10 @@ import java.security.KeyPair;
 import java.util.ArrayList;
 import java.util.List;
 
-import javax.annotation.ParametersAreNonnullByDefault;
 import javax.crypto.SecretKey;
 import javax.crypto.spec.SecretKeySpec;
 
+import edu.umd.cs.findbugs.annotations.Nullable;
 import org.shredzone.acme4j.connector.Connection;
 import org.shredzone.acme4j.connector.Resource;
 import org.shredzone.acme4j.exception.AcmeException;
@@ -38,16 +38,15 @@ import org.slf4j.LoggerFactory;
 /**
  * A builder for registering a new account.
  */
-@ParametersAreNonnullByDefault
 public class AccountBuilder {
     private static final Logger LOG = LoggerFactory.getLogger(AccountBuilder.class);
 
-    private List<URI> contacts = new ArrayList<>();
+    private final List<URI> contacts = new ArrayList<>();
-    private Boolean termsOfServiceAgreed;
+    private @Nullable Boolean termsOfServiceAgreed;
-    private Boolean onlyExisting;
+    private @Nullable Boolean onlyExisting;
-    private String keyIdentifier;
+    private @Nullable String keyIdentifier;
-    private KeyPair keyPair;
+    private @Nullable KeyPair keyPair;
-    private SecretKey macKey;
+    private @Nullable SecretKey macKey;
 
     /**
      * Add a contact URI to the list of contacts.

acme4j-client/src/main/java/org/shredzone/acme4j/AcmeJsonResource.java

@@ -16,8 +16,7 @@ package org.shredzone.acme4j;
 import java.net.URL;
 import java.util.Objects;
 
-import javax.annotation.ParametersAreNonnullByDefault;
+import edu.umd.cs.findbugs.annotations.Nullable;
-
 import org.shredzone.acme4j.connector.Connection;
 import org.shredzone.acme4j.exception.AcmeException;
 import org.shredzone.acme4j.exception.AcmeLazyLoadingException;
@@ -29,12 +28,11 @@ import org.slf4j.LoggerFactory;
 /**
  * An ACME resource that stores its state in a JSON structure.
  */
-@ParametersAreNonnullByDefault
 public abstract class AcmeJsonResource extends AcmeResource {
     private static final long serialVersionUID = -5060364275766082345L;
     private static final Logger LOG = LoggerFactory.getLogger(AcmeJsonResource.class);
 
-    private JSON data = null;
+    private @Nullable JSON data = null;
 
     /**
      * Create a new {@link AcmeJsonResource}.

acme4j-client/src/main/java/org/shredzone/acme4j/AcmeResource.java

@@ -17,16 +17,15 @@ import java.io.Serializable;
 import java.net.URL;
 import java.util.Objects;
 
-import javax.annotation.ParametersAreNonnullByDefault;
+import edu.umd.cs.findbugs.annotations.Nullable;
 
 /**
  * A generic ACME resource.
  */
-@ParametersAreNonnullByDefault
 public abstract class AcmeResource implements Serializable {
     private static final long serialVersionUID = -7930580802257379731L;
 
-    private transient Login login;
+    private transient @Nullable Login login;
     private final URL location;
 
     /**

acme4j-client/src/main/java/org/shredzone/acme4j/Authorization.java

@@ -20,9 +20,7 @@ import java.time.Instant;
 import java.util.Collections;
 import java.util.List;
 
-import javax.annotation.CheckForNull;
+import edu.umd.cs.findbugs.annotations.Nullable;
-import javax.annotation.ParametersAreNonnullByDefault;
-
 import org.shredzone.acme4j.challenge.Challenge;
 import org.shredzone.acme4j.connector.Connection;
 import org.shredzone.acme4j.exception.AcmeException;
@@ -36,7 +34,6 @@ import org.slf4j.LoggerFactory;
 /**
  * Represents an authorization request at the ACME server.
  */
-@ParametersAreNonnullByDefault
 public class Authorization extends AcmeJsonResource {
     private static final long serialVersionUID = -3116928998379417741L;
     private static final Logger LOG = LoggerFactory.getLogger(Authorization.class);
@@ -72,7 +69,7 @@ public class Authorization extends AcmeJsonResource {
     /**
      * Gets the expiry date of the authorization, if set by the server.
      */
-    @CheckForNull
+    @Nullable
     public Instant getExpires() {
         return getJSON().get("expires")
                     .map(Value::asString)
@@ -118,7 +115,7 @@ public class Authorization extends AcmeJsonResource {
      * @throws ClassCastException
      *             if the type does not match the expected Challenge class type
      */
-    @CheckForNull
+    @Nullable
     public <T extends Challenge> T findChallenge(final String type) {
         return (T) getChallenges().stream()
                 .filter(ch -> type.equals(ch.getType()))
@@ -136,7 +133,7 @@ public class Authorization extends AcmeJsonResource {
      * challenge, or if the challenge alone is not sufficient for authorization.
      * @since 2.8
      */
-    @CheckForNull
+    @Nullable
     public <T extends Challenge> T findChallenge(Class<T> type) {
         return getChallenges().stream()
                 .filter(type::isInstance)

acme4j-client/src/main/java/org/shredzone/acme4j/Certificate.java

@@ -25,10 +25,7 @@ import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 
-import javax.annotation.Nullable;
+import edu.umd.cs.findbugs.annotations.Nullable;
-import javax.annotation.ParametersAreNonnullByDefault;
-import javax.annotation.WillNotClose;
-
 import org.shredzone.acme4j.connector.Connection;
 import org.shredzone.acme4j.connector.Resource;
 import org.shredzone.acme4j.exception.AcmeException;
@@ -45,13 +42,12 @@ import org.slf4j.LoggerFactory;
  * Note that a certificate is immutable once it is issued. For renewal, a new certificate
  * must be ordered.
  */
-@ParametersAreNonnullByDefault
 public class Certificate extends AcmeResource {
     private static final long serialVersionUID = 7381527770159084201L;
     private static final Logger LOG = LoggerFactory.getLogger(Certificate.class);
 
-    private ArrayList<X509Certificate> certChain;
+    private @Nullable ArrayList<X509Certificate> certChain;
-    private ArrayList<URL> alternates;
+    private @Nullable ArrayList<URL> alternates;
 
     protected Certificate(Login login, URL certUrl) {
         super(login, certUrl);
@@ -121,7 +117,7 @@ public class Certificate extends AcmeResource {
      * @param out
      *            {@link Writer} to write to. The writer is not closed after use.
      */
-    public void writeCertificate(@WillNotClose Writer out) throws IOException {
+    public void writeCertificate(Writer out) throws IOException {
         try {
             for (X509Certificate cert : getCertificateChain()) {
                 AcmeUtils.writeToPem(cert.getEncoded(), AcmeUtils.PemLabel.CERTIFICATE, out);

acme4j-client/src/main/java/org/shredzone/acme4j/Identifier.java

@@ -21,9 +21,6 @@ import java.net.InetAddress;
 import java.net.UnknownHostException;
 import java.util.Map;
 
-import javax.annotation.ParametersAreNonnullByDefault;
-import javax.annotation.concurrent.Immutable;
-
 import org.shredzone.acme4j.exception.AcmeProtocolException;
 import org.shredzone.acme4j.toolbox.JSON;
 import org.shredzone.acme4j.toolbox.JSONBuilder;
@@ -38,8 +35,6 @@ import org.shredzone.acme4j.toolbox.JSONBuilder;
  *
  * @since 2.3
  */
-@ParametersAreNonnullByDefault
-@Immutable
 public class Identifier implements Serializable {
     private static final long serialVersionUID = -7777851842076362412L;
 

acme4j-client/src/main/java/org/shredzone/acme4j/Login.java

@@ -19,9 +19,6 @@ import java.net.URL;
 import java.security.KeyPair;
 import java.util.Objects;
 
-import javax.annotation.ParametersAreNonnullByDefault;
-import javax.annotation.concurrent.ThreadSafe;
-
 import org.shredzone.acme4j.challenge.Challenge;
 import org.shredzone.acme4j.connector.Connection;
 import org.shredzone.acme4j.exception.AcmeException;
@@ -37,8 +34,6 @@ import org.shredzone.acme4j.toolbox.JSON;
  * Note that {@link Login} objects are not serializable, as they contain a keypair and
  * volatile data.
  */
-@ParametersAreNonnullByDefault
-@ThreadSafe
 public class Login {
 
     private final Session session;

acme4j-client/src/main/java/org/shredzone/acme4j/Metadata.java

@@ -21,18 +21,13 @@ import java.time.Duration;
 import java.util.Collection;
 import java.util.Optional;
 
-import javax.annotation.CheckForNull;
+import edu.umd.cs.findbugs.annotations.Nullable;
-import javax.annotation.ParametersAreNonnullByDefault;
-import javax.annotation.concurrent.Immutable;
-
 import org.shredzone.acme4j.toolbox.JSON;
 import org.shredzone.acme4j.toolbox.JSON.Value;
 
 /**
  * Contains metadata related to the provider.
  */
-@ParametersAreNonnullByDefault
-@Immutable
 public class Metadata {
 
     private final JSON meta;
@@ -51,7 +46,7 @@ public class Metadata {
      * Returns an {@link URI} to the current terms of service, or {@code null} if not
      * available.
      */
-    @CheckForNull
+    @Nullable
     public URI getTermsOfService() {
         return meta.get("termsOfService").map(Value::asURI).orElse(null);
     }
@@ -60,7 +55,7 @@ public class Metadata {
      * Returns an {@link URL} to a website providing more information about the ACME
      * server. {@code null} if not available.
      */
-    @CheckForNull
+    @Nullable
     public URL getWebsite() {
         return meta.get("website").map(Value::asURL).orElse(null);
     }
@@ -100,6 +95,7 @@ public class Metadata {
      *
      * @since 2.3
      */
+    @Nullable
     public Duration getAutoRenewalMinLifetime() {
         Optional<JSON> ar = meta.get("auto-renewal").optional().map(Value::asObject);
         if (!ar.isPresent()) {
@@ -114,6 +110,7 @@ public class Metadata {
      *
      * @since 2.3
      */
+    @Nullable
     public Duration getAutoRenewalMaxDuration() {
         Optional<JSON> ar = meta.get("auto-renewal").optional().map(Value::asObject);
         if (!ar.isPresent()) {

acme4j-client/src/main/java/org/shredzone/acme4j/Order.java

@@ -21,9 +21,7 @@ import java.time.Instant;
 import java.util.Collections;
 import java.util.List;
 
-import javax.annotation.CheckForNull;
+import edu.umd.cs.findbugs.annotations.Nullable;
-import javax.annotation.ParametersAreNonnullByDefault;
-
 import org.shredzone.acme4j.connector.Connection;
 import org.shredzone.acme4j.exception.AcmeException;
 import org.shredzone.acme4j.toolbox.JSON;
@@ -35,7 +33,6 @@ import org.slf4j.LoggerFactory;
 /**
  * Represents a certificate order.
  */
-@ParametersAreNonnullByDefault
 public class Order extends AcmeJsonResource {
     private static final long serialVersionUID = 5435808648658292177L;
     private static final Logger LOG = LoggerFactory.getLogger(Order.class);
@@ -57,7 +54,7 @@ public class Order extends AcmeJsonResource {
     /**
      * Returns a {@link Problem} document if the order failed.
      */
-    @CheckForNull
+    @Nullable
     public Problem getError() {
         return getJSON().get("error").map(v -> v.asProblem(getLocation())).orElse(null);
     }
@@ -65,7 +62,7 @@ public class Order extends AcmeJsonResource {
     /**
      * Gets the expiry date of the authorization, if set by the server.
      */
-    @CheckForNull
+    @Nullable
     public Instant getExpires() {
         return getJSON().get("expires").map(Value::asInstant).orElse(null);
     }
@@ -86,7 +83,7 @@ public class Order extends AcmeJsonResource {
     /**
      * Gets the "not before" date that was used for the order, or {@code null}.
      */
-    @CheckForNull
+    @Nullable
     public Instant getNotBefore() {
         return getJSON().get("notBefore").map(Value::asInstant).orElse(null);
     }
@@ -94,7 +91,7 @@ public class Order extends AcmeJsonResource {
     /**
      * Gets the "not after" date that was used for the order, or {@code null}.
      */
-    @CheckForNull
+    @Nullable
     public Instant getNotAfter() {
         return getJSON().get("notAfter").map(Value::asInstant).orElse(null);
     }
@@ -124,7 +121,7 @@ public class Order extends AcmeJsonResource {
     /**
      * Gets the {@link Certificate} if it is available. {@code null} otherwise.
      */
-    @CheckForNull
+    @Nullable
     public Certificate getCertificate() {
         return getJSON().get("certificate")
                     .map(Value::asURL)
@@ -138,7 +135,7 @@ public class Order extends AcmeJsonResource {
      *
      * @since 2.6
      */
-    @CheckForNull
+    @Nullable
     public Certificate getAutoRenewalCertificate() {
         return getJSON().get("star-certificate")
                     .map(Value::asURL)
@@ -188,7 +185,7 @@ public class Order extends AcmeJsonResource {
      *
      * @since 2.3
      */
-    @CheckForNull
+    @Nullable
     public Instant getAutoRenewalStartDate() {
         return getJSON().get("auto-renewal")
                     .optional()
@@ -206,7 +203,7 @@ public class Order extends AcmeJsonResource {
      *
      * @since 2.3
      */
-    @CheckForNull
+    @Nullable
     public Instant getAutoRenewalEndDate() {
         return getJSON().get("auto-renewal")
                     .optional()
@@ -223,7 +220,7 @@ public class Order extends AcmeJsonResource {
      *
      * @since 2.3
      */
-    @CheckForNull
+    @Nullable
     public Duration getAutoRenewalLifetime() {
         return getJSON().get("auto-renewal")
                     .optional()
@@ -240,7 +237,7 @@ public class Order extends AcmeJsonResource {
      *
      * @since 2.7
      */
-    @CheckForNull
+    @Nullable
     public Duration getAutoRenewalLifetimeAdjust() {
         return getJSON().get("auto-renewal")
                     .optional()

acme4j-client/src/main/java/org/shredzone/acme4j/OrderBuilder.java

@@ -23,8 +23,7 @@ import java.util.Collection;
 import java.util.LinkedHashSet;
 import java.util.Set;
 
-import javax.annotation.ParametersAreNonnullByDefault;
+import edu.umd.cs.findbugs.annotations.Nullable;
-
 import org.shredzone.acme4j.connector.Connection;
 import org.shredzone.acme4j.connector.Resource;
 import org.shredzone.acme4j.exception.AcmeException;
@@ -36,20 +35,19 @@ import org.slf4j.LoggerFactory;
 /**
  * A builder for a new {@link Order} object.
  */
-@ParametersAreNonnullByDefault
 public class OrderBuilder {
     private static final Logger LOG = LoggerFactory.getLogger(OrderBuilder.class);
 
     private final Login login;
 
     private final Set<Identifier> identifierSet = new LinkedHashSet<>();
-    private Instant notBefore;
+    private @Nullable Instant notBefore;
-    private Instant notAfter;
+    private @Nullable Instant notAfter;
     private boolean autoRenewal;
-    private Instant autoRenewalStart;
+    private @Nullable Instant autoRenewalStart;
-    private Instant autoRenewalEnd;
+    private @Nullable Instant autoRenewalEnd;
-    private Duration autoRenewalLifetime;
+    private @Nullable Duration autoRenewalLifetime;
-    private Duration autoRenewalLifetimeAdjust;
+    private @Nullable Duration autoRenewalLifetimeAdjust;
     private boolean autoRenewalGet;
 
     /**

acme4j-client/src/main/java/org/shredzone/acme4j/Problem.java

@@ -22,10 +22,7 @@ import java.net.URISyntaxException;
 import java.net.URL;
 import java.util.List;
 
-import javax.annotation.CheckForNull;
+import edu.umd.cs.findbugs.annotations.Nullable;
-import javax.annotation.ParametersAreNonnullByDefault;
-import javax.annotation.concurrent.Immutable;
-
 import org.shredzone.acme4j.exception.AcmeProtocolException;
 import org.shredzone.acme4j.toolbox.JSON;
 import org.shredzone.acme4j.toolbox.JSON.Value;
@@ -35,8 +32,6 @@ import org.shredzone.acme4j.toolbox.JSON.Value;
  *
  * @see <a href="https://tools.ietf.org/html/rfc7807">RFC 7807</a>
  */
-@ParametersAreNonnullByDefault
-@Immutable
 public class Problem implements Serializable {
     private static final long serialVersionUID = -8418248862966754214L;
 
@@ -78,7 +73,7 @@ public class Problem implements Serializable {
      *
      * @see #toString()
      */
-    @CheckForNull
+    @Nullable
     public String getTitle() {
         return problemJson.get("title").map(Value::asString).orElse(null);
     }
@@ -89,7 +84,7 @@ public class Problem implements Serializable {
      *
      * @see #toString()
      */
-    @CheckForNull
+    @Nullable
     public String getDetail() {
         return problemJson.get("detail").map(Value::asString).orElse(null);
     }
@@ -98,7 +93,7 @@ public class Problem implements Serializable {
      * Returns an URI that identifies the specific occurence of the problem. It is always
      * an absolute URI.
      */
-    @CheckForNull
+    @Nullable
     public URI getInstance() {
         return problemJson.get("instance")
                         .map(Value::asString)
@@ -117,7 +112,7 @@ public class Problem implements Serializable {
      *
      * @since 2.3
      */
-    @CheckForNull
+    @Nullable
     public Identifier getIdentifier() {
         return problemJson.get("identifier")
                         .optional()

acme4j-client/src/main/java/org/shredzone/acme4j/RevocationReason.java

@@ -15,9 +15,7 @@ package org.shredzone.acme4j;
 
 import java.util.Arrays;
 
-import javax.annotation.CheckForNull;
+import edu.umd.cs.findbugs.annotations.Nullable;
-import javax.annotation.ParametersAreNonnullByDefault;
-import javax.annotation.concurrent.Immutable;
 
 /**
  * Enumeration of revocation reasons.
@@ -25,8 +23,6 @@ import javax.annotation.concurrent.Immutable;
  * @see <a href="https://tools.ietf.org/html/rfc5280#section-5.3.1">RFC 5280 Section
  *      5.3.1</a>
  */
-@ParametersAreNonnullByDefault
-@Immutable
 public enum RevocationReason {
 
     UNSPECIFIED(0),
@@ -60,7 +56,7 @@ public enum RevocationReason {
      *            Reason code as defined in RFC 5280
      * @return Matching {@link RevocationReason}, or {@code null} if not known
      */
-    @CheckForNull
+    @Nullable
     public static RevocationReason code(int reasonCode) {
         return Arrays.stream(values())
                 .filter(rr -> rr.reasonCode == reasonCode)

acme4j-client/src/main/java/org/shredzone/acme4j/Session.java

@@ -26,11 +26,7 @@ import java.util.ServiceLoader;
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.stream.StreamSupport;
 
-import javax.annotation.CheckForNull;
+import edu.umd.cs.findbugs.annotations.Nullable;
-import javax.annotation.Nullable;
-import javax.annotation.ParametersAreNonnullByDefault;
-import javax.annotation.concurrent.ThreadSafe;
-
 import org.shredzone.acme4j.connector.Connection;
 import org.shredzone.acme4j.connector.NetworkSettings;
 import org.shredzone.acme4j.connector.Resource;
@@ -43,8 +39,6 @@ import org.shredzone.acme4j.toolbox.JSON.Value;
 /**
  * A session stores the ACME server URI. It also tracks communication parameters.
  */
-@ParametersAreNonnullByDefault
-@ThreadSafe
 public class Session {
 
     private static final GenericAcmeProvider GENERIC_PROVIDER = new GenericAcmeProvider();
@@ -55,10 +49,10 @@ public class Session {
     private final URI serverUri;
     private final AcmeProvider provider;
 
-    private String nonce;
+    private @Nullable String nonce;
     private Locale locale = Locale.getDefault();
-    protected ZonedDateTime directoryLastModified;
+    protected @Nullable ZonedDateTime directoryLastModified;
-    protected ZonedDateTime directoryExpires;
+    protected @Nullable ZonedDateTime directoryExpires;
 
     /**
      * Creates a new {@link Session}.
@@ -143,7 +137,7 @@ public class Session {
     /**
      * Gets the last base64 encoded nonce, or {@code null} if the session is new.
      */
-    @CheckForNull
+    @Nullable
     public String getNonce() {
         return nonce;
     }
@@ -256,7 +250,7 @@ public class Session {
      * (directory has not been read yet or did not provide this information).
      * @since 2.10
      */
-    @CheckForNull
+    @Nullable
     public ZonedDateTime getDirectoryLastModified() {
         return directoryLastModified;
     }
@@ -282,7 +276,7 @@ public class Session {
      * information.
      * @since 2.10
      */
-    @CheckForNull
+    @Nullable
     public ZonedDateTime getDirectoryExpires() {
         return directoryExpires;
     }

acme4j-client/src/main/java/org/shredzone/acme4j/Status.java

@@ -15,14 +15,9 @@ package org.shredzone.acme4j;
 
 import java.util.Arrays;
 
-import javax.annotation.ParametersAreNonnullByDefault;
-import javax.annotation.concurrent.Immutable;
-
 /**
  * Status codes of challenges and authorizations.
  */
-@ParametersAreNonnullByDefault
-@Immutable
 public enum Status {
 
     /**

acme4j-client/src/main/java/org/shredzone/acme4j/challenge/Challenge.java

@@ -15,9 +15,7 @@ package org.shredzone.acme4j.challenge;
 
 import java.time.Instant;
 
-import javax.annotation.CheckForNull;
+import edu.umd.cs.findbugs.annotations.Nullable;
-import javax.annotation.ParametersAreNonnullByDefault;
-
 import org.shredzone.acme4j.AcmeJsonResource;
 import org.shredzone.acme4j.Login;
 import org.shredzone.acme4j.Problem;
@@ -40,7 +38,6 @@ import org.slf4j.LoggerFactory;
  * own type. {@link Challenge#prepareResponse(JSONBuilder)} should be overridden to put
  * all required data to the response.
  */
-@ParametersAreNonnullByDefault
 public class Challenge extends AcmeJsonResource {
     private static final long serialVersionUID = 2338794776848388099L;
     private static final Logger LOG = LoggerFactory.getLogger(Challenge.class);
@@ -84,7 +81,7 @@ public class Challenge extends AcmeJsonResource {
     /**
      * Returns the validation date, if returned by the server.
      */
-    @CheckForNull
+    @Nullable
     public Instant getValidated() {
         return getJSON().get(KEY_VALIDATED).map(Value::asInstant).orElse(null);
     }
@@ -94,7 +91,7 @@ public class Challenge extends AcmeJsonResource {
      * server. If there are multiple errors, they can be found in
      * {@link Problem#getSubProblems()}.
      */
-    @CheckForNull
+    @Nullable
     public Problem getError() {
         return getJSON().get(KEY_ERROR)
                     .map(it -> it.asProblem(getLocation()))

acme4j-client/src/main/java/org/shredzone/acme4j/challenge/Dns01Challenge.java

@@ -16,15 +16,12 @@ package org.shredzone.acme4j.challenge;
 import static org.shredzone.acme4j.toolbox.AcmeUtils.base64UrlEncode;
 import static org.shredzone.acme4j.toolbox.AcmeUtils.sha256hash;
 
-import javax.annotation.ParametersAreNonnullByDefault;
-
 import org.shredzone.acme4j.Login;
 import org.shredzone.acme4j.toolbox.JSON;
 
 /**
  * Implements the {@value TYPE} challenge.
  */
-@ParametersAreNonnullByDefault
 public class Dns01Challenge extends TokenChallenge {
     private static final long serialVersionUID = 6964687027713533075L;
 

acme4j-client/src/main/java/org/shredzone/acme4j/challenge/Http01Challenge.java

@@ -13,15 +13,12 @@
  */
 package org.shredzone.acme4j.challenge;
 
-import javax.annotation.ParametersAreNonnullByDefault;
-
 import org.shredzone.acme4j.Login;
 import org.shredzone.acme4j.toolbox.JSON;
 
 /**
  * Implements the {@value TYPE} challenge.
  */
-@ParametersAreNonnullByDefault
 public class Http01Challenge extends TokenChallenge {
     private static final long serialVersionUID = 3322211185872544605L;
 

acme4j-client/src/main/java/org/shredzone/acme4j/challenge/TlsAlpn01Challenge.java

@@ -15,8 +15,6 @@ package org.shredzone.acme4j.challenge;
 
 import static org.shredzone.acme4j.toolbox.AcmeUtils.sha256hash;
 
-import javax.annotation.ParametersAreNonnullByDefault;
-
 import org.shredzone.acme4j.Login;
 import org.shredzone.acme4j.toolbox.JSON;
 
@@ -25,7 +23,6 @@ import org.shredzone.acme4j.toolbox.JSON;
  *
  * @since 2.1
  */
-@ParametersAreNonnullByDefault
 public class TlsAlpn01Challenge extends TokenChallenge {
     private static final long serialVersionUID = -5590351078176091228L;
 

acme4j-client/src/main/java/org/shredzone/acme4j/challenge/TokenChallenge.java

@@ -17,8 +17,6 @@ import static org.shredzone.acme4j.toolbox.AcmeUtils.base64UrlEncode;
 
 import java.security.PublicKey;
 
-import javax.annotation.ParametersAreNonnullByDefault;
-
 import org.shredzone.acme4j.Login;
 import org.shredzone.acme4j.exception.AcmeProtocolException;
 import org.shredzone.acme4j.toolbox.AcmeUtils;
@@ -29,7 +27,6 @@ import org.shredzone.acme4j.toolbox.JoseUtils;
  * An extension of {@link Challenge} that handles challenges with a {@code token} and
  * {@code keyAuthorization}.
  */
-@ParametersAreNonnullByDefault
 public class TokenChallenge extends Challenge {
     private static final long serialVersionUID = 1634133407432681800L;
 

acme4j-client/src/main/java/org/shredzone/acme4j/challenge/package-info.java

@@ -0,0 +1,23 @@
+/*
+ * acme4j - Java ACME client
+ *
+ * Copyright (C) 2020 Richard "Shred" Körber
+ *   http://acme4j.shredzone.org
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ */
+
+@ReturnValuesAreNonnullByDefault
+@DefaultAnnotationForParameters(NonNull.class)
+@DefaultAnnotationForFields(NonNull.class)
+package org.shredzone.acme4j.challenge;
+
+import edu.umd.cs.findbugs.annotations.DefaultAnnotationForFields;
+import edu.umd.cs.findbugs.annotations.DefaultAnnotationForParameters;
+import edu.umd.cs.findbugs.annotations.NonNull;
+import edu.umd.cs.findbugs.annotations.ReturnValuesAreNonnullByDefault;

acme4j-client/src/main/java/org/shredzone/acme4j/connector/Connection.java

@@ -22,10 +22,7 @@ import java.util.Collection;
 import java.util.List;
 import java.util.Optional;
 
-import javax.annotation.CheckForNull;
+import edu.umd.cs.findbugs.annotations.Nullable;
-import javax.annotation.Nullable;
-import javax.annotation.ParametersAreNonnullByDefault;
-
 import org.shredzone.acme4j.Login;
 import org.shredzone.acme4j.Session;
 import org.shredzone.acme4j.exception.AcmeException;
@@ -37,7 +34,6 @@ import org.shredzone.acme4j.toolbox.JSONBuilder;
 /**
  * Connects to the ACME server and offers different methods for invoking the API.
  */
-@ParametersAreNonnullByDefault
 public interface Connection extends AutoCloseable {
 
     /**
@@ -166,7 +162,7 @@ public interface Connection extends AutoCloseable {
      *
      * @return Base64 encoded nonce, or {@code null} if no nonce header was set
      */
-    @CheckForNull
+    @Nullable
     String getNonce();
 
     /**
@@ -176,7 +172,7 @@ public interface Connection extends AutoCloseable {
      *
      * @return Location {@link URL}, or {@code null} if no Location header was set
      */
-    @CheckForNull
+    @Nullable
     URL getLocation();
 
     /**

acme4j-client/src/main/java/org/shredzone/acme4j/connector/DefaultConnection.java

@@ -41,10 +41,7 @@ import java.util.Optional;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
-import javax.annotation.CheckForNull;
+import edu.umd.cs.findbugs.annotations.Nullable;
-import javax.annotation.Nullable;
-import javax.annotation.ParametersAreNonnullByDefault;
-
 import org.shredzone.acme4j.Login;
 import org.shredzone.acme4j.Problem;
 import org.shredzone.acme4j.Session;
@@ -66,7 +63,6 @@ import org.slf4j.LoggerFactory;
 /**
  * Default implementation of {@link Connection}.
  */
-@ParametersAreNonnullByDefault
 public class DefaultConnection implements Connection {
     private static final Logger LOG = LoggerFactory.getLogger(DefaultConnection.class);
 
@@ -95,7 +91,7 @@ public class DefaultConnection implements Connection {
     private static final Pattern MAX_AGE_PATTERN = Pattern.compile("(?:^|.*?,)\\s*max-age=(\\d+)\\s*(?:,.*|$)", Pattern.CASE_INSENSITIVE);
 
     protected final HttpConnector httpConnector;
-    protected HttpURLConnection conn;
+    protected @Nullable  HttpURLConnection conn;
 
     /**
      * Creates a new {@link DefaultConnection}.
@@ -232,7 +228,7 @@ public class DefaultConnection implements Connection {
     }
 
     @Override
-    @CheckForNull
+    @Nullable
     public String getNonce() {
         assertConnectionIsOpen();
 
@@ -251,7 +247,7 @@ public class DefaultConnection implements Connection {
     }
 
     @Override
-    @CheckForNull
+    @Nullable
     public URL getLocation() {
         assertConnectionIsOpen();
 
@@ -625,7 +621,7 @@ public class DefaultConnection implements Connection {
      * @return Absolute URL of the given link, or {@code null} if the link was
      *         {@code null}.
      */
-    @CheckForNull
+    @Nullable
     private URL resolveRelative(@Nullable String link) {
         if (link == null) {
             return null;
@@ -647,7 +643,7 @@ public class DefaultConnection implements Connection {
      * @return Absolute URI of the given link, or {@code null} if the URI was
      *         {@code null}.
      */
-    @CheckForNull
+    @Nullable
     private URI resolveUri(@Nullable String uri) {
         if (uri == null) {
             return null;

acme4j-client/src/main/java/org/shredzone/acme4j/connector/HttpConnector.java

@@ -19,10 +19,6 @@ import java.net.HttpURLConnection;
 import java.net.URL;
 import java.util.Properties;
 
-import javax.annotation.OverridingMethodsMustInvokeSuper;
-import javax.annotation.ParametersAreNonnullByDefault;
-import javax.annotation.concurrent.ThreadSafe;
-
 import org.slf4j.LoggerFactory;
 
 /**
@@ -32,8 +28,6 @@ import org.slf4j.LoggerFactory;
  * Subclasses may reconfigure the {@link HttpURLConnection} and pin it to a concrete SSL
  * certificate.
  */
-@ParametersAreNonnullByDefault
-@ThreadSafe
 public class HttpConnector {
 
     private static final String USER_AGENT;
@@ -90,7 +84,6 @@ public class HttpConnector {
      * @param settings
      *         {@link NetworkSettings} with settings to be used
      */
-    @OverridingMethodsMustInvokeSuper
     protected void configure(HttpURLConnection conn, NetworkSettings settings) {
         int timeout = (int) settings.getTimeout().toMillis();
         conn.setConnectTimeout(timeout);

acme4j-client/src/main/java/org/shredzone/acme4j/connector/NetworkSettings.java

@@ -16,15 +16,13 @@ package org.shredzone.acme4j.connector;
 import java.net.Proxy;
 import java.time.Duration;
 
-import javax.annotation.Nullable;
+import edu.umd.cs.findbugs.annotations.Nullable;
-import javax.annotation.ParametersAreNonnullByDefault;
 
 /**
  * Contains network settings to be used for network connections.
  *
  * @since 2.8
  */
-@ParametersAreNonnullByDefault
 public class NetworkSettings {
 
     private Proxy proxy = Proxy.NO_PROXY;

acme4j-client/src/main/java/org/shredzone/acme4j/connector/Resource.java

@@ -13,14 +13,9 @@
  */
 package org.shredzone.acme4j.connector;
 
-import javax.annotation.ParametersAreNonnullByDefault;
-import javax.annotation.concurrent.Immutable;
-
 /**
  * Enumeration of resources.
  */
-@ParametersAreNonnullByDefault
-@Immutable
 public enum Resource {
 
     NEW_NONCE("newNonce"),

acme4j-client/src/main/java/org/shredzone/acme4j/connector/ResourceIterator.java

@@ -21,9 +21,7 @@ import java.util.NoSuchElementException;
 import java.util.Objects;
 import java.util.function.BiFunction;
 
-import javax.annotation.Nullable;
+import edu.umd.cs.findbugs.annotations.Nullable;
-import javax.annotation.ParametersAreNonnullByDefault;
-
 import org.shredzone.acme4j.AcmeResource;
 import org.shredzone.acme4j.Login;
 import org.shredzone.acme4j.Session;
@@ -38,7 +36,6 @@ import org.shredzone.acme4j.toolbox.JSON;
  * @param <T>
  *            {@link AcmeResource} type to iterate over
  */
-@ParametersAreNonnullByDefault
 public class ResourceIterator<T extends AcmeResource> implements Iterator<T> {
 
     private final Login login;
@@ -46,7 +43,7 @@ public class ResourceIterator<T extends AcmeResource> implements Iterator<T> {
     private final Deque<URL> urlList = new ArrayDeque<>();
     private final BiFunction<Login, URL, T> creator;
     private boolean eol = false;
-    private URL nextUrl;
+    private @Nullable URL nextUrl;
 
     /**
      * Creates a new {@link ResourceIterator}.

acme4j-client/src/main/java/org/shredzone/acme4j/connector/TrimmingInputStream.java

@@ -16,13 +16,10 @@ package org.shredzone.acme4j.connector;
 import java.io.IOException;
 import java.io.InputStream;
 
-import javax.annotation.ParametersAreNonnullByDefault;
-
 /**
  * Normalizes line separators in an InputStream. Converts all line separators to '\n'.
  * Multiple line separators are compressed to a single line separator.
  */
-@ParametersAreNonnullByDefault
 public class TrimmingInputStream extends InputStream {
 
     private final InputStream in;

acme4j-client/src/main/java/org/shredzone/acme4j/connector/package-info.java

@@ -0,0 +1,23 @@
+/*
+ * acme4j - Java ACME client
+ *
+ * Copyright (C) 2020 Richard "Shred" Körber
+ *   http://acme4j.shredzone.org
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ */
+
+@ReturnValuesAreNonnullByDefault
+@DefaultAnnotationForParameters(NonNull.class)
+@DefaultAnnotationForFields(NonNull.class)
+package org.shredzone.acme4j.connector;
+
+import edu.umd.cs.findbugs.annotations.DefaultAnnotationForFields;
+import edu.umd.cs.findbugs.annotations.DefaultAnnotationForParameters;
+import edu.umd.cs.findbugs.annotations.NonNull;
+import edu.umd.cs.findbugs.annotations.ReturnValuesAreNonnullByDefault;

acme4j-client/src/main/java/org/shredzone/acme4j/exception/AcmeException.java

@@ -13,14 +13,9 @@
  */
 package org.shredzone.acme4j.exception;
 
-import javax.annotation.ParametersAreNonnullByDefault;
-import javax.annotation.concurrent.Immutable;
-
 /**
  * A generic ACME exception.
  */
-@ParametersAreNonnullByDefault
-@Immutable
 public class AcmeException extends Exception {
     private static final long serialVersionUID = -2935088954705632025L;
 

acme4j-client/src/main/java/org/shredzone/acme4j/exception/AcmeLazyLoadingException.java

@@ -17,17 +17,12 @@ import static java.util.Objects.requireNonNull;
 
 import java.net.URL;
 
-import javax.annotation.ParametersAreNonnullByDefault;
-import javax.annotation.concurrent.Immutable;
-
 import org.shredzone.acme4j.AcmeResource;
 
 /**
  * This runtime exception is thrown when an {@link AcmeException} occured while trying to
  * lazy-load a resource from the ACME server.
  */
-@ParametersAreNonnullByDefault
-@Immutable
 public class AcmeLazyLoadingException extends RuntimeException {
     private static final long serialVersionUID = 1000353433913721901L;
 

acme4j-client/src/main/java/org/shredzone/acme4j/exception/AcmeNetworkException.java

@@ -15,15 +15,10 @@ package org.shredzone.acme4j.exception;
 
 import java.io.IOException;
 
-import javax.annotation.ParametersAreNonnullByDefault;
-import javax.annotation.concurrent.Immutable;
-
 /**
  * This exception is thrown when a network error occured while communicating with the
  * server.
  */
-@ParametersAreNonnullByDefault
-@Immutable
 public class AcmeNetworkException extends AcmeException {
     private static final long serialVersionUID = 2054398693543329179L;
 

acme4j-client/src/main/java/org/shredzone/acme4j/exception/AcmeProtocolException.java

@@ -13,15 +13,10 @@
  */
 package org.shredzone.acme4j.exception;
 
-import javax.annotation.ParametersAreNonnullByDefault;
-import javax.annotation.concurrent.Immutable;
-
 /**
  * This runtime exception is thrown on ACME protocol errors that should not occur. For
  * example, this exception is thrown when a server response could not be parsed.
  */
-@ParametersAreNonnullByDefault
-@Immutable
 public class AcmeProtocolException extends RuntimeException {
     private static final long serialVersionUID = 2031203835755725193L;
 

acme4j-client/src/main/java/org/shredzone/acme4j/exception/AcmeRateLimitedException.java

@@ -18,23 +18,17 @@ import java.time.Instant;
 import java.util.Collection;
 import java.util.Collections;
 
-import javax.annotation.CheckForNull;
+import edu.umd.cs.findbugs.annotations.Nullable;
-import javax.annotation.Nullable;
-import javax.annotation.ParametersAreNonnullByDefault;
-import javax.annotation.concurrent.Immutable;
-
 import org.shredzone.acme4j.Problem;
 
 /**
  * An exception that is thrown when a rate limit was exceeded.
  */
-@ParametersAreNonnullByDefault
-@Immutable
 public class AcmeRateLimitedException extends AcmeServerException {
     private static final long serialVersionUID = 4150484059796413069L;
 
-    private final Instant retryAfter;
+    private final @Nullable Instant retryAfter;
-    private final Collection<URL> documents;
+    private final @Nullable Collection<URL> documents;
 
     /**
      * Creates a new {@link AcmeRateLimitedException}.
@@ -59,7 +53,7 @@ public class AcmeRateLimitedException extends AcmeServerException {
      * Returns the moment the request is expected to succeed again. {@code null} if this
      * moment is not known.
      */
-    @CheckForNull
+    @Nullable
     public Instant getRetryAfter() {
         return retryAfter;
     }
@@ -68,7 +62,7 @@ public class AcmeRateLimitedException extends AcmeServerException {
      * Collection of URLs pointing to documents about the rate limit that was hit.
      * {@code null} if the server did not provide such URLs.
      */
-    @CheckForNull
+    @Nullable
     public Collection<URL> getDocuments() {
         return documents;
     }

acme4j-client/src/main/java/org/shredzone/acme4j/exception/AcmeRetryAfterException.java

@@ -16,15 +16,10 @@ package org.shredzone.acme4j.exception;
 import java.time.Instant;
 import java.util.Objects;
 
-import javax.annotation.ParametersAreNonnullByDefault;
-import javax.annotation.concurrent.Immutable;
-
 /**
  * This exception is thrown when a server side process has not been completed yet, and the
  * server returned an estimated retry date.
  */
-@ParametersAreNonnullByDefault
-@Immutable
 public class AcmeRetryAfterException extends AcmeException {
     private static final long serialVersionUID = 4461979121063649905L;
 

acme4j-client/src/main/java/org/shredzone/acme4j/exception/AcmeServerException.java

@@ -16,17 +16,12 @@ package org.shredzone.acme4j.exception;
 import java.net.URI;
 import java.util.Objects;
 
-import javax.annotation.ParametersAreNonnullByDefault;
-import javax.annotation.concurrent.Immutable;
-
 import org.shredzone.acme4j.Problem;
 
 /**
  * An exception that is thrown when the ACME server returned an error. It contains
  * further details of the cause.
  */
-@ParametersAreNonnullByDefault
-@Immutable
 public class AcmeServerException extends AcmeException {
     private static final long serialVersionUID = 5971622508467042792L;
 

acme4j-client/src/main/java/org/shredzone/acme4j/exception/AcmeUnauthorizedException.java

@@ -13,17 +13,12 @@
  */
 package org.shredzone.acme4j.exception;
 
-import javax.annotation.ParametersAreNonnullByDefault;
-import javax.annotation.concurrent.Immutable;
-
 import org.shredzone.acme4j.Problem;
 
 /**
  * An exception that is thrown when the client is not authorized. The details will give
  * an explanation for the reasons (e.g. "client not on a whitelist").
  */
-@ParametersAreNonnullByDefault
-@Immutable
 public class AcmeUnauthorizedException extends AcmeServerException {
     private static final long serialVersionUID = 9064697508262919366L;
 

acme4j-client/src/main/java/org/shredzone/acme4j/exception/AcmeUserActionRequiredException.java

@@ -17,11 +17,7 @@ import java.net.MalformedURLException;
 import java.net.URI;
 import java.net.URL;
 
-import javax.annotation.CheckForNull;
+import edu.umd.cs.findbugs.annotations.Nullable;
-import javax.annotation.Nullable;
-import javax.annotation.ParametersAreNonnullByDefault;
-import javax.annotation.concurrent.Immutable;
-
 import org.shredzone.acme4j.Problem;
 
 /**
@@ -30,12 +26,10 @@ import org.shredzone.acme4j.Problem;
  * Usually this exception is thrown when the terms of service have changed, and the CA
  * requires an agreement to the new terms before proceeding.
  */
-@ParametersAreNonnullByDefault
-@Immutable
 public class AcmeUserActionRequiredException extends AcmeServerException {
     private static final long serialVersionUID = 7719055447283858352L;
 
-    private final URI tosUri;
+    private final @Nullable URI tosUri;
 
     /**
      * Creates a new {@link AcmeUserActionRequiredException}.
@@ -54,7 +48,7 @@ public class AcmeUserActionRequiredException extends AcmeServerException {
      * Returns the {@link URI} of the terms-of-service document to accept, or {@code null}
      * if the server did not provide a link to such a document.
      */
-    @CheckForNull
+    @Nullable
     public URI getTermsOfServiceUri() {
         return tosUri;
     }

acme4j-client/src/main/java/org/shredzone/acme4j/exception/package-info.java

@@ -0,0 +1,23 @@
+/*
+ * acme4j - Java ACME client
+ *
+ * Copyright (C) 2020 Richard "Shred" Körber
+ *   http://acme4j.shredzone.org
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ */
+
+@ReturnValuesAreNonnullByDefault
+@DefaultAnnotationForParameters(NonNull.class)
+@DefaultAnnotationForFields(NonNull.class)
+package org.shredzone.acme4j.exception;
+
+import edu.umd.cs.findbugs.annotations.DefaultAnnotationForFields;
+import edu.umd.cs.findbugs.annotations.DefaultAnnotationForParameters;
+import edu.umd.cs.findbugs.annotations.NonNull;
+import edu.umd.cs.findbugs.annotations.ReturnValuesAreNonnullByDefault;

acme4j-client/src/main/java/org/shredzone/acme4j/package-info.java

@@ -0,0 +1,23 @@
+/*
+ * acme4j - Java ACME client
+ *
+ * Copyright (C) 2020 Richard "Shred" Körber
+ *   http://acme4j.shredzone.org
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ */
+
+@ReturnValuesAreNonnullByDefault
+@DefaultAnnotationForParameters(NonNull.class)
+@DefaultAnnotationForFields(NonNull.class)
+package org.shredzone.acme4j;
+
+import edu.umd.cs.findbugs.annotations.DefaultAnnotationForFields;
+import edu.umd.cs.findbugs.annotations.DefaultAnnotationForParameters;
+import edu.umd.cs.findbugs.annotations.NonNull;
+import edu.umd.cs.findbugs.annotations.ReturnValuesAreNonnullByDefault;

acme4j-client/src/main/java/org/shredzone/acme4j/provider/AbstractAcmeProvider.java

@@ -22,8 +22,6 @@ import java.util.Map;
 import java.util.Objects;
 import java.util.function.BiFunction;
 
-import javax.annotation.ParametersAreNonnullByDefault;
-
 import org.shredzone.acme4j.Login;
 import org.shredzone.acme4j.Session;
 import org.shredzone.acme4j.challenge.Challenge;
@@ -44,7 +42,6 @@ import org.shredzone.acme4j.toolbox.JSON;
  * Implementing classes must implement at least {@link AcmeProvider#accepts(URI)}
  * and {@link AbstractAcmeProvider#resolve(URI)}.
  */
-@ParametersAreNonnullByDefault
 public abstract class AbstractAcmeProvider implements AcmeProvider {
 
     private static final Map<String, BiFunction<Login, JSON, Challenge>> CHALLENGES = challengeMap();

acme4j-client/src/main/java/org/shredzone/acme4j/provider/AcmeProvider.java

@@ -17,9 +17,7 @@ import java.net.URI;
 import java.net.URL;
 import java.util.ServiceLoader;
 
-import javax.annotation.CheckForNull;
+import edu.umd.cs.findbugs.annotations.Nullable;
-import javax.annotation.ParametersAreNonnullByDefault;
-
 import org.shredzone.acme4j.Login;
 import org.shredzone.acme4j.Session;
 import org.shredzone.acme4j.challenge.Challenge;
@@ -33,7 +31,6 @@ import org.shredzone.acme4j.toolbox.JSON;
  * <p>
  * Provider implementations must be registered with Java's {@link ServiceLoader}.
  */
-@ParametersAreNonnullByDefault
 public interface AcmeProvider {
 
     /**
@@ -80,7 +77,7 @@ public interface AcmeProvider {
      * @return Directory data, as JSON object, or {@code null} if the directory has not
      * been changed since the last request.
      */
-    @CheckForNull
+    @Nullable
     JSON directory(Session session, URI serverUri) throws AcmeException;
 
     /**
@@ -93,7 +90,7 @@ public interface AcmeProvider {
      * @return {@link Challenge} instance, or {@code null} if this provider is unable to
      *         generate a matching {@link Challenge} instance.
      */
-    @CheckForNull
+    @Nullable
     Challenge createChallenge(Login login, JSON data);
 
 }

acme4j-client/src/main/java/org/shredzone/acme4j/provider/GenericAcmeProvider.java

@@ -17,15 +17,12 @@ import java.net.MalformedURLException;
 import java.net.URI;
 import java.net.URL;
 
-import javax.annotation.ParametersAreNonnullByDefault;
-
 /**
  * A generic {@link AcmeProvider}. It should be working for all ACME servers complying to
  * the ACME specifications.
  * <p>
  * The {@code serverUri} is either a http or https URI to the server's directory service.
  */
-@ParametersAreNonnullByDefault
 public class GenericAcmeProvider extends AbstractAcmeProvider {
 
     @Override

acme4j-client/src/main/java/org/shredzone/acme4j/provider/letsencrypt/LetsEncryptAcmeProvider.java

@@ -17,8 +17,6 @@ import java.net.MalformedURLException;
 import java.net.URI;
 import java.net.URL;
 
-import javax.annotation.ParametersAreNonnullByDefault;
-
 import org.shredzone.acme4j.exception.AcmeProtocolException;
 import org.shredzone.acme4j.provider.AbstractAcmeProvider;
 import org.shredzone.acme4j.provider.AcmeProvider;
@@ -33,7 +31,6 @@ import org.shredzone.acme4j.provider.AcmeProvider;
  *
  * @see <a href="https://letsencrypt.org/">Let's Encrypt</a>
  */
-@ParametersAreNonnullByDefault
 public class LetsEncryptAcmeProvider extends AbstractAcmeProvider {
 
     private static final String V02_DIRECTORY_URL = "https://acme-v02.api.letsencrypt.org/directory";

acme4j-client/src/main/java/org/shredzone/acme4j/provider/letsencrypt/package-info.java

@@ -0,0 +1,23 @@
+/*
+ * acme4j - Java ACME client
+ *
+ * Copyright (C) 2020 Richard "Shred" Körber
+ *   http://acme4j.shredzone.org
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ */
+
+@ReturnValuesAreNonnullByDefault
+@DefaultAnnotationForParameters(NonNull.class)
+@DefaultAnnotationForFields(NonNull.class)
+package org.shredzone.acme4j.provider.letsencrypt;
+
+import edu.umd.cs.findbugs.annotations.DefaultAnnotationForFields;
+import edu.umd.cs.findbugs.annotations.DefaultAnnotationForParameters;
+import edu.umd.cs.findbugs.annotations.NonNull;
+import edu.umd.cs.findbugs.annotations.ReturnValuesAreNonnullByDefault;

acme4j-client/src/main/java/org/shredzone/acme4j/provider/package-info.java

@@ -0,0 +1,23 @@
+/*
+ * acme4j - Java ACME client
+ *
+ * Copyright (C) 2020 Richard "Shred" Körber
+ *   http://acme4j.shredzone.org
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ */
+
+@ReturnValuesAreNonnullByDefault
+@DefaultAnnotationForParameters(NonNull.class)
+@DefaultAnnotationForFields(NonNull.class)
+package org.shredzone.acme4j.provider;
+
+import edu.umd.cs.findbugs.annotations.DefaultAnnotationForFields;
+import edu.umd.cs.findbugs.annotations.DefaultAnnotationForParameters;
+import edu.umd.cs.findbugs.annotations.NonNull;
+import edu.umd.cs.findbugs.annotations.ReturnValuesAreNonnullByDefault;

acme4j-client/src/main/java/org/shredzone/acme4j/provider/pebble/PebbleAcmeProvider.java

@@ -19,8 +19,6 @@ import java.net.URL;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
-import javax.annotation.ParametersAreNonnullByDefault;
-
 import org.shredzone.acme4j.connector.HttpConnector;
 import org.shredzone.acme4j.provider.AbstractAcmeProvider;
 import org.shredzone.acme4j.provider.AcmeProvider;
@@ -36,7 +34,6 @@ import org.shredzone.acme4j.provider.AcmeProvider;
  * possible to connect to an external Pebble server on the given {@code other-host} and
  * port. The port is optional, and if omitted, the standard port is used.
  */
-@ParametersAreNonnullByDefault
 public class PebbleAcmeProvider extends AbstractAcmeProvider {
 
     private static final Pattern HOST_PATTERN = Pattern.compile("^/([^:/]+)(?:\\:(\\d+))?/?$");

acme4j-client/src/main/java/org/shredzone/acme4j/provider/pebble/PebbleHttpConnector.java

@@ -22,14 +22,14 @@ import java.security.KeyStore;
 import java.security.KeyStoreException;
 import java.security.NoSuchAlgorithmException;
 import java.security.cert.CertificateException;
+import java.util.Objects;
 
-import javax.annotation.ParametersAreNonnullByDefault;
-import javax.annotation.concurrent.ThreadSafe;
 import javax.net.ssl.HttpsURLConnection;
 import javax.net.ssl.SSLContext;
 import javax.net.ssl.SSLSocketFactory;
 import javax.net.ssl.TrustManagerFactory;
 
+import edu.umd.cs.findbugs.annotations.Nullable;
 import org.shredzone.acme4j.connector.HttpConnector;
 import org.shredzone.acme4j.connector.NetworkSettings;
 
@@ -37,10 +37,8 @@ import org.shredzone.acme4j.connector.NetworkSettings;
  * {@link HttpConnector} to be used for Pebble. Pebble uses a static, self signed SSL
  * certificate.
  */
-@ParametersAreNonnullByDefault
-@ThreadSafe
 public class PebbleHttpConnector extends HttpConnector {
-    private static SSLSocketFactory sslSocketFactory;
+    private static @Nullable SSLSocketFactory sslSocketFactory = null;
 
     @Override
     public HttpURLConnection openConnection(URL url, NetworkSettings settings) throws IOException {
@@ -75,7 +73,7 @@ public class PebbleHttpConnector extends HttpConnector {
                 throw new IOException("Could not create truststore", ex);
             }
         }
-        return sslSocketFactory;
+        return Objects.requireNonNull(sslSocketFactory);
     }
 
 }

acme4j-client/src/main/java/org/shredzone/acme4j/provider/pebble/package-info.java

@@ -0,0 +1,23 @@
+/*
+ * acme4j - Java ACME client
+ *
+ * Copyright (C) 2020 Richard "Shred" Körber
+ *   http://acme4j.shredzone.org
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ */
+
+@ReturnValuesAreNonnullByDefault
+@DefaultAnnotationForParameters(NonNull.class)
+@DefaultAnnotationForFields(NonNull.class)
+package org.shredzone.acme4j.provider.pebble;
+
+import edu.umd.cs.findbugs.annotations.DefaultAnnotationForFields;
+import edu.umd.cs.findbugs.annotations.DefaultAnnotationForParameters;
+import edu.umd.cs.findbugs.annotations.NonNull;
+import edu.umd.cs.findbugs.annotations.ReturnValuesAreNonnullByDefault;

acme4j-client/src/main/java/org/shredzone/acme4j/toolbox/AcmeUtils.java

@@ -29,12 +29,7 @@ import java.util.Objects;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
-import javax.annotation.CheckForNull;
+import edu.umd.cs.findbugs.annotations.Nullable;
-import javax.annotation.Nullable;
-import javax.annotation.ParametersAreNonnullByDefault;
-import javax.annotation.WillNotClose;
-import javax.annotation.concurrent.Immutable;
-
 import org.shredzone.acme4j.exception.AcmeProtocolException;
 
 /**
@@ -43,7 +38,6 @@ import org.shredzone.acme4j.exception.AcmeProtocolException;
  * This class is internal. You may use it in your own code, but be warned that methods may
  * change their signature or disappear without prior announcement.
  */
-@ParametersAreNonnullByDefault
 public final class AcmeUtils {
     private static final char[] HEX = "0123456789abcdef".toCharArray();
     private static final String ACME_ERROR_PREFIX = "urn:ietf:params:acme:error:";
@@ -72,8 +66,6 @@ public final class AcmeUtils {
     /**
      * Enumeration of PEM labels.
      */
-    @ParametersAreNonnullByDefault
-    @Immutable
     public enum PemLabel {
         CERTIFICATE("CERTIFICATE"),
         CERTIFICATE_REQUEST("CERTIFICATE REQUEST"),
@@ -239,7 +231,7 @@ public final class AcmeUtils {
      *            Error type to strip the prefix from. {@code null} is safe.
      * @return Stripped error type, or {@code null} if the prefix was not found.
      */
-    @CheckForNull
+    @Nullable
     public static String stripErrorPrefix(@Nullable String type) {
         if (type != null && type.startsWith(ACME_ERROR_PREFIX)) {
             return type.substring(ACME_ERROR_PREFIX.length());
@@ -258,7 +250,7 @@ public final class AcmeUtils {
      * @param out
      *            {@link Writer} to write to. It will not be closed after use!
      */
-    public static void writeToPem(byte[] encoded, PemLabel label, @WillNotClose Writer out)
+    public static void writeToPem(byte[] encoded, PemLabel label, Writer out)
                 throws IOException {
         out.append("-----BEGIN ").append(label.toString()).append("-----\n");
         out.append(new String(PEM_ENCODER.encode(encoded), StandardCharsets.US_ASCII));
@@ -274,7 +266,7 @@ public final class AcmeUtils {
      * @throws AcmeProtocolException
      *             if the Content-Type header contains a different charset than "utf-8".
      */
-    @CheckForNull
+    @Nullable
     public static String getContentType(@Nullable String header) {
         if (header != null) {
             Matcher m = CONTENT_TYPE_PATTERN.matcher(header);

acme4j-client/src/main/java/org/shredzone/acme4j/toolbox/JSON.java

@@ -43,11 +43,7 @@ import java.util.function.Function;
 import java.util.stream.Stream;
 import java.util.stream.StreamSupport;
 
-import javax.annotation.Nullable;
+import edu.umd.cs.findbugs.annotations.Nullable;
-import javax.annotation.ParametersAreNonnullByDefault;
-import javax.annotation.WillClose;
-import javax.annotation.concurrent.Immutable;
-
 import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
 import org.jose4j.json.JsonUtil;
 import org.jose4j.lang.JoseException;
@@ -59,8 +55,6 @@ import org.shredzone.acme4j.exception.AcmeProtocolException;
 /**
  * A model containing a JSON result. The content is immutable.
  */
-@ParametersAreNonnullByDefault
-@Immutable
 public final class JSON implements Serializable {
     private static final long serialVersionUID = 3091273044605709204L;
 
@@ -101,7 +95,7 @@ public final class JSON implements Serializable {
      *            {@link InputStream} to read from. Will be closed after use.
      * @return {@link JSON} of the read content.
      */
-    public static JSON parse(@WillClose InputStream in) throws IOException {
+    public static JSON parse(InputStream in) throws IOException {
         try (BufferedReader reader = new BufferedReader(new InputStreamReader(in, "utf-8"))) {
             String json = reader.lines().map(String::trim).collect(joining());
             return parse(json);
@@ -205,8 +199,6 @@ public final class JSON implements Serializable {
     /**
      * Represents a JSON array.
      */
-    @ParametersAreNonnullByDefault
-    @Immutable
     public static final class Array implements Iterable<Value> {
         private final String path;
         private final List<Object> data;
@@ -275,11 +267,9 @@ public final class JSON implements Serializable {
      * All return values are never {@code null} unless specified otherwise. For optional
      * parameters, use {@link Value#optional()}.
      */
-    @ParametersAreNonnullByDefault
-    @Immutable
     public static final class Value {
         private final String path;
-        private final Object val;
+        private final @Nullable Object val;
 
         /**
          * Creates a new {@link Value}.
@@ -519,7 +509,6 @@ public final class JSON implements Serializable {
     /**
      * An {@link Iterator} over array {@link Value}.
      */
-    @ParametersAreNonnullByDefault
     private static class ValueIterator implements Iterator<Value> {
         private final Array array;
         private int index = 0;

acme4j-client/src/main/java/org/shredzone/acme4j/toolbox/JSONBuilder.java

@@ -26,9 +26,7 @@ import java.util.LinkedHashMap;
 import java.util.Map;
 import java.util.Objects;
 
-import javax.annotation.Nullable;
+import edu.umd.cs.findbugs.annotations.Nullable;
-import javax.annotation.ParametersAreNonnullByDefault;
-
 import org.jose4j.json.JsonUtil;
 
 /**
@@ -42,7 +40,6 @@ import org.jose4j.json.JsonUtil;
  * cb.array("array", 123, 456, 789);
  * </pre>
  */
-@ParametersAreNonnullByDefault
 public class JSONBuilder {
 
     private final Map<String, Object> data = new LinkedHashMap<>();

acme4j-client/src/main/java/org/shredzone/acme4j/toolbox/JoseUtils.java

@@ -18,10 +18,9 @@ import java.security.KeyPair;
 import java.security.PublicKey;
 import java.util.Map;
 
-import javax.annotation.Nullable;
-import javax.annotation.ParametersAreNonnullByDefault;
 import javax.crypto.SecretKey;
 
+import edu.umd.cs.findbugs.annotations.Nullable;
 import org.jose4j.jwk.EllipticCurveJsonWebKey;
 import org.jose4j.jwk.JsonWebKey;
 import org.jose4j.jwk.PublicJsonWebKey;
@@ -37,7 +36,6 @@ import org.slf4j.LoggerFactory;
  *
  * @since 2.7
  */
-@ParametersAreNonnullByDefault
 public final class JoseUtils {
 
     private static final Logger LOG = LoggerFactory.getLogger(JoseUtils.class);
@@ -65,7 +63,7 @@ public final class JoseUtils {
      * @return JSON structure of the JOSE request, ready to be sent.
      */
     public static JSONBuilder createJoseRequest(URL url, KeyPair keypair,
-            @Nullable JSONBuilder payload, @Nullable String nonce, @Nullable String kid) {
+                @Nullable JSONBuilder payload, @Nullable String nonce, @Nullable String kid) {
         try {
             PublicJsonWebKey jwk = PublicJsonWebKey.Factory.newPublicJwk(keypair.getPublic());
 

acme4j-client/src/main/java/org/shredzone/acme4j/toolbox/package-info.java

@@ -0,0 +1,23 @@
+/*
+ * acme4j - Java ACME client
+ *
+ * Copyright (C) 2020 Richard "Shred" Körber
+ *   http://acme4j.shredzone.org
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ */
+
+@ReturnValuesAreNonnullByDefault
+@DefaultAnnotationForParameters(NonNull.class)
+@DefaultAnnotationForFields(NonNull.class)
+package org.shredzone.acme4j.toolbox;
+
+import edu.umd.cs.findbugs.annotations.DefaultAnnotationForFields;
+import edu.umd.cs.findbugs.annotations.DefaultAnnotationForParameters;
+import edu.umd.cs.findbugs.annotations.NonNull;
+import edu.umd.cs.findbugs.annotations.ReturnValuesAreNonnullByDefault;

acme4j-client/src/test/java/org/shredzone/acme4j/provider/AbstractAcmeProviderTest.java

@@ -30,8 +30,6 @@ import java.time.temporal.ChronoUnit;
 import java.util.Optional;
 import java.util.concurrent.atomic.AtomicBoolean;
 
-import javax.annotation.ParametersAreNonnullByDefault;
-
 import org.junit.Test;
 import org.shredzone.acme4j.Login;
 import org.shredzone.acme4j.Session;
@@ -310,7 +308,6 @@ public class AbstractAcmeProviderTest {
         }
     }
 
-    @ParametersAreNonnullByDefault
     private static class TestAbstractAcmeProvider extends AbstractAcmeProvider {
         private final Connection connection;
 

acme4j-it/src/main/java/org/shredzone/acme4j/it/BammBammClient.java

@@ -17,8 +17,6 @@ import java.io.IOException;
 import java.util.Arrays;
 import java.util.Objects;
 
-import javax.annotation.ParametersAreNonnullByDefault;
-
 import org.apache.http.HttpResponse;
 import org.apache.http.HttpStatus;
 import org.apache.http.client.ClientProtocolException;
@@ -33,7 +31,6 @@ import org.shredzone.acme4j.toolbox.JSONBuilder;
 /**
  * The BammBamm client connects to the pebble-challtestsrv.
  */
-@ParametersAreNonnullByDefault
 public class BammBammClient {
     private static final HttpClient CLIENT = HttpClients.createDefault();
 

acme4j-it/src/main/java/org/shredzone/acme4j/it/package-info.java

@@ -0,0 +1,23 @@
+/*
+ * acme4j - Java ACME client
+ *
+ * Copyright (C) 2020 Richard "Shred" Körber
+ *   http://acme4j.shredzone.org
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ */
+
+@ReturnValuesAreNonnullByDefault
+@DefaultAnnotationForParameters(NonNull.class)
+@DefaultAnnotationForFields(NonNull.class)
+package org.shredzone.acme4j.it;
+
+import edu.umd.cs.findbugs.annotations.DefaultAnnotationForFields;
+import edu.umd.cs.findbugs.annotations.DefaultAnnotationForParameters;
+import edu.umd.cs.findbugs.annotations.NonNull;
+import edu.umd.cs.findbugs.annotations.ReturnValuesAreNonnullByDefault;

acme4j-utils/src/main/java/org/shredzone/acme4j/util/CSRBuilder.java

@@ -31,9 +31,7 @@ import java.util.Collection;
 import java.util.List;
 import java.util.Objects;
 
-import javax.annotation.ParametersAreNonnullByDefault;
+import edu.umd.cs.findbugs.annotations.Nullable;
-import javax.annotation.WillClose;
-
 import org.bouncycastle.asn1.pkcs.PKCSObjectIdentifiers;
 import org.bouncycastle.asn1.x500.X500Name;
 import org.bouncycastle.asn1.x500.X500NameBuilder;
@@ -57,7 +55,6 @@ import org.shredzone.acme4j.Identifier;
  * <p>
  * Requires {@code Bouncy Castle}. This class is part of the {@code acme4j-utils} module.
  */
-@ParametersAreNonnullByDefault
 public class CSRBuilder {
     private static final String SIGNATURE_ALG = "SHA256withRSA";
     private static final String EC_SIGNATURE_ALG = "SHA256withECDSA";
@@ -65,7 +62,7 @@ public class CSRBuilder {
     private final X500NameBuilder namebuilder = new X500NameBuilder(X500Name.getDefaultStyle());
     private final List<String> namelist = new ArrayList<>();
     private final List<InetAddress> iplist = new ArrayList<>();
-    private PKCS10CertificationRequest csr = null;
+    private @Nullable PKCS10CertificationRequest csr = null;
 
     /**
      * Adds a domain name to the CSR. The first domain name added will also be the
@@ -296,7 +293,7 @@ public class CSRBuilder {
      *            {@link Writer} to write the PEM file to. The {@link Writer} is closed
      *            after use.
      */
-    public void write(@WillClose Writer w) throws IOException {
+    public void write(Writer w) throws IOException {
         if (csr == null) {
             throw new IllegalStateException("sign CSR first");
         }
@@ -313,7 +310,7 @@ public class CSRBuilder {
      *            {@link OutputStream} to write the PEM file to. The {@link OutputStream}
      *            is closed after use.
      */
-    public void write(@WillClose OutputStream out) throws IOException {
+    public void write(OutputStream out) throws IOException {
         write(new OutputStreamWriter(out, "utf-8"));
     }
 

acme4j-utils/src/main/java/org/shredzone/acme4j/util/CertificateUtils.java

@@ -33,9 +33,6 @@ import java.util.Date;
 import java.util.Objects;
 import java.util.function.Function;
 
-import javax.annotation.ParametersAreNonnullByDefault;
-import javax.annotation.WillClose;
-
 import org.bouncycastle.asn1.ASN1Encodable;
 import org.bouncycastle.asn1.ASN1ObjectIdentifier;
 import org.bouncycastle.asn1.DEROctetString;
@@ -64,7 +61,6 @@ import org.shredzone.acme4j.challenge.TlsAlpn01Challenge;
  * <p>
  * Requires {@code Bouncy Castle}. This class is part of the {@code acme4j-utils} module.
  */
-@ParametersAreNonnullByDefault
 public final class CertificateUtils {
 
     /**
@@ -87,7 +83,7 @@ public final class CertificateUtils {
      *            closed after use.
      * @return CSR that was read
      */
-    public static PKCS10CertificationRequest readCSR(@WillClose InputStream in) throws IOException {
+    public static PKCS10CertificationRequest readCSR(InputStream in) throws IOException {
         try (PEMParser pemParser = new PEMParser(new InputStreamReader(in, StandardCharsets.US_ASCII))) {
             Object parsedObj = pemParser.readObject();
             if (!(parsedObj instanceof PKCS10CertificationRequest)) {

acme4j-utils/src/main/java/org/shredzone/acme4j/util/KeyPairUtils.java

@@ -23,9 +23,6 @@ import java.security.NoSuchAlgorithmException;
 import java.security.NoSuchProviderException;
 import java.security.SecureRandom;
 
-import javax.annotation.ParametersAreNonnullByDefault;
-import javax.annotation.WillClose;
-
 import org.bouncycastle.jce.ECNamedCurveTable;
 import org.bouncycastle.jce.spec.ECParameterSpec;
 import org.bouncycastle.openssl.PEMException;
@@ -39,7 +36,6 @@ import org.bouncycastle.openssl.jcajce.JcaPEMWriter;
  * <p>
  * Requires {@code Bouncy Castle}. This class is part of the {@code acme4j-utils} module.
  */
-@ParametersAreNonnullByDefault
 public class KeyPairUtils {
 
     private KeyPairUtils() {
@@ -104,7 +100,7 @@ public class KeyPairUtils {
      *            after use.
      * @return {@link KeyPair} read
      */
-    public static KeyPair readKeyPair(@WillClose Reader r) throws IOException {
+    public static KeyPair readKeyPair(Reader r) throws IOException {
         try (PEMParser parser = new PEMParser(r)) {
             PEMKeyPair keyPair = (PEMKeyPair) parser.readObject();
             return new JcaPEMKeyConverter().getKeyPair(keyPair);
@@ -122,7 +118,7 @@ public class KeyPairUtils {
      *            {@link Writer} to write the PEM file to. The {@link Writer} is closed
      *            after use.
      */
-    public static void writeKeyPair(KeyPair keypair, @WillClose Writer w) throws IOException {
+    public static void writeKeyPair(KeyPair keypair, Writer w) throws IOException {
         try (JcaPEMWriter jw = new JcaPEMWriter(w)) {
             jw.writeObject(keypair);
         }

acme4j-utils/src/main/java/org/shredzone/acme4j/util/package-info.java

@@ -0,0 +1,23 @@
+/*
+ * acme4j - Java ACME client
+ *
+ * Copyright (C) 2020 Richard "Shred" Körber
+ *   http://acme4j.shredzone.org
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ */
+
+@ReturnValuesAreNonnullByDefault
+@DefaultAnnotationForParameters(NonNull.class)
+@DefaultAnnotationForFields(NonNull.class)
+package org.shredzone.acme4j.util;
+
+import edu.umd.cs.findbugs.annotations.DefaultAnnotationForFields;
+import edu.umd.cs.findbugs.annotations.DefaultAnnotationForParameters;
+import edu.umd.cs.findbugs.annotations.NonNull;
+import edu.umd.cs.findbugs.annotations.ReturnValuesAreNonnullByDefault;

pom.xml

@@ -80,7 +80,7 @@
             <plugin>
                 <groupId>com.github.spotbugs</groupId>
                 <artifactId>spotbugs-maven-plugin</artifactId>
-                <version>3.1.12.2</version>
+                <version>4.0.0</version>
                 <configuration>
                     <excludeFilterFile>src/config/spotbugs-exclude.xml</excludeFilterFile>
                 </configuration>
@@ -171,16 +171,16 @@
     </build>
     <dependencies>
         <dependency>
-            <groupId>com.google.code.findbugs</groupId>
+            <groupId>com.github.spotbugs</groupId>
-            <artifactId>jsr305</artifactId>
+            <artifactId>spotbugs-annotations</artifactId>
-            <version>3.0.2</version>
+            <version>4.0.3</version>
-            <scope>provided</scope>
+            <optional>true</optional>
-        </dependency>
+            <exclusions>
-        <dependency>
+                <exclusion>
-            <groupId>com.google.code.findbugs</groupId>
+                    <groupId>com.google.code.findbugs</groupId>
-            <artifactId>annotations</artifactId>
+                    <artifactId>jsr305</artifactId>
-            <version>3.0.1</version>
+                </exclusion>
-            <scope>provided</scope>
+            </exclusions>
         </dependency>
         <dependency>
             <groupId>junit</groupId>

src/doc/docs/migration.md

@@ -4,7 +4,10 @@ This document will help you migrate your code to the latest _acme4j_ version.
 
 ## Migration to Version 2.10
 
+- In a preparation for Java 9 modules, the JSR305 null-safe annotations have been replaced by SpotBugs annotations. This _should_ have no impact on your code, as the method signatures themselves are unchanged. However, the compiler could now complain about some `null` dereferences that have been undetected before. Reason is that JSR305 uses the `javax.annotations` package, which leads to split packages in a Java 9 modular environment.
+  
 - When fetching the directory, acme4j now evaluates HTTP caching headers instead of just caching the directory for 1 hour. However, Let's Encrypt explicitly forbids caching, which means that a fresh copy of the directory is now fetched from the server every time it is needed. I don't like it, but it is the RFC conformous behavior. It needs to be [fixed on Let's Encrypt side](https://github.com/letsencrypt/boulder/issues/4814).
+  
 - `AcmeProvider.directory(Session, URI)` is now responsible for maintaining the cache. Implementations can use `Session.setDirectoryExpires()`, `Session.setDirectoryLastModified()`, and the respective getters, for keeping track of the local directory state. `AcmeProvider.directory(Session, URI)` may now return `null`, to indicate that the remote directory was unchanged and the local copy is still valid. It's not permitted to return `null` if `Session.hasDirectory()` returns `false`, though! If your `AcmeProvider` is derived from `AbstractAcmeProvider`, and you haven't overridden the `directory()` method, no migration is necessary.
 
 ## Migration to Version 2.9