Add ServiceUtils

src/main/java/cc/ryanc/halo/utils/ServiceUtils.java

@@ -0,0 +1,86 @@
+package cc.ryanc.halo.utils;
+
+import cc.ryanc.halo.logging.Logger;
+import org.springframework.util.Assert;
+import org.springframework.util.CollectionUtils;
+
+import java.util.*;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+
+/**
+ * Utilities for service.
+ *
+ * @author johnniang
+ */
+public class ServiceUtils {
+
+    private final static Logger LOGGER = Logger.getLogger(ServiceUtils.class);
+
+    private ServiceUtils() {
+    }
+
+    /**
+     * Fetches id to set.
+     *
+     * @param datas           data collection
+     * @param mappingFunction calculate the id in data list
+     * @param <ID>            id type
+     * @param <T>             data type
+     * @return a set of id
+     */
+    public static <ID, T> Set<ID> fetchProperty(final Collection<T> datas, Function<T, ID> mappingFunction) {
+        return CollectionUtils.isEmpty(datas) ?
+                Collections.emptySet() :
+                datas.stream().map(mappingFunction).collect(Collectors.toSet());
+    }
+
+    /**
+     * Converts a list to a list map where list contains id in ids.
+     *
+     * @param ids             id collection
+     * @param list            data list
+     * @param mappingFunction calculate the id in data list
+     * @param <ID>            id type
+     * @param <D>             data type
+     * @return a map which key is in ids and value containing in list
+     */
+    public static <ID, D> Map<ID, List<D>> convertToListMap(Collection<ID> ids, Collection<D> list, Function<D, ID> mappingFunction) {
+        Assert.notNull(mappingFunction, "mapping function must not be null");
+
+        if (CollectionUtils.isEmpty(ids) || CollectionUtils.isEmpty(list)) {
+            return Collections.emptyMap();
+        }
+
+        Map<ID, List<D>> resultMap = new HashMap<>();
+
+        list.forEach(data -> resultMap.computeIfAbsent(mappingFunction.apply(data), id -> new LinkedList<>()).add(data));
+
+        ids.forEach(id -> resultMap.putIfAbsent(id, Collections.emptyList()));
+
+        return resultMap;
+    }
+
+    /**
+     * Converts to map (key from the list data)
+     *
+     * @param list            data list
+     * @param mappingFunction calclulate the id from list data
+     * @param <ID>            id type
+     * @param <D>             data type
+     * @return a map which key from list data and value is data
+     */
+    public static <ID, D> Map<ID, D> convertToMap(Collection<D> list, Function<D, ID> mappingFunction) {
+        Assert.notNull(mappingFunction, "mapping function must not be null");
+
+        if (CollectionUtils.isEmpty(list)) {
+            return Collections.emptyMap();
+        }
+
+        Map<ID, D> resultMap = new HashMap<>();
+
+        list.forEach(data -> resultMap.putIfAbsent(mappingFunction.apply(data), data));
+
+        return resultMap;
+    }
+}