fix: not clearing the template engine cache after upgrading the theme (#2970)

#### What type of PR is this?

/kind improvement

#### What this PR does / why we need it:

通过在模板引擎管理器里添加clearCache方法，在升级主题后进行缓存刷新，让新模板内容生效。

#### Which issue(s) this PR fixes:

Fixes #2953 

#### Special notes for your reviewer:

#### Does this PR introduce a user-facing change?

```release-note
NONE
```

src/main/java/run/halo/app/core/extension/theme/ThemeEndpoint.java

@@ -37,6 +37,7 @@ import run.halo.app.extension.ReactiveExtensionClient;
 import run.halo.app.extension.router.IListRequest;
 import run.halo.app.extension.router.QueryParamBuildUtil;
 import run.halo.app.infra.ThemeRootGetter;
+import run.halo.app.theme.TemplateEngineManager;
 
 /**
  * Endpoint for managing themes.
@@ -54,11 +55,14 @@ public class ThemeEndpoint implements CustomEndpoint {
 
     private final ThemeService themeService;
 
+    private final TemplateEngineManager templateEngineManager;
+
     public ThemeEndpoint(ReactiveExtensionClient client, ThemeRootGetter themeRoot,
-        ThemeService themeService) {
+        ThemeService themeService, TemplateEngineManager templateEngineManager) {
         this.client = client;
         this.themeRoot = themeRoot;
         this.themeService = themeService;
+        this.templateEngineManager = templateEngineManager;
     }
 
     @Override
@@ -180,6 +184,9 @@ public class ThemeEndpoint implements CustomEndpoint {
                     return Mono.error(e);
                 }
             })
+            .flatMap((updatedTheme) -> templateEngineManager.clearCache(
+                    updatedTheme.getMetadata().getName())
+                .thenReturn(updatedTheme))
             .flatMap(updatedTheme -> ServerResponse.ok()
                 .bodyValue(updatedTheme));
     }

src/main/java/run/halo/app/theme/TemplateEngineManager.java

@@ -7,12 +7,14 @@ import org.springframework.boot.autoconfigure.thymeleaf.ThymeleafProperties;
 import org.springframework.stereotype.Component;
 import org.springframework.util.ConcurrentLruCache;
 import org.springframework.util.ResourceUtils;
+import org.thymeleaf.TemplateEngine;
 import org.thymeleaf.dialect.IDialect;
 import org.thymeleaf.spring6.ISpringWebFluxTemplateEngine;
 import org.thymeleaf.spring6.dialect.SpringStandardDialect;
 import org.thymeleaf.standard.expression.IStandardVariableExpressionEvaluator;
 import org.thymeleaf.templateresolver.FileTemplateResolver;
 import org.thymeleaf.templateresolver.ITemplateResolver;
+import reactor.core.publisher.Mono;
 import run.halo.app.infra.ExternalUrlSupplier;
 import run.halo.app.infra.exception.NotFoundException;
 import run.halo.app.theme.dialect.HaloProcessorDialect;
@@ -47,14 +49,17 @@ public class TemplateEngineManager {
 
     private final ObjectProvider<IDialect> dialects;
 
+    private final ThemeResolver themeResolver;
+
     public TemplateEngineManager(ThymeleafProperties thymeleafProperties,
         ExternalUrlSupplier externalUrlSupplier,
         ObjectProvider<ITemplateResolver> templateResolvers,
-        ObjectProvider<IDialect> dialects) {
+        ObjectProvider<IDialect> dialects, ThemeResolver themeResolver) {
         this.thymeleafProperties = thymeleafProperties;
         this.externalUrlSupplier = externalUrlSupplier;
         this.templateResolvers = templateResolvers;
         this.dialects = dialects;
+        this.themeResolver = themeResolver;
         engineCache = new ConcurrentLruCache<>(CACHE_SIZE_LIMIT, this::templateEngineGenerator);
     }
 
@@ -77,6 +82,16 @@ public class TemplateEngineManager {
         }
     }
 
+    public Mono<Void> clearCache(String themeName) {
+        return themeResolver.getThemeContext(themeName)
+            .doOnNext(themeContext -> {
+                TemplateEngine templateEngine =
+                    (TemplateEngine) engineCache.get(themeContext);
+                templateEngine.clearTemplateCache();
+            })
+            .then();
+    }
+
     private ISpringWebFluxTemplateEngine templateEngineGenerator(ThemeContext theme) {
         var engine = new SpringWebFluxTemplateEngine();
         engine.setEnableSpringELCompiler(thymeleafProperties.isEnableSpringElCompiler());

src/main/java/run/halo/app/theme/ThemeResolver.java

@@ -6,6 +6,7 @@ import org.apache.commons.lang3.StringUtils;
 import org.springframework.boot.autoconfigure.thymeleaf.ThymeleafProperties;
 import org.springframework.http.server.reactive.ServerHttpRequest;
 import org.springframework.stereotype.Component;
+import org.springframework.util.Assert;
 import reactor.core.publisher.Mono;
 import run.halo.app.infra.SystemConfigurableEnvironmentFetcher;
 import run.halo.app.infra.SystemSetting.Theme;
@@ -26,6 +27,22 @@ public class ThemeResolver {
 
     private final ThymeleafProperties thymeleafProperties;
 
+    public Mono<ThemeContext> getThemeContext(String themeName) {
+        Assert.hasText(themeName, "Theme name cannot be empty");
+        var path = FilePathUtils.combinePath(haloProperties.getWorkDir().toString(),
+            THEME_WORK_DIR, themeName);
+        return Mono.just(ThemeContext.builder().name(themeName).path(path))
+            .flatMap(builder -> environmentFetcher.fetch(Theme.GROUP, Theme.class)
+                .mapNotNull(Theme::getActive)
+                .map(activatedTheme -> {
+                    boolean active = StringUtils.equals(activatedTheme, themeName);
+                    return builder.active(active);
+                })
+                .defaultIfEmpty(builder.active(false))
+            )
+            .map(ThemeContext.ThemeContextBuilder::build);
+    }
+
     public Mono<ThemeContext> getTheme(ServerHttpRequest request) {
         return environmentFetcher.fetch(Theme.GROUP, Theme.class)
             .map(Theme::getActive)

src/test/java/run/halo/app/core/extension/reconciler/ThemeReconcilerTest.java

@@ -51,6 +51,7 @@ class ThemeReconcilerTest {
     @Mock
     private HaloProperties haloProperties;
 
+    @Mock
     private File defaultTheme;
 
     private Path tempDirectory;

src/test/java/run/halo/app/core/extension/theme/ThemeEndpointTest.java

@@ -4,6 +4,7 @@ import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.ArgumentMatchers.isA;
 import static org.mockito.Mockito.lenient;
+import static org.mockito.Mockito.times;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 import static org.springframework.web.reactive.function.BodyInserters.fromMultipartData;
@@ -32,6 +33,7 @@ import reactor.core.publisher.Mono;
 import run.halo.app.core.extension.Theme;
 import run.halo.app.extension.Metadata;
 import run.halo.app.infra.ThemeRootGetter;
+import run.halo.app.theme.TemplateEngineManager;
 
 /**
  * Tests for {@link ThemeEndpoint}.
@@ -48,6 +50,9 @@ class ThemeEndpointTest {
     @Mock
     ThemeService themeService;
 
+    @Mock
+    TemplateEngineManager templateEngineManager;
+
     @InjectMocks
     ThemeEndpoint themeEndpoint;
 
@@ -108,6 +113,9 @@ class ThemeEndpointTest {
             when(themeService.upgrade(eq("default"), isA(InputStream.class)))
                 .thenReturn(Mono.just(newTheme));
 
+            when(templateEngineManager.clearCache(eq("default")))
+                .thenReturn(Mono.empty());
+
             webTestClient.post()
                 .uri("/themes/default/upgrade")
                 .body(fromMultipartData(bodyBuilder.build()))
@@ -115,6 +123,8 @@ class ThemeEndpointTest {
                 .expectStatus().isOk();
 
             verify(themeService).upgrade(eq("default"), isA(InputStream.class));
+
+            verify(templateEngineManager, times(1)).clearCache(eq("default"));
         }
 
     }