PageHandlerAdapterFactory， handlerAdapters，handlerAdapterMap should unmodifiable

plugin-default-impl/nacos-default-auth-plugin/src/main/java/com/alibaba/nacos/plugin/auth/impl/persistence/handler/PageHandlerAdapterFactory.java

@@ -24,61 +24,52 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Collections;
+import java.util.function.Consumer;
 
 /**
  * pagination factory.
  *
  * @author huangKeMing
  */
 public class PageHandlerAdapterFactory {
-
- private static PageHandlerAdapterFactory instance;
-
- private List<PageHandlerAdapter> handlerAdapters;
-
- private Map<String, PageHandlerAdapter> handlerAdapterMap;
-
+
+ private final List<PageHandlerAdapter> handlerAdapters;
+
+ private final Map<String, PageHandlerAdapter> handlerAdapterMap;
+
  public List<PageHandlerAdapter> getHandlerAdapters() {
  return handlerAdapters;
  }
- 
+
  public Map<String, PageHandlerAdapter> getHandlerAdapterMap() {
  return handlerAdapterMap;
  }
- 
+
  private PageHandlerAdapterFactory() {
- handlerAdapters = new ArrayList<>(3);
- handlerAdapterMap = new HashMap<>(3);
- initHandlerAdapters();
- }
-
- public static PageHandlerAdapterFactory getInstance() {
- if (instance == null) {
- synchronized (PageHandlerAdapterFactory.class) {
- if (instance == null) {
- instance = new PageHandlerAdapterFactory();
- }
- }
- }
- return instance;
- }
-
- /**
- * init handler adapters.
- */
- private void initHandlerAdapters() {
+ List<PageHandlerAdapter> handlerAdapters = new ArrayList<>(3);
+ Map<String, PageHandlerAdapter> handlerAdapterMap = new HashMap<>(3);
+ Consumer<PageHandlerAdapter> addHandlerAdapter = handlerAdapter -> {
+ handlerAdapters.add(handlerAdapter);
+ handlerAdapterMap.put(handlerAdapter.getClass().getName(), handlerAdapter);
+ };
  // MysqlPageHandlerAdapter
- addHandlerAdapter(new MysqlPageHandlerAdapter());
+ addHandlerAdapter.accept(new MysqlPageHandlerAdapter());
  // DerbyPageHandlerAdapter
- addHandlerAdapter(new DerbyPageHandlerAdapter());
+ addHandlerAdapter.accept(new DerbyPageHandlerAdapter());
  // DefaultPageHandlerAdapter
- addHandlerAdapter(new DefaultPageHandlerAdapter());
+ addHandlerAdapter.accept(new DefaultPageHandlerAdapter());
+ this.handlerAdapters = Collections.unmodifiableList(handlerAdapters);
+ this.handlerAdapterMap = Collections.unmodifiableMap(handlerAdapterMap);
+ }
+
+ private static final class InstanceHolder {
+ static final PageHandlerAdapterFactory INSTANCE = new PageHandlerAdapterFactory();
  }
-
- private void addHandlerAdapter(PageHandlerAdapter handlerAdapter) {
- handlerAdapters.add(handlerAdapter);
- handlerAdapterMap.put(handlerAdapter.getClass().getName(), handlerAdapter);
+
+ public static PageHandlerAdapterFactory getInstance() {
+ return InstanceHolder.INSTANCE;
  }
- 
+
 }