diff --git a/dubbo-common/src/main/java/org/apache/dubbo/common/extension/ExtensionLoader.java b/dubbo-common/src/main/java/org/apache/dubbo/common/extension/ExtensionLoader.java
index e47e19d07fa..3f2709e8621 100644
--- a/dubbo-common/src/main/java/org/apache/dubbo/common/extension/ExtensionLoader.java
+++ b/dubbo-common/src/main/java/org/apache/dubbo/common/extension/ExtensionLoader.java
@@ -33,6 +33,7 @@
 import java.io.InputStreamReader;
 import java.lang.reflect.Method;
 import java.lang.reflect.Modifier;
+import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
@@ -71,9 +72,9 @@ public class ExtensionLoader<T> {
 
     private static final Pattern NAME_SEPARATOR = Pattern.compile("\\s*[,]+\\s*");
 
-    private static final ConcurrentMap<Class<?>, ExtensionLoader<?>> EXTENSION_LOADERS = new ConcurrentHashMap<Class<?>, ExtensionLoader<?>>();
+    private static final ConcurrentMap<Class<?>, ExtensionLoader<?>> EXTENSION_LOADERS = new ConcurrentHashMap<>();
 
-    private static final ConcurrentMap<Class<?>, Object> EXTENSION_INSTANCES = new ConcurrentHashMap<Class<?>, Object>();
+    private static final ConcurrentMap<Class<?>, Object> EXTENSION_INSTANCES = new ConcurrentHashMap<>();
 
     // ==============================
 
@@ -81,20 +82,20 @@ public class ExtensionLoader<T> {
 
     private final ExtensionFactory objectFactory;
 
-    private final ConcurrentMap<Class<?>, String> cachedNames = new ConcurrentHashMap<Class<?>, String>();
+    private final ConcurrentMap<Class<?>, String> cachedNames = new ConcurrentHashMap<>();
 
-    private final Holder<Map<String, Class<?>>> cachedClasses = new Holder<Map<String, Class<?>>>();
+    private final Holder<Map<String, Class<?>>> cachedClasses = new Holder<>();
 
-    private final Map<String, Object> cachedActivates = new ConcurrentHashMap<String, Object>();
-    private final ConcurrentMap<String, Holder<Object>> cachedInstances = new ConcurrentHashMap<String, Holder<Object>>();
-    private final Holder<Object> cachedAdaptiveInstance = new Holder<Object>();
+    private final Map<String, Object> cachedActivates = new ConcurrentHashMap<>();
+    private final ConcurrentMap<String, Holder<Object>> cachedInstances = new ConcurrentHashMap<>();
+    private final Holder<Object> cachedAdaptiveInstance = new Holder<>();
     private volatile Class<?> cachedAdaptiveClass = null;
     private String cachedDefaultName;
     private volatile Throwable createAdaptiveInstanceError;
 
     private Set<Class<?>> cachedWrapperClasses;
 
-    private Map<String, IllegalStateException> exceptions = new ConcurrentHashMap<String, IllegalStateException>();
+    private Map<String, IllegalStateException> exceptions = new ConcurrentHashMap<>();
 
     private ExtensionLoader(Class<?> type) {
         this.type = type;
@@ -111,11 +112,11 @@ public static <T> ExtensionLoader<T> getExtensionLoader(Class<T> type) {
             throw new IllegalArgumentException("Extension type == null");
         }
         if (!type.isInterface()) {
-            throw new IllegalArgumentException("Extension type (" + type + ") is not interface!");
+            throw new IllegalArgumentException("Extension type (" + type + ") is not an interface!");
         }
         if (!withExtensionAnnotation(type)) {
             throw new IllegalArgumentException("Extension type (" + type +
-                    ") is not extension, because WITHOUT @" + SPI.class.getSimpleName() + " Annotation!");
+                    ") is not an extension, because it is NOT annotated with @" + SPI.class.getSimpleName() + "!");
         }
 
         ExtensionLoader<T> loader = (ExtensionLoader<T>) EXTENSION_LOADERS.get(type);
@@ -201,8 +202,8 @@ public List<T> getActivateExtension(URL url, String key, String group) {
      * @see org.apache.dubbo.common.extension.Activate
      */
     public List<T> getActivateExtension(URL url, String[] values, String group) {
-        List<T> exts = new ArrayList<T>();
-        List<String> names = values == null ? new ArrayList<String>(0) : Arrays.asList(values);
+        List<T> exts = new ArrayList<>();
+        List<String> names = values == null ? new ArrayList<>(0) : Arrays.asList(values);
         if (!names.contains(Constants.REMOVE_VALUE_PREFIX + Constants.DEFAULT_KEY)) {
             getExtensionClasses();
             for (Map.Entry<String, Object> entry : cachedActivates.entrySet()) {
@@ -229,9 +230,9 @@ && isActive(activateValue, url)) {
                     }
                 }
             }
-            Collections.sort(exts, ActivateComparator.COMPARATOR);
+            exts.sort(ActivateComparator.COMPARATOR);
         }
-        List<T> usrs = new ArrayList<T>();
+        List<T> usrs = new ArrayList<>();
         for (int i = 0; i < names.size(); i++) {
             String name = names.get(i);
             if (!name.startsWith(Constants.REMOVE_VALUE_PREFIX)
@@ -297,12 +298,17 @@ public T getLoadedExtension(String name) {
         if (StringUtils.isEmpty(name)) {
             throw new IllegalArgumentException("Extension name == null");
         }
+        Holder<Object> holder = getOrCreateHolder(name);
+        return (T) holder.get();
+    }
+
+    private Holder<Object> getOrCreateHolder(String name) {
         Holder<Object> holder = cachedInstances.get(name);
         if (holder == null) {
-            cachedInstances.putIfAbsent(name, new Holder<Object>());
+            cachedInstances.putIfAbsent(name, new Holder<>());
             holder = cachedInstances.get(name);
         }
-        return (T) holder.get();
+        return holder;
     }
 
     /**
@@ -313,7 +319,7 @@ public T getLoadedExtension(String name) {
      * @see #getSupportedExtensions()
      */
     public Set<String> getLoadedExtensions() {
-        return Collections.unmodifiableSet(new TreeSet<String>(cachedInstances.keySet()));
+        return Collections.unmodifiableSet(new TreeSet<>(cachedInstances.keySet()));
     }
 
     public Object getLoadedAdaptiveExtensionInstances() {
@@ -332,11 +338,7 @@ public T getExtension(String name) {
         if ("true".equals(name)) {
             return getDefaultExtension();
         }
-        Holder<Object> holder = cachedInstances.get(name);
-        if (holder == null) {
-            cachedInstances.putIfAbsent(name, new Holder<Object>());
-            holder = cachedInstances.get(name);
-        }
+        Holder<Object> holder = getOrCreateHolder(name);
         Object instance = holder.get();
         if (instance == null) {
             synchronized (holder) {
@@ -371,7 +373,7 @@ public boolean hasExtension(String name) {
 
     public Set<String> getSupportedExtensions() {
         Map<String, Class<?>> clazzes = getExtensionClasses();
-        return Collections.unmodifiableSet(new TreeSet<String>(clazzes.keySet()));
+        return Collections.unmodifiableSet(new TreeSet<>(clazzes.keySet()));
     }
 
     /**
@@ -680,8 +682,7 @@ private void loadDirectory(Map<String, Class<?>> extensionClasses, String dir, S
 
     private void loadResource(Map<String, Class<?>> extensionClasses, ClassLoader classLoader, java.net.URL resourceURL) {
         try {
-            BufferedReader reader = new BufferedReader(new InputStreamReader(resourceURL.openStream(), "utf-8"));
-            try {
+            try (BufferedReader reader = new BufferedReader(new InputStreamReader(resourceURL.openStream(), StandardCharsets.UTF_8))) {
                 String line;
                 while ((line = reader.readLine()) != null) {
                     final int ci = line.indexOf('#');
@@ -706,8 +707,6 @@ private void loadResource(Map<String, Class<?>> extensionClasses, ClassLoader cl
                         }
                     }
                 }
-            } finally {
-                reader.close();
             }
         } catch (Throwable t) {
             logger.error("Exception occurred when loading extension class (interface: " +
@@ -733,7 +732,7 @@ private void loadClass(Map<String, Class<?>> extensionClasses, java.net.URL reso
                     throw new IllegalStateException("No such extension name for the class " + clazz.getName() + " in the config " + resourceURL);
                 }
             }
-            
+
             String[] names = NAME_SEPARATOR.split(name);
             if (ArrayUtils.isNotEmpty(names)) {
                 cacheActivateClass(clazz, names[0]);
@@ -798,7 +797,7 @@ private void cacheAdaptiveClass(Class<?> clazz) {
     }
 
     /**
-     * cache wrapper class 
+     * cache wrapper class
      * <p>
      * like: ProtocolFilterWrapper, ProtocolListenerWrapper
      */
@@ -810,7 +809,7 @@ private void cacheWrapperClass(Class<?> clazz) {
     }
 
     /**
-     * test if clazz is a wrapper class 
+     * test if clazz is a wrapper class
      * <p>
      * which has Constructor with given class type as its only argument
      */
diff --git a/dubbo-common/src/test/java/org/apache/dubbo/common/extension/ExtensionLoaderTest.java b/dubbo-common/src/test/java/org/apache/dubbo/common/extension/ExtensionLoaderTest.java
index b0e878ce60e..12d8aa92af7 100644
--- a/dubbo-common/src/test/java/org/apache/dubbo/common/extension/ExtensionLoaderTest.java
+++ b/dubbo-common/src/test/java/org/apache/dubbo/common/extension/ExtensionLoaderTest.java
@@ -87,7 +87,7 @@ public void test_getExtensionLoader_NotInterface() throws Exception {
             fail();
         } catch (IllegalArgumentException expected) {
             assertThat(expected.getMessage(),
-                    containsString("Extension type (class org.apache.dubbo.common.extension.ExtensionLoaderTest) is not interface"));
+                    containsString("Extension type (class org.apache.dubbo.common.extension.ExtensionLoaderTest) is not an interface"));
         }
     }
 
@@ -99,8 +99,8 @@ public void test_getExtensionLoader_NotSpiAnnotation() throws Exception {
         } catch (IllegalArgumentException expected) {
             assertThat(expected.getMessage(),
                     allOf(containsString("org.apache.dubbo.common.extension.NoSpiExt"),
-                            containsString("is not extension"),
-                            containsString("WITHOUT @SPI Annotation")));
+                            containsString("is not an extension"),
+                            containsString("NOT annotated with @SPI")));
         }
     }