extract 2 methods: (#3453)

isSetter: test if a method is a setter
getSetterProperty: get property for setter, for instance setVersion
return "version"

Author: wanghbxxxx

dubbo-common/src/main/java/org/apache/dubbo/common/extension/ExtensionLoader.java

@@ -544,9 +544,7 @@ private T injectExtension(T instance) {
         try {
             if (objectFactory != null) {
                 for (Method method : instance.getClass().getMethods()) {
-                    if (method.getName().startsWith("set")
-                            && method.getParameterTypes().length == 1
-                            && Modifier.isPublic(method.getModifiers())) {
+                    if (isSetter(method)) {
                         /**
                          * Check {@link DisableInject} to see if we need auto injection for this property
                          */
@@ -558,7 +556,7 @@ private T injectExtension(T instance) {
                             continue;
                         }
                         try {
-                            String property = method.getName().length() > 3 ? method.getName().substring(3, 4).toLowerCase() + method.getName().substring(4) : "";
+                            String property = getSetterProperty(method);
                             Object object = objectFactory.getExtension(pt, property);
                             if (object != null) {
                                 method.invoke(instance, object);
@@ -576,6 +574,30 @@ private T injectExtension(T instance) {
         return instance;
     }
 
+    /**
+     * get properties name for setter, for instance: setVersion, return "version"
+     * <p>
+     * return "", if setter name with length less than 3
+     */
+    private String getSetterProperty(Method method) {
+        return method.getName().length() > 3 ? method.getName().substring(3, 4).toLowerCase() + method.getName().substring(4) : "";
+    }
+
+    /**
+     * return true if and only if:
+     * <p>
+     * 1, public
+     * <p>
+     * 2, name starts with "set"
+     * <p>
+     * 3, only has one parameter
+     */
+    private boolean isSetter(Method method) {
+        return method.getName().startsWith("set")
+                && method.getParameterTypes().length == 1
+                && Modifier.isPublic(method.getModifiers());
+    }
+
     private Class<?> getExtensionClass(String name) {
         if (type == null) {
             throw new IllegalArgumentException("Extension type == null");