dubbo-common/src/main/java/com/alibaba/dubbo/common/ExtensionLoader.java - dubbo - Git at Google

 /*
  * Copyright 1999-2011 Alibaba Group.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
 package com.alibaba.dubbo.common;

 import java.io.BufferedReader;
 import java.io.InputStreamReader;
 import java.lang.reflect.Method;
 import java.lang.reflect.Modifier;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.Enumeration;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.Set;
 import java.util.TreeSet;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentMap;
 import java.util.regex.Pattern;

 import com.alibaba.dubbo.common.bytecode.ClassGenerator;
 import com.alibaba.dubbo.common.logger.Logger;
 import com.alibaba.dubbo.common.logger.LoggerFactory;
 import com.alibaba.dubbo.common.utils.ConcurrentHashSet;
 import com.alibaba.dubbo.common.utils.Reference;
 import com.alibaba.dubbo.common.utils.StringUtils;

 /**
  * Dubbo使用的扩展点获取。<p>
  * <ul>
  * <li>自动注入关联扩展点。</li>
  * <li>自动Wrap上扩展点的Wrap类。</li>
  * <li>缺省获得的的扩展点是一个Adaptive Instance。
  * </ul>
  *
  * @see <a href="http://java.sun.com/j2se/1.5.0/docs/guide/jar/jar.html#Service%20Provider">JDK5.0的自动发现机制实现</a>
  *
  * @author william.liangf
  * @author ding.lid
  *
  * @see Extension
  * @see Adaptive
  */
 public class ExtensionLoader<T> {

     private static final Logger logger = LoggerFactory.getLogger(ExtensionLoader.class);

 	private static final String SERVICES_DIRECTORY = "META-INF/services/";

     private static final Pattern NAME_SEPARATOR = Pattern.compile("\\s*[,]+\\s*");

     private static final ConcurrentMap<Class<?>, ExtensionLoader<?>> EXTENSION_LOADERS = new ConcurrentHashMap<Class<?>, ExtensionLoader<?>>();

     private final Class<?> type;

     private final Reference<Map<String, Class<?>>> cachedClasses = new Reference<Map<String,Class<?>>>();

 	private final ConcurrentMap<String, Reference<Object>> cachedInstances = new ConcurrentHashMap<String, Reference<Object>>();

     private volatile Class<?> cachedAdaptiveClass = null;

 	private final Reference<Object> cachedAdaptiveInstance = new Reference<Object>();
 	private volatile Throwable createAdaptiveInstanceError;

     private Set<Class<?>> cachedWrapperClasses;

     private String cachedDefaultName;

     private Map<String, IllegalStateException> exceptions = new ConcurrentHashMap<String, IllegalStateException>();

     @SuppressWarnings("unchecked")
     public static <T> ExtensionLoader<T> getExtensionLoader(Class<T> type) {
         if (type == null)
             throw new IllegalArgumentException("Extension type == null");

         ExtensionLoader<T> loader = (ExtensionLoader<T>) EXTENSION_LOADERS.get(type);
         if (loader == null) {
             EXTENSION_LOADERS.putIfAbsent(type, new ExtensionLoader<T>(type));
             loader = (ExtensionLoader<T>) EXTENSION_LOADERS.get(type);
         }
         return loader;
     }

     private ExtensionLoader(Class<?> type) {
         this.type = type;
     }

 	@SuppressWarnings("unchecked")
 	public T getExtension(String name) {
 		if (name == null || name.length() == 0)
 		    throw new IllegalArgumentException("Extension name == null");
 		Reference<Object> reference = cachedInstances.get(name);
 		if (reference == null) {
 		    cachedInstances.putIfAbsent(name, new Reference<Object>());
 		    reference = cachedInstances.get(name);
 		}
 		Object instance = reference.get();
 		if (instance == null) {
 		    synchronized (reference) {
 	            instance = reference.get();
 	            if (instance == null) {
 	                instance = createExtension(name);
 	                reference.set(instance);
 	            }
 	        }
 		}
 		return (T) instance;
 	}

 	/**
 	 * 返回缺省的扩展，如果没有设置则返回<code>null</code>。
 	 */
 	public T getDefaultExtension() {
         getExtensionClasses();
 	    if(null == cachedDefaultName || cachedDefaultName.length() == 0) {
 	        return null;
 	    }
 	    return getExtension(cachedDefaultName);
 	}

 	public boolean hasExtension(String name) {
 	    if (name == null || name.length() == 0)
 	        throw new IllegalArgumentException("Extension name == null");
 	    try {
 	        return getExtensionClass(name) != null;
 	    } catch (Throwable t) {
 	        return false;
 	    }
 	}

 	public Set<String> getSupportedExtensions() {
         Map<String, Class<?>> clazzes = getExtensionClasses();
         return Collections.unmodifiableSet(new TreeSet<String>(clazzes.keySet()));
     }

 	/**
 	 * 返回缺省的扩展点名，如果没有设置缺省则返回<code>null</code>。
 	 */
 	public String getDefaultExtensionName() {
 	    getExtensionClasses();
 	    return cachedDefaultName;
 	}


     @SuppressWarnings("unchecked")
     public T getAdaptiveExtension() {
         Object instance = cachedAdaptiveInstance.get();
         if (instance == null) {
             if(createAdaptiveInstanceError == null) {
                 synchronized (cachedAdaptiveInstance) {
                     instance = cachedAdaptiveInstance.get();
                     if (instance == null) {
                         try {
                             instance = createAdaptiveExtension();
                             cachedAdaptiveInstance.set(instance);
                         } catch (Throwable t) {
                             createAdaptiveInstanceError = t;
                             rethrowAsRuntime(t, "fail to create adaptive instance: ");
                         }
                     }
                 }
             }
             else {
                 rethrowAsRuntime(createAdaptiveInstanceError, "fail to create adaptive instance: ");
             }
         }

         return (T) instance;
     }

     private static void rethrowAsRuntime(Throwable t, String message) {
         if(t instanceof RuntimeException)
             throw (RuntimeException)t;
         else
             throw new IllegalStateException(message + t.toString(), t);
     }

     private IllegalStateException findException(String name) {
         for (Map.Entry<String, IllegalStateException> entry : exceptions.entrySet()) {
             if (entry.getKey().toLowerCase().contains(name.toLowerCase())) {
                 return entry.getValue();
             }
         }
         StringBuilder buf = new StringBuilder("No such extension " + type.getName() + " by name " + name + ", possible causes: ");
         int i = 1;
         for (Map.Entry<String, IllegalStateException> entry : exceptions.entrySet()) {
             buf.append("\r\n(");
             buf.append(i ++);
             buf.append(") ");
             buf.append(entry.getKey());
             buf.append(":\r\n");
             buf.append(StringUtils.toString(entry.getValue()));
         }
         return new IllegalStateException(buf.toString());
     }

     @SuppressWarnings("unchecked")
     private T createExtension(String name) {
         Class<?> clazz = getExtensionClasses().get(name);
         if (clazz == null) {
             throw findException(name);
         }
         try {
             T instance = injectExtension((T) clazz.newInstance());
             Set<Class<?>> wrapperClasses = cachedWrapperClasses;
             if (wrapperClasses != null && wrapperClasses.size() > 0) {
                 for (Class<?> wrapperClass : wrapperClasses) {
                     instance = injectExtension((T) wrapperClass.getConstructor(type).newInstance(instance));
                 }
             }
             return instance;
         } catch (Throwable t) {
             throw new IllegalStateException("Extension instance(name: " + name + ", class: " +
                     type + ")  could not be instantiated: " + t.getMessage(), t);
         }
     }

     private T injectExtension(T instance) {
         try {
             for (Method method : instance.getClass().getMethods()) {
                 if (method.getName().startsWith("set")
                         && method.getParameterTypes().length == 1
                         && Modifier.isPublic(method.getModifiers())) {
                     Class<?> pt = method.getParameterTypes()[0];
                     if (pt.isInterface() && getExtensionLoader(pt).getSupportedExtensions().size() > 0) {
                         try {
                             Object adaptive = getExtensionLoader(pt).getAdaptiveExtension();
                             method.invoke(instance, adaptive);
                         } catch (Exception e) {
                             logger.error("fail to inject via method " + method.getName()
                             		+ " of interface " + type.getName() + ": " + e.getMessage(), e);
                         }
                     }
                 }
             }
         } catch (Exception e) {
             logger.error(e.getMessage(), e);
         }
         return instance;
     }

 	private Class<?> getExtensionClass(String name) {
 	    if (type == null)
 	        throw new IllegalArgumentException("Extension type == null");
 	    if (name == null)
 	        throw new IllegalArgumentException("Extension name == null");
 	    Class<?> clazz = getExtensionClasses().get(name);
 	    if (clazz == null)
 	        throw new IllegalStateException("No such extension \"" + name + "\" for " + type.getName() + "!");
 	    return clazz;
 	}

 	private Map<String, Class<?>> getExtensionClasses() {
         Map<String, Class<?>> classes = cachedClasses.get();
         if (classes == null) {
             synchronized (cachedClasses) {
                 classes = cachedClasses.get();
                 if (classes == null) {
                     classes = loadExtensionClasses();
                     cachedClasses.set(classes);
                 }
             }
         }
         return classes;
 	}

     private Map<String, Class<?>> loadExtensionClasses() {
         final Extension defaultAnnotation = type.getAnnotation(Extension.class);
         if(defaultAnnotation != null) {
             String[] names = NAME_SEPARATOR.split(defaultAnnotation.value());
             if(names.length > 1) {
                 throw new IllegalStateException("more than 1 default extension name on extension " + type.getName()
                         + ": " + Arrays.toString(names));
             }
             if(names.length == 1) cachedDefaultName = names[0];
         }

         ClassLoader classLoader = findClassLoader();
         Map<String, Class<?>> extensionClasses = new HashMap<String, Class<?>>();
         String fileName = null;
         try {
             fileName = SERVICES_DIRECTORY + type.getName();
             Enumeration<java.net.URL> urls;
             if (classLoader != null) {
                 urls = classLoader.getResources(fileName);
             } else {
                 urls = ClassLoader.getSystemResources(fileName);
             }
             if (urls != null) {
                 while (urls.hasMoreElements()) {
                     java.net.URL url = urls.nextElement();
                     try {
                         BufferedReader reader = new BufferedReader(new InputStreamReader(url.openStream(), "utf-8"));
                         try {
                             String line = null;
                             while ((line = reader.readLine()) != null) {
                                 final int ci = line.indexOf('#');
                                 if (ci >= 0) line = line.substring(0, ci);
                                 line = line.trim();
                                 if (line.length() > 0) {
                                     try {
                                         Class<?> clazz = Class.forName(line, true, classLoader);
                                         if (! type.isAssignableFrom(clazz)) {
                                             throw new IllegalStateException("Error when load extension class(interface: " +
                                                     type + ", class line: " + clazz.getName() + "), class "
                                                     + clazz.getName() + "is not subtype of interface.");
                                         }
                                         if (clazz.isAnnotationPresent(Adaptive.class)) {
                                             if(cachedAdaptiveClass == null) {
                                                 cachedAdaptiveClass = clazz;
                                             } else if (! cachedAdaptiveClass.equals(clazz)) {
                                                 throw new IllegalStateException("More than 1 adaptive class found: "
                                                         + cachedAdaptiveClass.getClass().getName()
                                                         + ", " + clazz.getClass().getName());
                                             }
                                         } else {
                                             try {
                                                 clazz.getConstructor(type);
                                                 Set<Class<?>> wrappers = cachedWrapperClasses;
                                                 if (wrappers == null) {
                                                     cachedWrapperClasses = new ConcurrentHashSet<Class<?>>();
                                                     wrappers = cachedWrapperClasses;
                                                 }
                                                 wrappers.add(clazz);
                                             } catch (NoSuchMethodException e) {
                                                 clazz.getConstructor();
                                                 Extension extension = clazz.getAnnotation(Extension.class);
                                                 if (extension == null) {
                                                     throw new IllegalStateException("No such @Extension annotation in class " + clazz.getName());
                                                 }
                                                 String name = extension.value();
                                                 if (name == null || name.length() == 0) {
                                                     throw new IllegalStateException("Illegal @Extension annotation in class " + clazz.getName());
                                                 }
                                                 String[] names = NAME_SEPARATOR.split(name);
                                                 for (String n : names) {
                                                     Class<?> c = extensionClasses.get(n);
                                                     if (c == null) {
                                                         extensionClasses.put(n, clazz);
                                                     } else if (c != clazz) {
                                                         throw new IllegalStateException("Duplicate extension " + type.getName() + " name " + n + " on " + c.getName() + " and " + clazz.getName());
                                                     }
                                                 }
                                             }
                                         }
                                     } catch (Throwable t) {
                                         IllegalStateException e = new IllegalStateException("Failed to load extension class(interface: " + type + ", class line: " + line + ") in " + url + ", cause: " + t.getMessage(), t);
                                         exceptions.put(line, e);
                                     }
                                 }
                             } // end of while read lines
                         } finally {
                             reader.close();
                         }
                     } catch (Throwable t) {
                         logger.error("Exception when load extension class(interface: " +
                                             type + ", class file: " + url + ") in " + url, t);
                     }
                 } // end of while urls
             }
         } catch (Throwable t) {
             logger.error("Exception when load extension class(interface: " +
                     type + ", description file: " + fileName + ").", t);
         }
         return extensionClasses;
     }

     @SuppressWarnings("unchecked")
     private T createAdaptiveExtension() {
         try {
             return injectExtension((T) getAdaptiveExtensionClass().newInstance());
         } catch (Exception e) {
             throw new IllegalStateException("Can not create adaptive extenstion " + type + ", cause: " + e.getMessage(), e);
         }
     }

     private Class<?> getAdaptiveExtensionClass() {
         getExtensionClasses();
         if (cachedAdaptiveClass != null) {
             return cachedAdaptiveClass;
         }
         return cachedAdaptiveClass = createAdaptiveExtensionClass();
     }

     private Class<?> createAdaptiveExtensionClass() {
         ClassLoader classLoader = findClassLoader();

         Method[] methods = type.getMethods();
         boolean hasAdaptiveAnnotation = false;
         for(Method m : methods) {
             if(m.isAnnotationPresent(Adaptive.class)) {
                 hasAdaptiveAnnotation = true;
                 break;
             }
         }
         // 完全没有Adaptive方法，则不需要生成Adaptive类
         if(! hasAdaptiveAnnotation)
             throw new IllegalStateException("No adaptive method on extension " + type.getName() + ", refuse to create the adaptive class!");

         ClassGenerator cg = ClassGenerator.newInstance(classLoader);
         cg.setClassName(type.getName() + "$Adpative");
         cg.addInterface(type);
         cg.addDefaultConstructor();

         for (Method method : methods) {
             Class<?> rt = method.getReturnType();
             Class<?>[] pts = method.getParameterTypes();

             Adaptive adaptiveAnnotation = method.getAnnotation(Adaptive.class);
             StringBuilder code = new StringBuilder(512);
             if (adaptiveAnnotation == null) {
                 code.append("throw new UnsupportedOperationException(\"method ")
                         .append(method.toString()).append(" of interface ")
                         .append(type.getName()).append(" is not adaptive method!\");");
             } else {
                 int urlTypeIndex = -1;
                 for (int i = 0; i < pts.length; ++i) {
                     if (pts[i].equals(URL.class)) {
                         urlTypeIndex = i;
                         break;
                     }
                 }
                 // 有类型为URL的参数
                 if (urlTypeIndex != -1) {
                     // Null Point check
                     String s = String.format("if (arg%d == null)  { throw new IllegalArgumentException(\"url == null\"); }",
                                     urlTypeIndex);
                     code.append(s);

                     s = String.format("%s url = arg%d;", URL.class.getName(), urlTypeIndex);
                     code.append(s);
                 }
                 // 参数没有URL类型
                 else {
                     String attribMethod = null;

                     // 找到参数的URL属性
                     LBL_PTS:
                     for (int i = 0; i < pts.length; ++i) {
                         Method[] ms = pts[i].getMethods();
                         for (Method m : ms) {
                             String name = m.getName();
                             if ((name.startsWith("get") || name.length() > 3)
                                     && Modifier.isPublic(m.getModifiers())
                                     && !Modifier.isStatic(m.getModifiers())
                                     && m.getParameterTypes().length == 0
                                     && m.getReturnType() == URL.class) {
                                 urlTypeIndex = i;
                                 attribMethod = name;
                                 break LBL_PTS;
                             }
                         }
                     }
                     if(attribMethod == null) {
                         throw new IllegalStateException("fail to create adative class for interface " + type.getName()
                         		+ ": not found url parameter or url attribute in parameters of method " + method.getName());
                     }

                     // Null point check
                     String s = String.format("if (arg%d == null)  { throw new IllegalArgumentException(\"%s argument == null\"); }",
                                     urlTypeIndex, pts[urlTypeIndex].getName());
                     code.append(s);
                     s = String.format("if (arg%d.%s() == null)  { throw new IllegalArgumentException(\"%s argument %s() == null\"); }",
                                     urlTypeIndex, attribMethod, pts[urlTypeIndex].getName(), attribMethod);
                     code.append(s);

                     s = String.format("%s url = arg%d.%s();",URL.class.getName(), urlTypeIndex, attribMethod);
                     code.append(s);
                 }

                 String[] value = adaptiveAnnotation.value();
                 // 没有设置Key，则使用“扩展点接口名的点分隔 作为Key
                 if(value.length == 0) {
                     char[] charArray = type.getSimpleName().toCharArray();
                     StringBuilder sb = new StringBuilder(128);
                     for (int i = 0; i < charArray.length; i++) {
                         if(Character.isUpperCase(charArray[i])) {
                             if(i != 0) {
                                 sb.append(".");
                             }
                             sb.append(Character.toLowerCase(charArray[i]));
                         }
                         else {
                             sb.append(charArray[i]);
                         }
                     }
                     value = new String[] {sb.toString()};
                 }

                 String defaultExtName = cachedDefaultName;
                 String getNameCode = null;
                 for (int i = value.length - 1; i >= 0; --i) {
                     if(i == value.length - 1) {
                         if(null != defaultExtName) {
                             if(!"protocol".equals(value[i]))
                                 getNameCode = String.format("url.getParameter(\"%s\", \"%s\")", value[i], defaultExtName);
                             else
                                 getNameCode = String.format("( url.getProtocol() == null ? \"%s\" : url.getProtocol() )", defaultExtName);
                         }
                         else {
                             if(!"protocol".equals(value[i]))
                                 getNameCode = String.format("url.getParameter(\"%s\")", value[i]);
                             else
                                 getNameCode = "url.getProtocol()";
                         }
                     }
                     else {
                         if(!"protocol".equals(value[i]))
                             getNameCode = String.format("url.getParameter(\"%s\", %s)", value[i], getNameCode);
                         else
                             getNameCode = String.format("( url.getProtocol() == null ? (%s) : url.getProtocol() )", getNameCode);
                     }
                 }
                 code.append("String extName = ").append(getNameCode).append(";");
                 // check extName == null?
                 String s = String.format("if(extName == null) {" +
                 		"throw new IllegalStateException(\"Fail to get extension(%s) name from url(\" + url.toString() + \") use keys(%s)\"); }",
                         type.getName(), Arrays.toString(value));
                 code.append(s);

                 s = String.format("%s extension = (%<s)%s.getExtensionLoader(%s.class).getExtension(extName);",
                         type.getName(), ExtensionLoader.class.getName(), type.getName());
                 code.append(s);

                 // return statement
                 if (!rt.equals(void.class)) {
                     code.append("return ");
                 }

                 s = String.format("extension.%s(", method.getName());
                 code.append(s);
                 for (int i = 0; i < pts.length; i++) {
                     if (i != 0)
                         code.append(", ");
                     code.append("arg").append(i);
                 }
                 code.append(");");
             }

             cg.addMethod(method.getName(), method.getModifiers(), rt, pts,
                     method.getExceptionTypes(), code.toString());
         }
         return cg.toClass();
     }

     private static ClassLoader findClassLoader() {
         ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
         if (classLoader != null) {
             return classLoader;
         }
         classLoader = ExtensionLoader.class.getClassLoader();
         return classLoader;
     }

     @Override
     public String toString() {
         return this.getClass().getName() + "[" + type.getName() + "]";
     }

 }
	/*
	* Copyright 1999-2011 Alibaba Group.
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/
	package com.alibaba.dubbo.common;

	import java.io.BufferedReader;
	import java.io.InputStreamReader;
	import java.lang.reflect.Method;
	import java.lang.reflect.Modifier;
	import java.util.Arrays;
	import java.util.Collections;
	import java.util.Enumeration;
	import java.util.HashMap;
	import java.util.Map;
	import java.util.Set;
	import java.util.TreeSet;
	import java.util.concurrent.ConcurrentHashMap;
	import java.util.concurrent.ConcurrentMap;
	import java.util.regex.Pattern;

	import com.alibaba.dubbo.common.bytecode.ClassGenerator;
	import com.alibaba.dubbo.common.logger.Logger;
	import com.alibaba.dubbo.common.logger.LoggerFactory;
	import com.alibaba.dubbo.common.utils.ConcurrentHashSet;
	import com.alibaba.dubbo.common.utils.Reference;
	import com.alibaba.dubbo.common.utils.StringUtils;

	/**
	* Dubbo使用的扩展点获取。<p>
	* <ul>
	* <li>自动注入关联扩展点。</li>
	* <li>自动Wrap上扩展点的Wrap类。</li>
	* <li>缺省获得的的扩展点是一个Adaptive Instance。
	* </ul>
	*
	* @see <a href="http://java.sun.com/j2se/1.5.0/docs/guide/jar/jar.html#Service%20Provider">JDK5.0的自动发现机制实现</a>
	*
	* @author william.liangf
	* @author ding.lid
	*
	* @see Extension
	* @see Adaptive
	*/
	public class ExtensionLoader<T> {

	private static final Logger logger = LoggerFactory.getLogger(ExtensionLoader.class);

	private static final String SERVICES_DIRECTORY = "META-INF/services/";

	private static final Pattern NAME_SEPARATOR = Pattern.compile("\\s[,]+\\s");

	private static final ConcurrentMap<Class<?>, ExtensionLoader<?>> EXTENSION_LOADERS = new ConcurrentHashMap<Class<?>, ExtensionLoader<?>>();

	private final Class<?> type;

	private final Reference<Map<String, Class<?>>> cachedClasses = new Reference<Map<String,Class<?>>>();

	private final ConcurrentMap<String, Reference<Object>> cachedInstances = new ConcurrentHashMap<String, Reference<Object>>();

	private volatile Class<?> cachedAdaptiveClass = null;

	private final Reference<Object> cachedAdaptiveInstance = new Reference<Object>();
	private volatile Throwable createAdaptiveInstanceError;

	private Set<Class<?>> cachedWrapperClasses;

	private String cachedDefaultName;

	private Map<String, IllegalStateException> exceptions = new ConcurrentHashMap<String, IllegalStateException>();

	@SuppressWarnings("unchecked")
	public static <T> ExtensionLoader<T> getExtensionLoader(Class<T> type) {
	if (type == null)
	throw new IllegalArgumentException("Extension type == null");

	ExtensionLoader<T> loader = (ExtensionLoader<T>) EXTENSION_LOADERS.get(type);
	if (loader == null) {
	EXTENSION_LOADERS.putIfAbsent(type, new ExtensionLoader<T>(type));
	loader = (ExtensionLoader<T>) EXTENSION_LOADERS.get(type);
	}
	return loader;
	}

	private ExtensionLoader(Class<?> type) {
	this.type = type;
	}

	@SuppressWarnings("unchecked")
	public T getExtension(String name) {
	if (name == null \|\| name.length() == 0)
	throw new IllegalArgumentException("Extension name == null");
	Reference<Object> reference = cachedInstances.get(name);
	if (reference == null) {
	cachedInstances.putIfAbsent(name, new Reference<Object>());
	reference = cachedInstances.get(name);
	}
	Object instance = reference.get();
	if (instance == null) {
	synchronized (reference) {
	instance = reference.get();
	if (instance == null) {
	instance = createExtension(name);
	reference.set(instance);
	}
	}
	}
	return (T) instance;
	}

	/**
	* 返回缺省的扩展，如果没有设置则返回<code>null</code>。
	*/
	public T getDefaultExtension() {
	getExtensionClasses();
	if(null == cachedDefaultName \|\| cachedDefaultName.length() == 0) {
	return null;
	}
	return getExtension(cachedDefaultName);
	}

	public boolean hasExtension(String name) {
	if (name == null \|\| name.length() == 0)
	throw new IllegalArgumentException("Extension name == null");
	try {
	return getExtensionClass(name) != null;
	} catch (Throwable t) {
	return false;
	}
	}

	public Set<String> getSupportedExtensions() {
	Map<String, Class<?>> clazzes = getExtensionClasses();
	return Collections.unmodifiableSet(new TreeSet<String>(clazzes.keySet()));
	}

	/**
	* 返回缺省的扩展点名，如果没有设置缺省则返回<code>null</code>。
	*/
	public String getDefaultExtensionName() {
	getExtensionClasses();
	return cachedDefaultName;
	}


	@SuppressWarnings("unchecked")
	public T getAdaptiveExtension() {
	Object instance = cachedAdaptiveInstance.get();
	if (instance == null) {
	if(createAdaptiveInstanceError == null) {
	synchronized (cachedAdaptiveInstance) {
	instance = cachedAdaptiveInstance.get();
	if (instance == null) {
	try {
	instance = createAdaptiveExtension();
	cachedAdaptiveInstance.set(instance);
	} catch (Throwable t) {
	createAdaptiveInstanceError = t;
	rethrowAsRuntime(t, "fail to create adaptive instance: ");
	}
	}
	}
	}
	else {
	rethrowAsRuntime(createAdaptiveInstanceError, "fail to create adaptive instance: ");
	}
	}

	return (T) instance;
	}

	private static void rethrowAsRuntime(Throwable t, String message) {
	if(t instanceof RuntimeException)
	throw (RuntimeException)t;
	else
	throw new IllegalStateException(message + t.toString(), t);
	}

	private IllegalStateException findException(String name) {
	for (Map.Entry<String, IllegalStateException> entry : exceptions.entrySet()) {
	if (entry.getKey().toLowerCase().contains(name.toLowerCase())) {
	return entry.getValue();
	}
	}
	StringBuilder buf = new StringBuilder("No such extension " + type.getName() + " by name " + name + ", possible causes: ");
	int i = 1;
	for (Map.Entry<String, IllegalStateException> entry : exceptions.entrySet()) {
	buf.append("\r\n(");
	buf.append(i ++);
	buf.append(") ");
	buf.append(entry.getKey());
	buf.append(":\r\n");
	buf.append(StringUtils.toString(entry.getValue()));
	}
	return new IllegalStateException(buf.toString());
	}

	@SuppressWarnings("unchecked")
	private T createExtension(String name) {
	Class<?> clazz = getExtensionClasses().get(name);
	if (clazz == null) {
	throw findException(name);
	}
	try {
	T instance = injectExtension((T) clazz.newInstance());
	Set<Class<?>> wrapperClasses = cachedWrapperClasses;
	if (wrapperClasses != null && wrapperClasses.size() > 0) {
	for (Class<?> wrapperClass : wrapperClasses) {
	instance = injectExtension((T) wrapperClass.getConstructor(type).newInstance(instance));
	}
	}
	return instance;
	} catch (Throwable t) {
	throw new IllegalStateException("Extension instance(name: " + name + ", class: " +
	type + ") could not be instantiated: " + t.getMessage(), t);
	}
	}

	private T injectExtension(T instance) {
	try {
	for (Method method : instance.getClass().getMethods()) {
	if (method.getName().startsWith("set")
	&& method.getParameterTypes().length == 1
	&& Modifier.isPublic(method.getModifiers())) {
	Class<?> pt = method.getParameterTypes()[0];
	if (pt.isInterface() && getExtensionLoader(pt).getSupportedExtensions().size() > 0) {
	try {
	Object adaptive = getExtensionLoader(pt).getAdaptiveExtension();
	method.invoke(instance, adaptive);
	} catch (Exception e) {
	logger.error("fail to inject via method " + method.getName()
	+ " of interface " + type.getName() + ": " + e.getMessage(), e);
	}
	}
	}
	}
	} catch (Exception e) {
	logger.error(e.getMessage(), e);
	}
	return instance;
	}

	private Class<?> getExtensionClass(String name) {
	if (type == null)
	throw new IllegalArgumentException("Extension type == null");
	if (name == null)
	throw new IllegalArgumentException("Extension name == null");
	Class<?> clazz = getExtensionClasses().get(name);
	if (clazz == null)
	throw new IllegalStateException("No such extension \"" + name + "\" for " + type.getName() + "!");
	return clazz;
	}

	private Map<String, Class<?>> getExtensionClasses() {
	Map<String, Class<?>> classes = cachedClasses.get();
	if (classes == null) {
	synchronized (cachedClasses) {
	classes = cachedClasses.get();
	if (classes == null) {
	classes = loadExtensionClasses();
	cachedClasses.set(classes);
	}
	}
	}
	return classes;
	}

	private Map<String, Class<?>> loadExtensionClasses() {
	final Extension defaultAnnotation = type.getAnnotation(Extension.class);
	if(defaultAnnotation != null) {
	String[] names = NAME_SEPARATOR.split(defaultAnnotation.value());
	if(names.length > 1) {
	throw new IllegalStateException("more than 1 default extension name on extension " + type.getName()
	+ ": " + Arrays.toString(names));
	}
	if(names.length == 1) cachedDefaultName = names[0];
	}

	ClassLoader classLoader = findClassLoader();
	Map<String, Class<?>> extensionClasses = new HashMap<String, Class<?>>();
	String fileName = null;
	try {
	fileName = SERVICES_DIRECTORY + type.getName();
	Enumeration<java.net.URL> urls;
	if (classLoader != null) {
	urls = classLoader.getResources(fileName);
	} else {
	urls = ClassLoader.getSystemResources(fileName);
	}
	if (urls != null) {
	while (urls.hasMoreElements()) {
	java.net.URL url = urls.nextElement();
	try {
	BufferedReader reader = new BufferedReader(new InputStreamReader(url.openStream(), "utf-8"));
	try {
	String line = null;
	while ((line = reader.readLine()) != null) {
	final int ci = line.indexOf('#');
	if (ci >= 0) line = line.substring(0, ci);
	line = line.trim();
	if (line.length() > 0) {
	try {
	Class<?> clazz = Class.forName(line, true, classLoader);
	if (! type.isAssignableFrom(clazz)) {
	throw new IllegalStateException("Error when load extension class(interface: " +
	type + ", class line: " + clazz.getName() + "), class "
	+ clazz.getName() + "is not subtype of interface.");
	}
	if (clazz.isAnnotationPresent(Adaptive.class)) {
	if(cachedAdaptiveClass == null) {
	cachedAdaptiveClass = clazz;
	} else if (! cachedAdaptiveClass.equals(clazz)) {
	throw new IllegalStateException("More than 1 adaptive class found: "
	+ cachedAdaptiveClass.getClass().getName()
	+ ", " + clazz.getClass().getName());
	}
	} else {
	try {
	clazz.getConstructor(type);
	Set<Class<?>> wrappers = cachedWrapperClasses;
	if (wrappers == null) {
	cachedWrapperClasses = new ConcurrentHashSet<Class<?>>();
	wrappers = cachedWrapperClasses;
	}
	wrappers.add(clazz);
	} catch (NoSuchMethodException e) {
	clazz.getConstructor();
	Extension extension = clazz.getAnnotation(Extension.class);
	if (extension == null) {
	throw new IllegalStateException("No such @Extension annotation in class " + clazz.getName());
	}
	String name = extension.value();
	if (name == null \|\| name.length() == 0) {
	throw new IllegalStateException("Illegal @Extension annotation in class " + clazz.getName());
	}
	String[] names = NAME_SEPARATOR.split(name);
	for (String n : names) {
	Class<?> c = extensionClasses.get(n);
	if (c == null) {
	extensionClasses.put(n, clazz);
	} else if (c != clazz) {
	throw new IllegalStateException("Duplicate extension " + type.getName() + " name " + n + " on " + c.getName() + " and " + clazz.getName());
	}
	}
	}
	}
	} catch (Throwable t) {
	IllegalStateException e = new IllegalStateException("Failed to load extension class(interface: " + type + ", class line: " + line + ") in " + url + ", cause: " + t.getMessage(), t);
	exceptions.put(line, e);
	}
	}
	} // end of while read lines
	} finally {
	reader.close();
	}
	} catch (Throwable t) {
	logger.error("Exception when load extension class(interface: " +
	type + ", class file: " + url + ") in " + url, t);
	}
	} // end of while urls
	}
	} catch (Throwable t) {
	logger.error("Exception when load extension class(interface: " +
	type + ", description file: " + fileName + ").", t);
	}
	return extensionClasses;
	}

	@SuppressWarnings("unchecked")
	private T createAdaptiveExtension() {
	try {
	return injectExtension((T) getAdaptiveExtensionClass().newInstance());
	} catch (Exception e) {
	throw new IllegalStateException("Can not create adaptive extenstion " + type + ", cause: " + e.getMessage(), e);
	}
	}

	private Class<?> getAdaptiveExtensionClass() {
	getExtensionClasses();
	if (cachedAdaptiveClass != null) {
	return cachedAdaptiveClass;
	}
	return cachedAdaptiveClass = createAdaptiveExtensionClass();
	}

	private Class<?> createAdaptiveExtensionClass() {
	ClassLoader classLoader = findClassLoader();

	Method[] methods = type.getMethods();
	boolean hasAdaptiveAnnotation = false;
	for(Method m : methods) {
	if(m.isAnnotationPresent(Adaptive.class)) {
	hasAdaptiveAnnotation = true;
	break;
	}
	}
	// 完全没有Adaptive方法，则不需要生成Adaptive类
	if(! hasAdaptiveAnnotation)
	throw new IllegalStateException("No adaptive method on extension " + type.getName() + ", refuse to create the adaptive class!");

	ClassGenerator cg = ClassGenerator.newInstance(classLoader);
	cg.setClassName(type.getName() + "$Adpative");
	cg.addInterface(type);
	cg.addDefaultConstructor();

	for (Method method : methods) {
	Class<?> rt = method.getReturnType();
	Class<?>[] pts = method.getParameterTypes();

	Adaptive adaptiveAnnotation = method.getAnnotation(Adaptive.class);
	StringBuilder code = new StringBuilder(512);
	if (adaptiveAnnotation == null) {
	code.append("throw new UnsupportedOperationException(\"method ")
	.append(method.toString()).append(" of interface ")
	.append(type.getName()).append(" is not adaptive method!\");");
	} else {
	int urlTypeIndex = -1;
	for (int i = 0; i < pts.length; ++i) {
	if (pts[i].equals(URL.class)) {
	urlTypeIndex = i;
	break;
	}
	}
	// 有类型为URL的参数
	if (urlTypeIndex != -1) {
	// Null Point check
	String s = String.format("if (arg%d == null) { throw new IllegalArgumentException(\"url == null\"); }",
	urlTypeIndex);
	code.append(s);

	s = String.format("%s url = arg%d;", URL.class.getName(), urlTypeIndex);
	code.append(s);
	}
	// 参数没有URL类型
	else {
	String attribMethod = null;

	// 找到参数的URL属性
	LBL_PTS:
	for (int i = 0; i < pts.length; ++i) {
	Method[] ms = pts[i].getMethods();
	for (Method m : ms) {
	String name = m.getName();
	if ((name.startsWith("get") \|\| name.length() > 3)
	&& Modifier.isPublic(m.getModifiers())
	&& !Modifier.isStatic(m.getModifiers())
	&& m.getParameterTypes().length == 0
	&& m.getReturnType() == URL.class) {
	urlTypeIndex = i;
	attribMethod = name;
	break LBL_PTS;
	}
	}
	}
	if(attribMethod == null) {
	throw new IllegalStateException("fail to create adative class for interface " + type.getName()
	+ ": not found url parameter or url attribute in parameters of method " + method.getName());
	}

	// Null point check
	String s = String.format("if (arg%d == null) { throw new IllegalArgumentException(\"%s argument == null\"); }",
	urlTypeIndex, pts[urlTypeIndex].getName());
	code.append(s);
	s = String.format("if (arg%d.%s() == null) { throw new IllegalArgumentException(\"%s argument %s() == null\"); }",
	urlTypeIndex, attribMethod, pts[urlTypeIndex].getName(), attribMethod);
	code.append(s);

	s = String.format("%s url = arg%d.%s();",URL.class.getName(), urlTypeIndex, attribMethod);
	code.append(s);
	}

	String[] value = adaptiveAnnotation.value();
	// 没有设置Key，则使用“扩展点接口名的点分隔作为Key
	if(value.length == 0) {
	char[] charArray = type.getSimpleName().toCharArray();
	StringBuilder sb = new StringBuilder(128);
	for (int i = 0; i < charArray.length; i++) {
	if(Character.isUpperCase(charArray[i])) {
	if(i != 0) {
	sb.append(".");
	}
	sb.append(Character.toLowerCase(charArray[i]));
	}
	else {
	sb.append(charArray[i]);
	}
	}
	value = new String[] {sb.toString()};
	}

	String defaultExtName = cachedDefaultName;
	String getNameCode = null;
	for (int i = value.length - 1; i >= 0; --i) {
	if(i == value.length - 1) {
	if(null != defaultExtName) {
	if(!"protocol".equals(value[i]))
	getNameCode = String.format("url.getParameter(\"%s\", \"%s\")", value[i], defaultExtName);
	else
	getNameCode = String.format("( url.getProtocol() == null ? \"%s\" : url.getProtocol() )", defaultExtName);
	}
	else {
	if(!"protocol".equals(value[i]))
	getNameCode = String.format("url.getParameter(\"%s\")", value[i]);
	else
	getNameCode = "url.getProtocol()";
	}
	}
	else {
	if(!"protocol".equals(value[i]))
	getNameCode = String.format("url.getParameter(\"%s\", %s)", value[i], getNameCode);
	else
	getNameCode = String.format("( url.getProtocol() == null ? (%s) : url.getProtocol() )", getNameCode);
	}
	}
	code.append("String extName = ").append(getNameCode).append(";");
	// check extName == null?
	String s = String.format("if(extName == null) {" +
	"throw new IllegalStateException(\"Fail to get extension(%s) name from url(\" + url.toString() + \") use keys(%s)\"); }",
	type.getName(), Arrays.toString(value));
	code.append(s);

	s = String.format("%s extension = (%<s)%s.getExtensionLoader(%s.class).getExtension(extName);",
	type.getName(), ExtensionLoader.class.getName(), type.getName());
	code.append(s);

	// return statement
	if (!rt.equals(void.class)) {
	code.append("return ");
	}

	s = String.format("extension.%s(", method.getName());
	code.append(s);
	for (int i = 0; i < pts.length; i++) {
	if (i != 0)
	code.append(", ");
	code.append("arg").append(i);
	}
	code.append(");");
	}

	cg.addMethod(method.getName(), method.getModifiers(), rt, pts,
	method.getExceptionTypes(), code.toString());
	}
	return cg.toClass();
	}

	private static ClassLoader findClassLoader() {
	ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
	if (classLoader != null) {
	return classLoader;
	}
	classLoader = ExtensionLoader.class.getClassLoader();
	return classLoader;
	}

	@Override
	public String toString() {
	return this.getClass().getName() + "[" + type.getName() + "]";
	}

	}