@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE})
public @interface SPI {/*** 缺省扩展点名。*/String value() default "";}

@SPI("dubbo")
public interface Protocol {int getDefaultPort();@Adaptive<T> Exporter<T> export(Invoker<T> invoker) throws RpcException;@Adaptive<T> Invoker<T> refer(Class<T> type, URL url) throws RpcException;void destroy();}

public class ProtocolFilterWrapper implements Protocol {private final Protocol protocol;public ProtocolFilterWrapper(Protocol protocol) {if (protocol == null) {throw new IllegalArgumentException("protocol == null");}this.protocol = protocol;}..........
}

private String createAdaptiveExtensionClassCode() {StringBuilder codeBuidler = new StringBuilder();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!");codeBuidler.append("package " + type.getPackage().getName() + ";");codeBuidler.append("\nimport " + ExtensionLoader.class.getName() + ";");codeBuidler.append("\npublic class " + type.getSimpleName() + "$Adaptive" + " implements " + type.getCanonicalName() + " {");for (Method method : methods) {Class<?> rt = method.getReturnType();Class<?>[] pts = method.getParameterTypes();Class<?>[] ets = method.getExceptionTypes();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 checkString s = String.format("\nif (arg%d == null) throw new IllegalArgumentException(\"url == null\");",urlTypeIndex);code.append(s);s = String.format("\n%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 checkString s = String.format("\nif (arg%d == null) throw new IllegalArgumentException(\"%s argument == null\");",urlTypeIndex, pts[urlTypeIndex].getName());code.append(s);s = String.format("\nif (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Keyif (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()};}boolean hasInvocation = false;for (int i = 0; i < pts.length; ++i) {if (pts[i].getName().equals("com.alibaba.dubbo.rpc.Invocation")) {// Null Point checkString s = String.format("\nif (arg%d == null) throw new IllegalArgumentException(\"invocation == null\");", i);code.append(s);s = String.format("\nString methodName = arg%d.getMethodName();", i);code.append(s);hasInvocation = true;break;}}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]))if (hasInvocation)getNameCode = String.format("url.getMethodParameter(methodName, \"%s\", \"%s\")", value[i], defaultExtName);elsegetNameCode = String.format("url.getParameter(\"%s\", \"%s\")", value[i], defaultExtName);elsegetNameCode = String.format("( url.getProtocol() == null ? \"%s\" : url.getProtocol() )", defaultExtName);} else {if (!"protocol".equals(value[i]))if (hasInvocation)getNameCode = String.format("url.getMethodParameter(methodName, \"%s\", \"%s\")", value[i], defaultExtName);elsegetNameCode = String.format("url.getParameter(\"%s\")", value[i]);elsegetNameCode = "url.getProtocol()";}} else {if (!"protocol".equals(value[i]))if (hasInvocation)getNameCode = String.format("url.getMethodParameter(methodName, \"%s\", \"%s\")", value[i], defaultExtName);elsegetNameCode = String.format("url.getParameter(\"%s\", %s)", value[i], getNameCode);elsegetNameCode = String.format("url.getProtocol() == null ? (%s) : url.getProtocol()", getNameCode);}}code.append("\nString extName = ").append(getNameCode).append(";");// check extName == null?String s = String.format("\nif(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("\n%s extension = (%<s)%s.getExtensionLoader(%s.class).getExtension(extName);",type.getName(), ExtensionLoader.class.getSimpleName(), type.getName());code.append(s);// return statementif (!rt.equals(void.class)) {code.append("\nreturn ");}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(");");}codeBuidler.append("\npublic " + rt.getCanonicalName() + " " + method.getName() + "(");for (int i = 0; i < pts.length; i++) {if (i > 0) {codeBuidler.append(", ");}codeBuidler.append(pts[i].getCanonicalName());codeBuidler.append(" ");codeBuidler.append("arg" + i);}codeBuidler.append(")");if (ets.length > 0) {codeBuidler.append(" throws ");for (int i = 0; i < ets.length; i++) {if (i > 0) {codeBuidler.append(", ");}codeBuidler.append(ets[i].getCanonicalName());}}codeBuidler.append(" {");codeBuidler.append(code.toString());codeBuidler.append("\n}");}codeBuidler.append("\n}");if (logger.isDebugEnabled()) {logger.debug(codeBuidler.toString());}return codeBuidler.toString();}

private Class<?> createAdaptiveExtensionClass() {String code = createAdaptiveExtensionClassCode();ClassLoader classLoader = findClassLoader();com.alibaba.dubbo.common.compiler.Compiler compiler = ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.common.compiler.Compiler.class).getAdaptiveExtension();return compiler.compile(code, classLoader);}

private T createExtension(String name) {Class<?> clazz = getExtensionClasses().get(name);if (clazz == null) {throw findException(name);}try {T instance = (T) EXTENSION_INSTANCES.get(clazz);if (instance == null) {EXTENSION_INSTANCES.putIfAbsent(clazz, (T) clazz.newInstance());instance = (T) EXTENSION_INSTANCES.get(clazz);}injectExtension(instance);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 {if (objectFactory != null) {for (Method method : instance.getClass().getMethods()) {if (method.getName().startsWith("set")&& method.getParameterTypes().length == 1&& Modifier.isPublic(method.getModifiers())) {Class<?> pt = method.getParameterTypes()[0];try {String property = method.getName().length() > 3 ? method.getName().substring(3, 4).toLowerCase() + method.getName().substring(4) : "";Object object = objectFactory.getExtension(pt, property);if (object != null) {method.invoke(instance, object);}} 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;}

public <T> T getExtension(Class<T> type, String name) {if (type.isInterface() && type.isAnnotationPresent(SPI.class)) {ExtensionLoader<T> loader = ExtensionLoader.getExtensionLoader(type);if (loader.getSupportedExtensions().size() > 0) {return loader.getAdaptiveExtension();}}return null;}

public <T> T getExtension(Class<T> type, String name) {for (ApplicationContext context : contexts) {if (context.containsBean(name)) {Object bean = context.getBean(name);if (type.isInstance(bean)) {return (T) bean;}}}return null;}