概述
目录
一、概述
二、AdaptiveClassCodeGenerator
三、getExtension方法
四、getActivateExtension方法
一、概述
上一篇文章介绍了Dubbo的SPI机制ExtensionLoader源码，分析了ExtensionLoader如何从META-INFO/dubbo等目录下
获取service provider，并了解了它的缓存机制，缓存class字节码，缓存实例化异常Exception,缓存AdaptiveExtension实体对象，
以及它的自动注入ExtensionFactory的实现原理。
Dubbo源码分析之SPI(二) | ExtensionLoader_青枫绿屿的博客-CSDN博客
本文接着介绍ExtensionLoader通过JavassistCompiler动态生成AdaptiveExtension代码逻辑，并通过Protocol的加载进行实例分析和学习Dubbo的自动包装Wapper功能。
二、AdaptiveClassCodeGenerator
createAdaptiveExtensionClass方法中使用AdaptiveClassCodeGenerator动态生成代码，下面是生成的Protocol$Adaptive代码。
package org.apache.dubbo.rpc;
import org.apache.dubbo.common.extension.ExtensionLoader;
public class Protocol$Adaptive implements org.apache.dubbo.rpc.Protocol {
public void destroy() {
throw new UnsupportedOperationException(
"The method public abstract void org.apache.dubbo.rpc.Protocol.destroy() of interface org.apache.dubbo.rpc.Protocol is not adaptive method!");
}
public int getDefaultPort() {
throw new UnsupportedOperationException(
"The method public abstract int org.apache.dubbo.rpc.Protocol.getDefaultPort() of interface org.apache.dubbo.rpc.Protocol is not adaptive method!");
}
public org.apache.dubbo.rpc.Invoker refer(java.lang.Class arg0, org.apache.dubbo.common.URL arg1) throws org.apache.dubbo.rpc.RpcException {
if (arg1 == null)
throw new IllegalArgumentException("url == null");
org.apache.dubbo.common.URL url = arg1;
String extName = (url.getProtocol() == null ? "dubbo" : url.getProtocol());
if (extName == null)
throw new IllegalStateException(
"Failed to get extension (org.apache.dubbo.rpc.Protocol) name from url (" + url.toString() + ") use keys([protocol])");
org.apache.dubbo.rpc.Protocol extension = (org.apache.dubbo.rpc.Protocol) ExtensionLoader.getExtensionLoader(org.apache.dubbo.rpc.Protocol.class)
.getExtension(extName);
return extension.refer(arg0, arg1);
}
public org.apache.dubbo.rpc.Exporter export(org.apache.dubbo.rpc.Invoker arg0) throws org.apache.dubbo.rpc.RpcException {
if (arg0 == null)
throw new IllegalArgumentException("org.apache.dubbo.rpc.Invoker argument == null");
if (arg0.getUrl() == null)
throw new IllegalArgumentException("org.apache.dubbo.rpc.Invoker argument getUrl() == null");
org.apache.dubbo.common.URL url = arg0.getUrl();
String extName = (url.getProtocol() == null ? "dubbo" : url.getProtocol());
if (extName == null)
throw new IllegalStateException(
"Failed to get extension (org.apache.dubbo.rpc.Protocol) name from url (" + url.toString() + ") use keys([protocol])");
org.apache.dubbo.rpc.Protocol extension = (org.apache.dubbo.rpc.Protocol) ExtensionLoader.getExtensionLoader(org.apache.dubbo.rpc.Protocol.class)
.getExtension(extName);
return extension.export(arg0);
}
}其中destroy和getDefaultPort方法都是不支持的，会抛出异常UnsupportedOperationException。是因为接口上的Method，没有标注@Adaptive注解，只有标注@Adaptive注解的才会generateExtensionAssignment。
private String generateMethodContent(Method method) {
Adaptive adaptiveAnnotation = method.getAnnotation(Adaptive.class);
StringBuilder code = new StringBuilder(512);
if (adaptiveAnnotation == null) {
return generateUnsupported(method);
} else {
int urlTypeIndex = getUrlTypeIndex(method);
// found parameter in URL type
if (urlTypeIndex != -1) {
// Null Point check
code.append(generateUrlNullCheck(urlTypeIndex));
} else {
// did not find parameter in URL type
code.append(generateUrlAssignmentIndirectly(method));
}
String[] value = getMethodAdaptiveValue(adaptiveAnnotation);
boolean hasInvocation = hasInvocationArgument(method);
code.append(generateInvocationArgumentNullCheck(method));
code.append(generateExtNameAssignment(value, hasInvocation));
// check extName == null?
code.append(generateExtNameNullCheck(value));
code.append(generateExtensionAssignment());
// return statement
code.append(generateReturnAndInvocation(method));
}
return code.toString();
}refer和export方法在这里可以看到生成code的时候，会根据他们的协议去自动使用不同的协议处理器处理逻辑。
a)when the url is registry://224.5.6.7:1234/org.apache.dubbo.registry.RegistryService?application=dubbo-sample, then the protocol is RegistryProtocol
b)when the url is dubbo://224.5.6.7:1234/org.apache.dubbo.config.api.DemoService?application=dubbo-sample, thenthe protocol is DubboProtocol
c) Actually，when the {@link ExtensionLoader} init the {@link Protocol} instants,it will automatically wraps two layers, and eventually will get a ProtocolFilterWrapper or ProtocolListenerWrapper
private String generateExtNameAssignment(String[] value, boolean hasInvocation) {
// TODO: refactor it
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);
} else {
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])) {
if (hasInvocation) {
getNameCode = String.format("url.getMethodParameter(methodName, "%s", "%s")", value[i], defaultExtName);
} else {
getNameCode = String.format("url.getParameter("%s")", value[i]);
}
} else {
getNameCode = "url.getProtocol()";
}
}
} else {
if (!"protocol".equals(value[i])) {
if (hasInvocation) {
getNameCode = String.format("url.getMethodParameter(methodName, "%s", "%s")", value[i], defaultExtName);
} else {
getNameCode = String.format("url.getParameter("%s", %s)", value[i], getNameCode);
}
} else {
getNameCode = String.format("url.getProtocol() == null ? (%s) : url.getProtocol()", getNameCode);
}
}
}
return String.format(CODE_EXT_NAME_ASSIGNMENT, getNameCode);
}三、getExtension方法
ExtensionLoader还提供了通过name获取service provider的getExtension方法，为了保证线程安全采用了Holder对象持有name的实体类，具体创建逻辑在createExtension中。
public T getExtension(String name) {
if (StringUtils.isEmpty(name)) {
throw new IllegalArgumentException("Extension name == null");
}
if ("true".equals(name)) {
return getDefaultExtension();
}
final Holder<Object> holder = getOrCreateHolder(name);
Object instance = holder.get();
if (instance == null) {
synchronized (holder) {
instance = holder.get();
if (instance == null) {
instance = createExtension(name);
holder.set(instance);
}
}
}
return (T) instance;
}
createExtension方法，会去获取所有的Class，同样先从缓存EXTENSION_INSTANCES中获取实体对象，然后再实例化，如果此name的接口Type类型有包装类加载，会对当前实体进行包装。如DubboProtocol实际上会被包装3层（ProtocolListenerWrapper，ProtocolFilterWrapper，QosProtocolWrapper）。
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, clazz.newInstance());
instance = (T) EXTENSION_INSTANCES.get(clazz);
}
injectExtension(instance);
Set<Class<?>> wrapperClasses = cachedWrapperClasses;
if (CollectionUtils.isNotEmpty(wrapperClasses)) {
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 + ") couldn't be instantiated: " + t.getMessage(), t);
}
}四、getActivateExtension方法
Extensionloader还提供getActivateExtension方法，用来根据url的参数值选着不同的service provider。key，group参数分别为实现类上注解@Activate的value，grop值。
public List<T> getActivateExtension(URL url, String[] values) {
return getActivateExtension(url, values, null);
}
public List<T> getActivateExtension(URL url, String key, String group) {
String value = url.getParameter(key);
return getActivateExtension(url, StringUtils.isEmpty(value) ? null : COMMA_SPLIT_PATTERN.split(value), group);
}上面两个方法实际调用如下方法，cachedActivates为Extensionloader为@Activate注解的缓存map,key为服务提供者名称，value为Activate对象。然后再遍历Activate对象，找到与传入参数匹配的name,然后遍历再调用getExtension(name)获取所有服务提供者。
public List<T> getActivateExtension(URL url, String[] values, String group) {
List<T> exts = new ArrayList<>();
List<String> names = values == null ? new ArrayList<>(0) : Arrays.asList(values);
if (!names.contains(REMOVE_VALUE_PREFIX + DEFAULT_KEY)) {
getExtensionClasses();
for (Map.Entry<String, Object> entry : cachedActivates.entrySet()) {
String name = entry.getKey();
Object activate = entry.getValue();
String[] activateGroup, activateValue;
if (activate instanceof Activate) {
activateGroup = ((Activate) activate).group();
activateValue = ((Activate) activate).value();
} else if (activate instanceof com.alibaba.dubbo.common.extension.Activate) {
activateGroup = ((com.alibaba.dubbo.common.extension.Activate) activate).group();
activateValue = ((com.alibaba.dubbo.common.extension.Activate) activate).value();
} else {
continue;
}
if (isMatchGroup(group, activateGroup)) {
T ext = getExtension(name);
if (!names.contains(name)
&& !names.contains(REMOVE_VALUE_PREFIX + name)
&& isActive(activateValue, url)) {
exts.add(ext);
}
}
}
exts.sort(ActivateComparator.COMPARATOR);
}
List<T> usrs = new ArrayList<>();
for (int i = 0; i < names.size(); i++) {
String name = names.get(i);
if (!name.startsWith(REMOVE_VALUE_PREFIX)
&& !names.contains(REMOVE_VALUE_PREFIX + name)) {
if (DEFAULT_KEY.equals(name)) {
if (!usrs.isEmpty()) {
exts.addAll(0, usrs);
usrs.clear();
}
} else {
T ext = getExtension(name);
usrs.add(ext);
}
}
}
if (!usrs.isEmpty()) {
exts.addAll(usrs);
}
return exts;
}@Activate注解的缓存
private final Map<String, Object> cachedActivates = new ConcurrentHashMap<>();cachedActivates缓存方法，同时兼容alibaba包下旧的注解
private void cacheActivateClass(Class<?> clazz, String name) {
Activate activate = clazz.getAnnotation(Activate.class);
if (activate != null) {
cachedActivates.put(name, activate);
} else {
// support com.alibaba.dubbo.common.extension.Activate
com.alibaba.dubbo.common.extension.Activate oldActivate = clazz.getAnnotation(com.alibaba.dubbo.common.extension.Activate.class);
if (oldActivate != null) {
cachedActivates.put(name, oldActivate);
}
}
}最后
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