作者：光陆光陆光陆 | 来源：互联网 | 2023-09-24 10:57
【对这行代码进行源码分析】ExtensionLoader<Protocol>loaderExtensionLoader.
【对这行代码进行源码分析】
ExtensionLoader loader = ExtensionLoader.getExtensionLoader(Protocol.class);
final Protocol dubboProtocol = loader.getExtension("dubbo"); //要分析的源码
final Protocol adaptiveExtension = loader.getAdaptiveExtension();
【对上面第二行代码进行源码分析】
先看下第一行代码执行后的ExtensionLoader实例化的结果
其中
* type =interface com.alibaba.dubbo.rpc.Protocol
* ExtensionFactory objectFactory = AdaptiveExtensionFactory（适配类）
* AdaptiveExtensionFactory成员变量factories = [ SpringExtensionFactory实例，SpiExtensionFactory实例 ]
【 getExtension(String name)调用流程 】
ExtensionLoader loader = ExtensionLoader.getExtensionLoader(Protocol.class);
final Protocol dubboProtocol = loader.getExtension("dubbo");
--createExtension(name);
----getExtensionClasses() //获取扩展类
------loadExtensionClasses()
--------loadFile(Map> extensionClasses, String dir)
//ioc属性注入
----injectExtension(instance);
//aop+ioc属性注入 aop获得一个wrapper装饰类
----instance = injectExtension((T) wrapperClass.getConstructor(type).newInstance(instance));
【 createExtension(String name)源码 】
private T createExtension(String name) {
/**
* 从Holder>>cachedClasses缓存中获取所有的实现类map，
* 然后通过name获取到对应的实现类（此时只是一个对象实例，还没有属性注入）
*/
Class clazz = getExtensionClasses().get(name);
if (clazz == null) {
throw findException(name);
}
try {
/**
* 从 ConcurrentMap, Object> EXTENSION_INSTANCES 类缓存中获取到对应的实现类的Class对象，
* 如果没有，直接创建，之后放入缓存
*/
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> 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);
}
}
回头看下META-INF/dubbo/internal/com.alibaba.dubbo.rpc.Protocol文件内容
registry=com.alibaba.dubbo.registry.integration.RegistryProtocol
dubbo=com.alibaba.dubbo.rpc.protocol.dubbo.DubboProtocol
filter=com.alibaba.dubbo.rpc.protocol.ProtocolFilterWrapper
listener=com.alibaba.dubbo.rpc.protocol.ProtocolListenerWrapper
mock=com.alibaba.dubbo.rpc.support.MockProtocol
injvm=com.alibaba.dubbo.rpc.protocol.injvm.InjvmProtocol
rmi=com.alibaba.dubbo.rpc.protocol.rmi.RmiProtocol
hessian=com.alibaba.dubbo.rpc.protocol.hessian.HessianProtocol
com.alibaba.dubbo.rpc.protocol.http.HttpProtocol
com.alibaba.dubbo.rpc.protocol.webservice.WebServiceProtocol
thrift=com.alibaba.dubbo.rpc.protocol.thrift.ThriftProtocol
memcached=com.alibaba.dubbo.rpc.protocol.memcached.MemcachedProtocol
redis=com.alibaba.dubbo.rpc.protocol.redis.RedisProtocol
com.alibaba.dubbo.rpc.protocol.ProtocolFilterWrapper和com.alibaba.dubbo.rpc.protocol.ProtocolListenerWrapper，这两个类不含有@Adaptive注解且含有Protocol的单参数构造方法，符合这2个条件的类会被列入AOP增强类，会被防止在ExtensionLoader的实例缓存Set> cachedWrapperClasses;中。
此时的loader：
* type =interface com.alibaba.dubbo.rpc.Protocol
* ExtensionFactory objectFactory = AdaptiveExtensionFactory（适配类）
* AdaptiveExtensionFactory成员变量factories = [ SpringExtensionFactory实例，SpiExtensionFactory实例 ]
* cachedWrapperClasses = [ class ProtocolListenerWrapper, class ProtocolFilterWrapper ]
再来看createExtension(String name )中的aop红色部分代码，即dubbo的aop部分。
Set> wrapperClasses = cachedWrapperClasses;
if (wrapperClasses != null && wrapperClasses.size() > 0) {
for (Class wrapperClass : wrapperClasses) {
instance = injectExtension((T) wrapperClass.getConstructor(type).newInstance(instance));
}
}
在cachedWrapperClasses中缓存两个AOP增强类：ProtocolListenerWrapper和ProtocolFilterWrapper。
首先获取ProtocolListenerWrapper的单参数构造方法，然后创建ProtocolWrapper实例，最后完成对ProtocolListenerWrapper实例的属性注入，注意此时的instance = ProtocolListenerWrapper实例，而不是之前的DubboProtocol实例，之后使用ProtocolFilterWrapper以同样的方式进行包装，只是此时的ProtocolFilterWrapper包装的是ProtocolListenerWrapper实例。
instance = ProtocolFilterWrapper实例{
protocol = ProtocolListenerWrapper实例{
protocol = DubboProtocol实例
}
}
【 ProtocolListenerWrapper源码 】
/**
* ListenerProtocol
*
* @author william.liangf
*/
public class ProtocolListenerWrapper implements Protocol {
private final Protocol protocol;
public ProtocolListenerWrapper(Protocol protocol) {
if (protocol == null) {
throw new IllegalArgumentException("protocol == null");
}
this.protocol = protocol;
}
public int getDefaultPort() {
return protocol.getDefaultPort();
}
public Exporter export(Invoker invoker) throws RpcException {
if (Constants.REGISTRY_PROTOCOL.equals(invoker.getUrl().getProtocol())) {
return protocol.export(invoker);
}
return new ListenerExporterWrapper(protocol.export(invoker),
Collections.unmodifiableList(ExtensionLoader.getExtensionLoader(ExporterListener.class)
.getActivateExtension(invoker.getUrl(), Constants.EXPORTER_LISTENER_KEY)));
}
public Invoker refer(Class type, URL url) throws RpcException {
if (Constants.REGISTRY_PROTOCOL.equals(url.getProtocol())) {
return protocol.refer(type, url);
}
return new ListenerInvokerWrapper(protocol.refer(type, url),
Collections.unmodifiableList(
ExtensionLoader.getExtensionLoader(InvokerListener.class)
.getActivateExtension(url, Constants.INVOKER_LISTENER_KEY)));
}
public void destroy() {
protocol.destroy();
}
}
【 ProtocolFilterWrapper源码 】
/**
* ListenerProtocol
*
* @author william.liangf
*/
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 static Invoker buildInvokerChain(final Invoker invoker, String key, String group) {
Invoker last = invoker;
List filters = ExtensionLoader.getExtensionLoader(Filter.class).getActivateExtension(invoker.getUrl(), key, group);
if (filters.size() > 0) {
for (int i = filters.size() - 1; i >= 0; i--) {
final Filter filter = filters.get(i);
final Invoker next = last;
last = new Invoker() {
public Class getInterface() {
return invoker.getInterface();
}
public URL getUrl() {
return invoker.getUrl();
}
public boolean isAvailable() {
return invoker.isAvailable();
}
public Result invoke(Invocation invocation) throws RpcException {
return filter.invoke(next, invocation);
}
public void destroy() {
invoker.destroy();
}
@Override
public String toString() {
return invoker.toString();
}
};
}
}
return last;
}
public int getDefaultPort() {
return protocol.getDefaultPort();
}
public Exporter export(Invoker invoker) throws RpcException {
if (Constants.REGISTRY_PROTOCOL.equals(invoker.getUrl().getProtocol())) {
return protocol.export(invoker);
}
return protocol.export(buildInvokerChain(invoker, Constants.SERVICE_FILTER_KEY, Constants.PROVIDER));
}
public Invoker refer(Class type, URL url) throws RpcException {
if (Constants.REGISTRY_PROTOCOL.equals(url.getProtocol())) {
return protocol.refer(type, url);
}
return buildInvokerChain(protocol.refer(type, url), Constants.REFERENCE_FILTER_KEY, Constants.CONSUMER);
}
public void destroy() {
protocol.destroy();
}
}
【结果】
最后返回的instance是ProtocolFilterWrapper对象，
final Protocol dubboProtocol = loader.getExtension("dubbo");
这句代码最后的dubboProtocol是ProtocolFilterWrapper实例。
【参考文章】
https://www.cnblogs.com/java-zhao/p/7478136.html
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