1、jdk spi
spi服务发现即动态替换发现的机制
比如有个接口，在运行时动态的给它添加实现，只需要添加一个实现
Demo https://github.com/luozhonghua/dubbo-spiDemo
2、Dubbo SPI
2.1、可以方便的获取某一个想要的扩展实现
2.2、对于扩展实现IOC依赖注入功能
2.3、对扩展采用装饰器模式进行功能增强，类似AOP实现的功能
以Protocol协议为例
1、Protocol接口说明
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.rpc;
import com.alibaba.dubbo.common.URL;
import com.alibaba.dubbo.common.extension.Adaptive;
import com.alibaba.dubbo.common.extension.SPI;
/**
* Protocol. (API/SPI, Singleton, ThreadSafe)
* dubbo协议
*/
@SPI("dubbo")
public interface Protocol {
/**
* 获取缺省端口,当用户没有配置端口时使用
* Get default port when user doesn't config the port.
*
* @return default port
*/
int getDefaultPort();
/**
* 暴露远程服务
* Export service for remote invocation: <br>
*
* 协议在接收请求时，应记录请求来源方地址信息：RpcContext.getContext().setRemoteAddress();
* 1. Protocol should record request source address after receive a request:
* RpcContext.getContext().setRemoteAddress();<br>
*
* export()必须是幂等的，也就是暴露同一个URL的Invoker两次，和暴露一次没有区别
* 2. export() must be idempotent, that is, there's no difference between invoking once and invoking twice when
* export the same URL<br>
*
* export()传入的Invoker由框架实现并传入，协议不需要关心
* 3. Invoker instance is passed in by the framework, protocol needs not to care <br>
*
* @param <T> Service type 服务的类型
* @param invoker Service invoker 服务的执行体
* @return exporter reference for exported service, useful for unexport the service later 暴露服务的引用,用于取消暴露
* @throws RpcException thrown when error occurs during export the service, for example: port is occupied 当暴露服务出错时抛出，比如端口已占用
*/
@Adaptive
<T> Exporter<T> export(Invoker<T> invoker) throws RpcException;
/**
* 引用远程服务
* Refer a remote service: <br>
*
* 当用户调用refer()所返回的Invoker对象的invoke()方法时,协议需相应执行同URL远端export()传入的Invoker对象的invoke()方法
* 1. When user calls `invoke()` method of `Invoker` object which's returned from `refer()` call, the protocol
* needs to correspondingly execute `invoke()` method of `Invoker` object <br>
*
* refer()返回的Invoker由协议实现，协议通常需要在此Invoker中发送远程请求
* 2. It's protocol's responsibility to implement `Invoker` which's returned from `refer()`. Generally speaking,
* protocol sends remote request in the `Invoker` implementation. <br>
*
* 当url中有设置check=false时，连接失败不能抛出异常，并内部自动恢复
* 3. When there's check=false set in URL, the implementation must not throw exception but try to recover when
* connection fails.
*
* @param <T> Service type 服务的类型
* @param type Service class 服务的类型类
* @param url URL address for the remote service 远程服务的URL地址
* @return invoker service's local proxy 服务的本地代理
* @throws RpcException when there's any error while connecting to the service provider 当连接服务提供方失败时抛出
*/
@Adaptive
<T> Invoker<T> refer(Class<T> type, URL url) throws RpcException;
/**释放协议
* Destroy protocol: <br>
* 取消该协议所有已经暴露和引用的服务
* 1. Cancel all services this protocol exports and refers <br>
* 释放协议所占用的所有资源，比如连接和端口
* 2. Release all occupied resources, for example: connection, port, etc. <br>
* 协议在释放后，依然能暴露和引用新的服务
* 3. Protocol can continue to export and refer new service even after it's destroyed.
*/
void destroy();
}2,实现类List
3,继承关系tree
4、工厂模式
ExtensionLoader是如何来加载Protocol.class这些实现类?
1、先解析Protocol上的Extension注解(@Adaptive)的name,存至String cachedDefaultName属性中，作为默认的实现
2、到类路径下的加载 META-INF/services/com.alibaba.dubbo.rpc.Protocol文件
看下测试用例 --debugger跟进去吧
/**
* Created by luozhonghua on 2018/5/26.
*/
public class ProtocolTest_1 {
@Test
public void test_destroyWontCloseAllProtocol() throws Exception {
// Protocol autowireProtocol = ExtensionLoader.getExtensionLoader(Protocol.class).getAdaptiveExtension();
//Protocol InjvmProtocol = ExtensionLoader.getExtensionLoader(Protocol.class).getExtension("mock");
Filter InjvmProtocol = ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.rpc.Filter.class).getAdaptiveExtension();
try {
// InjvmProtocol.destroy();
// autowireProtocol.destroy();
} catch (UnsupportedOperationException expected) {
assertThat(expected.getMessage(), containsString("of interface com.alibaba.dubbo.rpc.Protocol is not adaptive method!"));
}
}
}
5、动态代理模式
ExtensionLoader 的 Adaptive 实现是典型的动态代理实现。Dubbo需要灵活地控制实现类，即在调用阶段动态地根据参数决定调用哪个实现类，所以采用先生成代理类的方法，能够做到灵活的调用。生成代理类的代码是 ExtensionLoader 的createAdaptiveExtensionClassCode 方法。代理类的主要逻辑是获取 URL 参数中指定参数的值作为获取实现类的 key
/**
* 根据URL传参获取指定实现类的key
* @return
*/
private String createAdaptiveExtensionClassCode() {
StringBuilder codeBuidler = new StringBuilder();
Method[] methods = type.getMethods();// 根据反射获取方法集合
boolean hasAdaptiveAnnotation = false;
for (Method m : methods) {
if (m.isAnnotationPresent(Adaptive.class)) { //是否使用了@Adaptive
hasAdaptiveAnnotation = true;
break;
}
}
// no need to generate adaptive class since there's no adaptive method found.
if (!hasAdaptiveAnnotation)
throw new IllegalStateException("No adaptive method on extension " + type.getName() + ", refuse to create the adaptive class!");
//组合类路径
codeBuidler.append("package " + type.getPackage().getName() + ";");
codeBuidler.append("\nimport " + ExtensionLoader.class.getName() + ";");
codeBuidler.append("\npublic class " + type.getSimpleName() + "$Adaptive" + " implements " + type.getCanonicalName() + " {");
//存在@Adaptive
for (Method method : methods) {
Class<?> rt = method.getReturnType();// 获取方法返回值类型
Class<?>[] pts = method.getParameterTypes();// 获取方法参数类型
Class<?>[] ets = method.getExceptionTypes(); // 获取方法异常类型
Adaptive adaptiveAnnotation = method.getAnnotation(Adaptive.class); // 获取Adaptive的注解信息
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 {
//不存在注解信息,根据方法参数类型获取UEL位置
int urlTypeIndex = -1;
for (int i = 0; i < pts.length; ++i) {
if (pts[i].equals(URL.class)) {
urlTypeIndex = i;
break;
}
}
// found parameter in URL type
if (urlTypeIndex != -1) {
// Null Point check
String 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);
}
// did not find parameter in URL type
else {
String attribMethod = null;
// find URL getter method
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 adaptive 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("\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);
}
//获取组件属性值
String[] value = adaptiveAnnotation.value();
// value is not set, use the value generated from class name as the key
if (value.length == 0) {
//比如获取最后一个.Protocol包名一个个拆分后组合新的字符串数组{"protocol"}
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 check
String 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);
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);
}
}
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 statement
if (!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();
}
测试用例public class RpcFilterTest extends TestCase {
private Protocol protocol = ExtensionLoader.getExtensionLoader(Protocol.class).getAdaptiveExtension();
private ProxyFactory proxy = ExtensionLoader.getExtensionLoader(ProxyFactory.class).getAdaptiveExtension();
public void testRpcFilter() throws Exception {
DemoService service = new DemoServiceImpl();
URL url = URL.valueOf("dubbo://192.168.176.136:9092/com.alibaba.dubbo.rpc.DemoService?service.filter=echo");//TODO 后续..
protocol.export(proxy.getInvoker(service, DemoService.class, url));
service = proxy.getProxy(protocol.refer(DemoService.class, url));
assertEquals("123", service.echo("123"));
// cast to EchoService
EchoService echo = proxy.getProxy(protocol.refer(EchoService.class, url));
assertEquals(echo.$echo("test"), "test");
assertEquals(echo.$echo("abcdefg"), "abcdefg");
assertEquals(echo.$echo(1234), 1234);
}
}后续其他组件源码中围绕spi解析装饰器模式、责任链模式，观察者模式，双亲模式等等
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