Dubbo之SPI机制详解
spi机制的思想提供一种更加灵活的，可插拔式的机制。本文分别对比了java和dubbo的spi的实现的区别，重点讨论dubbo的实现原理。java
java spi机制
SPI，Service Provider Interface，主要是被框架的开发人员使用，好比java.sql.Driver接口，其余不一样厂商能够针对同一接口作出不一样的实现，mysql和postgresql都有不一样的实现提供给用户，而Java的SPI机制能够为某个接口寻找服务实现。mysql
当服务的提供者提供了一种接口的实现以后，须要在classpath下的META-INF/services/目录里建立一个以服务接口命名的文件，这个文件里的内容就是这个接口的具体的实现类。当其余的程序须要这个服务的时候，就能够经过查找这个jar包（通常都是以jar包作依赖）的META-INF/services/中的配置文件，配置文件中有接口的具体实现类名，能够根据这个类名进行加载实例化，就可使用该服务了。JDK中查找服务的实现的工具类是：java.util.ServiceLoadersql
由于本文的主体内容是dubbo，因此这边就不对ServiceLoader的源码进行深刻的解析。这边写了一个例子。express
package com.shang.spi;
/**
* @author shang
* @date 2019/1/5
*/
public interface DubboService {
void sayHello();
}
DubboService的实现类AppleServiceapache
package com.shang.spi;
/**
* @author shang
* @date 2019/1/5
*/
public class AppleService implements DubboService {
@Override
public void sayHello() {
System.out.println("apple");
}
}
package com.shang.spi;
import java.util.Iterator;
import java.util.ServiceLoader;
/**
* @author shang
* @date 2019/1/5
*/
public class ServiceMain {
public static void main(String[] args) {
ServiceLoader<DubboService> spiLoader = ServiceLoader.load(DubboService.class);
Iterator<DubboService> iteratorSpi = spiLoader.iterator();
while (iteratorSpi.hasNext()) {
DubboService dubboService = iteratorSpi.next();
dubboService.sayHello();
}
}
}
dubbo spi机制
dubbo的spi实现原理和java spi类似，只不过加强了一些功能和优化。java spi的是把全部的spi都加载到内存，但对于dubbo来讲可能只须要加载用户指定的实现方式，而不须要所有加载进来，所有加载也会有性能问题，因此dubbo实现的是在有用到的时候去加载这些扩展组件。缓存
spi机制有几个重要的注解：
一、@SPI注解，被此注解标记的接口，就表示是一个可扩展的接口，并标注默认值。
二、@Adaptive注解，有两种注解方式：一种是注解在类上，一种是注解在方法上。
三、@Activate注解，此注解须要注解在类上或者方法上，并注明被激活的条件，以及全部的被激活实现类中的排序信息app
本文重点分析1和2的解析过程，3实际上是在loadFile的时候可能被激活。框架
何时加载扩展类？
public class ReferenceConfig<T> extends AbstractReferenceConfig {
private static final long serialVersionUID = -5864351140409987595L;
private static final Protocol refprotocol = ExtensionLoader.getExtensionLoader(Protocol.class).getAdaptiveExtension();
private static final Cluster cluster = ExtensionLoader.getExtensionLoader(Cluster.class).getAdaptiveExtension();
private static final ProxyFactory proxyFactory = ExtensionLoader.getExtensionLoader(ProxyFactory.class).getAdaptiveExtension();
...
}
咱们来看下消费者生成refer的代码。从ReferenceConfig这个类中咱们能够看到须要初始化的扩展类有Protocol、Cluster和ProxyFactory。那么其实就是须要的时候再去加载。全部的实现都在ExtensionLoader类中。这个类也不负责，一千行左右的代码。
下面咱们就跟着Protocol的扩展来看下源码的实现方式。less
Protocol refprotocol = ExtensionLoader.getExtensionLoader(Protocol.class).getAdaptiveExtension();
在看实现的代码以前咱们先看加Protocol这个扩展类，为了尽可能的简洁删除了一些包路径和注释。
能够看到Protocol的spi的默认值是dubbo，这个在初始化类的时候颇有用，假如你的Protocol实现类有不少，在dubbo中就有：ide
@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();
default void destroyServer() {
//空实现
}
}
那么spi的Adaptive就是一种自适应的注解，具体是怎么实现的咱们继续看代码。
public static <T> ExtensionLoader<T> getExtensionLoader(Class<T> type) {
if (type == null)
throw new IllegalArgumentException("Extension type == null");
if(!type.isInterface()) {
throw new IllegalArgumentException("Extension type(" + type + ") is not interface!");
}
if(!withExtensionAnnotation(type)) {
throw new IllegalArgumentException("Extension type(" + type +
") is not extension, because WITHOUT @" + SPI.class.getSimpleName() + " Annotation!");
}
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;
}
getExtensionLoader方法最主要的实现就是把全部的扩展放到EXTENSION_LOADERS这个容器中，避免二次加载。
private static final ConcurrentMap<Class<?>, ExtensionLoader<?>> EXTENSION_LOADERS = new ConcurrentHashMap<Class<?>, ExtensionLoader<?>>();
如何实现自适应扩展机制的？
下面其实就是为了获取自适应的扩展机制，Adaptive这个注解的自适应。调用的路径大概是这样的：
getAdaptiveExtension()-->
createAdaptiveExtension()-->
getAdaptiveExtensionClass()-->
getExtensionClasses()-->
loadExtensionClasses()
public T getAdaptiveExtension() {
Object instance = cachedAdaptiveInstance.get();
if (instance == null) {
if(createAdaptiveInstanceError == null) {
synchronized (cachedAdaptiveInstance) {
instance = cachedAdaptiveInstance.get();
if (instance == null) {
try {
//建立自适应扩展
instance = createAdaptiveExtension();
//设置缓存
cachedAdaptiveInstance.set(instance);
} catch (Throwable t) {
createAdaptiveInstanceError = t;
throw new IllegalStateException("fail to create adaptive instance: " + t.toString(), t);
}
}
}
}
else {
throw new IllegalStateException("fail to create adaptive instance: " + createAdaptiveInstanceError.toString(), createAdaptiveInstanceError);
}
}
return (T) instance;
}
createAdaptiveExtension经过名字就能能够知道这是建立自适应的扩展对象
private T createAdaptiveExtension() {
try {
//获取自适应扩展类，经过反射实例化
return injectExtension((T) getAdaptiveExtensionClass().newInstance());
} catch (Exception e) {
throw new IllegalStateException("Can not create adaptive extenstion " + type + ", cause: " + e.getMessage(), e);
}
}
路径：getAdaptiveExtensionClass->getExtensionClasses->loadExtensionClasses->loadFile
cachedAdaptiveClass会在loadFile进行获取
private Class<?> getAdaptiveExtensionClass() {
getExtensionClasses();
//若是缓存中已经找到自适应类的话直接返回，意思也就是这个spi有Adaptive的注解类
//好比：当前获取的自适应实现类是AdaptiveExtensionFactory或者是AdaptiveCompiler，就直接返回，这两个类是特殊用处的，不用代码生成，而是现成的代码
if (cachedAdaptiveClass != null) {
return cachedAdaptiveClass;
}
//不然须要代理类生成相关代理
return cachedAdaptiveClass = createAdaptiveExtensionClass();
}
getExtensionClasses->loadFile直接从文件加载
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;
}
// 此方法已经getExtensionClasses方法同步过。
private Map<String, Class<?>> loadExtensionClasses() {
final SPI defaultAnnotation = type.getAnnotation(SPI.class);
if(defaultAnnotation != null) {
String value = defaultAnnotation.value();
if(value != null && (value = value.trim()).length() > 0) {
String[] names = NAME_SEPARATOR.split(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];
}
}
Map<String, Class<?>> extensionClasses = new HashMap<String, Class<?>>();
//从文件加载
loadFile(extensionClasses, DUBBO_INTERNAL_DIRECTORY);
loadFile(extensionClasses, DUBBO_DIRECTORY);
loadFile(extensionClasses, SERVICES_DIRECTORY);
return extensionClasses;
}
主动加载相关type的spi子类
private void loadFile(Map<String, Class<?>> extensionClasses, String dir) {
String fileName = dir + type.getName();
try {
Enumeration<java.net.URL> urls;
ClassLoader classLoader = findClassLoader();
if (classLoader != null) {
urls = classLoader.getResources(fileName);
} else {
urls = ClassLoader.getSystemResources(fileName);
}
if (urls != null) {
while (urls.hasMoreElements()) {
//配置文件路径
java.net.URL url = urls.nextElement();
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(url.openStream(), "utf-8"));
try {
String line = null;
//每次处理一行
while ((line = reader.readLine()) != null) {
//#号之后的为注释
final int ci = line.indexOf('#');
//注释去掉
if (ci >= 0) line = line.substring(0, ci);
line = line.trim();
if (line.length() > 0) {
try {
String name = null;
//=号以前的为扩展名字，后面的为扩展类实现的全限定名
int i = line.indexOf('=');
if (i > 0) {
name = line.substring(0, i).trim();
line = line.substring(i + 1).trim();
}
if (line.length() > 0) {
//加载扩展类的实现
Class<?> clazz = Class.forName(line, true, classLoader);
//查看类型是否匹配
//type是Protocol接口
//clazz就是Protocol的各个实现类
if (! type.isAssignableFrom(clazz)) {
throw new IllegalStateException();
}
//若是实现类是@Adaptive类型的，会赋值给cachedAdaptiveClass，这个用来存放被@Adaptive注解的实现类
if (clazz.isAnnotationPresent(Adaptive.class)) {
if(cachedAdaptiveClass == null) {
cachedAdaptiveClass = clazz;
} else if (! cachedAdaptiveClass.equals(clazz)) {
throw new IllegalStateException();
}
} else {//不是@Adaptice类型的类，就是没有注解@Adaptive的实现类
try {//判断是不是wrapper类型
//若是获得的实现类的构造方法中的参数是扩展点类型的，就是一个Wrapper类
//好比ProtocolFilterWrapper，实现了Protocol类，
//而它的构造方法是这样public ProtocolFilterWrapper(Protocol protocol)
//就说明这个类是一个包装类
clazz.getConstructor(type);
//cachedWrapperClasses用来存放当前扩展点实现类中的包装类
Set<Class<?>> wrappers = cachedWrapperClasses;
if (wrappers == null) {
cachedWrapperClasses = new ConcurrentHashSet<Class<?>>();
wrappers = cachedWrapperClasses;
}
wrappers.add(clazz);
} catch (NoSuchMethodException e) {
//没有上面提到的构造器，则说明不是wrapper类型
//获取无参构造
clazz.getConstructor();
//没有名字，就是配置文件中没有xxx=xxxx.com.xxx这种
if (name == null || name.length() == 0) {
//去找@Extension注解中配置的值
name = findAnnotationName(clazz);
//若是还没找到名字，从类名中获取
if (name == null || name.length() == 0) {
//好比clazz是DubboProtocol，type是Protocol
//这里获得的name就是dubbo
if (clazz.getSimpleName().length() > type.getSimpleName().length()
&& clazz.getSimpleName().endsWith(type.getSimpleName())) {
name = clazz.getSimpleName().substring(0, clazz.getSimpleName().length() - type.getSimpleName().length()).toLowerCase();
} else {
throw new IllegalStateException("No such extension name for the class " + clazz.getName() + " in the config " + url);
}
}
}
//有可能配置了多个名字
String[] names = NAME_SEPARATOR.split(name);
if (names != null && names.length > 0) {
//是不是Active类型的类
Activate activate = clazz.getAnnotation(Activate.class);
if (activate != null) {
//第一个名字做为键，放进cachedActivates这个map中缓存
cachedActivates.put(names[0], activate);
}
for (String n : names) {
if (! cachedNames.containsKey(clazz)) {
//放入Extension实现类与名称映射的缓存中去，每一个class只对应第一个名称有效
cachedNames.put(clazz, n);
}
Class<?> c = extensionClasses.get(n);
if (c == null) {
//放入到extensionClasses缓存中去，多个name可能对应一份extensionClasses
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) { }
}
} // end of while read lines
} finally {
reader.close();
}
} catch (Throwable t) { }
} // end of while urls
}
} catch (Throwable t) { }
}
好了，仍是要回到getAdaptiveExtensionClass这个方法，上面的loadFile是按规则加载了全部的type类型的spi类，那么若是生成自适应类呢？
咱们继续看createAdaptiveExtensionClass这个方法的createAdaptiveExtensionClassCode
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);
}
编写自适应代理类
createAdaptiveExtensionClassCode的代码有点长，具体就是生成代理类，咱们先看下代码：
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;
}
}
// 彻底没有Adaptive方法，则不须要生成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() + "$Adpative" + " 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 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);
}
// 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("\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 做为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()};
}
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(pts[i].getCanonicalName());
}
}
codeBuidler.append(" {");
codeBuidler.append(code.toString());
codeBuidler.append("\n}");
}
codeBuidler.append("\n}");
if (logger.isDebugEnabled()) {
logger.debug(codeBuidler.toString());
}
return codeBuidler.toString();
}
那么他生成的代理类是怎么样的呢？咱们仍是以com.alibaba.dubbo.rpc.Protocol 为例，他生成的代理类就是Protocol$Adpative，中间多了一个$。
import com.alibaba.dubbo.common.extension.ExtensionLoader;
public class Protocol$Adpative implements com.alibaba.dubbo.rpc.Protocol {
public com.alibaba.dubbo.rpc.Invoker refer(java.lang.Class arg0, com.alibaba.dubbo.common.URL arg1) throws java.lang.Class {
if (arg1 == null) throw new IllegalArgumentException("url == null");
com.alibaba.dubbo.common.URL url = arg1;
String extName = ( url.getProtocol() == null ? "dubbo" : url.getProtocol() );
if(extName == null) throw new IllegalStateException("Fail to get extension(com.alibaba.dubbo.rpc.Protocol) name from url(" + url.toString() + ") use keys([protocol])");
com.alibaba.dubbo.rpc.Protocol extension = (com.alibaba.dubbo.rpc.Protocol)ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.rpc.Protocol.class).getExtension(extName);
return extension.refer(arg0, arg1);
}
public com.alibaba.dubbo.rpc.Exporter export(com.alibaba.dubbo.rpc.Invoker arg0) throws com.alibaba.dubbo.rpc.Invoker {
if (arg0 == null) throw new IllegalArgumentException("com.alibaba.dubbo.rpc.Invoker argument == null");
if (arg0.getUrl() == null) throw new IllegalArgumentException("com.alibaba.dubbo.rpc.Invoker argument getUrl() == null");com.alibaba.dubbo.common.URL url = arg0.getUrl();
String extName = ( url.getProtocol() == null ? "dubbo" : url.getProtocol() );
if(extName == null) throw new IllegalStateException("Fail to get extension(com.alibaba.dubbo.rpc.Protocol) name from url(" + url.toString() + ") use keys([protocol])");
com.alibaba.dubbo.rpc.Protocol extension = (com.alibaba.dubbo.rpc.Protocol)ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.rpc.Protocol.class).getExtension(extName);
return extension.export(arg0);
}
public void destroy() {
throw new UnsupportedOperationException("method public abstract void com.alibaba.dubbo.rpc.Protocol.destroy() of interface com.alibaba.dubbo.rpc.Protocol is not adaptive method!");
}
public int getDefaultPort() {
throw new UnsupportedOperationException("method public abstract int com.alibaba.dubbo.rpc.Protocol.getDefaultPort() of interface com.alibaba.dubbo.rpc.Protocol is not adaptive method!");
}
}
其余的类型的代理代码生成是相似的，上面的代码是硬编码，须要把他编译并加载到内存中，具体仍是要回到createAdaptiveExtensionClass这个方法，代码在上面，这里就再也不贴了，须要经过Compiler这个类找到对应的自适应实现，这里获得的就是AdaptiveCompiler，最后调用compiler.compile(code, classLoader);来编译上面生成的类并返回，先进入AdaptiveCompiler的compile方法：
public Class<?> compile(String code, ClassLoader classLoader) {
Compiler compiler;
ExtensionLoader<Compiler> loader = ExtensionLoader.getExtensionLoader(Compiler.class);
//默认的Compiler名字
String name = DEFAULT_COMPILER; // copy reference
//有指定了Compiler名字，就使用指定的名字来找到Compiler实现类
if (name != null && name.length() > 0) {
compiler = loader.getExtension(name);
} else {//没有指定Compiler名字，就查找默认的Compiler的实现类
compiler = loader.getDefaultExtension();
}
return compiler.compile(code, classLoader);
}
/*
* 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.compiler;
import com.alibaba.dubbo.common.extension.SPI;
/**
* Compiler. (SPI, Singleton, ThreadSafe)
*
* @author william.liangf
*/
@SPI("javassist")
public interface Compiler {
/**
* Compile java source code.
*
* @param code Java source code
* @param classLoader TODO
* @return Compiled class
*/
Class<?> compile(String code, ClassLoader classLoader);
}
至此整个自适应的代理方式都已经解析完了。可是我以为实现的有点过于复杂了，是适应类的存在是颇有必要的吗？我以为也未必。 感受在spi的实现中插入了Adaptive等的实现是把简单的spi机制搞得复杂化了，绕了一大圈去解决一个自适应代理类等方式是否能够简单化。
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