写在前面
阅读源码是比较耗时的，特别是经过千锤百炼的经典源码，创造者不易，阅读者更加不要轻易断定结论，像我之前有详细了解过spring cache源码模块也并非那么容易，如果很久不再读，也差不多忘记，如果理解了或理解的深度不够的（没形成源码架构体系）前提下会发生的；在经典源码面前，会发现之前工作范围内的框架源码不值得一提吧，本人在实现100万+QPS秒杀架构演进中，为了背后的密码必然会将涉及比较关键的和经典的源码进行深入剖析，总体大致有spring系（sc,sb,dubbo），DB中间件系(Sharding-Sphere)，其他的底层框架或组件太多，或许遇到了才有空解读
进入主题
spi是什么？其实就面向接口编码，也不是什么dubbo发明的，jdk spi原本就有，不过有其性能和扩展的缺陷，dubbo参考了spring ioc等优势，将原来全名限定的改写了K,V形式，dubbo全域无感知rpc实现都是借道spi
1、jdkspi ServiceLoader主要作用
1.读取服务提供配置文件
2.newInstance实例化配置文件中列举的服务提供类，所以服务提供类需要有默认的构造方法
3.将实例化的服务提供类存储起来，即LinkedHashMap<String,S>providers=newLinkedHashMap<>()
jdk spi实现源码: https://github.com/luozhonghua/dubbo-spiDemo
2、Dubbo改进了JDK标准的SPI的以下问题
JDK标准的SPI会一次性实例化扩展点所有实现，如果有扩展实现初始化很耗时，但如果没用上也加载，会很浪费资源。
如果扩展点加载失败，连扩展点的名称都拿不到了。比如：JDK标准的ScriptEngine，通过getName();获取脚本类型的名称，但如果RubyScriptEngine因为所依赖的jruby.jar不存在，导致RubyScriptEngine类加载失败，这个失败原因被吃掉了，和ruby对应不起来，当用户执行ruby脚本时，会报不支持ruby，而不是真正失败的原因。
增加了对扩展点IoC和AOP的支持，一个扩展点可以直接setter注入其它扩展点。
约定：
在扩展类的jar包内，放置扩展点配置文件：META-INF/dubbo/接口全限定名，内容为：配置名=扩展实现类全限定名，多个实现类用换行符分隔。
(注意：这里的配置文件是放在你自己的jar包内，不是dubbo本身的jar包内，Dubbo会全ClassPath扫描所有jar包内同名的这个文件，然后进行合并)
扩展Dubbo的协议示例：
在协议的实现jar包内放置文本文件META-INF/dubbo/internal/com.alibaba.dubbo.rpc.Protocol
filter=com.alibaba.dubbo.rpc.protocol.ProtocolFilterWrapper
listener=com.alibaba.dubbo.rpc.protocol.ProtocolListenerWrapper
mock=com.alibaba.dubbo.rpc.support.MockProtocol
我们看下dubbo扩展 spi有哪些东西
就几个类，很简单吧，核心就这几个
ExtensionLoader #扩展点载入器扩展点 用于查找，校验，加载等核心逻辑的实现类 (载入Dubbo中的各种可配置组件，比如动态代理方式（ProxyFactory）、负载均衡策略（LoadBalance）、RCP协议（Protocol）、拦截器（Filter）、容器类型（Container）、集群方式（Cluster）和注册中心类型（RegistryFactory）....)
Dubbo为了应对各种场景，它的所有内部组件都是通过ExtensionLoader SPI的方式来管理的，这也是为什么Dubbo需要将服务提供者配置文件设计成KV键值对形式，这个K就是我们在Dubbo配置文件或注解中用到的K，Dubbo直接通过服务接口（上面提到的ProxyFactory、LoadBalance、Protocol、Filter等）和配置的K从ExtensionLoader拿到服务提供的实现类
Activate #自动激活加载扩展的注解
Adaptive #自适应扩展点的注解
SPI #扩展点注解
Wrapper #包装类，如果声明了包装类的提供者，则默认将当次决策的provider包装起来并返回包装类。容器判定是否为包装类的依据为是否有一个参数为接口类型的构造参数。Wrapper可以有多个，会被按顺序依次嵌套
假设spi定义如下：
A=a.b.c
B=a.b.wrapper1
C=a.b.wrapper2
则返回的wrapper的最终结构为B–C–A
Adaptive的决策过程，最终还是会通过容器IOC获得当次调用的扩展点来完成调用
我们根据上面这个执行调用总图来逐步分析
自适应扩展工厂关系图，说明由自适应@Adaptive为关键点的工厂管理扩展点@SPI
1、AdaptiveExtensionFactory解读
/** * AdaptiveExtensionFactory * * 默认实现 * AdaptiveExtensionFactotry被@Adaptive注解注释，也就是它就是ExtensionFactory对应的自适应扩展实现(每个扩展点最多只能有一个自适应实现，如果所有实现中没有被@Adaptive注释的，那么dubbo会动态生成一个自适应实现类)，也就是说，所有对ExtensionFactory调用的地方，实际上调用的都是AdpativeExtensionFactory */ @Adaptive public class AdaptiveExtensionFactory implements ExtensionFactory { private final List<ExtensionFactory> factories; public AdaptiveExtensionFactory() { ExtensionLoader<ExtensionFactory> loader = ExtensionLoader.getExtensionLoader(ExtensionFactory.class); List<ExtensionFactory> list = new ArrayList<ExtensionFactory>(); for (String name : loader.getSupportedExtensions()) { // 将所有ExtensionFactory实现保存起来 list.add(loader.getExtension(name)); } factories = Collections.unmodifiableList(list); } public <T> T getExtension(Class<T> type, String name) { // 依次遍历各个ExtensionFactory实现的getExtension方法，一旦获取到Extension即返回 // 如果遍历完所有的ExtensionFactory实现均无法找到Extension,则返回null for (ExtensionFactory factory : factories) { T extension = factory.getExtension(type, name); if (extension != null) { return extension; } } return null; } }
2、ExtensionLoader扩展点加载器--主要逻辑管理类
/*
* 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.common.extension;
import com.alibaba.dubbo.common.Constants;
import com.alibaba.dubbo.common.URL;
import com.alibaba.dubbo.common.extension.support.ActivateComparator;
import com.alibaba.dubbo.common.logger.Logger;
import com.alibaba.dubbo.common.logger.LoggerFactory;
import com.alibaba.dubbo.common.utils.ConcurrentHashSet;
import com.alibaba.dubbo.common.utils.ConfigUtils;
import com.alibaba.dubbo.common.utils.Holder;
import com.alibaba.dubbo.common.utils.StringUtils;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.TreeSet;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.regex.Pattern;
/**
* Load dubbo extensions
* <ul>
* <li>auto inject dependency extension </li>
* <li>auto wrap extension in wrapper </li>
* <li>default extension is an adaptive instance</li>
* </ul>
*
* @see <a href="http://java.sun.com/j2se/1.5.0/docs/guide/jar/jar.html#Service%20Provider">Service Provider in Java 5</a>
* @see com.alibaba.dubbo.common.extension.SPI
* @see com.alibaba.dubbo.common.extension.Adaptive
* @see com.alibaba.dubbo.common.extension.Activate
*/
public class ExtensionLoader<T> {
private static final Logger logger = LoggerFactory.getLogger(ExtensionLoader.class);
private static final String SERVICES_DIRECTORY = "META-INF/services/";
private static final String DUBBO_DIRECTORY = "META-INF/dubbo/";
private static final String DUBBO_INTERNAL_DIRECTORY = DUBBO_DIRECTORY + "internal/";
private static final Pattern NAME_SEPARATOR = Pattern.compile("\\s*[,]+\\s*");
private static final ConcurrentMap<Class<?>, ExtensionLoader<?>> EXTENSION_LOADERS = new ConcurrentHashMap<Class<?>, ExtensionLoader<?>>();
private static final ConcurrentMap<Class<?>, Object> EXTENSION_INSTANCES = new ConcurrentHashMap<Class<?>, Object>();
// ==============================
private final Class<?> type;
private final ExtensionFactory objectFactory;
private final ConcurrentMap<Class<?>, String> cachedNames = new ConcurrentHashMap<Class<?>, String>();
private final Holder<Map<String, Class<?>>> cachedClasses = new Holder<Map<String, Class<?>>>();
private final Map<String, Activate> cachedActivates = new ConcurrentHashMap<String, Activate>();
private final ConcurrentMap<String, Holder<Object>> cachedInstances = new ConcurrentHashMap<String, Holder<Object>>();
private final Holder<Object> cachedAdaptiveInstance = new Holder<Object>();
private volatile Class<?> cachedAdaptiveClass = null;
private String cachedDefaultName;
private volatile Throwable createAdaptiveInstanceError;
private Set<Class<?>> cachedWrapperClasses;
private Map<String, IllegalStateException> exceptions = new ConcurrentHashMap<String, IllegalStateException>();
// 如果扩展类型是ExtensionFactory,那么则设置为null
// 这里通过getAdaptiveExtension方法获取一个运行时自适应的扩展类型(每个Extension只能有一个@Adaptive类型的实现，如果没有dubbo会动态生成一个类)
private ExtensionLoader(Class<?> type) {
this.type = type;
objectFactory = (type == ExtensionFactory.class ? null : ExtensionLoader.getExtensionLoader(ExtensionFactory.class).getAdaptiveExtension());
}
private static <T> boolean withExtensionAnnotation(Class<T> type) {
return type.isAnnotationPresent(SPI.class);
}
@SuppressWarnings("unchecked")
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)) { // 只接受使用@SPI注解注释的接口类型
throw new IllegalArgumentException("Extension type(" + type +
") is not extension, because WITHOUT @" + SPI.class.getSimpleName() + " Annotation!");
}
//先从静态缓存中获取对应的ExtensionLoader实例
ExtensionLoader<T> loader = (ExtensionLoader<T>) EXTENSION_LOADERS.get(type);
if (loader == null) {
// 为Extension类型创建ExtensionLoader实例,并放入静态缓存
EXTENSION_LOADERS.putIfAbsent(type, new ExtensionLoader<T>(type));
loader = (ExtensionLoader<T>) EXTENSION_LOADERS.get(type);
}
return loader;
}
private static ClassLoader findClassLoader() {
return ExtensionLoader.class.getClassLoader();
}
public String getExtensionName(T extensionInstance) {
return getExtensionName(extensionInstance.getClass());
}
public String getExtensionName(Class<?> extensionClass) {
return cachedNames.get(extensionClass);
}
/**
* This is equivalent to {@code getActivateExtension(url, key, null)}
*
* @param url url
* @param key url parameter key which used to get extension point names
* @return extension list which are activated.
* @see #getActivateExtension(com.alibaba.dubbo.common.URL, String, String)
*/
public List<T> getActivateExtension(URL url, String key) {
return getActivateExtension(url, key, null);
}
/**
* This is equivalent to {@code getActivateExtension(url, values, null)}
*
* @param url url
* @param values extension point names
* @return extension list which are activated
* @see #getActivateExtension(com.alibaba.dubbo.common.URL, String[], String)
*/
public List<T> getActivateExtension(URL url, String[] values) {
return getActivateExtension(url, values, null);
}
/**
* This is equivalent to {@code getActivateExtension(url, url.getParameter(key).split(","), null)}
*
* @param url url
* @param key url parameter key which used to get extension point names
* @param group group
* @return extension list which are activated.
* @see #getActivateExtension(com.alibaba.dubbo.common.URL, String[], String)
*/
public List<T> getActivateExtension(URL url, String key, String group) {
String value = url.getParameter(key);
return getActivateExtension(url, value == null || value.length() == 0 ? null : Constants.COMMA_SPLIT_PATTERN.split(value), group);
}
/**
* 获取当前扩展的所有可自动激活的实例实现
* Get activate extensions.
*
* @param url url
* @param values extension point names
* @param group group
* @return extension list which are activated
* @see com.alibaba.dubbo.common.extension.Activate
*/
public List<T> getActivateExtension(URL url, String[] values, String group) {
List<T> exts = new ArrayList<T>();
List<String> names = values == null ? new ArrayList<String>(0) : Arrays.asList(values); // 解析配置要使用的名称
if (!names.contains(Constants.REMOVE_VALUE_PREFIX + Constants.DEFAULT_KEY)) { // 如果未配置"-default",则加载所有Activates扩展(names指定的扩展)
getExtensionClasses();//收集的缓存数据: 加载当前Extension所有实现,会获取到当前Extension中所有@Active实现,赋值给cachedActivates变量
for (Map.Entry<String, Activate> entry : cachedActivates.entrySet()) { // 遍历当前扩展所有的@Activate扩展
String name = entry.getKey();
Activate activate = entry.getValue();
if (isMatchGroup(group, activate.group())) {// 判断group是否满足,group为null则直接返回true
T ext = getExtension(name);//获取扩展实例
if (!names.contains(name) // 排除names指定的扩展;并且如果names中没有指定移除该扩展(-name)，且当前url匹配结果显示可激活才进行使用
&& !names.contains(Constants.REMOVE_VALUE_PREFIX + name)
&& isActive(activate, url)) {
exts.add(ext);
}
}
}
Collections.sort(exts, ActivateComparator.COMPARATOR);
}
// 对names指定的扩展进行专门的处理
List<T> usrs = new ArrayList<T>();
for (int i = 0; i < names.size(); i++) {// 遍历names指定的扩展名
String name = names.get(i);
if (!name.startsWith(Constants.REMOVE_VALUE_PREFIX) // 未设置移除该扩展
&& !names.contains(Constants.REMOVE_VALUE_PREFIX + name)) {
if (Constants.DEFAULT_KEY.equals(name)) { // default表示上面已经加载并且排序的exts,将排在default之前的Activate扩展放置到default组之前,例如:ext1,default,ext2
if (usrs.size() > 0) { // 如果此时user不为空,则user中存放的是配置在default之前的Activate扩展
exts.addAll(0, usrs);// 注意index是0,放在default前面
usrs.clear();// 放到default之前,然后清空
}
} else {
T ext = getExtension(name);
usrs.add(ext);
}
}
}
if (usrs.size() > 0) {// 这里留下的都是配置在default之后的
exts.addAll(usrs);// 添加到default排序之后
}
return exts;
}
private boolean isMatchGroup(String group, String[] groups) {
if (group == null || group.length() == 0) {
return true;
}
if (groups != null && groups.length > 0) {
for (String g : groups) {
if (group.equals(g)) {
return true;
}
}
}
return false;
}
private boolean isActive(Activate activate, URL url) {
String[] keys = activate.value();
if (keys == null || keys.length == 0) {
return true;
}
for (String key : keys) {
for (Map.Entry<String, String> entry : url.getParameters().entrySet()) {
String k = entry.getKey();
String v = entry.getValue();
if ((k.equals(key) || k.endsWith("." + key))
&& ConfigUtils.isNotEmpty(v)) {
return true;
}
}
}
return false;
}
/**
* Get extension's instance. Return <code>null</code> if extension is not found or is not initialized. Pls. note
* that this method will not trigger extension load.
* <p>
* In order to trigger extension load, call {@link #getExtension(String)} instead.
*
* @see #getExtension(String)
*/
@SuppressWarnings("unchecked")
public T getLoadedExtension(String name) {
if (name == null || name.length() == 0)
throw new IllegalArgumentException("Extension name == null");
Holder<Object> holder = cachedInstances.get(name);
if (holder == null) {
cachedInstances.putIfAbsent(name, new Holder<Object>());
holder = cachedInstances.get(name);
}
return (T) holder.get();
}
/**
* Return the list of extensions which are already loaded.
* <p>
* Usually {@link #getSupportedExtensions()} should be called in order to get all extensions.
*
* @see #getSupportedExtensions()
*/
public Set<String> getLoadedExtensions() {
return Collections.unmodifiableSet(new TreeSet<String>(cachedInstances.keySet()));
}
/**
* 获取ExtensionLoader实例代表的扩展的指定实现,以扩展实现的名字作为参数
* Find the extension with the given name. If the specified name is not found, then {@link IllegalStateException}
* will be thrown.
*/
@SuppressWarnings("unchecked")
public T getExtension(String name) {
if (name == null || name.length() == 0)
throw new IllegalArgumentException("Extension name == null");
if ("true".equals(name)) { // 判断是否是获取默认实现
return getDefaultExtension();
}
Holder<Object> holder = cachedInstances.get(name); //根据名字从holder缓存获取扩展点实例
if (holder == null) { //存放缓存再取出
cachedInstances.putIfAbsent(name, new Holder<Object>());
holder = cachedInstances.get(name);
}
Object instance = holder.get();
if (instance == null) { //holder缓存依然不存在则创建扩展点实例,再次进行缓存
synchronized (holder) {
instance = holder.get();
if (instance == null) {
instance = createExtension(name);
holder.set(instance);
}
}
}
return (T) instance;
}
/**
* Return default extension, return <code>null</code> if it's not configured.
*/
public T getDefaultExtension() {
getExtensionClasses();
if (null == cachedDefaultName || cachedDefaultName.length() == 0
|| "true".equals(cachedDefaultName)) {
return null;
}
return getExtension(cachedDefaultName);
}
public boolean hasExtension(String name) {
if (name == null || name.length() == 0)
throw new IllegalArgumentException("Extension name == null");
try {
return getExtensionClass(name) != null;
} catch (Throwable t) {
return false;
}
}
public Set<String> getSupportedExtensions() {
Map<String, Class<?>> clazzes = getExtensionClasses();
return Collections.unmodifiableSet(new TreeSet<String>(clazzes.keySet()));
}
/**
* Return default extension name, return <code>null</code> if not configured.
*/
public String getDefaultExtensionName() {
getExtensionClasses();
return cachedDefaultName;
}
/**
* Register new extension via API
*
* @param name extension name
* @param clazz extension class
* @throws IllegalStateException when extension with the same name has already been registered.
*/
public void addExtension(String name, Class<?> clazz) {
getExtensionClasses(); // load classes
if (!type.isAssignableFrom(clazz)) {
throw new IllegalStateException("Input type " +
clazz + "not implement Extension " + type);
}
if (clazz.isInterface()) {
throw new IllegalStateException("Input type " +
clazz + "can not be interface!");
}
if (!clazz.isAnnotationPresent(Adaptive.class)) {
if (StringUtils.isBlank(name)) {
throw new IllegalStateException("Extension name is blank (Extension " + type + ")!");
}
if (cachedClasses.get().containsKey(name)) {
throw new IllegalStateException("Extension name " +
name + " already existed(Extension " + type + ")!");
}
cachedNames.put(clazz, name);
cachedClasses.get().put(name, clazz);
} else {
if (cachedAdaptiveClass != null) {
throw new IllegalStateException("Adaptive Extension already existed(Extension " + type + ")!");
}
cachedAdaptiveClass = clazz;
}
}
/**
* Replace the existing extension via API
*
* @param name extension name
* @param clazz extension class
* @throws IllegalStateException when extension to be placed doesn't exist
* @deprecated not recommended any longer, and use only when test
*/
@Deprecated
public void replaceExtension(String name, Class<?> clazz) {
getExtensionClasses(); // load classes
if (!type.isAssignableFrom(clazz)) {
throw new IllegalStateException("Input type " +
clazz + "not implement Extension " + type);
}
if (clazz.isInterface()) {
throw new IllegalStateException("Input type " +
clazz + "can not be interface!");
}
if (!clazz.isAnnotationPresent(Adaptive.class)) {
if (StringUtils.isBlank(name)) {
throw new IllegalStateException("Extension name is blank (Extension " + type + ")!");
}
if (!cachedClasses.get().containsKey(name)) {
throw new IllegalStateException("Extension name " +
name + " not existed(Extension " + type + ")!");
}
cachedNames.put(clazz, name);
cachedClasses.get().put(name, clazz);
cachedInstances.remove(name);
} else {
if (cachedAdaptiveClass == null) {
throw new IllegalStateException("Adaptive Extension not existed(Extension " + type + ")!");
}
cachedAdaptiveClass = clazz;
cachedAdaptiveInstance.set(null);
}
}
@SuppressWarnings("unchecked")
public T getAdaptiveExtension() {
Object instance = cachedAdaptiveInstance.get();// 首先判断是否已经有缓存的实例对象
if (instance == null) {
if (createAdaptiveInstanceError == null) {
synchronized (cachedAdaptiveInstance) {
instance = cachedAdaptiveInstance.get();
if (instance == null) {
try {
instance = createAdaptiveExtension();// 没有缓存的实例，创建新的AdaptiveExtension实例
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;
}
private IllegalStateException findException(String name) {
for (Map.Entry<String, IllegalStateException> entry : exceptions.entrySet()) {
if (entry.getKey().toLowerCase().contains(name.toLowerCase())) {
return entry.getValue();
}
}
StringBuilder buf = new StringBuilder("No such extension " + type.getName() + " by name " + name);
int i = 1;
for (Map.Entry<String, IllegalStateException> entry : exceptions.entrySet()) {
if (i == 1) {
buf.append(", possible causes: ");
}
buf.append("\r\n(");
buf.append(i++);
buf.append(") ");
buf.append(entry.getKey());
buf.append(":\r\n");
buf.append(StringUtils.toString(entry.getValue()));
}
return new IllegalStateException(buf.toString());
}
/**
*
* @param name 指定名称
* @return 如果无缓存则创建
*/
@SuppressWarnings("unchecked")
private T createExtension(String name) {
Class<?> clazz = getExtensionClasses().get(name); // getExtensionClass内部使用cachedClasses缓存
if (clazz == null) {
throw findException(name);
}
try {
T instance = (T) EXTENSION_INSTANCES.get(clazz); // 从已创建Extension实例缓存中获取
if (instance == null) {
EXTENSION_INSTANCES.putIfAbsent(clazz, (T) clazz.newInstance());
instance = (T) EXTENSION_INSTANCES.get(clazz);
}
injectExtension(instance); // 属性注入
// Wrapper类型进行包装，层层包裹
Set<Class<?>> wrapperClasses = cachedWrapperClasses;
if (wrapperClasses != null && wrapperClasses.size() > 0) {
for (Class<?> wrapperClass : wrapperClasses) {
instance = injectExtension((T) wrapperClass.getConstructor(type).newInstance(instance)); //循环遍历所有wrapper实现，实例化wrapper并进行扩展点注入
}
}
return instance;
} catch (Throwable t) {
throw new IllegalStateException("Extension instance(name: " + name + ", class: " +
type + ") could not be instantiated: " + t.getMessage(), t);
}
}
/**扩展点自动注入
* @param instance
* @return 返回实例
*/
private T injectExtension(T instance) {
try {
if (objectFactory != null) {
for (Method method : instance.getClass().getMethods()) {
if (method.getName().startsWith("set") // 处理所有set方法
&& method.getParameterTypes().length == 1
&& Modifier.isPublic(method.getModifiers())) {
Class<?> pt = method.getParameterTypes()[0]; // 获取set方法参数类型
try {
// 获取setter对应的property名称
String property = method.getName().length() > 3 ? method.getName().substring(3, 4).toLowerCase() + method.getName().substring(4) : "";
Object object = objectFactory.getExtension(pt, property); // 根据类型,名称信息从ExtensionFactory获取
if (object != null) {// 非空,set方法的参数是扩展点类型，那么进行注入
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;
}
/**
*从缓存中取实例
* @param name 存放实例MAP的key
* @return 返回实例
*/
private Class<?> getExtensionClass(String name) {
if (type == null)
throw new IllegalArgumentException("Extension type == null");
if (name == null)
throw new IllegalArgumentException("Extension name == null");
Class<?> clazz = getExtensionClasses().get(name);
if (clazz == null)
throw new IllegalStateException("No such extension \"" + name + "\" for " + type.getName() + "!");
return clazz;
}
/**
* 加载当前扩展所有实现，看是否有实现被标注为@Adaptive
* @return map缓存实例
*/
private Map<String, Class<?>> getExtensionClasses() {
Map<String, Class<?>> classes = cachedClasses.get();// 判断是否已经加载了当前Extension的所有实现类
if (classes == null) {
synchronized (cachedClasses) {
classes = cachedClasses.get();
if (classes == null) {
classes = loadExtensionClasses(); // 如果还没有加载Extension的实现，则进行扫描META-INF下文件进行加载,完成后赋值给cachedClasses变量
cachedClasses.set(classes);
}
}
}
return classes;
}
/**
* 进行是否存在@spi注解校验,如不存在就从
* 扩展配置文件取
* @return 返回是否存在要调用的接口实例
*/
// synchronized in getExtensionClasses
private Map<String, Class<?>> loadExtensionClasses() {
final SPI defaultAnnotation = type.getAnnotation(SPI.class);
if (defaultAnnotation != null) {
String value = defaultAnnotation.value();// 解析当前Extension配置的默认实现名，赋值给cachedDefaultName属性
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];
}
}
// 从配置文件中加载扩展实现类 META-INF/dubbo/internal/ META-INF/dubbo/ META-INF/services/
Map<String, Class<?>> extensionClasses = new HashMap<String, Class<?>>();
loadFile(extensionClasses, DUBBO_INTERNAL_DIRECTORY);
loadFile(extensionClasses, DUBBO_DIRECTORY);
loadFile(extensionClasses, SERVICES_DIRECTORY);
return extensionClasses;
}
private void loadFile(Map<String, Class<?>> extensionClasses, String dir) {
String fileName = dir + type.getName(); // 配置文件名称,扫描整个classpath
try {
Enumeration<java.net.URL> urls; // 先获取该路径下所有文件
ClassLoader classLoader = findClassLoader();
if (classLoader != null) {
urls = classLoader.getResources(fileName);
} else {
urls = ClassLoader.getSystemResources(fileName);
}
if (urls != null) {
while (urls.hasMoreElements()) { // 遍历这些文件并进行处理
java.net.URL url = urls.nextElement(); // 获取配置文件路径
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(url.openStream(), "utf-8"));
try {
String line = null;
while ((line = reader.readLine()) != null) { // 一行一行读取(一行一个配置)
final int ci = line.indexOf('#');
if (ci >= 0) line = line.substring(0, ci);
line = line.trim();
if (line.length() > 0) {
try {
String name = null;
int i = line.indexOf('='); // 等号分割(配置文件k-v)
if (i > 0) {
name = line.substring(0, i).trim(); // 扩展名称
line = line.substring(i + 1).trim();// 扩展实现类
}
if (line.length() > 0) {
Class<?> clazz = Class.forName(line, true, classLoader); // 加载扩展实现类
if (!type.isAssignableFrom(clazz)) { //Wrapper类型
throw new IllegalStateException("Error when load extension class(interface: " +
type + ", class line: " + clazz.getName() + "), class "
+ clazz.getName() + "is not subtype of interface.");
}
if (clazz.isAnnotationPresent(Adaptive.class)) {//判断该实现类是否@Adaptive,是的话不会放入extensionClasses/cachedClasses缓存
if (cachedAdaptiveClass == null) { // 第一个赋值给cachedAdaptiveClass属性
cachedAdaptiveClass = clazz;
} else if (!cachedAdaptiveClass.equals(clazz)) {// 只能有一个@Adaptive实现,出现第二个就报错了
throw new IllegalStateException("More than 1 adaptive class found: "
+ cachedAdaptiveClass.getClass().getName()
+ ", " + clazz.getClass().getName());
}
} else {// 不是@Adaptive类型
try {
clazz.getConstructor(type);// 判断是否Wrapper类型
Set<Class<?>> wrappers = cachedWrapperClasses;
if (wrappers == null) {
cachedWrapperClasses = new ConcurrentHashSet<Class<?>>();//ConcurrentHashSet由ConcurrentHashMap实现
wrappers = cachedWrapperClasses;
}
wrappers.add(clazz);//放入到Wrapper实现类缓存中
} catch (NoSuchMethodException e) {//不是Wrapper类型，普通实现类型
clazz.getConstructor();
if (name == null || name.length() == 0) {
name = findAnnotationName(clazz);
if (name == null || name.length() == 0) {
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);
}
}
}
String[] names = NAME_SEPARATOR.split(name);
if (names != null && names.length > 0) {// 看是否配置了多个name
Activate activate = clazz.getAnnotation(Activate.class);// 获取@Activate类型
if (activate != null) {
cachedActivates.put(names[0], activate);
}
for (String n : names) { // 遍历所有name
if (!cachedNames.containsKey(clazz)) { //缓存不存在当前Wrapper则缓存
cachedNames.put(clazz, n);// 放入Extension实现类与名称映射缓存,每个class只对应第一个名称有效
}
Class<?> c = extensionClasses.get(n);
if (c == null) {
extensionClasses.put(n, clazz);// 放入到extensionClasses缓存,多个name可能对应一个Class
} else if (c != clazz) { // 存在重名
throw new IllegalStateException("Duplicate extension " + type.getName() + " name " + n + " on " + c.getName() + " and " + clazz.getName());
}
}
}
}
}
}
} catch (Throwable t) {
IllegalStateException e = new IllegalStateException("Failed to load extension class(interface: " + type + ", class line: " + line + ") in " + url + ", cause: " + t.getMessage(), t);
exceptions.put(line, e);
}
}
} // end of while read lines
} finally {
reader.close();
}
} catch (Throwable t) {
logger.error("Exception when load extension class(interface: " +
type + ", class file: " + url + ") in " + url, t);
}
} // end of while urls
}
} catch (Throwable t) {
logger.error("Exception when load extension class(interface: " +
type + ", description file: " + fileName + ").", t);
}
}
@SuppressWarnings("deprecation")
private String findAnnotationName(Class<?> clazz) {
com.alibaba.dubbo.common.Extension extension = clazz.getAnnotation(com.alibaba.dubbo.common.Extension.class);
if (extension == null) {
String name = clazz.getSimpleName();
if (name.endsWith(type.getSimpleName())) {
name = name.substring(0, name.length() - type.getSimpleName().length());
}
return name.toLowerCase();
}
return extension.value();
}
@SuppressWarnings("unchecked")
private T createAdaptiveExtension() {
try {
return injectExtension((T) getAdaptiveExtensionClass().newInstance());//先获取AdaptiveExtensionClass,在获取其实例，最后进行注入处理
} catch (Exception e) {
throw new IllegalStateException("Can not create adaptive extension " + type + ", cause: " + e.getMessage(), e);
}
}
/**
*
* @return 取到最终的自适应实现类型
*/
private Class<?> getAdaptiveExtensionClass() {
getExtensionClasses();// 加载当前Extension的所有实现,如果有@Adaptive类型，则会赋值为cachedAdaptiveClass属性缓存起来
if (cachedAdaptiveClass != null) {
return cachedAdaptiveClass;
}
return cachedAdaptiveClass = createAdaptiveExtensionClass();// 没有找到@Adaptive类型实现，则动态创建一个AdaptiveExtensionClass
}
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 String createAdaptiveExtensionClassCode() {
StringBuilder codeBuidler = new StringBuilder();
Method[] methods = type.getMethods();
boolean hasAdaptiveAnnotation = false;
for (Method m : methods) {
if (m.isAnnotationPresent(Adaptive.class)) { //@Adaptive类型实现
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!");
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;
}
}
// 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);
}
String[] value = adaptiveAnnotation.value();
// value is not set, use the value generated from class name as the 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(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();
}
@Override
public String toString() {
return this.getClass().getName() + "[" + type.getName() + "]";
}
}参考
http://wely.iteye.com/blog/2304718
http://manzhizhen.iteye.com/blog/2380052
https://blog.csdn.net/szwandcj/article/details/56831239
https://blog.csdn.net/szwandcj/article/details/56831351
https://blog.csdn.net/szwandcj/article/details/50587277
https://blog.csdn.net/chaoyuehu/article/details/79484036
https://blog.csdn.net/chaoyuehu/article/details/79505522
https://blog.csdn.net/chaoyuehu/article/month/2018/03