dubbo extension扩展点 源代码
1.首先我们创建一些类，我们再一步一步的进行分析dubbo的扩展点的源代码
public class DefaultExtensionImpl implements MyInterface {
@Override
public String sayHello(String name, String type) {
return this.getClass().getName() + " " + name + " " + type;
}
}
public class ExtensionTest {
@SuppressWarnings("rawtypes")
public static void main(String[] args) {
System.out.println("!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!");
ExtensionLoader extensionLoader = ExtensionLoader
.getExtensionLoader(MyInterface.class);
MyInterface myFirstExtension = (MyInterface) extensionLoader
.getAdaptiveExtension();
System.out.println(myFirstExtension.sayHello("xxx",
ExtensionType.defaults));
}
}public class ExtensionType {
public static final String defaults = "defaults";
public static final String other = "other";
}@Adaptive
public class MyAdaptiveExtension implements MyInterface {
@SuppressWarnings("rawtypes")
@Override
public String sayHello(String name, String type) {
ExtensionLoader extensionLoader = ExtensionLoader
.getExtensionLoader(MyInterface.class);
MyInterface extension = (MyInterface) extensionLoader
.getDefaultExtension();
if (ExtensionType.defaults.equals(type)) {
extension = (MyInterface) extensionLoader
.getExtension("defaults");
}
if (ExtensionType.other.equals(type)) {
extension = (MyInterface) extensionLoader
.getExtension("other");
}
return extension.sayHello(name, type);
}
}@SPI("defaults")
public interface MyInterface {
public String sayHello(String name, String type);
}public class OtherExtensionImpl implements MyInterface {
@Override
public String sayHello(String name, String type) {
return this.getClass().getName() + " " + name + " " + type;
}
}com.alibaba.dubbo.demo.extensiontest.MyInterface内容：
defaults=com.alibaba.dubbo.demo.extensiontest.DefaultExtensionImpl
other=com.alibaba.dubbo.demo.extensiontest.OtherExtensionImpl
adaptive=com.alibaba.dubbo.demo.extensiontest.MyAdaptiveExtension
运行的结果
2.现在需要创建一个ExtensionLoader对象 ，ExtensionLoader是个单例，但是提供了一个getExtensionLoader方法
@SuppressWarnings("unchecked")
public static ExtensionLoader getExtensionLoader(Class type) {
// 不能为空
if (type == null)
throw new IllegalArgumentException("Extension type == null");
// 接口
if (!type.isInterface()) {
throw new IllegalArgumentException("Extension type(" + type
+ ") is not interface!");
}
// spi类型
if (!withExtensionAnnotation(type)) {
throw new IllegalArgumentException("Extension type(" + type
+ ") is not extension, because WITHOUT @"
+ SPI.class.getSimpleName() + " Annotation!");
}
// 先从EXTENSION_LOADERS获取ExtensionLoader
ExtensionLoader loader = (ExtensionLoader) EXTENSION_LOADERS
.get(type);
// 新建一个ExtensionLoader对象
if (loader == null) {
EXTENSION_LOADERS.putIfAbsent(type, new ExtensionLoader(type));
loader = (ExtensionLoader) EXTENSION_LOADERS.get(type);
}
return loader;
} 3.创建一个ExtensionLoader对象
private ExtensionLoader(Class type) {
this.type = type;
//如果type是ExtensionFactory.class返回null 如果不是的话 那么就创建一个type为ExtensionFactory.class的对象，之后再调用getAdaptiveExtension方法
objectFactory = (type == ExtensionFactory.class ? null : ExtensionLoader.getExtensionLoader(ExtensionFactory.class).getAdaptiveExtension());
}4.调用getAdaptiveExtension方法
@SuppressWarnings("unchecked")
public T getAdaptiveExtension() {
//先从cachedAdaptiveInstance(自适应的实现类，该类需要有@Adaptive注解)获取，不为null的话那么直接返回
Object instance = cachedAdaptiveInstance.get();
if (instance == null) {
if(createAdaptiveInstanceError == null) {
synchronized (cachedAdaptiveInstance) {
instance = cachedAdaptiveInstance.get();
if (instance == null) {
try {
//如果为null的话 调用createAdaptiveExtension方法
instance = createAdaptiveExtension();
//获取到实例之后，set到cachedAdaptiveInstance里
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;
}@SuppressWarnings("unchecked")
private T createAdaptiveExtension() {
try {
return injectExtension((T) getAdaptiveExtensionClass().newInstance());
} catch (Exception e) {
throw new IllegalStateException("Can not create adaptive extenstion " + type + ", cause: " + e.getMessage(), e);
}
}6.调用getAdaptiveExtensionClass方法
private Class getAdaptiveExtensionClass() {
getExtensionClasses();
//如果cachedAdaptiveClass不为空 直接返回
if (cachedAdaptiveClass != null) {
return cachedAdaptiveClass;
}
return cachedAdaptiveClass = createAdaptiveExtensionClass();
}7.调用getExtensionClasses方法
private Map> getExtensionClasses() {
//从cachedClasses获取
Map> classes = cachedClasses.get();
if (classes == null) {
synchronized (cachedClasses) {
classes = cachedClasses.get();
if (classes == null) {
//如果为null的话，开始进行读取配置文件
classes = loadExtensionClasses();
//放入到cachedClasses对象里
cachedClasses.set(classes);
}
}
}
return classes;
} 8.调用loadExtensionClasses方法
private Map> loadExtensionClasses() {
final SPI defaultAnnotation = type.getAnnotation(SPI.class);
if(defaultAnnotation != null) {
String value = defaultAnnotation.value();
//如果value不为空的话 赋值cachedDefaultName
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> extensionClasses = new HashMap>();
//读取配置文件META-INF/dubbo/internal/
loadFile(extensionClasses, DUBBO_INTERNAL_DIRECTORY);
//读取配置文件META-INF/dubbo/
loadFile(extensionClasses, DUBBO_DIRECTORY);
//读取配置文件META-INF/services/
loadFile(extensionClasses, SERVICES_DIRECTORY);
return extensionClasses;
} 9.调用loadFile方法
private void loadFile(Map> extensionClasses, String dir) {
String fileName = dir + type.getName();
try {
Enumeration urls;
ClassLoader classLoader = findClassLoader();
if (classLoader != null) {
urls = classLoader.getResources(fileName);
} else {
urls = ClassLoader.getSystemResources(fileName);
}
//如果文件路径不为空的话
if (urls != null) {
//进行遍历
while (urls.hasMoreElements()) {
java.net.URL url = urls.nextElement();
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(url.openStream(), "utf-8"));
try {
String line = null;
while ((line = reader.readLine()) != null) {
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('=');
if (i > 0) {
//获取类的名称
name = line.substring(0, i).trim();
line = line.substring(i + 1).trim();
}
if (line.length() > 0) {
//获取类
Class clazz = Class.forName(line, true, classLoader);
//判断该类是不是实现该接口
if (! type.isAssignableFrom(clazz)) {
throw new IllegalStateException("Error when load extension class(interface: " +
type + ", class line: " + clazz.getName() + "), class "
+ clazz.getName() + "is not subtype of interface.");
}
//判断该类是否是一个自适应的adaptive的类
if (clazz.isAnnotationPresent(Adaptive.class)) {
if(cachedAdaptiveClass == null) {
cachedAdaptiveClass = clazz;
} else if (! cachedAdaptiveClass.equals(clazz)) {
throw new IllegalStateException("More than 1 adaptive class found: "
+ cachedAdaptiveClass.getClass().getName()
+ ", " + clazz.getClass().getName());
}
} else {
try {
//判断是不是装饰类
clazz.getConstructor(type);
Set> wrappers = cachedWrapperClasses;
if (wrappers == null) {
cachedWrapperClasses = new ConcurrentHashSet>();
wrappers = cachedWrapperClasses;
}
wrappers.add(clazz);
} catch (NoSuchMethodException e) {
//普通的实现类
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) {
Activate activate = clazz.getAnnotation(Activate.class);
if (activate != null) {
cachedActivates.put(names[0], activate);
}
for (String n : names) {
if (! cachedNames.containsKey(clazz)) {
//进行赋值
cachedNames.put(clazz, n);
}
Class c = extensionClasses.get(n);
if (c == null) {
//进行赋值
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) {
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);
}
}
10.创建AdaptiveExtensionFactory实例
@Adaptive
public class AdaptiveExtensionFactory implements ExtensionFactory {
private final List factories;
public AdaptiveExtensionFactory() {
ExtensionLoader loader = ExtensionLoader.getExtensionLoader(ExtensionFactory.class);
List list = new ArrayList();
//loader.getSupportedExtensions() 获取extensions的实现类的key
for (String name : loader.getSupportedExtensions()) {
//获取extension的实现类
list.add(loader.getExtension(name));
}
factories = Collections.unmodifiableList(list);
}
public T getExtension(Class type, String name) {
for (ExtensionFactory factory : factories) {
T extension = factory.getExtension(type, name);
if (extension != null) {
return extension;
}
}
return null;
}
} 11.调用getExtension方法
@SuppressWarnings("unchecked")
public T getExtension(String name) {
if (name == null || name.length() == 0)
throw new IllegalArgumentException("Extension name == null");
if ("true".equals(name)) {
return getDefaultExtension();
}
Holder12.调用createExtension方法
@SuppressWarnings("unchecked")
private T createExtension(String name) {
Class clazz = getExtensionClasses().get(name);
if (clazz == null) {
throw findException(name);
}
try {
//EXTENSION_INSTANCES里是否有实现类
T instance = (T) EXTENSION_INSTANCES.get(clazz);
//没有的话创建对象 赋值到EXTENSION_INSTANCES
if (instance == null) {
EXTENSION_INSTANCES.putIfAbsent(clazz, (T) clazz.newInstance());
instance = (T) EXTENSION_INSTANCES.get(clazz);
}
//注入
injectExtension(instance);
//进行包装
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);
}
} 到此ExtensionLoader已经创建完成。