Dubbo扩展点加载机制 - ToB企服应用市场:ToB评测及商务社交产业平台

import com.alibaba.dubbo.common.Constants;
import com.alibaba.dubbo.common.URL;
import com.alibaba.dubbo.common.extension.ExtensionLoader;
import com.alibaba.dubbo.rpc.Exporter;
import com.alibaba.dubbo.rpc.Invoker;
import com.alibaba.dubbo.rpc.Protocol;
public class ProtocolFilterWrapper implements Protocol {
private final Protocol protocol;
public ProtocolFilterWrapper(Protocol protocol) {
this.protocol = protocol;
}
@Override
public int getDefaultPort() {
return protocol.getDefaultPort();
}
@Override
public Exporter<T> export(Exporter<T> exporter) {
return new InvokerDelegator<>(wrapInvoker(exporter.getInvoker()), exporter);
}
@Override
public <T> Invoker<T> refer(Class<T> type, URL url) {
return wrapInvoker(protocol.refer(type, url));
}
private <T> Invoker<T> wrapInvoker(Invoker<T> invoker) {
URL url = invoker.getUrl();
// 获取所有激活的过滤器
List<Filter> filters = ExtensionLoader.getExtensionLoader(Filter.class).getActivateExtension(url, Constants.KEYS, Constants.DEFAULT_KEY);
if (filters.size() == 0) {
return invoker;
}
return new FilterChainWrapper(invoker, filters);
}

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/**
* @param extensionClasses ExtensionLoader#cachedClasses 成员变量
* @param resourceURL
* @param clazz ExtensionLoader#loadResource 中加载 Class.forName( 类全限定名 )
* @param name ExtensionLoader#loadResource 中在配置文件中设置的别名
* 上两参数请参考 com.alibaba.dubbo.common.extension.SPI
* @throws NoSuchMethodException
*/
private void loadClass(Map<String, Class<?>> extensionClasses, java.net.URL resourceURL, Class<?> clazz, String name) throws NoSuchMethodException {
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.");
}
if (clazz.isAnnotationPresent(Adaptive.class)) {
// 由于调用者 ExtensionLoader.loadResource 循环调用了 loadClass ，如果类上标注了 @Adaptive 注解，则该类为 Adaptive 类，并且只能有一个
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 if (isWrapperClass(clazz)) {
// 判断为包装类,则维护到 ExtensionLoader.cachedWrapperClasses
Set<Class<?>> wrappers = cachedWrapperClasses;
if (wrappers == null) {
cachedWrapperClasses = new ConcurrentHashSet<Class<?>>();
wrappers = cachedWrapperClasses;
}
wrappers.add(clazz);
} else {
clazz.getConstructor();
if (name == null || name.length() == 0) {
// 如果没有名字则尝试扫描 @Extension 注解， Extension 注解已经弃用了
name = findAnnotationName(clazz);
if (name.length() == 0) {
throw new IllegalStateException("No such extension name for the class " + clazz.getName() + " in the config " + resourceURL);
}
}
// 将首个类上@Activate 信息维护到 ExtensionLoader.cachedActivates 中
// 将别名维护到 ExtensionLoader.cachedNames 中
// 将别名&类维护到 ExtensionLoader#cachedClasses 中
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)) {
cachedNames.put(clazz, n);
}
Class<?> c = extensionClasses.get(n);
if (c == null) {
extensionClasses.put(n, clazz);
} else if (c != clazz) {
throw new IllegalStateException("Duplicate extension " + type.getName() + " name " + n + " on " + c.getName() + " and " + clazz.getName());
}
}
}
}
}

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/**
* 创建扩展实例
* @param name 别名
* @return
*/
private T createExtension(String name) {
Class<?> clazz = getExtensionClasses().get(name);
if (clazz == null) {
throw findException(name);
}
try {
// 先尝试从缓存中获取实例
T instance = (T) EXTENSION_INSTANCES.get(clazz);
if (instance == null) {
// 不存在的话则通过反射创建实例
EXTENSION_INSTANCES.putIfAbsent(clazz, clazz.newInstance());
instance = (T) EXTENSION_INSTANCES.get(clazz);
}
// 反射执行 setter 方法
injectExtension(instance);
Set<Class<?>> wrapperClasses = cachedWrapperClasses;
if (wrapperClasses != null && !wrapperClasses.isEmpty()) {
// 检查是否有包装类
for (Class<?> wrapperClass : wrapperClasses) {
// 通过反射创建包装类实例,再执行包装实例的 setter 方法, 最后更新包装类实例
// 这里我们能看出包装类需要实现接口，并且包装类需要有一个构造函数，构造参数是接口类型
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);
}
}

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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);
}

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