开篇
这篇文章尝试分析Protocol的getAdaptiveExtension过程，和dubbo之ExtensionFactory获取适应扩展过程分析不一样的过程在于ExtensionFactory的扩展类是定义的AdaptiveExtensionFactory，而Protocol的适应扩展是动态生成的。
所以重点关注下Protocol$Adaptive的动态生成过程，文中会有动态生成后的源码。
引用例子
说明：
- ExtensionLoader的使用分两步走，先getExtensionLoader后getAdaptiveExtension。
- getExtensionLoader返回对应类的ExtensionLoader。
- getAdaptiveExtension返回对应类的AdaptiveExtension。
- Protocol会返回Protocol$Adaptive的扩展类.
public class ServiceConfig<T> extends AbstractServiceConfig {
private static final Protocol protocol = ExtensionLoader.getExtensionLoader(Protocol.class).getAdaptiveExtension();
}ExtensionLoader介绍
- 核心部分可以参考dubbo之ExtensionFactory获取适应扩展过程分析的ExtensionLoader介绍。
- Protocol对应的ExtensionLoader的objectFactory为AdaptiveExtensionFactory。
- 非ExtensionFactory的ExtensionLoader的objectFactory都是AdaptiveExtensionFactory。
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<>();
private static final ConcurrentMap<Class<?>, Object> EXTENSION_INSTANCES = new ConcurrentHashMap<>();
private final Class<?> type;
private final ExtensionFactory objectFactory;
private final ConcurrentMap<Class<?>, String> cachedNames = new ConcurrentHashMap<>();
private final Holder<Map<String, Class<?>>> cachedClasses = new Holder<>();
private final Map<String, Object> cachedActivates = new ConcurrentHashMap<>();
private final ConcurrentMap<String, Holder<Object>> cachedInstances = new ConcurrentHashMap<>();
private final Holder<Object> cachedAdaptiveInstance = new Holder<>();
private volatile Class<?> cachedAdaptiveClass = null;
private String cachedDefaultName;
private volatile Throwable createAdaptiveInstanceError;
private Set<Class<?>> cachedWrapperClasses;
private Map<String, IllegalStateException> exceptions = new ConcurrentHashMap<>();
private ExtensionLoader(Class<?> type) {
this.type = type;
objectFactory = (type == ExtensionFactory.class ? null : ExtensionLoader.getExtensionLoader(ExtensionFactory.class).getAdaptiveExtension());
}
@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 an interface!");
}
if (!withExtensionAnnotation(type)) {
throw new IllegalArgumentException("Extension type (" + type +
") is not an extension, because it is NOT annotated with @" + SPI.class.getSimpleName() + "!");
}
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;
}
}
createAdaptiveExtension
- 按照getAdaptiveExtension => createAdaptiveExtension => getAdaptiveExtensionClass => createAdaptiveExtensionClass流程创建AdaptiveExtensionClass。
- new AdaptiveClassCodeGenerator(type, cachedDefaultName).generate()负责生成Protocol$Adaptive的源码。
public class ExtensionLoader<T> {
public T getAdaptiveExtension() {
Object instance = cachedAdaptiveInstance.get();
if (instance == null) {
if (createAdaptiveInstanceError != null) {
throw new IllegalStateException("Failed to create adaptive instance: " +
createAdaptiveInstanceError.toString(),
createAdaptiveInstanceError);
}
synchronized (cachedAdaptiveInstance) {
instance = cachedAdaptiveInstance.get();
if (instance == null) {
try {
instance = createAdaptiveExtension();
cachedAdaptiveInstance.set(instance);
} catch (Throwable t) {
createAdaptiveInstanceError = t;
throw new IllegalStateException("Failed to create adaptive instance: " + t.toString(), t);
}
}
}
}
return (T) instance;
}
private T createAdaptiveExtension() {
try {
return injectExtension((T) getAdaptiveExtensionClass().newInstance());
} catch (Exception e) {
throw new IllegalStateException("Can't create adaptive extension " + type + ", cause: " + e.getMessage(), e);
}
}
private Class<?> getAdaptiveExtensionClass() {
getExtensionClasses();
if (cachedAdaptiveClass != null) {
return cachedAdaptiveClass;
}
return cachedAdaptiveClass = createAdaptiveExtensionClass();
}
private Class<?> createAdaptiveExtensionClass() {
String code = new AdaptiveClassCodeGenerator(type, cachedDefaultName).generate();
ClassLoader classLoader = findClassLoader();
org.apache.dubbo.common.compiler.Compiler compiler = ExtensionLoader.getExtensionLoader(org.apache.dubbo.common.compiler.Compiler.class).getAdaptiveExtension();
return compiler.compile(code, classLoader);
}
}AdaptiveClassCodeGenerator
说明：
- generate()方法是生成目标类的主干方法，其主要分为如下几个步骤：
- 生成package信息。
- 生成import信息，只导入了ExtensionLoader类，其余的类都通过全限定名的方式来使用。
- 生成类声明信息。
- 生成各个方法的实现。
public class AdaptiveClassCodeGenerator {
public AdaptiveClassCodeGenerator(Class<?> type, String defaultExtName) {
this.type = type;
this.defaultExtName = defaultExtName;
}
public String generate() {
// no need to generate adaptive class since there's no adaptive method found.
if (!hasAdaptiveMethod()) {
throw new IllegalStateException("No adaptive method exist on extension " + type.getName() + ", refuse to create the adaptive class!");
}
StringBuilder code = new StringBuilder();
// 生成package信息
code.append(generatePackageInfo());
// 生成import信息，这里只导入了ExtensionLoader类，其余的类都通过全限定名的方式来使用
code.append(generateImports());
// 生成类声明信息
code.append(generateClassDeclaration());
// 为各个方法生成实现方法信息
Method[] methods = type.getMethods();
for (Method method : methods) {
code.append(generateMethod(method));
}
code.append("}");
if (logger.isDebugEnabled()) {
logger.debug(code.toString());
}
return code.toString();
}
}Protocol$Adaptive
说明：
- Protocol本身通过SPI注解。
- 通过@Adaptive注解的方法在AdaptiveClassCodeGenerator的generate()重新生成源码。
- 没有通过@Adaptive注解的方法的方法体内会抛异常。
- 在Protocol$Adaptive的export和refer方法通过ExtensionLoader.getExtensionLoader().getExtension()动态获取扩展。
- 根据URL动态获取扩展名，String extName = ( url.getProtocol() == null ? "dubbo" : url.getProtocol())。
package org.apache.dubbo.rpc;
import org.apache.dubbo.common.URL;
import org.apache.dubbo.common.extension.Adaptive;
import org.apache.dubbo.common.extension.SPI;
@SPI("dubbo")
public interface Protocol {
int getDefaultPort();
@Adaptive
<T> Exporter<T> export(Invoker<T> invoker) throws RpcException;
@Adaptive
<T> Invoker<T> refer(Class<T> type, URL url) throws RpcException;
void destroy();
}package org.apache.dubbo.rpc;
import org.apache.dubbo.common.extension.ExtensionLoader;
public class Protocol$Adaptive implements org.apache.dubbo.rpc.Protocol {
public void destroy() {
throw new UnsupportedOperationException("The method public abstract void org.apache.dubbo.rpc.Protocol.destroy() of interface org.apache.dubbo.rpc.Protocol is not adaptive method!");
}
public int getDefaultPort() {
throw new UnsupportedOperationException("The method public abstract int org.apache.dubbo.rpc.Protocol.getDefaultPort() of interface org.apache.dubbo.rpc.Protocol is not adaptive method!");
}
public org.apache.dubbo.rpc.Exporter export(org.apache.dubbo.rpc.Invoker arg0) throws org.apache.dubbo.rpc.RpcException {
if (arg0 == null) throw new IllegalArgumentException("org.apache.dubbo.rpc.Invoker argument == null");
if (arg0.getUrl() == null) throw new IllegalArgumentException("org.apache.dubbo.rpc.Invoker argument getUrl() == null");
org.apache.dubbo.common.URL url = arg0.getUrl();
String extName = ( url.getProtocol() == null ? "dubbo" : url.getProtocol() );
if(extName == null) throw new IllegalStateException("Failed to get extension (org.apache.dubbo.rpc.Protocol) name from url (" + url.toString() + ") use keys([protocol])");
org.apache.dubbo.rpc.Protocol extension = (org.apache.dubbo.rpc.Protocol)ExtensionLoader.getExtensionLoader(org.apache.dubbo.rpc.Protocol.class).getExtension(extName);
return extension.export(arg0);
}
public org.apache.dubbo.rpc.Invoker refer(java.lang.Class arg0, org.apache.dubbo.common.URL arg1) throws org.apache.dubbo.rpc.RpcException {
if (arg1 == null) throw new IllegalArgumentException("url == null");
org.apache.dubbo.common.URL url = arg1;
String extName = ( url.getProtocol() == null ? "dubbo" : url.getProtocol() );
if(extName == null) throw new IllegalStateException("Failed to get extension (org.apache.dubbo.rpc.Protocol) name from url (" + url.toString() + ") use keys([protocol])");
org.apache.dubbo.rpc.Protocol extension = (org.apache.dubbo.rpc.Protocol)ExtensionLoader.getExtensionLoader(org.apache.dubbo.rpc.Protocol.class).getExtension(extName);
return extension.refer(arg0, arg1);
}
}
