Dubbo之ProxyFactory解析

开篇

阅读Dubbo的服务发布的源码的时候发现有PROXY_FACTORY.getInvoker()的代码，这部分涉及了javassist动态生成源码的逻辑，因为动态生成代码所以没法直观看到逻辑，借此写一篇分析文章，便于看到这部分逻辑的人能够更好的理解。

因为涉及到查看动态生成代码的逻辑，需要使用arthas工具反编译类查看动态生成的Wrapper类内容，涉及arthas
)工具的简单使用。

ProxyFactory适配器

private static final ProxyFactory PROXY_FACTORY = ExtensionLoader.getExtensionLoader(ProxyFactory.class).getAdaptiveExtension();

• 以上是ProxyFactory生成的代码逻辑，非常简单，通过getAdaptiveExtension()方法生成代码。继续查看ProxyFactory的适配器代码。
• PROXY_FACTORY这里是ProxyFactory$Adaptive。

ProxyFactory

@SPI("javassist")
public interface ProxyFactory {

    @Adaptive({PROXY_KEY})
    <T> T getProxy(Invoker<T> invoker) throws RpcException;

    @Adaptive({PROXY_KEY})
    <T> T getProxy(Invoker<T> invoker, boolean generic) throws RpcException;

    @Adaptive({PROXY_KEY})
    <T> Invoker<T> getInvoker(T proxy, Class<T> type, URL url) throws RpcException;

}

• 以上是ProxyFactory包括的几个方法，且都用@Adaptive进行修饰，所以在适配器生成的代码当中这几个方法都会被重新实现。
• @SPI("javassist")的注解表明动态扩展extName默认值使用“javassist”。
• 继续阅读ProxyFactory生成的代码ProxyFactory$Adaptive。

ProxyFactory$Adaptive

package org.apache.dubbo.rpc;

import org.apache.dubbo.common.extension.ExtensionLoader;


public class ProxyFactory$Adaptive implements org.apache.dubbo.rpc.ProxyFactory {

    public org.apache.dubbo.rpc.Invoker getInvoker(java.lang.Object arg0,
        java.lang.Class arg1, org.apache.dubbo.common.URL arg2)
        throws org.apache.dubbo.rpc.RpcException {
        if (arg2 == null) {
            throw new IllegalArgumentException("url == null");
        }

        org.apache.dubbo.common.URL url = arg2;
        String extName = url.getParameter("proxy", "javassist");

        if (extName == null) {
            throw new IllegalStateException(
                "Failed to get extension (org.apache.dubbo.rpc.ProxyFactory) name from url (" +
                url.toString() + ") use keys([proxy])");
        }

        org.apache.dubbo.rpc.ProxyFactory extension = (org.apache.dubbo.rpc.ProxyFactory) ExtensionLoader.getExtensionLoader(org.apache.dubbo.rpc.ProxyFactory.class).getExtension(extName);

        return extension.getInvoker(arg0, arg1, arg2);
    }

    public java.lang.Object getProxy(org.apache.dubbo.rpc.Invoker arg0,
        boolean arg1) 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.getParameter("proxy", "javassist");

        if (extName == null) {
            throw new IllegalStateException(
                "Failed to get extension (org.apache.dubbo.rpc.ProxyFactory) name from url (" +
                url.toString() + ") use keys([proxy])");
        }

        org.apache.dubbo.rpc.ProxyFactory extension = (org.apache.dubbo.rpc.ProxyFactory) ExtensionLoader.getExtensionLoader(org.apache.dubbo.rpc.ProxyFactory.class).getExtension(extName);

        return extension.getProxy(arg0, arg1);
    }

    public java.lang.Object getProxy(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.getParameter("proxy", "javassist");

        if (extName == null) {
            throw new IllegalStateException(
                "Failed to get extension (org.apache.dubbo.rpc.ProxyFactory) name from url (" +
                url.toString() + ") use keys([proxy])");
        }

        org.apache.dubbo.rpc.ProxyFactory extension = (org.apache.dubbo.rpc.ProxyFactory) ExtensionLoader.getExtensionLoader(org.apache.dubbo.rpc.ProxyFactory.class).getExtension(extName);

        return extension.getProxy(arg0);
    }
}

• 以上代码针对ProxyFactory的带有@Adaptive的注解的方法重新生成了代码。
• 方法内部通过 ExtensionLoader.getExtensionLoader(ProxyFactory.class)
  .getExtension(extName)动态根据extName获取子类对象。
• 扩展名从URL中获取，通过extName = url.getParameter("proxy", "javassist")。
• ProxyFactory的实现类图如下图所示，这里关注JavassistProxyFactory。

exportLocal()方法

• exportLocal方法调用PROXY_FACTORY.getInvoker()获取Invoker对象，外面通过协议protocol.export()导出一下。
• PROXY_FACTORY.getInvoker()调用ProxyFactory$Adaptive的getInvoker()方法。
• getInvoker()方法内部执行 extension = (org.apache.dubbo.rpc.ProxyFactory) ExtensionLoader.getExtensionLoader(org.apache.dubbo.rpc.ProxyFactory.class).getExtension(extName)返回JavassistProxyFactory对象。
• 暂时只关注getInvoker()方法，ref是接口类对象如DemoServiceImpl，interfaceClass为接口类如DemoService。

    private void exportLocal(URL url) {
        URL local = URLBuilder.from(url)
                .setProtocol(LOCAL_PROTOCOL)
                .setHost(LOCALHOST_VALUE)
                .setPort(0)
                .build();
        Exporter<?> exporter = protocol.export(
                PROXY_FACTORY.getInvoker(ref, (Class) interfaceClass, local));
        exporters.add(exporter);
        logger.info("Export dubbo service " + interfaceClass.getName() + " to local registry url : " + local);
    }

JavassistProxyFactory

• JavassistProxyFactory的getInvoker()方法内部执行动作：创建包装类Wrapper和创建AbstractProxyInvoker对象。
• Wrapper.getWrapper()方法内部通过javassist方法生成包装类。
• AbstractProxyInvoker类实现Invoker，通过调用invoke() => doInvoke() => wrapper.invokeMethod()实现调用。

public class JavassistProxyFactory extends AbstractProxyFactory {

    @Override
    @SuppressWarnings("unchecked")
    public <T> T getProxy(Invoker<T> invoker, Class<?>[] interfaces) {
        return (T) Proxy.getProxy(interfaces).newInstance(new InvokerInvocationHandler(invoker));
    }

    @Override
    public <T> Invoker<T> getInvoker(T proxy, Class<T> type, URL url) {
        // TODO Wrapper cannot handle this scenario correctly: the classname contains '$'
        final Wrapper wrapper = Wrapper.getWrapper(proxy.getClass().getName().indexOf('$') < 0 ? proxy.getClass() : type);
        return new AbstractProxyInvoker<T>(proxy, type, url) {
            @Override
            protected Object doInvoke(T proxy, String methodName,
                                      Class<?>[] parameterTypes,
                                      Object[] arguments) throws Throwable {
                return wrapper.invokeMethod(proxy, methodName, parameterTypes, arguments);
            }
        };
    }
}

public abstract class AbstractProxyInvoker<T> implements Invoker<T> {
    Logger logger = LoggerFactory.getLogger(AbstractProxyInvoker.class);

    private final T proxy;

    private final Class<T> type;

    private final URL url;

    public AbstractProxyInvoker(T proxy, Class<T> type, URL url) {
        if (proxy == null) {
            throw new IllegalArgumentException("proxy == null");
        }
        if (type == null) {
            throw new IllegalArgumentException("interface == null");
        }
        if (!type.isInstance(proxy)) {
            throw new IllegalArgumentException(proxy.getClass().getName() + " not implement interface " + type);
        }
        this.proxy = proxy;
        this.type = type;
        this.url = url;
    }

    @Override
    public Result invoke(Invocation invocation) throws RpcException {
        try {
            Object value = doInvoke(proxy, invocation.getMethodName(), invocation.getParameterTypes(), invocation.getArguments());
            CompletableFuture<Object> future = wrapWithFuture(value, invocation);
            AsyncRpcResult asyncRpcResult = new AsyncRpcResult(invocation);
            future.whenComplete((obj, t) -> {
                AppResponse result = new AppResponse();
                if (t != null) {
                    if (t instanceof CompletionException) {
                        result.setException(t.getCause());
                    } else {
                        result.setException(t);
                    }
                } else {
                    result.setValue(obj);
                }
                asyncRpcResult.complete(result);
            });
            return asyncRpcResult;
        } catch (InvocationTargetException e) {
            if (RpcContext.getContext().isAsyncStarted() && !RpcContext.getContext().stopAsync()) {
                logger.error("Provider async started, but got an exception from the original method, cannot write the exception back to consumer because an async result may have returned the new thread.", e);
            }
            return AsyncRpcResult.newDefaultAsyncResult(null, e.getTargetException(), invocation);
        } catch (Throwable e) {
            throw new RpcException("Failed to invoke remote proxy method " + invocation.getMethodName() + " to " + getUrl() + ", cause: " + e.getMessage(), e);
        }
    }
}

getWrapper()方法

• 通过makeWrapper()方法生成Wrapper对象。
• makeWrapper()方法通过javassist生成代码，逻辑复杂，通过arthas方法反编译查看。

    public static Wrapper getWrapper(Class<?> c) {
        while (ClassGenerator.isDynamicClass(c)) // can not wrapper on dynamic class.
        {
            c = c.getSuperclass();
        }

        if (c == Object.class) {
            return OBJECT_WRAPPER;
        }
        // 缓存作用
        Wrapper ret = WRAPPER_MAP.get(c);
        if (ret == null) {
            // 生成Wrapper类,这边逻辑比较难懂,下面先通过arthas生成具体的Wrapper类观察一下
            ret = makeWrapper(c);
            WRAPPER_MAP.put(c, ret);
        }
        return ret;
    }

    private static Wrapper makeWrapper(Class<?> c) {
        if (c.isPrimitive()) {
            throw new IllegalArgumentException("Can not create wrapper for primitive type: " + c);
        }

        String name = c.getName();
        ClassLoader cl = ClassUtils.getClassLoader(c);

        StringBuilder c1 = new StringBuilder("public void setPropertyValue(Object o, String n, Object v){ ");
        StringBuilder c2 = new StringBuilder("public Object getPropertyValue(Object o, String n){ ");
        StringBuilder c3 = new StringBuilder("public Object invokeMethod(Object o, String n, Class[] p, Object[] v) throws " + InvocationTargetException.class.getName() + "{ ");

        c1.append(name).append(" w; try{ w = ((").append(name).append(")$1); }catch(Throwable e){ throw new IllegalArgumentException(e); }");
        c2.append(name).append(" w; try{ w = ((").append(name).append(")$1); }catch(Throwable e){ throw new IllegalArgumentException(e); }");
        c3.append(name).append(" w; try{ w = ((").append(name).append(")$1); }catch(Throwable e){ throw new IllegalArgumentException(e); }");

        Map<String, Class<?>> pts = new HashMap<>(); // <property name, property types>
        Map<String, Method> ms = new LinkedHashMap<>(); // <method desc, Method instance>
        List<String> mns = new ArrayList<>(); // method names.
        List<String> dmns = new ArrayList<>(); // declaring method names.

        // get all public field.
        for (Field f : c.getFields()) {
            String fn = f.getName();
            Class<?> ft = f.getType();
            if (Modifier.isStatic(f.getModifiers()) || Modifier.isTransient(f.getModifiers())) {
                continue;
            }

            c1.append(" if( $2.equals(\"").append(fn).append("\") ){ w.").append(fn).append("=").append(arg(ft, "$3")).append("; return; }");
            c2.append(" if( $2.equals(\"").append(fn).append("\") ){ return ($w)w.").append(fn).append("; }");
            pts.put(fn, ft);
        }

        Method[] methods = c.getMethods();
        // get all public method.
        boolean hasMethod = hasMethods(methods);
        if (hasMethod) {
            c3.append(" try{");
            for (Method m : methods) {
                //ignore Object's method.
                if (m.getDeclaringClass() == Object.class) {
                    continue;
                }

                String mn = m.getName();
                c3.append(" if( \"").append(mn).append("\".equals( $2 ) ");
                int len = m.getParameterTypes().length;
                c3.append(" && ").append(" $3.length == ").append(len);

                boolean override = false;
                for (Method m2 : methods) {
                    if (m != m2 && m.getName().equals(m2.getName())) {
                        override = true;
                        break;
                    }
                }
                if (override) {
                    if (len > 0) {
                        for (int l = 0; l < len; l++) {
                            c3.append(" && ").append(" $3[").append(l).append("].getName().equals(\"")
                                    .append(m.getParameterTypes()[l].getName()).append("\")");
                        }
                    }
                }

                c3.append(" ) { ");

                if (m.getReturnType() == Void.TYPE) {
                    c3.append(" w.").append(mn).append('(').append(args(m.getParameterTypes(), "$4")).append(");").append(" return null;");
                } else {
                    c3.append(" return ($w)w.").append(mn).append('(').append(args(m.getParameterTypes(), "$4")).append(");");
                }

                c3.append(" }");

                mns.add(mn);
                if (m.getDeclaringClass() == c) {
                    dmns.add(mn);
                }
                ms.put(ReflectUtils.getDesc(m), m);
            }
            c3.append(" } catch(Throwable e) { ");
            c3.append("     throw new java.lang.reflect.InvocationTargetException(e); ");
            c3.append(" }");
        }

        c3.append(" throw new " + NoSuchMethodException.class.getName() + "(\"Not found method \\\"\"+$2+\"\\\" in class " + c.getName() + ".\"); }");

        // deal with get/set method.
        Matcher matcher;
        for (Map.Entry<String, Method> entry : ms.entrySet()) {
            String md = entry.getKey();
            Method method = entry.getValue();
            if ((matcher = ReflectUtils.GETTER_METHOD_DESC_PATTERN.matcher(md)).matches()) {
                String pn = propertyName(matcher.group(1));
                c2.append(" if( $2.equals(\"").append(pn).append("\") ){ return ($w)w.").append(method.getName()).append("(); }");
                pts.put(pn, method.getReturnType());
            } else if ((matcher = ReflectUtils.IS_HAS_CAN_METHOD_DESC_PATTERN.matcher(md)).matches()) {
                String pn = propertyName(matcher.group(1));
                c2.append(" if( $2.equals(\"").append(pn).append("\") ){ return ($w)w.").append(method.getName()).append("(); }");
                pts.put(pn, method.getReturnType());
            } else if ((matcher = ReflectUtils.SETTER_METHOD_DESC_PATTERN.matcher(md)).matches()) {
                Class<?> pt = method.getParameterTypes()[0];
                String pn = propertyName(matcher.group(1));
                c1.append(" if( $2.equals(\"").append(pn).append("\") ){ w.").append(method.getName()).append("(").append(arg(pt, "$3")).append("); return; }");
                pts.put(pn, pt);
            }
        }
        c1.append(" throw new " + NoSuchPropertyException.class.getName() + "(\"Not found property \\\"\"+$2+\"\\\" field or setter method in class " + c.getName() + ".\"); }");
        c2.append(" throw new " + NoSuchPropertyException.class.getName() + "(\"Not found property \\\"\"+$2+\"\\\" field or setter method in class " + c.getName() + ".\"); }");

        // make class
        long id = WRAPPER_CLASS_COUNTER.getAndIncrement();
        ClassGenerator cc = ClassGenerator.newInstance(cl);
        cc.setClassName((Modifier.isPublic(c.getModifiers()) ? Wrapper.class.getName() : c.getName() + "$sw") + id);
        cc.setSuperClass(Wrapper.class);

        cc.addDefaultConstructor();
        cc.addField("public static String[] pns;"); // property name array.
        cc.addField("public static " + Map.class.getName() + " pts;"); // property type map.
        cc.addField("public static String[] mns;"); // all method name array.
        cc.addField("public static String[] dmns;"); // declared method name array.
        for (int i = 0, len = ms.size(); i < len; i++) {
            cc.addField("public static Class[] mts" + i + ";");
        }

        cc.addMethod("public String[] getPropertyNames(){ return pns; }");
        cc.addMethod("public boolean hasProperty(String n){ return pts.containsKey($1); }");
        cc.addMethod("public Class getPropertyType(String n){ return (Class)pts.get($1); }");
        cc.addMethod("public String[] getMethodNames(){ return mns; }");
        cc.addMethod("public String[] getDeclaredMethodNames(){ return dmns; }");
        cc.addMethod(c1.toString());
        cc.addMethod(c2.toString());
        cc.addMethod(c3.toString());

        try {
            Class<?> wc = cc.toClass();
            // setup static field.
            wc.getField("pts").set(null, pts);
            wc.getField("pns").set(null, pts.keySet().toArray(new String[0]));
            wc.getField("mns").set(null, mns.toArray(new String[0]));
            wc.getField("dmns").set(null, dmns.toArray(new String[0]));
            int ix = 0;
            for (Method m : ms.values()) {
                wc.getField("mts" + ix++).set(null, m.getParameterTypes());
            }
            return (Wrapper) wc.newInstance();
        } catch (RuntimeException e) {
            throw e;
        } catch (Throwable e) {
            throw new RuntimeException(e.getMessage(), e);
        } finally {
            cc.release();
            ms.clear();
            mns.clear();
            dmns.clear();
        }
    }

Wrapper1

• Wrapper1是通过javassist新生成的包装类对象。
• Wrapper1的invokeMethod()方法内部调用服务DemoServiceImpl的发布的方法。

package org.apache.dubbo.common.bytecode;

import java.lang.reflect.InvocationTargetException;
import java.util.Map;
import org.apache.dubbo.common.bytecode.ClassGenerator;
import org.apache.dubbo.common.bytecode.NoSuchMethodException;
import org.apache.dubbo.common.bytecode.NoSuchPropertyException;
import org.apache.dubbo.common.bytecode.Wrapper;
import org.apache.dubbo.demo.provider.DemoServiceImpl;

public class Wrapper1 extends Wrapper implements ClassGenerator.DC {
    public static String[] pns;
    public static Map pts;
    public static String[] mns;
    public static String[] dmns;
    public static Class[] mts0;

    public String[] getMethodNames() {
        return mns;
    }

    public Class getPropertyType(String string) {
        return (Class)pts.get(string);
    }

    public String[] getDeclaredMethodNames() {
        return dmns;
    }

    public String[] getPropertyNames() {
        return pns;
    }

    public boolean hasProperty(String string) {
        return pts.containsKey(string);
    }

    public Object getPropertyValue(Object object, String string) {
        try {
            DemoServiceImpl demoServiceImpl = (DemoServiceImpl)object;
        }
        catch (Throwable throwable) {
            throw new IllegalArgumentException(throwable);
        }
        throw new NoSuchPropertyException(new StringBuffer().append("Not found property \"").append(string).append("\" field or setter method in class org.apache.dubbo.demo.provider.DemoServiceImpl.").toString());
    }

    public void setPropertyValue(Object object, String string, Object object2) {
        try {
            DemoServiceImpl demoServiceImpl = (DemoServiceImpl)object;
        }
        catch (Throwable throwable) {
            throw new IllegalArgumentException(throwable);
        }
        throw new NoSuchPropertyException(new StringBuffer().append("Not found property \"").append(string).append("\" field or setter method in class org.apache.dubbo.demo.provider.DemoServiceImpl.").toString());
    }

    public Object invokeMethod(Object object, String string, Class[] arrclass, Object[] arrobject) throws InvocationTargetException {
        DemoServiceImpl demoServiceImpl;
        try {
            demoServiceImpl = (DemoServiceImpl)object;
        }
        catch (Throwable throwable) {
            throw new IllegalArgumentException(throwable);
        }
        try {
            if ("sayHello".equals(string) && arrclass.length == 1) {
                return demoServiceImpl.sayHello((String)arrobject[0]);
            }
        }
        catch (Throwable throwable) {
            throw new InvocationTargetException(throwable);
        }
        throw new NoSuchMethodException(new StringBuffer().append("Not found method \"").append(string).append("\" in class org.apache.dubbo.demo.provider.DemoServiceImpl.").toString());
    }
}

整体流程概括

• 1、ProxyFactory获取适配器对象ProxyFactory$Adaptive。
• 2、ProxyFactory$Adaptive对象内部获取javassist对应的JavassistProxyFactory对象。
• 3、JavassistProxyFactory通过getInvoker()方法获取包装类对象Wrapper1，包装类Wrapper1内部通过invokeMethod()方法执行真正发布服务的方法。

Arthas代码反编译

• 1、首先启动Provider服务提供者程序，将断点放置到ret = makerWrapper(c)这里，确定这里的c是DemoServiceImpl，然后运行程序至下一步，观察ret的名字。如下图，可以发现生成的Wrapper类是叫Wrapper1，然后放开断点，让程序走完，服务提供者处于运行状态。

• 2、通过Arthas查看生成的Wrapper1到底是什么? 首先下载它的jar包，下载地址。然后打开cmd，执行以下命令。注意2是对应Provider程序的序号，需要和你自己程序对应。输入2后可以发现连上了Arthas。然后使用sc命令查找Wrapper1具体对应的是哪个class文件，最后使用jad命令反编译，查看Wrapper1类对应的Java文件具体内容。

最后，我们可以得到Wrapper1的Java文件

参考文章

Dubbo中JavaAssist的Wrapper.getWrapper生成代理分析