Hessian解析及应用（整合Spring）

        Hessian是一个轻量级的remoting onhttp工具，使用简单的方法提供了RMI的功能。 相比WebService，Hessian更简单、快捷。------来自百度百科。

        看官网简介吧：http://hessian.caucho.com/index.xtp

        The Hessian binary web service protocol makes web services usable without requiring a large framework, and without learning yet another alphabet soup of protocols. Because it is a binary protocol, it is well-suited to sending binary data without any need to extend the protocol with attachments.

        此文使用hessian为hessian-4.0.7，源码及jar包请自行下载。------当然是java版了，咱也不会别的。

        开搞吧！

        除了提供下载，Hessian官网上貌似就下面几句话有用了（可能是Hessian使用起来很简单的原因吧）。

        开搞吧，两个应用，Client（hessianclient）调用Server（hessianserver）提供的服务并展示返回内容。

        创建公共接口（单独打包成Jar，方便多个项目使用）。

package com.skyjoo.hessiancommon.interfaces;

public interface HessianExampleInterface {
    public String hello(String name);
}

        就一个hello方法，返回String......

        在Server中提供该接口的实现。

package com.skyjoo.hessianserver.interfacesImpl;

import com.skyjoo.hessiancommon.interfaces.HessianExampleInterface;


public class HessianExampleInterfaceImpl implements HessianExampleInterface {

    @Override
    public String hello(String name) {
        return "Hello " + name + ",Welcome to Hessian World!!!";
    }

}

        像上面这样肯定是没法工作的，只要有WebService经验或了解过Axis的类似开源框架的童鞋肯定都知道关键的是发布服务......

        介绍中的"轻量级"说明发布服务应该是很简单的......

        本文结合Spring，看一下配置吧。

<bean class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
        <property name="order" value="100" />
        <property name="urlMap">
            <map>
                <entry key="/remote/hessianService.htm" value-ref="exampleService" />
            </map>
        </property>
</bean>
<bean id="exampleService"
        class="org.springframework.remoting.caucho.HessianServiceExporter">
        <property name="service" ref="hessianExampleService" />
        <property name="serviceInterface"
            value="com.skyjoo.hessiancommon.interfaces.HessianExampleInterface" />
</bean>
<bean id="hessianExampleService"
        class="com.skyjoo.hessianserver.interfacesImpl.HessianExampleInterfaceImpl" />

    

    <entry key="/remote/hessianService.htm" value-ref="exampleService" />

    将某个地址对应到Bean上，这里的Bean为org.springframework.remoting.caucho.HessianServiceExporter。该Bean的service属性即服务端对公共接口的实现，serviceInterface即公共接口。还是很容易就能理解的。
    接着就是Client的内容。

    <bean id="hessianService"
        class="org.springframework.remoting.caucho.HessianProxyFactoryBean">
        <property name="serviceUrl" value="http://localhost:8090/hessianserver/remote/hessianService.htm" />
        <property name="serviceInterface"
            value="com.skyjoo.hessiancommon.interfaces.HessianExampleInterface" />
    </bean>

        使用org.springframework.remoting.caucho.HessianProxyFactoryBean，serviceUrl为服务地址，serviceInterface为公共接口。看serviceUrl的内容

    http://localhost:8090/hessianserver/remote/hessianService.htm

    前半部分是服务部署地址，后半部分为<entry key="/remote/hessianService.htm" value-ref="exampleService"/>配置中指定的key。

    然后......然后就没有了，Spring怎么装配Bean的，平时怎么使用Bean的，就怎么玩吧。
    测试内容

@Controller
public class Test {
    @Autowired
    private HessianExampleInterface hessianService;

    @RequestMapping("/hello")
    public void hello(@RequestParam("username") String username, ModelMap model) {
        model.put("helloUser", hessianService.hello(username));
    }
}

        和使用普通的Bean一模一样。

（这图上的好无聊~~~~~~~~~~~）

    只是简单的实现了一个例子，还没能深入的学习、理解hessian的内容。
--------------------------------------------------------------------华丽丽的分割线---------------------------------------------------------------

    未完待续......
    
    昨天只是简单的例子，现在续上......
    Hessian在Spring中的工作流程如下：
    （1）客户端：
    a.发送远程请求：
        客户端程序-->调用公共接口的方法-->Hessian拦截器拦截请求-->封装远程调用请求-->Hessian代理-->通过HTTP协议发送远程请求代理到服务端
    b.接收远程调用响应：
        远程调用结果-->HTTP响应-->客户端
    （2）服务端：
    a.接收远程调用请求：
        HessianServiceExporter接收请求-->将远程调用对象封装为HessianSkeleton框架-->HessianSkeleton处理远程调用请求
    b.返回远程调用响应：
        HessianSkeleton封装远程调用处理结果-->HTTP响应-->客户端
    下图是通过hessian一次完成调用的示意图

    在上面的例子中，Spring通过HessianProxyFactoryBean管理Hessian客户端。
    HessianProxyFactoryBean.java

public class HessianProxyFactoryBean extends HessianClientInterceptor implements FactoryBean<Object> {
    //远程调用代理对象
    private Object serviceProxy;
    //Spring IoC依赖注入完成后的回调方法
    @Override
    public void afterPropertiesSet() {
        super.afterPropertiesSet();
        //设置远程代理对象，getServiceInterface()即获取配置中的serviceInterface（公共接口）
        //HessianProxyFactoryBean 继HessianClientInterceptor ，本身就是一个拦截器，所以传入拦截器为this
        this.serviceProxy = new ProxyFactory(getServiceInterface(), this).getProxy(getBeanClassLoader());
    }

    //返回远程调用代理对象
    public Object getObject() {
        return this.serviceProxy;
    }
    //获取对象类型（即公共接口）
    public Class<?> getObjectType() {
        return getServiceInterface();
    }
    //判断是否是单例,Spring默认管理对象都是单例的
    public boolean isSingleton() {
        return true;
    }

}

    HessianProxyFactoryBean最核心的功能是在IoC容器回调方法中产生远程调用代理对象，将代理对象的拦截器设置为HessianClientInterceptor。

public class HessianClientInterceptor extends UrlBasedRemoteAccessor implements MethodInterceptor {  
    //创建Hessiann代理工厂  
    private HessianProxyFactory proxyFactory = new HessianProxyFactory();  
    //Hessian代理  
    private Object hessianProxy;  
    //设置Hessian代理工厂  
    public void setProxyFactory(HessianProxyFactory proxyFactory) {  
        this.proxyFactory = (proxyFactory != null ? proxyFactory : new HessianProxyFactory());  
    }  
    //设置Hessian序列化工厂  
    public void setSerializerFactory(SerializerFactory serializerFactory) {  
        this.proxyFactory.setSerializerFactory(serializerFactory);  
    }  
    //设置Hessian是否发送java集合类型对象  
    public void setSendCollectionType(boolean sendCollectionType) {  
    this.proxyFactory.getSerializerFactory().setSendCollectionType(sendCollectionType);  
    }  
    //设置远程调用时是否重载方法  
    public void setOverloadEnabled(boolean overloadEnabled) {  
        this.proxyFactory.setOverloadEnabled(overloadEnabled);  
    }  
    //设置远程调用用户名  
    public void setUsername(String username) {  
        this.proxyFactory.setUser(username);  
    }  
    //设置远程调用密码  
    public void setPassword(String password) {  
        this.proxyFactory.setPassword(password);  
    }  
    //设置是否使用Hessian的Debug调试模式  
    public void setDebug(boolean debug) {  
        this.proxyFactory.setDebug(debug);  
    }  
    //设置是否使用chunked端口发送Hessian请求  
    public void setChunkedPost(boolean chunkedPost) {  
        this.proxyFactory.setChunkedPost(chunkedPost);  
    }  
    //设置Hessian等待响应的超时时长  
    public void setReadTimeout(long timeout) {  
        this.proxyFactory.setReadTimeout(timeout);  
    }  
    //设置是否使用Hessain版本2协议解析请求和响应  
    public void setHessian2(boolean hessian2) {  
        this.proxyFactory.setHessian2Request(hessian2);  
        this.proxyFactory.setHessian2Reply(hessian2);  
    }  
    //设置是否使用Hessian版本2协议解析请求  
    public void setHessian2Request(boolean hessian2) {  
        this.proxyFactory.setHessian2Request(hessian2);  
    }  
    //设置是否使用Hessian版本2协议解析响应  
    public void setHessian2Reply(boolean hessian2) {  
        this.proxyFactory.setHessian2Reply(hessian2);  
    }  
//子类HessianProxyFactoryBean的回调方法调用此回调方法  
    public void afterPropertiesSet() {  
        //调用其父类UrlBasedRemoteAccessor的回调方法获取客户端配置的请求url  
        super.afterPropertiesSet();  
        //初始化Hessian代理  
        prepare();  
    }  
    //初始化Hessian代理  
    public void prepare() throws RemoteLookupFailureException {  
        try {  
            //创建Hessian代理  
            this.hessianProxy = createHessianProxy(this.proxyFactory);  
        }  
        catch (MalformedURLException ex) {  
            throw new RemoteLookupFailureException("Service URL [" + getServiceUrl() + "] is invalid", ex);  
        }  
    }  
    //创建Hessian代理  
    protected Object createHessianProxy(HessianProxyFactory proxyFactory) throws MalformedURLException {  
        Assert.notNull(getServiceInterface(), "'serviceInterface' is required");  
        //使用Hessian代理工厂创建Hessian代理  
        return proxyFactory.create(getServiceInterface(), getServiceUrl());  
    }  
    //拦截器客户端请求的方法  
    public Object invoke(MethodInvocation invocation) throws Throwable {  
        if (this.hessianProxy == null) {  
            throw new IllegalStateException("HessianClientInterceptor is not properly initialized - " +  
                    "invoke 'prepare' before attempting any operations");  
        }  
        //获取当前环境中线程类加载器  
        ClassLoader originalClassLoader = overrideThreadContextClassLoader();  
        try {  
        //调用Hessian代理的方法，是Hessian远程调用的入口方法，使用JDK反射机制  
            return invocation.getMethod().invoke(this.hessianProxy, invocation.getArguments());  
        }  
        //处理Hessian远程调用中的异常  
        catch (InvocationTargetException ex) {  
            Throwable targetEx = ex.getTargetException();  
            if (targetEx instanceof InvocationTargetException) {  
                targetEx = ((InvocationTargetException) targetEx).getTargetException();  
            }  
            if (targetEx instanceof HessianConnectionException) {  
                throw convertHessianAccessException(targetEx);  
            }  
            else if (targetEx instanceof HessianException || targetEx instanceof HessianRuntimeException) {  
                Throwable cause = targetEx.getCause();  
                throw convertHessianAccessException(cause != null ? cause : targetEx);  
            }  
            else if (targetEx instanceof UndeclaredThrowableException) {  
                UndeclaredThrowableException utex = (UndeclaredThrowableException) targetEx;  
                throw convertHessianAccessException(utex.getUndeclaredThrowable());  
            }  
            else {  
                throw targetEx;  
            }  
        }  
        catch (Throwable ex) {  
            throw new RemoteProxyFailureException(  
                    "Failed to invoke Hessian proxy for remote service [" + getServiceUrl() + "]", ex);  
        }  
        //重置类加载器  
        finally {  
            resetThreadContextClassLoader(originalClassLoader);  
        }  
    }  
    //将Hessian异常转换为Spring远程调用异常  
    protected RemoteAccessException convertHessianAccessException(Throwable ex) {  
        if (ex instanceof HessianConnectionException || ex instanceof ConnectException) {  
            return new RemoteConnectFailureException(  
                    "Cannot connect to Hessian remote service at [" + getServiceUrl() + "]", ex);  
        }  
        else {  
            return new RemoteAccessException(  
                "Cannot access Hessian remote service at [" + getServiceUrl() + "]", ex);  
        }  
    }  
}  

    上面源码中最重要的方法是对远程调用拦截的方法invoke，在该方法中使用JDK的反射机制调用Hessian代理对象的指定方法。而Hessian代理是由Hessain代理器工厂HessianProxyFactory产生的，这个Hessian代理器工厂是有Hessian提供的。
    接着看Hessian的具体实现，这块已经和Spring没有关系了。
    HessianProxy是hessian client处理客户端请求的核心类，采用proxy模式，代理客户端对远程接口的调用，hessian client的主程序的时序图如下：

    HessianProxy在invoke方法中实现对调用方法数参数的序列化为预定格式的输出流，调用sendRequest发送请求，获取返回输入流。
    HessianProxy.java

public Object invoke(Object proxy, Method method, Object []args)
    throws Throwable
  {
    String mangleName;

    synchronized (_mangleMap) {
      mangleName = _mangleMap.get(method);
    }

    if (mangleName == null) {
      String methodName = method.getName();
      Class<?> []params = method.getParameterTypes();

      // equals and hashCode are special cased
      if (methodName.equals("equals")
      && params.length == 1 && params[0].equals(Object.class)) {
    Object value = args[0];
    if (value == null || ! Proxy.isProxyClass(value.getClass()))
      return Boolean.FALSE;

    Object proxyHandler = Proxy.getInvocationHandler(value);

    if (! (proxyHandler instanceof HessianProxy))
      return Boolean.FALSE;
    
    HessianProxy handler = (HessianProxy) proxyHandler;

    return new Boolean(_url.equals(handler.getURL()));
      }
      else if (methodName.equals("hashCode") && params.length == 0)
    return new Integer(_url.hashCode());
      else if (methodName.equals("getHessianType"))
    return proxy.getClass().getInterfaces()[0].getName();
      else if (methodName.equals("getHessianURL"))
    return _url.toString();
      else if (methodName.equals("toString") && params.length == 0)
    return "HessianProxy[" + _url + "]";
      
      if (! _factory.isOverloadEnabled())
    mangleName = method.getName();
      else
        mangleName = mangleName(method);

      synchronized (_mangleMap) {
    _mangleMap.put(method, mangleName);
      }
    }

    InputStream is = null;
    HessianConnection conn = null;
    
    try {
      if (log.isLoggable(Level.FINER))
    log.finer("Hessian[" + _url + "] calling " + mangleName);
      
      conn = sendRequest(mangleName, args);

      is = conn.getInputStream();

      if (log.isLoggable(Level.FINEST)) {
    PrintWriter dbg = new PrintWriter(new LogWriter(log));
    HessianDebugInputStream dIs
      = new HessianDebugInputStream(is, dbg);

    dIs.startTop2();
    
    is = dIs;
      }

      AbstractHessianInput in;

      int code = is.read();

      if (code == 'H') {
    int major = is.read();
    int minor = is.read();

    in = _factory.getHessian2Input(is);

    Object value = in.readReply(method.getReturnType());

    return value;
      }
      else if (code == 'r') {
    int major = is.read();
    int minor = is.read();
    
    in = _factory.getHessianInput(is);

    in.startReplyBody();

    Object value = in.readObject(method.getReturnType());

    if (value instanceof InputStream) {
      value = new ResultInputStream(conn, is, in, (InputStream) value);
      is = null;
      conn = null;
    }
    else
      in.completeReply();

    return value;
      }
      else
    throw new HessianProtocolException("'" + (char) code + "' is an unknown code");
    } catch (HessianProtocolException e) {
      throw new HessianRuntimeException(e);
    } finally {
      try {
    if (is != null)
      is.close();
      } catch (Exception e) {
    log.log(Level.FINE, e.toString(), e);
      }
      
      try {
    if (conn != null)
      conn.destroy();
      } catch (Exception e) {
    log.log(Level.FINE, e.toString(), e);
      }
    }
  }

    1~47行主要是把methodName缓存起来和过滤一些特殊调用，java反射是个比较耗性能的操作，把methodName缓存起来可以避免每次调用都要从method里得到methodName。另外，对equals、hashCode、getHessianType、getHessianURL等特殊方法的远程调用，直接在本地处理。56行调用了sendRequest方法，在sendRequest方法中初始化连接，调用AbstractHessianOutput包装网络输出流，通过AbstractHessianOutput.call(methodName, args)完成网络输出。
    到这里client先告一段落吧，网络怎么输出的等等没去看......


    Server端通过HessianServiceExporter处理远程调用请求。HessianServiceExporter实现了HttpRequestHandler接口，通过handleRequest方法处理请求。

public class HessianServiceExporter extends HessianExporter implements HttpRequestHandler {

    /**
     * Processes the incoming Hessian request and creates a Hessian response.
     */
    public void handleRequest(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        if (!"POST".equals(request.getMethod())) {
            throw new HttpRequestMethodNotSupportedException(request.getMethod(),
                    new String[] {"POST"}, "HessianServiceExporter only supports POST requests");
        }

        response.setContentType(CONTENT_TYPE_HESSIAN);
        try {
          invoke(request.getInputStream(), response.getOutputStream());
        }
        catch (Throwable ex) {
          throw new NestedServletException("Hessian skeleton invocation failed", ex);
        }
    }

}

    HessianServiceExporter继承了HessianExporter，调用父类的invoke处理输入流。在HessianExporter的invoke中调用了HessianSkeleton.invoke(InputStream is, OutputStream os)。
    HessianSkeleton是Hessian server端的核心类，主要功能是接收网络输入流（被包装为AbstractHessianInput），反序列化输入流得到methodName和参数，然后根据配置的service，通过反射调用实现类的方法，得到结果后序列化为输出流返回给客户端，流程如下：

    HessianSkeleton核心的反射调用非常清晰

public void invoke(Object service,
                     AbstractHessianInput in,
                     AbstractHessianOutput out)
    throws Exception
  {
    ServiceContext context = ServiceContext.getContext();

    // backward compatibility for some frameworks that don't read
    // the call type first
    in.skipOptionalCall();

    // Hessian 1.0 backward compatibility
    String header;
    while ((header = in.readHeader()) != null) {
      Object value = in.readObject();

      context.addHeader(header, value);
    }

    String methodName = in.readMethod();
    int argLength = in.readMethodArgLength();

    Method method;

    method = getMethod(methodName + "__" + argLength);

    if (method == null)
      method = getMethod(methodName);

    if (method != null) {
    }
    else if ("_hessian_getAttribute".equals(methodName)) {
      String attrName = in.readString();
      in.completeCall();

      String value = null;

      if ("java.api.class".equals(attrName))
        value = getAPIClassName();
      else if ("java.home.class".equals(attrName))
        value = getHomeClassName();
      else if ("java.object.class".equals(attrName))
        value = getObjectClassName();

      out.writeReply(value);
      out.close();
      return;
    }
    else if (method == null) {
      out.writeFault("NoSuchMethodException",
                     "The service has no method named: " + in.getMethod(),
                     null);
      out.close();
      return;
    }

    Class<?> []args = method.getParameterTypes();

    if (argLength != args.length && argLength >= 0) {
      out.writeFault("NoSuchMethod",
                     "method " + method + " argument length mismatch, received length=" + argLength,
                     null);
      out.close();
      return;
    }

    Object []values = new Object[args.length];

    for (int i = 0; i < args.length; i++) {
      // XXX: needs Marshal object
      values[i] = in.readObject(args[i]);
    }

    Object result = null;

    try {
      result = method.invoke(service, values);
    } catch (Exception e) {
      Throwable e1 = e;
      if (e1 instanceof InvocationTargetException)
        e1 = ((InvocationTargetException) e).getTargetException();

      log.log(Level.FINE, this + " " + e1.toString(), e1);

      out.writeFault("ServiceException", e1.getMessage(), e1);
      out.close();
      return;
    }

    // The complete call needs to be after the invoke to handle a
    // trailing InputStream
    in.completeCall();

    out.writeReply(result);

    out.close();
  }

    关键在于输入输出流的序列化，这部分内容暂未了解......