Hessian解析及应用（整合Spring）

2022-02-26 15:59:05

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。

  1 public class HessianClientInterceptor extends UrlBasedRemoteAccessor implements MethodInterceptor {  
  2     //创建Hessiann代理工厂  
  3     private HessianProxyFactory proxyFactory = new HessianProxyFactory();  
  4     //Hessian代理  
  5     private Object hessianProxy;  
  6     //设置Hessian代理工厂  
  7     public void setProxyFactory(HessianProxyFactory proxyFactory) {  
  8         this.proxyFactory = (proxyFactory != null ? proxyFactory : new HessianProxyFactory());  
  9     }  
 10     //设置Hessian序列化工厂  
 11     public void setSerializerFactory(SerializerFactory serializerFactory) {  
 12         this.proxyFactory.setSerializerFactory(serializerFactory);  
 13     }  
 14     //设置Hessian是否发送java集合类型对象  
 15     public void setSendCollectionType(boolean sendCollectionType) {  
 16     this.proxyFactory.getSerializerFactory().setSendCollectionType(sendCollectionType);  
 17     }  
 18     //设置远程调用时是否重载方法  
 19     public void setOverloadEnabled(boolean overloadEnabled) {  
 20         this.proxyFactory.setOverloadEnabled(overloadEnabled);  
 21     }  
 22     //设置远程调用用户名  
 23     public void setUsername(String username) {  
 24         this.proxyFactory.setUser(username);  
 25     }  
 26     //设置远程调用密码  
 27     public void setPassword(String password) {  
 28         this.proxyFactory.setPassword(password);  
 29     }  
 30     //设置是否使用Hessian的Debug调试模式  
 31     public void setDebug(boolean debug) {  
 32         this.proxyFactory.setDebug(debug);  
 33     }  
 34     //设置是否使用chunked端口发送Hessian请求  
 35     public void setChunkedPost(boolean chunkedPost) {  
 36         this.proxyFactory.setChunkedPost(chunkedPost);  
 37     }  
 38     //设置Hessian等待响应的超时时长  
 39     public void setReadTimeout(long timeout) {  
 40         this.proxyFactory.setReadTimeout(timeout);  
 41     }  
 42     //设置是否使用Hessain版本2协议解析请求和响应  
 43     public void setHessian2(boolean hessian2) {  
 44         this.proxyFactory.setHessian2Request(hessian2);  
 45         this.proxyFactory.setHessian2Reply(hessian2);  
 46     }  
 47     //设置是否使用Hessian版本2协议解析请求  
 48     public void setHessian2Request(boolean hessian2) {  
 49         this.proxyFactory.setHessian2Request(hessian2);  
 50     }  
 51     //设置是否使用Hessian版本2协议解析响应  
 52     public void setHessian2Reply(boolean hessian2) {  
 53         this.proxyFactory.setHessian2Reply(hessian2);  
 54     }  
 55 //子类HessianProxyFactoryBean的回调方法调用此回调方法  
 56     public void afterPropertiesSet() {  
 57         //调用其父类UrlBasedRemoteAccessor的回调方法获取客户端配置的请求url  
 58         super.afterPropertiesSet();  
 59         //初始化Hessian代理  
 60         prepare();  
 61     }  
 62     //初始化Hessian代理  
 63     public void prepare() throws RemoteLookupFailureException {  
 64         try {  
 65             //创建Hessian代理  
 66             this.hessianProxy = createHessianProxy(this.proxyFactory);  
 67         }  
 68         catch (MalformedURLException ex) {  
 69             throw new RemoteLookupFailureException("Service URL [" + getServiceUrl() + "] is invalid", ex);  
 70         }  
 71     }  
 72     //创建Hessian代理  
 73     protected Object createHessianProxy(HessianProxyFactory proxyFactory) throws MalformedURLException {  
 74         Assert.notNull(getServiceInterface(), "'serviceInterface' is required");  
 75         //使用Hessian代理工厂创建Hessian代理  
 76         return proxyFactory.create(getServiceInterface(), getServiceUrl());  
 77     }  
 78     //拦截器客户端请求的方法  
 79     public Object invoke(MethodInvocation invocation) throws Throwable {  
 80         if (this.hessianProxy == null) {  
 81             throw new IllegalStateException("HessianClientInterceptor is not properly initialized - " +  
 82                     "invoke 'prepare' before attempting any operations");  
 83         }  
 84         //获取当前环境中线程类加载器  
 85         ClassLoader originalClassLoader = overrideThreadContextClassLoader();  
 86         try {  
 87         //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  
 88             return invocation.getMethod().invoke(this.hessianProxy, invocation.getArguments());  
 89         }  
 90         //处理Hessian远程调用中的异常  
 91         catch (InvocationTargetException ex) {  
 92             Throwable targetEx = ex.getTargetException();  
 93             if (targetEx instanceof InvocationTargetException) {  
 94                 targetEx = ((InvocationTargetException) targetEx).getTargetException();  
 95             }  
 96             if (targetEx instanceof HessianConnectionException) {  
 97                 throw convertHessianAccessException(targetEx);  
 98             }  
 99             else if (targetEx instanceof HessianException || targetEx instanceof HessianRuntimeException) {  
100                 Throwable cause = targetEx.getCause();  
101                 throw convertHessianAccessException(cause != null ? cause : targetEx);  
102             }  
103             else if (targetEx instanceof UndeclaredThrowableException) {  
104                 UndeclaredThrowableException utex = (UndeclaredThrowableException) targetEx;  
105                 throw convertHessianAccessException(utex.getUndeclaredThrowable());  
106             }  
107             else {  
108                 throw targetEx;  
109             }  
110         }  
111         catch (Throwable ex) {  
112             throw new RemoteProxyFailureException(  
113                     "Failed to invoke Hessian proxy for remote service [" + getServiceUrl() + "]", ex);  
114         }  
115         //重置类加载器  
116         finally {  
117             resetThreadContextClassLoader(originalClassLoader);  
118         }  
119     }  
120     //将Hessian异常转换为Spring远程调用异常  
121     protected RemoteAccessException convertHessianAccessException(Throwable ex) {  
122         if (ex instanceof HessianConnectionException || ex instanceof ConnectException) {  
123             return new RemoteConnectFailureException(  
124                     "Cannot connect to Hessian remote service at [" + getServiceUrl() + "]", ex);  
125         }  
126         else {  
127             return new RemoteAccessException(  
128                 "Cannot access Hessian remote service at [" + getServiceUrl() + "]", ex);  
129         }  
130     }  
131 }

    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

  1 public Object invoke(Object proxy, Method method, Object []args)
  2     throws Throwable
  3   {
  4     String mangleName;
  5 
  6     synchronized (_mangleMap) {
  7       mangleName = _mangleMap.get(method);
  8     }
  9 
 10     if (mangleName == null) {
 11       String methodName = method.getName();
 12       Class<?> []params = method.getParameterTypes();
 13 
 14       // equals and hashCode are special cased
 15       if (methodName.equals("equals")
 16       && params.length == 1 && params[0].equals(Object.class)) {
 17     Object value = args[0];
 18     if (value == null || ! Proxy.isProxyClass(value.getClass()))
 19       return Boolean.FALSE;
 20 
 21     Object proxyHandler = Proxy.getInvocationHandler(value);
 22 
 23     if (! (proxyHandler instanceof HessianProxy))
 24       return Boolean.FALSE;
 25     
 26     HessianProxy handler = (HessianProxy) proxyHandler;
 27 
 28     return new Boolean(_url.equals(handler.getURL()));
 29       }
 30       else if (methodName.equals("hashCode") && params.length == 0)
 31     return new Integer(_url.hashCode());
 32       else if (methodName.equals("getHessianType"))
 33     return proxy.getClass().getInterfaces()[0].getName();
 34       else if (methodName.equals("getHessianURL"))
 35     return _url.toString();
 36       else if (methodName.equals("toString") && params.length == 0)
 37     return "HessianProxy[" + _url + "]";
 38       
 39       if (! _factory.isOverloadEnabled())
 40     mangleName = method.getName();
 41       else
 42         mangleName = mangleName(method);
 43 
 44       synchronized (_mangleMap) {
 45     _mangleMap.put(method, mangleName);
 46       }
 47     }
 48 
 49     InputStream is = null;
 50     HessianConnection conn = null;
 51     
 52     try {
 53       if (log.isLoggable(Level.FINER))
 54     log.finer("Hessian[" + _url + "] calling " + mangleName);
 55       
 56       conn = sendRequest(mangleName, args);
 57 
 58       is = conn.getInputStream();
 59 
 60       if (log.isLoggable(Level.FINEST)) {
 61     PrintWriter dbg = new PrintWriter(new LogWriter(log));
 62     HessianDebugInputStream dIs
 63       = new HessianDebugInputStream(is, dbg);
 64 
 65     dIs.startTop2();
 66     
 67     is = dIs;
 68       }
 69 
 70       AbstractHessianInput in;
 71 
 72       int code = is.read();
 73 
 74       if (code == 'H') {
 75     int major = is.read();
 76     int minor = is.read();
 77 
 78     in = _factory.getHessian2Input(is);
 79 
 80     Object value = in.readReply(method.getReturnType());
 81 
 82     return value;
 83       }
 84       else if (code == 'r') {
 85     int major = is.read();
 86     int minor = is.read();
 87     
 88     in = _factory.getHessianInput(is);
 89 
 90     in.startReplyBody();
 91 
 92     Object value = in.readObject(method.getReturnType());
 93 
 94     if (value instanceof InputStream) {
 95       value = new ResultInputStream(conn, is, in, (InputStream) value);
 96       is = null;
 97       conn = null;
 98     }
 99     else
100       in.completeReply();
101 
102     return value;
103       }
104       else
105     throw new HessianProtocolException("'" + (char) code + "' is an unknown code");
106     } catch (HessianProtocolException e) {
107       throw new HessianRuntimeException(e);
108     } finally {
109       try {
110     if (is != null)
111       is.close();
112       } catch (Exception e) {
113     log.log(Level.FINE, e.toString(), e);
114       }
115       
116       try {
117     if (conn != null)
118       conn.destroy();
119       } catch (Exception e) {
120     log.log(Level.FINE, e.toString(), e);
121       }
122     }
123   }

    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。

 1 public class HessianServiceExporter extends HessianExporter implements HttpRequestHandler {
 2 
 3     /**
 4      * Processes the incoming Hessian request and creates a Hessian response.
 5      */
 6     public void handleRequest(HttpServletRequest request, HttpServletResponse response)
 7             throws ServletException, IOException {
 8 
 9         if (!"POST".equals(request.getMethod())) {
10             throw new HttpRequestMethodNotSupportedException(request.getMethod(),
11                     new String[] {"POST"}, "HessianServiceExporter only supports POST requests");
12         }
13 
14         response.setContentType(CONTENT_TYPE_HESSIAN);
15         try {
16           invoke(request.getInputStream(), response.getOutputStream());
17         }
18         catch (Throwable ex) {
19           throw new NestedServletException("Hessian skeleton invocation failed", ex);
20         }
21     }
22 
23 }

    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

 1 public void invoke(Object service,
 2                      AbstractHessianInput in,
 3                      AbstractHessianOutput out)
 4     throws Exception
 5   {
 6     ServiceContext context = ServiceContext.getContext();
 7 
 8     // backward compatibility for some frameworks that don't read
 9     // the call type first
10     in.skipOptionalCall();
11 
12     // Hessian 1.0 backward compatibility
13     String header;
14     while ((header = in.readHeader()) != null) {
15       Object value = in.readObject();
16 
17       context.addHeader(header, value);
18     }
19 
20     String methodName = in.readMethod();
21     int argLength = in.readMethodArgLength();
22 
23     Method method;
24 
25     method = getMethod(methodName + "__" + argLength);
26 
27     if (method == null)
28       method = getMethod(methodName);
29 
30     if (method != null) {
31     }
32     else if ("_hessian_getAttribute".equals(methodName)) {
33       String attrName = in.readString();
34       in.completeCall();
35 
36       String value = null;
37 
38       if ("java.api.class".equals(attrName))
39         value = getAPIClassName();
40       else if ("java.home.class".equals(attrName))
41         value = getHomeClassName();
42       else if ("java.object.class".equals(attrName))
43         value = getObjectClassName();
44 
45       out.writeReply(value);
46       out.close();
47       return;
48     }
49     else if (method == null) {
50       out.writeFault("NoSuchMethodException",
51                      "The service has no method named: " + in.getMethod(),
52                      null);
53       out.close();
54       return;
55     }
56 
57     Class<?> []args = method.getParameterTypes();
58 
59     if (argLength != args.length && argLength >= 0) {
60       out.writeFault("NoSuchMethod",
61                      "method " + method + " argument length mismatch, received length=" + argLength,
62                      null);
63       out.close();
64       return;
65     }
66 
67     Object []values = new Object[args.length];
68 
69     for (int i = 0; i < args.length; i++) {
70       // XXX: needs Marshal object
71       values[i] = in.readObject(args[i]);
72     }
73 
74     Object result = null;
75 
76     try {
77       result = method.invoke(service, values);
78     } catch (Exception e) {
79       Throwable e1 = e;
80       if (e1 instanceof InvocationTargetException)
81         e1 = ((InvocationTargetException) e).getTargetException();
82 
83       log.log(Level.FINE, this + " " + e1.toString(), e1);
84 
85       out.writeFault("ServiceException", e1.getMessage(), e1);
86       out.close();
87       return;
88     }
89 
90     // The complete call needs to be after the invoke to handle a
91     // trailing InputStream
92     in.completeCall();
93 
94     out.writeReply(result);
95 
96     out.close();
97   }

    关键在于输入输出流的序列化，这部分内容暂未了解......

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