一、简介

Hessian基于http协议的rpc远程调用协议的实现，采用二进制格式传输的服务框架，比soap web service更轻量、更简单高效。

二、源码分析

Hession通过ThreadLocal保证服务层对象上下文信息线程安全，具体如下代码所示

1. ServiceContext.java类，将服务层对象需要用得到的属性注入到上下文中，采用了多例设计，源码如下

public class ServiceContext {@b@  private static final ThreadLocal<ServiceContext> _localContext@b@    = new ThreadLocal<ServiceContext>();@b@@b@  private ServletRequest _request;@b@  private ServletResponse _response;@b@  private String _serviceName;@b@  private String _objectId;@b@  private int _count;@b@  private HashMap _headers = new HashMap();@b@@b@  private ServiceContext(){}@b@  @b@  /**@b@   * Sets the request object prior to calling the service's method.@b@   *@b@   * @param request the calling servlet request@b@   * @param serviceId the service identifier@b@   * @param objectId the object identifier@b@   */@b@  public static void begin(ServletRequest request,@b@                           ServletResponse response,@b@                           String serviceName,@b@                           String objectId)@b@    throws ServletException@b@  {@b@    ServiceContext context = (ServiceContext) _localContext.get();@b@@b@    if (context == null) {@b@      context = new ServiceContext();@b@      _localContext.set(context);@b@    }@b@@b@    context._request = request;@b@    context._response = response;@b@    context._serviceName = serviceName;@b@    context._objectId = objectId;@b@    context._count++;@b@  }@b@@b@  public static ServiceContext getContext()@b@  {@b@    return (ServiceContext) _localContext.get();@b@  }@b@  @b@  public void addHeader(String header, Object value)@b@  {@b@    _headers.put(header, value);@b@  }@b@  @b@  public Object getHeader(String header)@b@  {@b@    return _headers.get(header);@b@  }@b@@b@...@b@@b@  /**@b@   * Cleanup at the end of a request.@b@   */@b@  public static void end()@b@  {@b@    ServiceContext context = (ServiceContext) _localContext.get();@b@@b@    if (context != null && --context._count == 0) {@b@      context._request = null;@b@      context._response = null;@b@@b@      context._headers.clear();@b@      @b@      _localContext.set(null);@b@    }@b@  }@b@@b@...@b@}

2. 在控制调用HessianServlet中，注入使用，过程如下HessianServlet.java类代码片段

    ...@b@    @b@    ServiceContext.begin(req, res, serviceId, objectId);//初始化当前调用线程上下文对象@b@@b@    try {@b@    @b@      InputStream is = request.getInputStream();@b@      OutputStream os = response.getOutputStream();@b@      response.setContentType("x-application/hessian");@b@      SerializerFactory serializerFactory = getSerializerFactory();@b@@b@      invoke(is, os, objectId, serializerFactory); //使用上下文对象信息@b@    } catch (RuntimeException e) {@b@      throw e;@b@    } catch (ServletException e) {@b@      throw e;@b@    } catch (Throwable e) {@b@      throw new ServletException(e);@b@    } finally {@b@      ServiceContext.end(); //释放线程内存@b@    }@b@    ...

3. 主服务必须继承父类HessianServlet,在web.xml配置注册servlet子服务类(搜索服务SearchService)，如下

<servlet>@b@        <servlet-name>SearchService</servlet-name>@b@        <display-name>SearchRpcService</display-name>@b@        <servlet-class>@b@            com.xwood.search.service.impl.SearchServiceImpl@b@        </servlet-class>@b@        <init-param>@b@            <param-name>home-api</param-name>@b@            <param-value>@b@                com.xwood.search.service.ISearchService@b@            </param-value>@b@        </init-param>@b@        <init-param>@b@            <param-name>home-class</param-name>@b@            <param-value>@b@                com.xwood.search.service.impl.SearchServiceImpl@b@            </param-value>@b@        </init-param>@b@    </servlet>@b@    <servlet-mapping>@b@        <servlet-name>SearchService</servlet-name>@b@        <url-pattern>/search</url-pattern>@b@    </servlet-mapping>

其中必须配置初始化home-api、home-class分别对应服务的接口、实现类（实现类必须继承com.caucho.hessian.server.HessianServlet），这两个配置分别对应HessianServlet源码的初始化方法init中进行类加载，如下所示

package com.caucho.hessian.server;@b@...@b@public class HessianServlet extends GenericServlet@b@{@b@ ...@b@ @b@  public void init(ServletConfig config)@b@    throws ServletException@b@  {@b@    super.init(config);@b@    try@b@    {@b@      String className;@b@      Class homeClass;@b@      if (this._homeImpl != null) break label125:@b@@b@      if (getInitParameter("home-class") != null) {@b@        className = getInitParameter("home-class");@b@        homeClass = loadClass(className);@b@        this._homeImpl = homeClass.newInstance();@b@        init(this._homeImpl);@b@      }else if (getInitParameter("service-class") != null) {@b@        className = getInitParameter("service-class");@b@        homeClass = loadClass(className);@b@        this._homeImpl = homeClass.newInstance();@b@        init(this._homeImpl);@b@      }else {@b@        if (getClass().equals(HessianServlet.class))@b@          throw new ServletException("server must extend HessianServlet");@b@        this._homeImpl = this;@b@      }@b@      if (this._homeAPI != null) label125: break label231:@b@      if (getInitParameter("home-api") != null) {@b@        className = getInitParameter("home-api");@b@        this._homeAPI = loadClass(className);@b@      }else if (getInitParameter("api-class") != null) {@b@        className = getInitParameter("api-class");@b@@b@        this._homeAPI = loadClass(className);@b@      }else if (this._homeImpl != null) {@b@        this._homeAPI = findRemoteAPI(this._homeImpl.getClass());@b@        if (this._homeAPI == null)@b@          this._homeAPI = this._homeImpl.getClass();@b@      }@b@      if (this._objectImpl != null) label231: break label279:@b@@b@      if (getInitParameter("object-class") != null) {@b@        className = getInitParameter("object-class");@b@        Class objectClass = loadClass(className);@b@        this._objectImpl = objectClass.newInstance();@b@        init(this._objectImpl);@b@      }@b@@b@      if (this._objectAPI != null) label279: break label335:@b@      if (getInitParameter("object-api") != null) {@b@        className = getInitParameter("object-api");@b@        this._objectAPI = loadClass(className);@b@      }else if (this._objectImpl != null) {@b@        this._objectAPI = this._objectImpl.getClass();@b@      }@b@      label335: this._homeSkeleton = new HessianSkeleton(this._homeImpl, this._homeAPI);@b@      if (this._objectAPI != null)@b@        this._homeSkeleton.setObjectClass(this._objectAPI);@b@      if (this._objectImpl != null) {@b@        this._objectSkeleton = new HessianSkeleton(this._objectImpl, this._objectAPI);@b@        this._objectSkeleton.setHomeClass(this._homeAPI);@b@      }else {@b@        this._objectSkeleton = this._homeSkeleton;@b@      }@b@      if ("true".equals(getInitParameter("debug")))@b@        this._isDebug = true;@b@@b@      if ("false".equals(getInitParameter("send-collection-type")))@b@        setSendCollectionType(false);@b@    } catch (ServletException e) {@b@      throw e;@b@    } catch (Exception e) {@b@      throw new ServletException(e);@b@    }@b@  }@b@...@b@  }@b@}

三、相关下载

hessian-4.0.7.jar，点击下载,如需要下载其他更多版本

<dependency>@b@  <groupId>hessian</groupId>@b@  <artifactId>hessian</artifactId>@b@  <version>3.0.20</version>@b@</dependency>

spring-2.0.8.jar(org.springframework.remoting.caucho.HessianProxyFactoryBean),点击下载，源码下载，源码视图链接

git源码分享,点击浏览

hessian简单项目实例（包含依赖包&完整源码），点击下载