Flex Remote Object中直接使用HttpSession的方法

文章来源：http://flexhome.iteye.com/blog/157144
Flex Remote Object可以是POJO,JavaBean或是EJB。在面向服务的架构中(Service Oriented Architecture),我们可以用Remote Object来作为Service Facade，利用应用服务器提供的persistent service来储存状态信息。
Flex既可以提供stateful或stateless的remote object, 另外还有session servlet让mxml获取/和储存session中的内容。这一切听上去都很完美，但是有一个问题，Flex Remote Object本身是无法获得任何有关Running Context的信息，也就是说，你无法从你的 Remote Object 中获得 HttpSession, HttpRequest 和 ServletContext。 所谓的 Flex Session servlet只是让MXML获得session的内容，而不是直接让Remote Object获得session。

Remote Object为什么需要获得HttpRequest, HttpSession?
既然Flex提供了stateful的remote object为什么还要让remote object获得Running Context呢？问题在于Flex中的stateful是基于应用服务器的http session，而且你无法控制AMFGateway建立remote object的过程。打个简单的比方，我们知道一般的应用服务器中，session的时限只有20分钟，而在很多系统的登陆过程中却有选择保持登陆几个月的选项。

其具体实现上就是利用cookie来储存id和password hash，通过控制cookie的存活时间来实现的。而在服务器端，一旦session过期了，则可以从cookie中获得id和password hash重新登陆一遍，从而达到自动认证用户的目的。

如果你的Remote Object无法获得 HttpServletRequest, HttpSession，你就无法实现上述的情况。另外，对于小型的应用来说，直接在Remote object中获得servlet context并利用它来储存/获得共享的资源，可以大大降低开发的复杂程度。

解决方案
要让Remote Object获得HttpSession,HttpRequest和ServletContext并不是一件容易的事情。这里提供了我的一种方法，供大家参考。希望能抛砖引玉，让大家提出更好，更有效的方案。

这个方法的基本思路是利用JAVA提供的 ThreadLocal Object。当服务器接收到一个HTTP请求后，这个请求的整个处理过程是运行在同一个线程中的。

每个HTTP请求的处理会都运行在各自独立的线程中。而在Flex中，所有AMF Remote Object 的请求都需要通过 AMF Gateway Servlet，而Remote Object 的建立和调用恰恰就是运行在这个HTTP请求的线程中。

有了这个原则，我们就可以建立一个Context Object,每当请求建立的时候，就可以把这个请求放入 Context 的 ThreadLocal 中，而当 Remote Object 被AMF Gateway Servlet调用的时候，就可以通过访问 Context 的ThreadLoca l来获得其所对应的那个请求。

而截获发送到AMF Gateway的请求则可以通过Servlet Filter来实现。废话不说了，看代码吧！  1. 添加以下内容到WEB-INF/web.xml中
<filter>
<filter-name>AMFSessionFilter </filter-name>
<filter-class>com.netop.forum.servlets.AMFSessionFilter </filter-class>
<filter>

<filter-mapping>
<filter-name>AMFSessionFilter </filter-name>
<servlet-name>AMFGatewayServlet </servlet-name>
<filter-mapping>


2. AMFSessionFilter的代码

/*
* Created on 1/07/2004
*/
package com.netop.forum.servlets;


import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.*;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
* @author Zombie
* @version 0.5
*/

public class AMFSessionFilter implements Filter
{
private static Log log = LogFactory.getLog(AMFSessionFilter.class);

public void init(FilterConfig config)
{
log.info("Init AMFSessionFilter filter");
}

public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws ServletException,IOException
{
AMFContext.setCurrentContext((HttpServletRequest)request, (HttpServletResponse)response);
chain.doFilter(request,response);
}

public void destroy()
{
log.info("Destory AMFSessionFilter filter");
}
}



3. AMFContext的代码

/*
* Created on 1/07/2004
*/
package com.netop.forum.servlets;


import javax.servlet.*;
import javax.servlet.http.*;
import com.netop.forum.business.*;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
* @author Zombie
* @version 0.5
*/
public class AMFContext
{

/**
* Context Attribute key for the connection the factory
*/
public final static String CONNECTION_FACTORY_KEY = "sqlMapFactory";

/**
* The log
*/
private static Log log = LogFactory.getLog(AMFContext.class);

/**
* ThreadLocal object for storing object in current thread.
*/
private static ThreadLocal tl = new ThreadLocal();

/**
* Set current context
*
* @param request The HttpRequest object
* @param response The HttpResponses object
*/
static public void setCurrentContext(HttpServletRequest request, HttpServletResponse response)
{
AMFContext c = getCurrentContext();
if (c == null)
{
c = new AMFContext(request,response);
tl.set(c);
}
else
{
c.setRequest(request);
c.setResponse(response);
}
}

/**
* Get current context value
* @return The current context
*/
static public AMFContext getCurrentContext()
{
return (AMFContext)tl.get();
}





//----------------------------------------------------------
//
// Class members
//
//----------------------------------------------------------

/**
* The http request object. The lifecycle of the request object is defined as the request
* scope. It may be reused in another incoming connection, so dont use it in another thread.
*/
private HttpServletRequest request;

/**
* The http response object. The lifecycle of the response object is defined as the request
* scope. Dont use it in another thread. Also dont write output to the response when it is
* used in the context, but you may get or set some response header when it is safe.
*/
private HttpServletResponse response;


/**
* The constructor is private, to get an instance of the AMFContext, please use
* getCurrentContext() method.
*
* @param request
* @param response
*/
private AMFContext (HttpServletRequest request, HttpServletResponse response)
{
this.request = request;
this.response = response;
}


/**
* Get request object
*
* @return Http request object
*/
public HttpServletRequest getRequest()
{
return request;
}

/**
* Set request object
*
* @param Http request object
*/
public void setRequest(HttpServletRequest request)
{
this.request = request;
}

/**
* Get response object
*
* @return Http response object
*/
public HttpServletResponse getResponse()
{
return response;
}

/**
* Set response object
*
* @param response Http response object
*/
public void setResponse(HttpServletResponse response)
{
this.response = response;
}

/**
* Get the servlet context
* @return
*/
public ServletContext getServletContext()
{
HttpSession session = this.getSession();
return session.getServletContext();
}

/**
* Get the current running session
* @return
*/
public HttpSession getSession()
{
return request.getSession();
}


/**
* Get an object stored in the session.
*
* @param attr Attribute Name
* @return The value stored under the attribute name.
*/
public Object getSessionAttribute(String attr)
{
HttpSession session = this.getSession();
return session.getAttribute(attr);
}

/**
* Store an object in the session.
*
* @param attr Attribute Name
* @param value The value.
*/
public void setSessionAttribute(String attr, Object value)
{
HttpSession session = this.getSession();
session.setAttribute(attr, value);
}

/**
* Get an object stored in the servlet context.
*
* @param attr Attribute Name
* @return The value stored under the attribute name.
*/
public Object getContextAttribute(String attr)
{
ServletContext sc = this.getServletContext();
return sc.getAttribute(attr);
}

/**
* Store an object in the servlet context.
*
* @param attr Attribute Name
* @param value The value.
*/
public void setContextAttribute(String attr, Object value)
{
ServletContext sc = this.getServletContext();
sc.setAttribute(attr,value);
}

/**
* Get an object stored in the current request.
*
* @param attr Attribute Name
* @return The value stored under the attribute name.
*/
public Object getRequestAttribute(String attr)
{
return request.getAttribute(attr);
}

/**
* Store an object in the current request.
*
* @param attr Attribute Name
* @param value The value.
*/
public void setRequestAttribute(String attr, Object value)
{
request.setAttribute(attr,value);
}


/**
* Get the connection factory from the servlet context. The connection factory is in the
* application scope.
*
* @return The connection factory for creating sqlMap objects.
*/
public ConnectionFactory getConnectionFactory()
{
ConnectionFactory factory =(ConnectionFactory)this.getContextAttribute(CONNECTION_FACTORY_KEY);
if (factory == null)
{
try
{
factory = new ConnectionFactory();
// factory is lazy instantiated, so we need to invoke it once to make sure it is ok.
factory.getSqlMap();
this.setContextAttribute(CONNECTION_FACTORY_KEY, factory);
}
catch (Throwable e)
{
log.fatal("Can not create connection factory: "+e.getMessage(), e);
}
}
return factory;
}

}


4. 如何在remote object中使用AMFContext


class YouRemoteService
{
public void serviceMethod()
{
AMFContext context = AMFContext.getCurrentContext();
HttpSession = context.getSession();
ServletContext = context.getServletContext();

HttpServletRequest request = context.getRequest();
HttpServletResponse response = context.getResponse();

context.setSessionAttribute("attr","value");
context.setContextAttribute("attr","value");

}
}