webwork结合memcached实现sna架构

实现思路，使用一个拦截器实现session的处理：

1. 获取sessionId，查找sessionAttribute（自定义hashmap）
2. 设置session attribute到webwork
3. 监控session attribute，一旦发现修改，则持久化到cache中

使用方法：

1、配置拦截器

<interceptor class="com.comwave.sna.interceptor.SNAInterceptor" name="snaInterceptor"></interceptor>

<interceptor-ref name="snaInterceptor"></interceptor-ref>

2、配置spring

<bean class="com.comwave.sna.cache.provider.MemcachedCacheManager" id="cacheManager" destroy-method="close"></bean>
  <constructor-arg value="127.0.0.1:11212"></constructor-arg>
 

如果使用struct2，则需要修改相应的接口，并增加setCacheManager方法

代码非常简单，cookieId的值并没有自己实现，简单借用应用服务器的sessionId，当然你以可以实现自己的sessionId算法。

看了楼主的代码。
楼主是用memcached实现了ActionContext的session。
挺棒 !!

有几个问题：
<1> 只要serverlist一样，是不是memcached server就是同一个实例？
<2> 是否代码中要约定大家不能使用HttpSession了

1、是，只要serverList一样
2、是，不能直接使用httpSession，应该使用ActionContext的session，不过webwork或struct直接使用httpsession的情况应该不多

和其他方案相比最大的特点就是简单，并且能支持webwork或struct支持的任何应用服务器而无需修改代码，可以方便的切换到其他cache实现。缺点就是不支持其他web framework。我们公司的项目都是用webwork或struct，所以这样就够用了。

是struts2.0吧。

是struct2.0

这种方案有一个小问题:
如果项目用到的包自己用到了httpsession，failover就会出问题。

如果使用了Acegi之类直接使用httpsession的话，解决方法也不会太复杂，不过需要使用filter，可以这么搞：

/**
 * $Revision: 1.0 $
 * Created: 2007-6-1
 * $Date: 2007-6-1 $
 * 
 * Author: Keven Chen
 */
package com.comwave.sna.filter;

import java.io.IOException;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.Enumeration;
import java.util.Iterator;

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.Cookie;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

import com.comwave.sna.SessionMap;
import com.comwave.sna.cache.provider.MemcachedCacheManager;

/**
 * @author Keven Chen
 * @version $Revision 1.0 $
 *
 */
public class SNAFilter implements Filter {
	private static final String REMOVE_ATTRIBUTE_METHOD = "removeAttribute";
	private static final String SET_ATTRIBUTE_METHOD = "setAttribute";
	private static final String GET_SESSION_METHOD = "getSession";
	
	private static final String SERVER_LIST = "serverList";
	private static final String SESSION_NAME = "cookie-session-id";
	
	private MemcachedCacheManager cacheManager;
	
	public void init(FilterConfig config) throws ServletException {
		String serverList = config.getInitParameter(SERVER_LIST);
		if(serverList == null || serverList.trim().length() ==0){
			throw new ServletException("SNAFilter missing serverList parameter.");
		}
		cacheManager = new MemcachedCacheManager(serverList);
	}
	
	public void destroy() {
		if (cacheManager != null) {
			cacheManager.close();
		}
	}

	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
			throws IOException, ServletException {
		final HttpServletRequest hrequest = (HttpServletRequest) request;
		final HttpServletResponse hresponse = (HttpServletResponse) response;
		
		String sessionId = getSessionId(hrequest,hresponse);
		SessionMap session = getSession(sessionId);
		initialHttpSession(session,hrequest.getSession());
		try {
			chain.doFilter(proxyRequest(hrequest,session), hresponse);
		} finally {
			if(session.isClear() || session.isEmpty()){
				boolean result = cacheManager.flushCache(sessionId);
			}
			else if(session.isModified()){
				session.setModified(false);
				boolean result = cacheManager.putToCache(sessionId, session);
			}
		}
	}
	
	private HttpServletRequest proxyRequest(final HttpServletRequest request,final SessionMap session){
		final HttpSession hSession = request.getSession();
		return (HttpServletRequest) Proxy.newProxyInstance(HttpServletRequest.class.getClassLoader(),
				new Class[] { HttpServletRequest.class }, new InvocationHandler() {
					private HttpSession proxySession = null;
					
					public Object invoke(Object proxy, Method method, Object[] args)
							throws Throwable {
						if(method.getName().equalsIgnoreCase(GET_SESSION_METHOD)){
							if(proxySession == null){
								proxySession = proxySession(hSession,session);
							}
							return proxySession;
						}
						return method.invoke(request, args);
					}
				});
	}
	
	private HttpSession proxySession(final HttpSession hsession,final SessionMap session){
		return (HttpSession) Proxy.newProxyInstance(HttpSession.class.getClassLoader(), new Class[] {HttpSession.class}, new InvocationHandler() {
			public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
				String methodName = method.getName();
				if(methodName.equalsIgnoreCase(SET_ATTRIBUTE_METHOD)){
					System.out.println("name:"+args[0]+",value:"+args[1]);
					session.put(args[0], args[1]);
				}
				else if(methodName.equalsIgnoreCase(REMOVE_ATTRIBUTE_METHOD)){
					System.out.println("remove:"+args[0]);
					session.remove(args[0]);
				}
				return method.invoke(hsession, args);
			}
		
		});
	}
	
	private void initialHttpSession(SessionMap session, HttpSession hsession){
		Enumeration oldAttributes = hsession.getAttributeNames();
		while(oldAttributes.hasMoreElements()){
			hsession.removeAttribute((String)oldAttributes.nextElement());
		}
		
		Iterator newAttributes = session.keySet().iterator();
		while(newAttributes.hasNext()){
			String attribute = (String) newAttributes.next();
			hsession.setAttribute(attribute, session.get(attribute));
		}
	}

	private String getSessionId(HttpServletRequest request,HttpServletResponse hresponse){
		Cookie[] cookies = request.getCookies();
		String sessionId = null ;
		if (cookies != null) {
			for (int i = 0; cookies != null && i < cookies.length; i++) {
				if (SESSION_NAME.equals(cookies[i].getName())) {
					sessionId = cookies[i].getValue();
					break;
				}
			}
		}
		if(sessionId == null || sessionId.trim().length() == 0){
			sessionId = buildSessionId(request);
			createCookie(sessionId,hresponse);
		}
		return sessionId;
	}
	
	private void createCookie(String sessionId,HttpServletResponse response) {
		Cookie cookie = new Cookie(SESSION_NAME,sessionId);
		cookie.setPath("/");
		response.addCookie(cookie);
	}

	private String buildSessionId(HttpServletRequest request) {
		return request.getSession().getId();
	}
	
	protected SessionMap getSession(String Id){
		Object value = cacheManager.getFromCache(Id);
		if(value == null){
			return new SessionMap();
		}
		return (SessionMap) value;
	}
}

当然你得在web.xml配置filter

不过，如果有第三方lib直接调用HttpSession.getId()这个方法，估计会有问题，没有测试过，推测而已。