本文章主要目的是配置session共享，为了巩固基础，捎带介绍了一些基础知识（网上搜索后觉得最全面的特引过来，节省时间），基础扎实的可以自动忽略。

基础篇：

1.了解java web中的session与cookie。

2.如何封装request和session这两个web项目中最常用的对象（以解决乱码为例）

进阶篇：

3.利用memcache实现session共享

    在开发过程中，为了缓解访问压力，往往需要配置负载均衡，也就是相同的项目放在多台机子上，保证一台机子挂了，网站仍然可以正常访问，除了需要使用相同的数据源，资料源之外，最大的问题莫过于session的共享了。这里session共享的核心在于改变原来session中的键值对存放在每台机子各自的内存中的情况，而是把session中的内容集中存放在一个nosql数据库中。

3.1封装request对象：

package com.sse.roadshow.session;


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


import com.sse.roadshow.common.SpyMemcachedManager;


public class HttpServletRequestWrapper extends
javax.servlet.http.HttpServletRequestWrapper {


String sid = "";

private SpyMemcachedManager spyMemcachedManager;


public HttpServletRequestWrapper(String sid, HttpServletRequest request,SpyMemcachedManager spyMemcachedManager) {
super(request);
this.sid = sid;
this.spyMemcachedManager = spyMemcachedManager;
}


public HttpSession getSession(boolean create) {
return new HttpSessionSidWrapper(this.sid, super.getSession(create), this.spyMemcachedManager);
}


public HttpSession getSession() {
return new HttpSessionSidWrapper(this.sid, super.getSession(), this.spyMemcachedManager);
}


}

通过封装传递数据源，并且覆盖getSession方法，自定义的session对象在下一步

3.2封装session对象

package com.sse.roadshow.session;

import java.util.Enumeration;

import java.util.HashMap;

import java.util.Map;

import javax.servlet.http.HttpSession;

import com.sse.roadshow.common.Constants;

import com.sse.roadshow.common.SpyMemcachedManager;

import com.sse.roadshow.vo.Enumerator;

publicclass HttpSessionSidWrapper extends HttpSessionWrapper {

private Stringsid = "";

privateMap map =new HashMap();

private SpyMemcachedManagerspyMemcachedManager;

@SuppressWarnings("rawtypes")

public HttpSessionSidWrapper(Stringsid, HttpSession session, SpyMemcachedManagerspyMemcachedManager) {

super(session);

if (spyMemcachedManager ==null) {

System.out.println("spyMemcachedManager is null.....");

return;

}

this.spyMemcachedManager =spyMemcachedManager;

this.sid =sid;

MapmemSession = null;

memSession = (Map)this.spyMemcachedManager.get(sid);

//sid没有加入到session中，需要初始化session，替换为自定义session

if (memSession ==null) {

// System.out.println("memSession is null");

memSession =new HashMap();

// this.spyMemcachedManager.set(sid, memSession, Constants.SPMEM_EXPTIME);

if (session !=null) {

Enumeration<String>names = session.getAttributeNames();

while (names.hasMoreElements()) {

Stringkey = (String) names.nextElement();

memSession.put(key,session.getAttribute(key));

}

}

}

this.map =memSession;

}

public Object getAttribute(Stringkey) {

if (this.map !=null && this.map.containsKey(key)) {

returnthis.map.get(key);

}else {

returnnull;

}

}

@SuppressWarnings({"unchecked", "rawtypes" })

public Enumeration getAttributeNames() {

return (new Enumerator(this.map.keySet(),true));

// return super.getAttributeNames();

}

publicvoid invalidate() {

// super.invalidate();

this.map.clear();

longs1= System.currentTimeMillis();

try {

spyMemcachedManager.delete(sid);

System.out.print("removeSession sid is:" +sid);

}

finally{

System.out.println(System.currentTimeMillis() -s1);

}

}

publicvoid removeAttribute(String name) {

// super.removeAttribute(name);

this.map.remove(name);

attributeChange();

// System.out.print("removeAttribute");

// System.out.println("key : " + name);

}

@SuppressWarnings("unchecked")

publicvoid setAttribute(String name, Object value) {

// super.setAttribute(name, value);

this.map.put(name,value);

attributeChange();

// System.out.print("setAttribute-");

// System.out.println("key : " + name + ", value : " + value);

}

privatevoid attributeChange() {

spyMemcachedManager.set(sid,this.map, Constants.MYFILTER_COOKIE_EXPTIME);

}

}

3.3引入我们刚才封装好的request对象：

使用过滤器过滤对应路径的请求，引入自定义request：

3.3.1自定义过滤器：

package com.sse.roadshow.filter;


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


import org.springframework.web.context.support.WebApplicationContextUtils;


import com.sse.roadshow.common.Constants;
import com.sse.roadshow.common.SpyMemcachedManager;
import com.sse.roadshow.common.Util;
import com.sse.roadshow.session.HttpServletRequestWrapper;


public class MemcachedSessionFilter extends HttpServlet implements Filter {


/**
* 
*/
private static final long serialVersionUID = 8928219999641126613L;


// private FilterConfig filterConfig;


private String cookieDomain = "";


private String cookiePath = "/";

private SpyMemcachedManager spyMemcachedManager;


public void doFilter(ServletRequest servletRequest,
ServletResponse servletResponse, FilterChain filterChain)
throws IOException, ServletException {
String sessionId = "XmlBeanDefinitionReaderSid";

HttpServletRequest request = (HttpServletRequest) servletRequest;
HttpServletResponse response = (HttpServletResponse) servletResponse;


Cookie cookies[] = request.getCookies();
Cookie sCookie = null;


String sid = "";
if (cookies != null && cookies.length > 0) {
for (int i = 0; i < cookies.length; i++) {
sCookie = cookies[i];
if (sCookie.getName().equals(sessionId)) {
sid = sCookie.getValue();
}
}
}


if (sid == null || sid.length() == 0) {
sid = java.util.UUID.randomUUID().toString();
Cookie mycookies = new Cookie(sessionId, sid);
mycookies.setMaxAge(-1);
mycookies.setPath("/");
mycookies.setHttpOnly(true);
mycookies.setDomain(Constants.DOMAIN);
response.addCookie(mycookies);
}
spyMemcachedManager = getBean(request);
filterChain.doFilter(new HttpServletRequestWrapper(sid, request, spyMemcachedManager),
servletResponse);
}


private SpyMemcachedManager getBean(HttpServletRequest request) {
if(Util.isNull(spyMemcachedManager)) {
spyMemcachedManager = WebApplicationContextUtils.getWebApplicationContext(request.getServletContext()).getBean(SpyMemcachedManager.class);
}
return spyMemcachedManager;
}

public void init(FilterConfig filterConfig) throws ServletException {
// this.filterConfig = filterConfig;
// this.sessionId = filterConfig.getInitParameter("sessionId");
this.cookiePath = filterConfig.getInitParameter("cookiePath");
if (this.cookiePath == null || this.cookiePath.length() == 0) {
this.cookiePath = "/";
}

this.cookieDomain = filterConfig.getInitParameter("cookieDomain");
if (this.cookieDomain == null) {
this.cookieDomain = Constants.DOMAIN;
}
}


public SpyMemcachedManager getSpyMemcachedManager() {
return spyMemcachedManager;
}


public void setSpyMemcachedManager(SpyMemcachedManager spyMemcachedManager) {
this.spyMemcachedManager = spyMemcachedManager;
}


}

3.3.2.在web.xml中配置filter:

 <!-- session共享过滤器 -->

   <filter>

    <filter-name>mySessionFilter</filter-name>

   <filter-class>com.sse.roadshow.filter.MemcachedSessionFilter</filter-class>

  </filter>

  <filter-mapping>

    <filter-name>mySessionFilter</filter-name>

    <url-pattern>/*</url-pattern>

  </filter-mapping>

这样session共享就配置完毕了。

java项目使用memcache实现session共享+session基础