Memcache存储session，修改tomcat源码，实现全站二级域名session共享

上篇文章中的方案，在外部显式的使用memcache来替代session，虽然可以达到各个服务器session共享的目的，但是改变了开发人员获取session的方式。

本篇介绍的方法可以在不重构原来代码，不改变代码习惯的情况下，实现session共享的目的。

两种方法各有利弊，第一种方法编码方式改变比较大，开发人员可能不习惯，但是不受服务器类型的影响;第二种方法，针对tomcat服务器，需要修改tomcat源码，但是不需要重构代码，代码中对session的操作还和以前一样。

第二种方式主要做两处改动：

1，使用memcache来覆盖tomcat对session的实现。将session存入memcache中。

package org.apache.catalina.session;

import java.io.*;

import com.danga.MemCached.*;
import org.apache.catalina.*;

public class MemcachedManager extends StandardManager {
    protected MemCachedClient mc = null;
    protected SockIOPool pool = null;
    protected String sockPoolName = "snasessionsock";
    protected String serverlist = "192.168.2.194:12000";
    protected String snaidPerfix = "snaid";
    protected String snaidFlag = "true";
    public MemcachedManager() {
        super();
    }

    public Session findSession(String id) throws IOException {
        Session session = super.findSession(id);
        if (session == null && id != null) {
            try {
                Object sid = mc.get(this.getSnaidPerfix() + id);
                if (sid != null) {
                    session = createSession(id);
                }
            } catch (Exception ex) {
                ex.printStackTrace();
            }
        }
        return session;
    }

    public Session createSession(String sessionId) {
        Session session = super.createSession(sessionId);
        mc.set(this.getSnaidPerfix() + session.getId(), snaidFlag);
        return session;
    }

    protected StandardSession getNewSession() {
        return new MemcachedSession(this, mc);
    }

    protected void initPool() {
        try {
            if (pool == null) {
                try {
                    pool = SockIOPool.getInstance();
                    pool.setServers(serverlist.split(","));
                    pool.setInitConn(5);
                    pool.setMinConn(5);
                    pool.setMaxConn(50);
                    pool.setMaintSleep(30);
                    pool.setNagle(false);
                    pool.initialize();
                } catch (Exception ex) {
//                    log.error("error:", ex);
                }
            }
        } catch (Exception ex) {
//            log.error("error:", ex);
        }

        if (mc == null) {
            mc = new MemCachedClient();
//            mc.setPoolName(sockPoolName);
            mc.setCompressEnable(false);
            mc.setCompressThreshold(0);
        }
    }

    protected void closePool() {
        if (mc != null) {
            try {
            } catch (Exception ex) {
//                log.error("error:", ex);
            }
            mc = null;
        }
        if (pool != null) {
            try {
                pool.shutDown();
            } catch (Exception ex) {
//                log.error("error:", ex);
            }
        }
    }

    public String getSockPoolName() {
        return sockPoolName;
    }

    public String getServerlist() {
        return serverlist;
    }

    public String getSnaidPerfix() {
        return snaidPerfix;
    }

    public String getSnaidFlag() {
        return snaidFlag;
    }

    public void setSockPoolName(String sockPoolName) {
        this.sockPoolName = sockPoolName;
    }

    public void setServerlist(String serverlist) {
        this.serverlist = serverlist;
    }

    public void setSnaidPerfix(String snaidPerfix) {
        this.snaidPerfix = snaidPerfix;
    }

    public void setSnaidFlag(String snaidFlag) {
        this.snaidFlag = snaidFlag;
    }

    protected String generateSessionId() {
        if (this.getJvmRoute() != null) {
            return java.util.UUID.randomUUID().toString() + '.' +
                    this.getJvmRoute();
        }
        return java.util.UUID.randomUUID().toString();
    }

    public void start() throws LifecycleException {
        this.setPathname(""); // must disable session persistence across Tomcat restarts
        super.start();
        this.initPool();
    }

    public void stop() throws LifecycleException {
        super.stop();
        this.closePool();
    }
}

---------------------------------------------------------------------------------------------------

package org.apache.catalina.session;

import com.danga.MemCached.*;
import org.apache.catalina.*;

public class MemcachedSession extends StandardSession {
    protected transient MemCachedClient mc = null;
    public MemcachedSession(Manager manager,
                            MemCachedClient mc) {
        super(manager);
        this.mc = mc;
    }


    public Object getAttribute(String name) {
        Object obj = super.getAttribute(name);
        if (obj != null && !(obj instanceof java.io.Serializable)) {
            return obj;
        }
        String key = name + this.getId();
        obj = mc.get(key);
        return obj;
    }

    public void setAttribute(String name, Object value) {
        removeAttribute(name);
        super.setAttribute(name, value);
        if (value != null && value instanceof java.io.Serializable) {
            String key = name + this.getId();
            mc.set(key, value);
        }
    }

    protected void removeAttributeInternal(String name, boolean notify) {
        super.removeAttributeInternal(name, notify);
        String key = name + this.getId();
        mc.delete(key);
    }

    public void expire(boolean notify) {
        mc.delete(((MemcachedManager) manager).getSnaidPerfix() + this.getId());
        super.expire(notify);
    }

}

(可以使用自己项目中memcache的操作类来替代上面两个类的memcache操作）

将两个类打jar包，置于tomcat/lib下

修改tomcat/conf/context.xml文件，内容如下：

	delegate="true"/> 
    
    WEB-INF/web.xml
 org.apache.catalina.session.MemcachedManager" serverlist="192.168.2.194:12000" snaidPerfix="snaid" snaidFlag="true">
	

经过以上的修改，tomcat对session的操作会自动使用org.apache.catalina.session.MemcachedManager 来替代。

2，修改tomcat源码，使tomcat在向客户端setcookie的时候，设置cookie的作用域为全站。这样可以所有的tomcat共用一个JSESSIONID。

下载tomcat的源码。

修改org.apache.catalina.connector.Request.java

    /**
     * Configures the given JSESSIONID cookie.
     *
     * @param cookie The JSESSIONID cookie to be configured
     */
    protected void configureSessionCookie(Cookie cookie) {
        cookie.setMaxAge(-1);
        String contextPath = null;
        if (!connector.getEmptySessionPath() && (getContext() != null)) {
            contextPath = getContext().getEncodedPath();
        }
        if ((contextPath != null) && (contextPath.length() > 0)) {
            cookie.setPath(contextPath);
        } else {
            cookie.setPath("/");
        }
        //added by sufeng,make tomcat jsessionid cross docin.com
        if (null != System.getProperty("sessionShareDomain") && !"".equals(System.getProperty("sessionShareDomain")))
            cookie.setDomain(System.getProperty("sessionShareDomain"));
        //added by sufeng end
        if (isSecure()) {
            cookie.setSecure(true);
        }
    }

1. 在tomcat/conf/catalina.properties 中添加
2. sessionShareDomain=sufeng.com
4. 
5. 重新访问，会发现，JSEESIONID的作用域变成了sufeng.com，这样在两个子域的tomcat服务器可以共享同一个sessionid，并通过相同的sessionid到memcache中取session数据。不对tomcat源码进行修改，两个二级域的tomcat将分别生成不同的JSESSION值，并且作用域是自己的二级域名。即图中上面的两个cookie。
7. 参考：
8. http://www.javayou.com/diary/8534
9. http://www.javaeye.com/topic/81641
10. http://soyul.javaeye.com/blog/445838
11. http://apache.freelamp.com/tomcat/tomcat-6/v6.0.20/src/apache-tomcat-6.0.20-src.zip