tomcat 二级域名 共享session 的方法

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     Tomcat下，不同的二级域名，Session默认是不共享的，因为Cookie名称为JSESSIONID的Cookie根域是默认是没设置的，访问 不同的二级域名，其Cookie就重新生成，而session就是根据这个Cookie来生成的，所以在不同的二级域名下生成的Session也不一样。 找到了其原因，就可根据这个原因对Tomcat在生成Session时进行相应的修改(注：本文针对Tomcat 6.0)。     单个web项目运行在tomcat上但是却使用多个子域名，如：     - site.com      - www.site.com      - sub1.site.com      - sub2.site.com      - etc.      这样会导致session的不能共享，在网络上查找的并却最快的解决办法。      解决办法：Usage:  - compile CrossSubdomainSessionValve & put it in a .jar file  - put that .jar file in $CATALINA_HOME/lib directory  - include a <Valve className="org.three3s.valves.CrossSubdomainSessionValve"/> in  $CATALINA_HOME/conf/server.xml      Java代码  package org.three3s.valves;    import java.io.*;    import javax.servlet.*;  import javax.servlet.http.*;    import org.apache.catalina.*;  import org.apache.catalina.connector.*;  import org.apache.catalina.valves.*;  import org.apache.tomcat.util.buf.*;  import org.apache.tomcat.util.http.*;    /** <p>Replaces the domain of the session cookie generated by Tomcat with a domain that allows that  * session cookie to be shared across subdomains.  This valve digs down into the response headers  * and replaces the Set-Cookie header for the session cookie, instead of futilely trying to  * modify an existing Cookie object like the example at http://www.esus.be/blog/?p=3.  That  * approach does not work (at least as of Tomcat 6.0.14) because the  * <code>org.apache.catalina.connector.Response.addCookieInternal</code> method renders the  * cookie into the Set-Cookie response header immediately, making any subsequent modifying calls  * on the Cookie object ultimately pointless.</p>  *  * <p>This results in a single, cross-subdomain session cookie on the client that allows the  * session to be shared across all subdomains.  However, see the {@link getCookieDomain(Request)}  * method for limits on the subdomains.</p>  *  * <p>Note though, that this approach will fail if the response has already been committed.  Thus,  * this valve forces Tomcat to generate the session cookie and then replaces it before invoking  * the next valve in the chain.  Hopefully this is early enough in the valve-processing chain  * that the response will not have already been c