tomcat共享多个web应用会话的实现方法-JSP技巧-JSP编程-硕编程

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tomcat共享多个web应用会话的实现方法

问题

今天有位朋友问了个问题，大致是：tomcat下两个java web，一个是商城，一个是直播，从商城登录后，再跳转到直播，发现处于非登录状态。

解决思路

将session抽出来成一个session服务，统一通过该服务操作session。

tomcat内部用会话管理器获取会话时遍历所有context内的会话。

方案1

重写获取session方法即可。

方案2

找了源码发现已经支持类似遍历所有context内的会话的形式，首先获取session时，如果cresscontext属性为true，则会在获取不到时尝试遍历所有context是否存在该sessionid，如果存在则在本context根据sessionid创建自己的session对象。

 public httpsession getsession(boolean create) {

    if (crosscontext) {

      // there cannot be a session if no context has been assigned yet
      if (context == null)
        return (null);

      // return the current session if it exists and is valid
      if (session != null && session.isvalid()) {
        return (session.getsession());
      }

      httpsession other = super.getsession(false);
      if (create && (other == null)) {
        // first create a session in the first context: the problem is
        // that the top level request is the only one which can 
        // create the cookie safely
        other = super.getsession(true);
      }
      if (other != null) {
        session localsession = null;
        try {
          localsession =
            context.getmanager().findsession(other.getid());
          if (localsession != null && !localsession.isvalid()) {
            localsession = null;
          }
        } catch (ioexception e) {
          // ignore
        }
        if (localsession == null && create) {
          localsession = 
            context.getmanager().createsession(other.getid());
        }
        if (localsession != null) {
          localsession.access();
          session = localsession;
          return session.getsession();
        }
      }
      return null;

    } else {
      return super.getsession(create);
    }

  }

context（web应用）获取跨应用session时通过类似下面操作获取：

request.getsession().getservletcontext().getcontext("/app2").getattribute("att2");

这是因为request会根据cookies的sessionid获取到session对象，这时不会报找不到，因为前面已经根据其他sessionid创建了一个session对象，然后getcontext操作会获取对应url的context，接着进行会话操作。

public servletcontext getcontext(string uri) {

    // validate the format of the specified argument
    if (uri == null || !uri.startswith("/")) {
      return null;
    }

    context child = null;
    try {
      // look for an exact match
      container host = context.getparent();
      child = (context) host.findchild(uri);

      // non-running contexts should be ignored.
      if (child != null && !child.getstate().isavailable()) {
        child = null;
      }

      // remove any version information and use the mapper
      if (child == null) {
        int i = uri.indexof("##");
        if (i > -1) {
          uri = uri.substring(0, i);
        }
        // note: this could be more efficient with a dedicated mapper
        //    method but such an implementation would require some
        //    refactoring of the mapper to avoid copy/paste of
        //    existing code.
        messagebytes hostmb = messagebytes.newinstance();
        hostmb.setstring(host.getname());

        messagebytes pathmb = messagebytes.newinstance();
        pathmb.setstring(uri);

        mappingdata mappingdata = new mappingdata();
        ((engine) host.getparent()).getservice().findconnectors()[0].getmapper().map(
            hostmb, pathmb, null, mappingdata);
        child = (context) mappingdata.context;
      }
    } catch (throwable t) {
      exceptionutils.handlethrowable(t);
      return null;
    }

    if (child == null) {
      return null;
    }

    if (context.getcrosscontext()) {
      // if crosscontext is enabled, can always return the context
      return child.getservletcontext();
    } else if (child == context) {
      // can still return the current context
      return context.getservletcontext();
    } else {
      // nothing to return
      return null;
    }
  }

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