tomcat共享多个web应用会话的实现方法

 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);    }  }

request.getSession().getServletContext().getContext("/app2").getAttribute("att2"); 

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;    }  }