<h2>问题</h2>    <p>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。</p>    <h2>解决思路</h2>    <ol>     <li>将session抽出来成一个session服务，统一通过该服务操作session。</li>     <li>tomcat内部用会话管理器获取会话时遍历所有context内的会话。</li>    </ol>    <h2>方案1</h2>    <p>重写获取session方法即可。</p>    <h2>方案2</h2>    <p>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。</p>    <pre>  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);          }        }</pre>    <p>context（web应用）获取跨应用session时通过类似下面操作获取：</p>    <pre>  request.getSession().getServletContext().getContext("/app2").getAttribute("att2"); </pre>    <p>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。</p>    <pre>  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;          }      }</pre>    <p> </p>    <p>来自：http://blog.csdn.net/wangyangzhizhou/article/details/56477576</p>    <p> </p>