tomcat共享多個web應用會話的實現方法

問題

今天有位朋友問了個問題，大致是：tomcat下兩個Java web，一個是商城，一個是直播，從商城登錄后，再跳轉到直播，發現處于非登錄狀態。

解決思路

1. 將session抽出來成一個session服務，統一通過該服務操作session。
2. tomcat內部用會話管理器獲取會話時遍歷所有context內的會話。
   

方案1

重寫獲取session方法即可。

方案2

找了源碼發現已經支持類似遍歷所有context內的會話的形式，首先獲取session時，如果cressContext屬性為true，則會在獲取不到時嘗試遍歷所有context是否存在該sessionid，如果存在則在本context根據sessionid創建自己的session對象。

 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應用）獲取跨應用session時通過類似下面操作獲取：

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

這是因為request會根據cookies的sessionid獲取到session對象，這時不會報找不到，因為前面已經根據其他sessionid創建了一個session對象，然后getContext操作會獲取對應url的context，接著進行會話操作。

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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