tomcat如何共享多個web應用會話

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);
    }

}</pre> 

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;
        }
    }
 
  
 
 
  
來自：http://blog.csdn.net/wangyangzhizhou/article/details/56477576