Cannot forward after response has been committed-蒲公英云

Cannot forward after response has been committed

矫情吗；* 2022-06-10 03:59 190阅读 0赞

之前在使用Servlet的时候，总是在 doGet()/doPost() 的最后一行才使用请求转发或者重定向。如果需要根据条件来判断进行不同的请求转发或者重定向，代码如下：

@Override
protected void doGet(final HttpServletRequest req, final HttpServletResponse resp)
        throws ServletException, IOException {
    if (req.getSession().getAttribute(AttrConsts.LOGIN_USER) == null) {
        req.getRequestDispatcher(PathConsts.PATH_PREFIX + PathConsts.LOGIN_PAGE).forward(req, resp);
    }
    req.getRequestDispatcher(PathConsts.PATH_PREFIX + PathConsts.MAIN_PAGE).forward(req, resp);
}

上边的代码在执行后会报如下异常：

java.lang.IllegalStateException: Cannot forward after response has been committe

报异常的原因是重复转发或者重定向了请求，如果有多个转发或者重定向，需要在每个转发或者重定向请求之后加上return语句(最后一个请求转发或者重定向不需要加return)，如下：

@Override
protected void doGet(final HttpServletRequest req, final HttpServletResponse resp)
        throws ServletException, IOException {
    if (req.getSession().getAttribute(AttrConsts.LOGIN_USER) == null) {
        req.getRequestDispatcher(PathConsts.PATH_PREFIX + PathConsts.LOGIN_PAGE).forward(req, resp);
        return;
    }
    req.getRequestDispatcher(PathConsts.PATH_PREFIX + PathConsts.MAIN_PAGE).forward(req, resp);
}