在过滤器中重定向时停止进一步处理

【问题标题】：Stop further processing when redirecting in a filter在过滤器中重定向时停止进一步处理
【发布时间】：2012-01-16 18:28:33
【问题描述】：

我有 URLRewirteFilter，它检查请求的域是否以 www 开头。并重定向到无 www url。当请求被重定向时，如何停止进一步处理（调用 JSF 应用程序、调用 servlet 等）？到目前为止，我有这个：

    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
    HttpServletRequest req = (HttpServletRequest) request;
    String sn = req.getServerName().toLowerCase();
    if (sn.startsWith("www.")) {
        String url = "http://" + getDefaultDomain() + req.getContextPath() + req.getRequestURI();
        HttpServletResponse resp = (HttpServletResponse) response;
        resp.reset();
        resp.setStatus(HttpServletResponse.SC_MOVED_PERMANENTLY);
        resp.setHeader("Location", url);
    }
    chain.doFilter(request, response);
}

【问题讨论】：

标签： java servlet-filters

【解决方案1】：

只需将return 语句添加到if 的末尾

if (sn.startsWith("www.")) {
    String url = "http://" + getDefaultDomain() + req.getContextPath() + req.getRequestURI();
    HttpServletResponse resp = (HttpServletResponse) response;
    resp.reset();
    resp.setStatus(HttpServletResponse.SC_MOVED_PERMANENTLY);
    resp.setHeader("Location", url);
    return;
}
chain.doFilter(request, response);

或添加else

if (sn.startsWith("www.")) {
    String url = "http://" + getDefaultDomain() + req.getContextPath() + req.getRequestURI();
    HttpServletResponse resp = (HttpServletResponse) response;
    resp.reset();
    resp.setStatus(HttpServletResponse.SC_MOVED_PERMANENTLY);
    resp.setHeader("Location", url);
} else {
    chain.doFilter(request, response);
}

另见：

java.lang.IllegalStateException: Cannot (forward | sendRedirect | create session) after response has been committed

【讨论】：

基本不要打电话chain.doFilter