filter中流未关闭引发的问题getWriter() has already been called for this response-蒲公英云

filter中流未关闭引发的问题getWriter() has already been called for this response

た入场券 2021-12-22 20:45 502阅读 0赞

【引言】

在上一篇博客中，写了Spring MVC和Spring Boot框架中如何实现自定义filter，文章结尾提到了filter中遇到的问题，如下：

IllegalStateException: getWriter() has already been called for this response

【问题代码】

public class LoginFilter implements Filter{
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
    }
    @Override
    public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws IOException, ServletException {
        ...
        PrintWriter out = null;
        ...
        out = resp.getWriter();
        //判断是否已经登录，没登录返回登录url
        if(user.notLogin()){
            ReturnMsg msg = new ReturnMsg();
            msg.setCode("111111");
            msg.setMessage("用户未登录");
            out.writer(JSON.toJSONString(msg));
            out.close();
            return;
        }
        ...
        chain.dofilter(req,resp);
    }
    @Override
    public void destroy() {
    }
}

【问题原因】

在上面的代码中，可以发现，只有当进入未登录的逻辑才会将流关闭，而如果登录之后，再次进入这个filter，就会出现以上异常。所以将代码修改了一版，如下：

public class LoginFilter implements Filter{
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
    }
    @Override
    public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws IOException, ServletException {
        ...
        PrintWriter out = null;
        ...
        try {
            //判断是否已经登录，没登录返回登录url
            if(user.notLogin()){
                ReturnMsg msg = new ReturnMsg();
                msg.setCode();
                msg.setMessage();
                out = resp.getWriter();
                out.writer(JSON.toJSONString(msg));
                out.close();
                return;
            }
        } finally {
            if(out!=null){
                out.flush();
                out.close();
            }
        }
        ...
        chain.dofilter(req,resp);
    }
    @Override
    public void destroy() {
    }
}