servlet系列之IllegalStateException

「爱情、让人受尽委屈。」 2021-09-30 06:36 147阅读 0赞

IllegalStateException在java web开发中比较常见，**IllegalStateException的根本原因是java servlet在提交响应后，还尝试写内容**。

所以避免IllegalStateException的一个好方法就是提交响应，比如forward或者redirect之后，就不要再写内容，一个方法是在redirect之后加上return;

比如这个比较常见的IllegalStateException，原因就是已经sendRedirect，提交响应了，然后还尝试写内容，这样就导致了IllegalStateException

Java.lang.IllegalStateException: Cannot call sendRedirect() after the response has been committed

下面给出会异常的代码：

public class LoginFilter extends OncePerRequestFilter{
       ...
    	@Override
    	protected void doFilterInternal(final HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
    			throws ServletException, IOException {
    		HttpServletRequest wrappedRequest = new RemoteUserRequestWrapper(request);
    		if (StringUtils.isEmpty(wrappedRequest.getRemoteUser()) ) {
    			response.sendRedirect("login.do");
    			//return;
    		}
    		filterChain.doFilter(new RemoteUserRequestWrapper(request), response);
    	}
    }

这段代码response.sendRedirect之后，跳到 login.do，login.do里的代码逻辑是有再次重定向等等逻辑的，然后Filter里代码，没return，执行后是会IllegalStateException的

然后只要在sendRedirect之后加上return就可以：

public class LoginFilter extends OncePerRequestFilter{
       ...
    	@Override
    	protected void doFilterInternal(final HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
    			throws ServletException, IOException {
    		HttpServletRequest wrappedRequest = new RemoteUserRequestWrapper(request);
    		if (StringUtils.isEmpty(wrappedRequest.getRemoteUser()) ) {
    			response.sendRedirect("login.do");
    			return;
    		}
    		filterChain.doFilter(new RemoteUserRequestWrapper(request), response);
    	}
    }