if (needExclude) {
    log.debug("拦截......");
    if (session.getAttribute("sysUser") == null) {
        log.debug("未登录...");
        try {
            response.sendRedirect("/index");
            //target = "/index";
        } catch (Exception e) {
            e.printStackTrace();
        }
    }else {
        log.debug("登陆放行......");
    }
}
log.debug("下一个handler......");
next.handle(target, request, response, isHandled);

上面代码 会报错

2016-11-04 15:01:59
 [] [] [DEBUG]-[Thread: qtp2112978551-22]-[com.lt.handler.PermissionHandler.handle()]: target:/ser/2231

2016-11-04 15:01:59
 [] [] [DEBUG]-[Thread: qtp2112978551-22]-[com.lt.handler.PermissionHandler.handle()]: 拦截......

2016-11-04 15:01:59
 [] [] [DEBUG]-[Thread: qtp2112978551-22]-[com.lt.handler.PermissionHandler.handle()]: 未登录...

2016-11-04 15:01:59
 [] [] [DEBUG]-[Thread: qtp2112978551-22]-[com.lt.handler.PermissionHandler.handle()]: 下一个handler......

JFinal action report -------- 2016-11-04 15:01:59 ------------------------------
Controller  : com.lt.controller.SerController.(SerController.java:1)
Method      : Ser2231
Interceptor : com.lt.Interceptor.ExceptionInterceptor.(ExceptionInterceptor.java:1)
--------------------------------------------------------------------------------

2016-11-04 15:01:59
 [] [] [ERROR]-[Thread: qtp2112978551-22]-[com.jfinal.core.ActionHandler.handle()]: /ser/2231
com.jfinal.render.RenderException: java.lang.IllegalStateException: Committed
	at com.jfinal.render.JspRender.render(JspRender.java:69)
	at com.jfinal.core.ActionHandler.handle(ActionHandler.java:97)
	at com.lt.handler.PermissionHandler.handle(PermissionHandler.java:55)
	at com.jfinal.ext.handler.ContextPathHandler.handle(ContextPathHandler.java:47)
	at com.jfinal.core.JFinalFilter.doFilter(JFinalFilter.java:72)
	at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1307)
	at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:453)
	at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:137)
	at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:560)
	at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:231)
	at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1072)
	at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:382)
	at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:193)
	at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1006)
	at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:135)
	at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:116)
	at org.eclipse.jetty.server.Server.handle(Server.java:365)
	at org.eclipse.jetty.server.AbstractHttpConnection.handleRequest(AbstractHttpConnection.java:485)
	at org.eclipse.jetty.server.AbstractHttpConnection.headerComplete(AbstractHttpConnection.java:926)
	at org.eclipse.jetty.server.AbstractHttpConnection$RequestHandler.headerComplete(AbstractHttpConnection.java:988)
	at org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:635)
	at org.eclipse.jetty.http.HttpParser.parseAvailable(HttpParser.java:235)
	at org.eclipse.jetty.server.AsyncHttpConnection.handle(AsyncHttpConnection.java:82)
	at org.eclipse.jetty.io.nio.SelectChannelEndPoint.handle(SelectChannelEndPoint.java:628)
	at org.eclipse.jetty.io.nio.SelectChannelEndPoint$1.run(SelectChannelEndPoint.java:52)
	at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:608)
	at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:543)
	at java.lang.Thread.run(Thread.java:662)
Caused by: java.lang.IllegalStateException: Committed
	at org.eclipse.jetty.server.Response.resetBuffer(Response.java:1136)
	at org.eclipse.jetty.server.Dispatcher.forward(Dispatcher.java:204)
	at org.eclipse.jetty.server.Dispatcher.forward(Dispatcher.java:103)
	at com.jfinal.render.JspRender.render(JspRender.java:67)
	... 27 more

没有重定向，不知道为什么，程序继续执行。

在重定向下面加上return；还是会报错

2016-11-04 15:07:30
 [] [] [DEBUG]-[Thread: qtp2112978551-22]-[com.lt.handler.PermissionHandler.handle()]: target:/ser/2231

2016-11-04 15:07:30
 [] [] [DEBUG]-[Thread: qtp2112978551-22]-[com.lt.handler.PermissionHandler.handle()]: 拦截......

2016-11-04 15:07:30
 [] [] [DEBUG]-[Thread: qtp2112978551-22]-[com.lt.handler.PermissionHandler.handle()]: 未登录...
2016-11-04 15:07:30.718:WARN:oejs.Response:Committed before 404 null
2016-11-04 15:07:30.718:WARN:oejs.ServletHandler:/lt/ser/2231
java.lang.IllegalStateException: Committed
	at org.eclipse.jetty.server.Response.resetBuffer(Response.java:1136)
	at org.eclipse.jetty.server.Response.sendError(Response.java:314)
	at org.eclipse.jetty.server.Response.sendError(Response.java:416)
	at org.eclipse.jetty.servlet.DefaultServlet.doGet(DefaultServlet.java:486)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:735)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:848)
	at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:669)
	at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1336)
	at com.jfinal.core.JFinalFilter.doFilter(JFinalFilter.java:82)
	at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1307)
	at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:453)
	at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:137)
	at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:560)
	at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:231)
	at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1072)
	at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:382)
	at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:193)
	at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1006)
	at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:135)
	at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:116)
	at org.eclipse.jetty.server.Server.handle(Server.java:365)
	at org.eclipse.jetty.server.AbstractHttpConnection.handleRequest(AbstractHttpConnection.java:485)
	at org.eclipse.jetty.server.AbstractHttpConnection.headerComplete(AbstractHttpConnection.java:926)
	at org.eclipse.jetty.server.AbstractHttpConnection$RequestHandler.headerComplete(AbstractHttpConnection.java:988)
	at org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:635)
	at org.eclipse.jetty.http.HttpParser.parseAvailable(HttpParser.java:235)
	at org.eclipse.jetty.server.AsyncHttpConnection.handle(AsyncHttpConnection.java:82)
	at org.eclipse.jetty.io.nio.SelectChannelEndPoint.handle(SelectChannelEndPoint.java:628)
	at org.eclipse.jetty.io.nio.SelectChannelEndPoint$1.run(SelectChannelEndPoint.java:52)
	at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:608)
	at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:543)
	at java.lang.Thread.run(Thread.java:662)

使用target可以跳转。

以前的帖子说target不能跳转，要用重定向。现在反过来有点懵。。。。