关于Filter中的两个异常，重定向后要加Return

这是个很常见的问题，度娘和谷歌动手就能查到，可是今天还是遇到了，因为一直做业务研发，没有直接关注这些细节。

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这两个异常如下：

java.lang.IllegalStateException: Cannot forward after response has been committed
	at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:313)
	at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:301)
	at com.servlet.MyServlet2.doGet(MyServlet2.java:22)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:690)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
	at com.filter.MyFilter.doFilter(MyFilter.java:48)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:228)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:104)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:216)
	at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
	at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:634)
	at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:445)
	at java.lang.Thread.run(Unknown Source)

 

java.lang.IllegalStateException
	at org.apache.catalina.connector.ResponseFacade.sendError(ResponseFacade.java:407)
	at org.apache.catalina.servlets.DefaultServlet.serveResource(DefaultServlet.java:662)
	at org.apache.catalina.servlets.DefaultServlet.doGet(DefaultServlet.java:325)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:690)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
	at com.filter.MyFilter.doFilter(MyFilter.java:48)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:228)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:104)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:216)
	at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
	at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:634)
	at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:445)
	at java.lang.Thread.run(Unknown Source)

 

只要在重定向后加return就可以了。

public void doFilter(ServletRequest request, ServletResponse response,
		FilterChain chain) throws IOException, ServletException {
	request.setCharacterEncoding("UTF-8");
	response.setCharacterEncoding("UTF-8");		
	HttpServletRequest hrequest = (HttpServletRequest)request;
	String path = hrequest.getContextPath();
	String basePath = hrequest.getScheme()+"://"+hrequest.getServerName()+":"+hrequest.getServerPort()+path+"/";
	// 获得请求的全路径
	String reUrl = hrequest.getRequestURL().toString();
	// 是否包含参数
	int index = reUrl.indexOf("?");
	String re = "";
	if(index == -1){
		re = reUrl.substring(basePath.length());
	}else{
		re = reUrl.substring(basePath.length(), index);
	}
	// 是否是请求资源
	if(!isResource(re)){
		// 是否有访问的权限
		boolean isCheck = ConnUril.checkUrl(re);
		if(!isCheck){
			request.getRequestDispatcher("/error.jsp").forward(request,response);
			// 必须加返回，否则报错
			return ;
		}
	}
	// 继续执行
	chain.doFilter(request, response);
}

 

报错原因很简单，转向后再去执行关于response的操作，就等于执行了两遍转向，因此会报错！

 

问题简单，也需要留意，再简单的问题也是问题，成功在细节和那些别人以为是傻冒的问题中。

 

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