代碼：

package FirstFilter;

import java.io.IOException;

import javax.servlet.Filter;

import javax.servlet.FilterChain;

import javax.servlet.FilterConfig;

import javax.servlet.ServletException;

import javax.servlet.ServletRequest;

import javax.servlet.ServletResponse;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

/*

?* ?導(dǎo)入的jar包是javax.servlet.*;

?* ?step:1-----

?* ?在web.xml文件中配置，實例化一個Filter實例

*/

public class firstFilter implements Filter{

? ?//step:4

public void destroy() {

// TODO Auto-generated method stub

System.out.println("服務(wù)器關(guān)閉，銷毀Filter ?執(zhí)行destory方法");

}

? ? //step:3

public void doFilter(ServletRequest arg0, ServletResponse arg1,

FilterChain arg2) throws IOException, ServletException {

System.out.println("開始運行doFilter--");

//重定向

HttpServletResponse response=(HttpServletResponse) arg1;

response.sendRedirect("index.jsp");?

// HttpServletRequest request = (HttpServletRequest) arg0; ?

// ? ?request.getRequestDispatcher("index.jsp").forward(arg0, arg1); ?

arg2.doFilter(arg0, arg1);

System.out.println("結(jié)束運行doFilter--");

}

? ?// step:2

public void init(FilterConfig arg0) throws ServletException {

// TODO Auto-generated method stub

System.out.println("Filter初始化方法:init()");

}

}

配置文件：

<filter>

? ? ? <filter-name>Filter</filter-name>

? ? ? ?<filter-class>FirstFilter.firstFilter</filter-class>

? ? ??

? ? ? ? ?</filter>

??

? <filter-mapping>

? ?<filter-name>Filter</filter-name>

? ?<url-pattern>/index.jsp</url-pattern>

? ? <dispatcher>REQUEST</dispatcher> ?

? </filter-mapping>

</web-app>

錯誤提示：

type?Exception report

message?javax.servlet.ServletException: java.lang.IllegalStateException: Cannot create a session after the response has been committed

description?The server encountered an internal error that prevented it from fulfilling this request.

exception

org.apache.jasper.JasperException: javax.servlet.ServletException: java.lang.IllegalStateException: Cannot create a session after the response has been committed
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:549)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:455)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
FirstFilter.firstFilter.doFilter(firstFilter.java:35)

root cause

javax.servlet.ServletException: java.lang.IllegalStateException: Cannot create a session after the response has been committed
org.apache.jsp.index_jsp._jspService(index_jsp.java:99)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
FirstFilter.firstFilter.doFilter(firstFilter.java:35)

root cause

java.lang.IllegalStateException: Cannot create a session after the response has been committed
org.apache.catalina.connector.Request.doGetSession(Request.java:2886)
org.apache.catalina.connector.Request.getSession(Request.java:2316)
org.apache.catalina.connector.RequestFacade.getSession(RequestFacade.java:898)
org.apache.catalina.connector.RequestFacade.getSession(RequestFacade.java:910)
org.apache.jasper.runtime.PageContextImpl._initialize(PageContextImpl.java:146)
org.apache.jasper.runtime.PageContextImpl.initialize(PageContextImpl.java:125)
org.apache.jasper.runtime.JspFactoryImpl.internalGetPageContext(JspFactoryImpl.java:112)
org.apache.jasper.runtime.JspFactoryImpl.getPageContext(JspFactoryImpl.java:65)
org.apache.jsp.index_jsp._jspService(index_jsp.java:54)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
FirstFilter.firstFilter.doFilter(firstFilter.java:35)

note?The full stack trace of the root cause is available in the Apache Tomcat/7.0.42 logs.