Filter(五)FilterChain执行顺序

当使用多个Filter时，这些Filter将形成一个Filter链，web服务器在实例化Filter对象时，会将此Filter链传递给doFilter的FilterChain参数。当一个Filter执行doFilter方法时，在此方法中执行FilterChain参数的doFilter方法，将会执行下一个Filter(Filter链下一个还是Filter时)或者访问WEB资源(Filter链中没有Filter了),如图所示:

下面是在web.xml中配置多个Filter,通过程序来演示各个Filter的其执行先后顺序。

<filter>  <filter-name>FilterUtils</filter-name>  <filter-class>cn.itcast.utils.FilterUtils</filter-class>    </filter>  <filter-mapping>  <filter-name>FilterUtils</filter-name>  <url-pattern>/*</url-pattern>  <dispatcher>REQUEST</dispatcher>  </filter-mapping>    <filter>  <filter-name>EncodeFilter</filter-name>  <filter-class>cn.itcast.utils.EncodeFilter</filter-class>  <init-param>  <param-name>encoding</param-name>  <param-value>UTF-8</param-value>  </init-param>    </filter>  <filter-mapping>  <filter-name>EncodeFilter</filter-name>  <url-pattern>/*</url-pattern>  <dispatcher>REQUEST</dispatcher>  </filter-mapping>    <filter>  <filter-name>FilterJsp</filter-name>  <filter-class>cn.itcast.utils.FilterJsp</filter-class>    </filter>  <filter-mapping>  <filter-name>FilterJsp</filter-name>  <url-pattern>/*</url-pattern>  <dispatcher>REQUEST</dispatcher>  </filter-mapping>

三个Filter

public class FilterUtils implements Filter {@Overridepublic void destroy() {// TODO Auto-generated method stubSystem.out.println("FilterUtils destory....");}@Overridepublic void doFilter(ServletRequest req, ServletResponse resp,FilterChain chain) throws IOException, ServletException {System.out.println("FilterUtils start....");chain.doFilter(req, resp);System.out.println("FilterUtils end....");}@Overridepublic void init(FilterConfig config) throws ServletException {System.out.println("FilterUtils init....");}}

public class EncodeFilter implements Filter {private String encode;@Overridepublic void destroy() {// TODO Auto-generated method stubSystem.out.println("EncodeFilter destroy....");}@Overridepublic void doFilter(ServletRequest req, ServletResponse resp,FilterChain chain) throws IOException, ServletException {// TODO Auto-generated method stub//req.setCharacterEncoding(encode);//resp.setCharacterEncoding(encode);//resp.setContentType("text/html;charset="+encode+"");//chain.doFilter(req, resp);System.out.println("EncodeFilter start....");chain.doFilter(req, resp);System.out.println("EncodeFilter end....");}@Overridepublic void init(FilterConfig filterConfig) throws ServletException {// TODO Auto-generated method stub//encode = filterConfig.getInitParameter("encoding");System.out.println("EncodeFilter init....");}}

public class FilterJsp implements Filter {@Overridepublic void destroy() {// TODO Auto-generated method stubSystem.out.println("FilterJSP destory....");}@Overridepublic void doFilter(ServletRequest req, ServletResponse resp,FilterChain chain) throws IOException, ServletException {// TODO Auto-generated method stub//System.out.println("do Filter....");//req.setCharacterEncoding("UTF-8");//resp.setCharacterEncoding("UTF-8");//resp.setContentType("text/html;charset=UTF-8");//chain.doFilter(req, resp);System.out.println("FilterJsp start....");chain.doFilter(req, resp);System.out.println("FilterJsp end....");}@Overridepublic void init(FilterConfig config) throws ServletException {// TODO Auto-generated method stub//System.out.println("init....");//System.out.println("Filter Name is:"+config.getFilterName());//Enumeration enumation = config.getInitParameterNames();//String name;//while(enumation.hasMoreElements()){//name = (String) enumation.nextElement();//System.out.println("name is:"+name);//System.out.println("value is:"+config.getInitParameter(name));//}System.out.println("FilterJsp init....");}}

//初始化结果:

FilterUtils init....EncodeFilter init....FilterJsp init....

//访问WEB资源时的结果

FilterUtils start....EncodeFilter start....FilterJsp start....你好中国FilterJsp end....EncodeFilter end....FilterUtils end....

//web服务器关闭时结果:

FilterUtils destory....EncodeFilter destroy....FilterJSP destory....