java web过滤器

filter元素和filter-mapping元素
<filter>过滤器元素将一个名字和实现javax.servlet.Filter的接口的类相关联。
 1 新建一个类 Encoding Filter   
package cn.bupt.duming.util;
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;
public class EncodingFilter implements Filter{
private FilterConfig config = null ;

private String targetEncoding = "ASCLL" ;




public void destroy() {
// TODO Auto-generated method stub
config = null ;
this.targetEncoding = null ;


}
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
// TODO Auto-generated method stub

System.out.println("targetEncoding " + this.targetEncoding +"\n");

//执行代码

request.setCharacterEncoding(this.targetEncoding) ;

chain.doFilter(request, response) ;

}
public void init(FilterConfig config) throws ServletException {
// TODO Auto-generated method stub

this.config = config ;

//从配置文件中读取初始化参数（目标编码）

this.targetEncoding = config.getInitParameter("encoding") ;

}

}
2 配置Filter类。在web.xml中配置该filter 
<filter>
<filter-name>EncodingFilter</filter-name>
<filter-class>cn.bupt.duming.util.EncodingFilter</filter-class>
<init-param>
<param-name>encoding</param-name>
<param-value>GB2312</param-value>
</init-param>

</filter>

<filter-mapping>
<filter-name>EncodingFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
3 重新运行该应用
会在控制台打印  targetEncoding GB2312 ， 说明配置成功。