web.xml配置详解之filter

一.定义

<filter>
	<filter-name>encodingfilter</filter-name>
	<filter-class>com.my.app.EncodingFilter</filter-class>
	<init-param>
		<param-name>encoding</param-name>
		<param-value>UTF-8</param-value>
	</init-param>
</filter>
<filter-mapping>
	<filter-name>encodingfilter</filter-name>
	<url-pattern>/*</url-pattern>
</filter-mapping>

 

二.作用
        用于指定WEB容器的过滤器，在请求和响应对象在Servlet处理之前和之后，可以通过此过滤器对这两个对象进行处理。

 

三.备注
        filter-class 中指定的过滤器类须继承 javax.servlet.Filter 具有须有以下三种方法
        init(FilterConfig filterConfig)：初始化;一般情况下时读取配置文件中的init-param参数值 如 filterConfig.getInitParameter("encoding")
        doFilter(...)：用于对request,response进行处理，并能过chain.doFilter(...) 交过下一个控制器
        destroy()：资源销毁

 

四.示例：如编码过滤器
        web.xml配置

<filter>
	<filter-name>encodingfilter</filter-name>
	<filter-class>com.my.app.EncodingFilter</filter-class>
	<init-param>
		<param-name>encoding</param-name>
		<param-value>UTF-8</param-value>
	</init-param>
</filter>
<filter-mapping>
	<filter-name>encodingfilter</filter-name>
	<url-pattern>/*</url-pattern>
</filter-mapping>

 

package com.myapp;  
  
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;  
  
/** 
 * 
 */  
public class EncodingFilter implements Filter {  
  
    /** 
     * 配置中默认的字符编码 
     */  
    protected String encoding = null;    
    protected FilterConfig filterConfig;  
    /** 
     * 当没有指定默认编码时是否允许跳过过滤 
     */  
    protected boolean ignore = true;   
    /** 
     *  
     */  
    public EncodingFilter() {  
        // TODO Auto-generated constructor stub   
    }  
  
    /* (non-Javadoc) 
     * @see javax.servlet.Filter#destroy() 
     */  
    public void destroy() {  
        // TODO Auto-generated method stub   
        this.encoding=null;  
        this.filterConfig=null;  
    }  
      
    /* (non-Javadoc) 
     * @see javax.servlet.Filter#doFilter(javax.servlet.ServletRequest, javax.servlet.ServletResponse, javax.servlet.FilterChain) 
     */  
    public void doFilter(ServletRequest request, ServletResponse response,  
            FilterChain chain) throws IOException, ServletException {  
        // TODO Auto-generated method stub   
        HttpServletRequest hRequest=(HttpServletRequest)request;  
        HttpServletResponse hResponse=(HttpServletResponse)response;  
        //Conditionally select and set the character encoding to be used     
        if(ignore || hRequest.getCharacterEncoding()==null){  
            String coding=selectEncoding(hRequest);  
            if(coding!=null){  
                hRequest.setCharacterEncoding(coding);  
                hResponse.setCharacterEncoding(coding);  
            }  
        }  
        //将控制器传向下一个filter   
        chain.doFilter(hRequest, hResponse);  
  
    }  
  
    /* (non-Javadoc) 
     * @see javax.servlet.Filter#init(javax.servlet.FilterConfig) 
     */  
    public void init(FilterConfig filterConfig) throws ServletException {  
        // TODO Auto-generated method stub   
        this.filterConfig=filterConfig;  
        this.encoding=filterConfig.getInitParameter("encoding");  
        System.out.println(this.encoding);  
        String value = filterConfig.getInitParameter("ignore");  
        if (value == null) {  
            this.ignore = true;  
        } else if (value.equalsIgnoreCase("true")) {  
            this.ignore = true;  
        } else if (value.equalsIgnoreCase("yes")) {  
            this.ignore = true;  
        } else {  
            this.ignore = false;  
        }  
    }  
    protected String selectEncoding(ServletRequest request) {  
        return (this.encoding);  
    }
}

        init方法是在WEB应用启动就会调用,doFilter则是在访问filter-mapping映射到的url时会调用。

 

文章来源：http://blog.csdn.net/liaoxiaohua1981/article/details/6761053