web.xml配置详解之filter

 

• 定义

encodingfilter
com.my.app.EncodingFilter

encoding
UTF-8



encodingfilter
/*

• 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。

• 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

• 示例：如编码过滤器

web.xml配置

encodingfilter
com.my.app.EncodingFilter

encoding
UTF-8



encodingfilter
/*

Java 代码

/**
 * 
 */
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;

/**
 * @author louisliao
 *
 */
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。