web.xml配置详解之filter

转自 http://blog.csdn.net/liaoxiaohua1981/article/details/6761053、

　　

<pre class="html" name="code" style="display: none;"><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></pre><br>
<pre></pre>
<pre></pre>

　　

 

 

• 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

• <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;
  
  /**
   * @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。