- 定義
<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>
- 作用
用於指定WEB容器的過濾器,在請求和響應對象在Servlet處理之前和之後,可以通過此過濾器對這兩個對象進行處理。
- 備註
filter-class 中指定的過濾器類須繼承 javax.servlet.Filter 具有須有以下三種方法
init(FilterConfig filterConfig):初始化;一般情況下時讀取配置文件中的init-param參數值 如 filterConfig.getInitParameter("encoding")
doFilter(...):用於對request,response進行處理,並能過chain.doFilter(...) 交過下一個控制器
destroy():資源銷燬
- 示例:如編碼過濾器
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>
Java 代碼/** * */ 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 { /** * 配置中默認的字符編碼 */ protected String encoding = null; protected FilterConfig filterConfig; /** * 當沒有指定默認編碼時是否允許跳過過濾 */ 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); } } //將控制器傳向下一個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應用啓動就會調用,doFilter則是在訪問filter-mapping映射到的url時會調用。