轉自:http://blog.csdn.net/liaoxiaohua1981/article/details/6761053
- 定義
- <pre class="html" name="code"><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。