web.xml配置详解之filter
编程技术 / houtizong 发布于 3年前 75
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
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