web项目中的过滤器及其XML配置

过滤器Filter就像一个一个哨卡，用户的请求需要经过Filter
并且可以有多个过滤器
 
过滤器实现自动转换编码
过滤器实体：

package top.yibobo.web.filter;
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{
	private String encoder;
	@Override
	public void doFilter(ServletRequest arg0, ServletResponse arg1, FilterChain arg2)
			throws IOException, ServletException {
		HttpServletRequest req=(HttpServletRequest)arg0;
		//设置请求对象的字符集
		req.setCharacterEncoding(encoder);
		HttpServletResponse resp = (HttpServletResponse)arg1;
		resp.setContentType("text/html;charset="+encoder);
		arg2.doFilter(req, resp);
		System.out.println("完成字符集"+encoder+"转换");
	}
	@Override
	public void init(FilterConfig filterConfig) throws ServletException {
		this.encoder=filterConfig.getInitParameter("encoder");
	}
}

 
XML文件的配置

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
  <display-name>jsp10</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  	<!-- 部署字符集转换过滤器 -->
  	<filter>
  		<filter-name>encodingFilter</filter-name>
  		<filter-class>top.yibobo.web.filter.EncodingFilter</filter-class>
  		<!-- 参数 -->
  		<init-param>
  			<param-name>encoder</param-name>
  			<param-value>UTF-8</param-value>
  		</init-param>
  	</filter>
  	<!-- 过滤器拦截哪些URL -->
  	<filter-mapping>
  		<filter-name>encodingFilter</filter-name>
  		<url-pattern>/*</url-pattern>
  	</filter-mapping>
</web-app>

/*代表的是过滤当前项目所有的页面。即每个页面都会经过过滤器，所以再也不用设置request和response的编码了
并且想要改成什么字符集编码，只需要在XML里面改一下就行，不需要动代码