java中的过滤器 --Filter_过滤器里写构造函数java-优快云博客

本文深入探讨了Java中用于处理中文乱码问题的字符编码过滤器。通过实现Filter接口，自定义过滤器类，该过滤器可在Web应用中统一设置字符编码，确保数据正确解析，避免乱码出现。文章提供了完整的代码示例和web.xml配置说明。

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java中的过滤器 --Filter

package 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;

/*
 * 字符编码过滤器
*/
public class Encodingfilter implements Filter {
    //定义属性保存字符编码集
        String encoding;
        
    //构造函数
    public Encodingfilter() {
        System.out.println("过滤器构造函数！");
    }
    //销毁的方法
    public void destroy() {
        System.out.println("过滤器销毁！");
    }
    //过滤的方法
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        System.out.println("过滤器开始过滤！");
        
        //中文乱码处理
        response.setContentType("text/html;charset="+encoding);
        response.setCharacterEncoding(encoding);
        request.setCharacterEncoding(encoding);
        
        //chain对象就是过滤器链对象
        //chain对象的doFilter方法令请求往下一个过滤器传递
        chain.doFilter(request, response);
    }

    //初始化的方法
    public void init(FilterConfig fConfig) throws ServletException {
        System.out.println("过滤器初始化！");
        
        //从配置文件中读取字符编码集
        encoding = fConfig.getInitParameter("encoding");
    }

}

package 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;

/*
 * 字符编码过滤器
*/
public class Encodingfilter implements Filter {
    //定义属性保存字符编码集
        String encoding;
        
    //构造函数
    public Encodingfilter() {
        System.out.println("过滤器构造函数！");
    }
    //销毁的方法
    public void destroy() {
        System.out.println("过滤器销毁！");
    }
    //过滤的方法
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        System.out.println("过滤器开始过滤！");
        
        //中文乱码处理
        response.setContentType("text/html;charset="+encoding);
        response.setCharacterEncoding(encoding);
        request.setCharacterEncoding(encoding);
        
        //chain对象就是过滤器链对象
        //chain对象的doFilter方法令请求往下一个过滤器传递
        chain.doFilter(request, response);
    }

    //初始化的方法
    public void init(FilterConfig fConfig) throws ServletException {
        System.out.println("过滤器初始化！");
        
        //从配置文件中读取字符编码集
        encoding = fConfig.getInitParameter("encoding");
    }

}

xml配置：

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
  <display-name>ch03</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>


  <context-param>
    <param-name>userName</param-name>
    <param-value>sa</param-value>
  </context-param>
  <context-param>
    <param-name>pwd</param-name>
    <param-value>888</param-value>
  </context-param>
  
  <!--过滤器-->
  <filter>
    <display-name>Encodingfilter</display-name>
    <filter-name>Encodingfilter</filter-name>
    <filter-class>filter.Encodingfilter</filter-class>
    <!--初始化-->
    <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>  <!--/*代表所有-->
  </filter-mapping>
  
</web-app>