4.3过滤器和监听器——过滤器案例，设置全站统一编码

JAVAWEB学习文章索引点这里
由于接受参数的时候可能有中文字符，所以需要设置字符编码。但是如果所有的页面都进行设置字符编码这样代码的重复量很大。所以我们直接在过滤器中统一进行设置。
首先写一个登录页面：

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title>Insert title here</title>
</head>
<body>
<a href="CharacterServlet?name=张三&password=123">使用GET方式传递参数</a>
<hr/>
使用post方式传递尝试
<form method="post" action="CharacterServlet">
    用户：<input name="name" value="张三"/><br/>
    密码：<input name="password" value="123"/><br/>
    <input type="submit" value="登录"/>
</form>
</body>
</html>

然后写其对应的servlet

package com.servlet;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.test.EncodeTest;

@WebServlet("/CharacterServlet")
public class CharacterServlet extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String name = request.getParameter("name");
        String password = request.getParameter("password");
        response.getWriter().println(name +".."+password);
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

}

对这个servlet进行过滤，不过设置为/*指定为全站过滤

package com.filter;

import java.io.IOException;
import java.io.UnsupportedEncodingException;

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.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;

@WebFilter("/*")
public class CharacterFilter implements Filter {
    public void destroy() {
    }
    public void init(FilterConfig fConfig) throws ServletException {
    }
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        HttpServletRequest request2 = (HttpServletRequest)request;
        request.setCharacterEncoding("utf-8");
        response.setContentType("text/html;charset=utf-8");
        //将request进行包装
        MyRequest myRequest = new MyRequest(request2);
        chain.doFilter(myRequest, response);
    }
}
class MyRequest extends HttpServletRequestWrapper{
    private HttpServletRequest request;
    public MyRequest(HttpServletRequest request) {
        super(request);
        this.request = request;
    }
    //增强getParameter方法
    @Override
    public String getParameter(String name) {
        String value = request.getParameter(name);
        if(value == null) {
            return null;
        }
        //如果已经是utf-8的编码就不在执行下面的代码了
        if("utf-8".equals(EncodeTest.test(value))) {
            return value;
        }
        String method = request.getMethod();
        //判断是不是get方法
        if("GET".equalsIgnoreCase(method)) {
            try {
                value = new String(value.getBytes("iso-8859-1"), "utf-8");
            } catch (UnsupportedEncodingException e) {
                e.printStackTrace();
            }   
        }
        return value;
    }
}
/**
 * 用于测试字符集编码
 * */
class EncodeTest {
    private static String str2;
    public static String test(String str){
        if(str == null)
            return null;
        str2 = str;
        try {
            str2 = new String(str2.getBytes("iso-8859-1"), "iso-8859-1");
            if(str.equals(str2)) {
                return "iso-8859-1";
            }
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
        str2 = str;
        try {
            str2 = new String(str2.getBytes("utf-8"), "utf-8");
            if(str.equals(str2)) {
                return "utf-8";
            }
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
        return null;
    }
}

4.3过滤器和监听器——过滤器案例，设置全站统一编码

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