5.2Demo 使用包装者模式解决全局乱码

1.总结Filter的作用？

公共代码的提取
可以对request和response中的方法进行增强(装饰者模式/动态代理)
进行权限控制

2.对方法进行增强 1.继承 2.装饰者模式 3.动态代理

3.页面代码

<%@ 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>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
	<!-- 1.写表单控件 -->
	<form action="/web24filter/encodingServlet" method="get">
		<input type="text" name="username" >
		<input type="submit" value="提交">
	</form>
</body>
</html>

4.filter

package com.xiaowei.web.zhuanma;

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

//2.实现接口
public class EncodingFilter implements Filter {

	// 3.重写接口方法 在web.xml文件中配置
	public void doFilter(ServletRequest request, ServletResponse response,
			FilterChain chain) throws IOException, ServletException {
		/*
		 * 装饰者模式(包装)
		 * 
		 * 1、增强类与被增强的类要实现统一接口 2、在增强类中传入被增强的类 3、需要增强的方法重写 不需要增强的方法调用被增强对象的
		 */
		// 4.被增强的对象
		HttpServletRequest req = (HttpServletRequest) request;

		// 5.创建增强的对象
		EnhanceRequest enhanceReq = new EnhanceRequest(req);

		// 9.放行
		chain.doFilter(enhanceReq, response);

	}

	public void destroy() {
	}

	public void init(FilterConfig filterConfig) throws ServletException {
	}

}

// 6.创建增强的类 通过查看源码 继承他实际上就相当于实现了相同的接口
// public class HttpServletRequestWrapper extends ServletRequestWrapper
// implements
// HttpServletRequest
class EnhanceRequest extends HttpServletRequestWrapper {
	
	private HttpServletRequest request;

	// 7.构造方法
	// 7.通过写构造方法 实现在增强类中传入被增强的类
	public EnhanceRequest(HttpServletRequest request) {
		super(request);
		this.request = request;
	}

	// 8.重写增强的方法
	// 8.对getParamer()方法进行增强
	public String getParameter(String name) {
		String parameter = request.getParameter(name);// 这获得的是乱码
		String str = null;
		try {
			str = new String(parameter.getBytes("iso8859-1"), "UTF-8");
		} catch (UnsupportedEncodingException e) {
			e.printStackTrace();
		}
		return str;
	}
}

5.测试类

package com.xiaowei.web.zhuanma;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class EncodingServlet extends HttpServlet {

	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		String parameter = request.getParameter("username");
		System.out.println(parameter);
	}

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

5.2Demo 使用包装者模式解决全局乱码

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