JavaWeb 使用Filter实现统一全站编码（教材学习笔记）

1、编写form.jsp页面

在web-chapter08的WebContent目录中，编写一个form.jsp页面，该页面用于提交用户登陆的表单信息，代码如下：

<%@ page language="java" contentType="text/html; charset=utf-8"
	pageEncoding="utf-8" import="java.util.*"%>
<!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">
</head>
<center>
	<h3>用户登录</h3>
</center>
<body style="text-align: center;">
	<a href="<%=request.getContextPath()%>/CharacterServlet?name=传智播客&password=123456">单击超链接登录</a>
	<form action="<%=request.getContextPath()%>/CharacterServlet"
		method="post">
		<table border="1" width="600px" cellpadding="0" cellspacing="0"
			align="center">
			<tr>
				<td height="30" align="center">用户名：</td>
				<td>&nbsp;<input type="text" name="name" />
				</td>
			</tr>
			<tr>
				<td height="30" align="center">密 &nbsp; 码：</td>
				<td>&nbsp;<input type="password" name="password" />
				</td>
			</tr>
			<tr>
				<td height="30" colspan="2" align="center">
				<input type="submit" value="登录" />
				 &nbsp;&nbsp;&nbsp;&nbsp;
				<input type="reset" value="重置" />
			    </td>
			</tr>
		</table>
	</form>
</body>

2、创建servlet

创建一个名为CharacterServlet类，该类用于获取用户输入的请求参数，并将参数发送到控制台

代码如下：

package cn.itcast.chapter08.filter;
import java.io.IOException;
import javax.servlet.*;
import javax.servlet.http.*;
public class CharacterServlet extends HttpServlet {
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		System.out.println(request.getParameter("name"));
		System.out.println(request.getParameter("password"));
	}
	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		doGet(request, response);
	}
}

3、创建过滤器

创建一个名为CharacterFilter类，该类用于拦截用户的请求访问，实现统一全站编码，只是针对请求的方式不同，解决乱码的方式也不相同，代码如下：

package cn.itcast.chapter08.filter;
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class CharacterFilter implements Filter {
	public void init(FilterConfig filterConfig) throws ServletException {
	}
	public void doFilter(ServletRequest req, ServletResponse resp,
			FilterChain chain) throws IOException, ServletException {
		HttpServletRequest request = (HttpServletRequest) req;
		HttpServletResponse response = (HttpServletResponse) resp;
		// 拦截所有的请求 解决全站中文乱码
		// 指定 request 和 response 的编码
		request.setCharacterEncoding("utf-8"); // 只对消息体有效
		response.setContentType("text/html;charset=utf-8");
		// 对request进行包装
		CharacterRequest characterRequest = new CharacterRequest(request);
		chain.doFilter(characterRequest, response);
	}
	public void destroy() {
	}
}
// 继承 默认包装类HttpServletRequestWrapper
class CharacterRequest extends HttpServletRequestWrapper {
	private HttpServletRequest request;
	public CharacterRequest(HttpServletRequest request) {
		super(request);
		this.request = request;
	}
	// 子类继承父类一定会覆写一些方法，此处用于重写getParamter()方法
	public String getParameter(String name) {
		// 调用被包装对象的getParameter()方法，获得请求参数
		String value = super.getParameter(name);
		if (value == null)
			return null;
		// 判断请求方式
		String method = super.getMethod();
		if ("get".equalsIgnoreCase(method)) {
			try {
					value = new String(value.getBytes("iso-8859-1"), "utf-8");
			} catch (UnsupportedEncodingException e) {
				throw new RuntimeException(e);
			}
		}
		// 解决乱码后返回结果
		return value;
	}
}

4、配置映射信息

在web.xml中配置CharacterFilter以及CharacterServlet的映射信息

代码如下：

<servlet>
		<description></description>
		<display-name>CharacterServlet</display-name>
		<servlet-name>CharacterServlet</servlet-name>
		<servlet-class>cn.itcast.chapter08.filter.CharacterServlet</servlet-class>
	</servlet>
	<servlet-mapping>
		<servlet-name>CharacterServlet</servlet-name>
		<url-pattern>/CharacterServlet</url-pattern>
	</servlet-mapping>
	<filter>
		<filter-name>CharacterFilter</filter-name>
		<filter-class>cn.itcast.chapter08.filter.CharacterFilter</filter-class>
	</filter>
	<filter-mapping>
		<filter-name>CharacterFilter</filter-name>
		<url-pattern>/*</url-pattern>
	</filter-mapping>

5、启动tomcat，进行测试

在网址栏输入http://localhost:8080/web-chapter08/form.jsp，结果如下：

点击登录后，控制台输出了用户名以及密码，将form.jsp的表单提交方式改为get之后再次点击登录，观察就会发现控制台输出的用户名和密码与刚刚使用post方式提交的表单是一致的，说明过滤器Filter起作用了