过滤器 - 案例学习 - 《Web编程学习笔记》

过滤器配置

这里的第一个案例是修改字符编码的过滤器，但是实际上我编写的这个留言板并没有存在乱码的问题。

index.jsp

<%@ page language="java" contentType="text/html; charset=utf-8"
    pageEncoding="utf-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>系统登录</title>
</head>
<body>
    <form action="login.jsp" method="post">
           <table>
                <tr>
                    <td class="td1">用户名</td>
                    <td><input type="text" class="input1" name="username"></td>
                </tr>
                <tr>
                <td class="td1">密码</td>
                <td><input type="password" class="input1" name="password"></td>
                </tr>
                <tr>
                <td class="td1" colspan="2">
                    <input type="checkbox" name="remember" value="true" checked="checked"> 记住用户名</td>
                </tr>
                <tr>
                    <td colspan="2">
                        <div class="btn-red">
                            <input type="submit" value="登录" id="login-btn">
                        </div>
                    </td>
                </tr>
            </table>
    </form>
</body>
</html>

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
<%
    String username = request.getParameter("username");
    String password = request.getParameter("password");
    session.setAttribute("username", username);
    response.sendRedirect(request.getContextPath()+"/message.jsp");
%>
</body>
</html>

message.jsp
这里的session我改成了application是因为我把留言的功能封装成了一个servlet addMessage，但是没有找到session的作用域，就用了application的作用域，如果用application的作用域这里会出现一个问题，数据共享。就类似于数据库的功能了哈哈。
然后我现在找到了怎么设置session了，ServletRequest request = new ServletRequest;然后request.getSession()就是那个session了。

<%@ page language="java" contentType="text/html; charset=utf-8"
    pageEncoding="utf-8"%>
<%@ page import="java.util.*,model.*" %>    
<%
    String user = (String)session.getAttribute("username");
    String subFlag = request.getParameter("subFlag");
//    List <Message> messages = (List)application.getAttribute("messages");
    List <Message> messages = (List)session.getAttribute("messages");
%>    
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>留言板</title>
<script type="text/javascript">
    var subFlag = "<%=subFlag %>";
    if(subFlag=='1'){
        alert("留言成功！");
    }
</script>
</head>
<body>
<!-- <form action="<%=request.getContextPath() %>/addMessage"> -->
<form action="messageSub.jsp">
        <div align="center">
    <h1>留言板</h1>
    <lable>
    留言人<input id="user" type="text" name="user" value="<%=user %>" readonly>
    </lable>
        <lable>
    标题<input id="user" type="text" name="title" >
    </lable>
        <lable>
    内容<input id="user" type="text" name="content">
    </lable>
        <input type="submit" value="提交">
        </div>
        <hr>
        <hr>
    <table border="1" align="center">
    <tr>
        <th>留言人</th>
        <th>标题</th>
        <th>内容</th>
    </tr>
    <%
        if(messages !=null){
            for(Message message:messages){
                %>
                    <tr>
                        <td><%=user %></td>
                        <td><%=message.getTitle() %></td>
                        <td><%=message.getContent() %></td>
                    </tr>
                <%
            }
        }
    %>
    </table>
</form>
</body>
</html>

messageSub.jsp

<%@ page language="java" contentType="text/html; charset=utf-8"
    pageEncoding="utf-8"%>
<%@ page import="java.util.*,model.*" %>
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Insert title here</title>
</head>
<body>
<%
String title = request.getParameter("title");
String content = request.getParameter("content");
Message message = new Message();
message.setTitle(title);
message.setContent(content);
//从session中获取messages属性
//ServletContext context = this.getServletContext();
//List<Message> messages =(List)context.getAttribute("messages");
List<Message> messages =(List)session.getAttribute("messages");
if(messages == null){
    //如果session中没有messages属性，创建一个，并且把当前的messages赋值给他
    messages = new ArrayList<Message>();
//    context.setAttribute("messages", messages);
    session.setAttribute("messages", messages);
}
//messages队列中添加获取到的message
messages.add(message);
response.sendRedirect(request.getContextPath()+"/message.jsp?subFlag=1");
System.out.println(title+content);
%>
</body>
</html>

web.xml

<?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_4_0.xsd" id="WebApp_ID" version="4.0">
  <display-name>FilterDemo</display-name>
  <welcome-file-list>
    <welcome-file>index.jsp</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>
  <filter>
    <!-- 注册过滤器 -->
      <filter-name>characterEncodingFilter</filter-name>
      <filter-class>filter.CharacterEncodingFilter</filter-class>
      <init-param>
          <param-name>charset</param-name>
          <param-value>utf-8</param-value>
      </init-param>
  </filter>
    <filter>
    <!-- 注册过滤器 -->
      <filter-name>SessionFilter</filter-name>
      <filter-class>filter.SessionFilter</filter-class>
  </filter>
  <filter-mapping>
  <!-- 指定过滤器映射，对所有的请求都使用characterEncodingFilter的过滤器 -->
      <filter-name>characterEncodingFilter</filter-name>
      <url-pattern>/*</url-pattern>
  </filter-mapping>
    <filter-mapping>
    <!-- 用户登录安全控制过滤器配置,用户在留言时进行过滤 -->
      <filter-name>SessionFilter</filter-name>
      <url-pattern>/message.jsp</url-pattern>
  </filter-mapping>
</web-app>

CharacterEncodingFilter

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;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class CharacterEncodingFilter implements Filter {
    //创建一个类属性
    private FilterConfig config;
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        // TODO Auto-generated method stub
        System.out.println("我要开始过滤啦");
        //这里的获取编码格式是xml文件中的initparam名为charset的value
        request.setCharacterEncoding(config.getInitParameter("charset"));
        //通知web服务器，拦截处理已完成，请进行下一步操作，请进行下一步操作
        chain.doFilter(request, response);

    }

    @Override
    public void destroy() {

        Filter.super.destroy();
    }

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        this.config = filterConfig;
    }


}

SessionFilter

package filter;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class SessionFilter implements Filter {

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {

        HttpServletRequest hrequest = (HttpServletRequest)request;
        HttpServletResponse hresponse = (HttpServletResponse)response;

        String userName = (String)hrequest.getSession().getAttribute("username");

        if(userName == null) {
            hresponse.sendRedirect(hrequest.getContextPath()+"/index.jsp?flag=1");
            return ;
        }else {
            chain.doFilter(hrequest, hresponse);
            return ;
        }

    }

}

过滤器配置

web.xml文件中
的子元素dispatcher

REQUEST

默认是REQUEST

INCLUDE

通过include访问方式访问所对应的url-pattern，INCLUDE，例如,过滤器就会被执行

FORWARD

通过forward调用的FORWARD,例如request.getRequestDispatcher(‘/test.jsp’).forward(request,response)l; 过滤器就会被执行

ERROR

通过异常过来的，使用error过滤器
ERROR
同时，配置文件中可以写

404
/xx.jsp