第十章 过滤器

第十章 过滤器

Servlet API中提供了一个Filter接口，开发web应用时，如果编写的Java类实现了这个接口，则把这个java类称之为过滤器Filter。通过Filter技术，开发人员可以实现用户在访问某个目标资源之前，对访问的请求和响应进行拦截，如下所示：

在web应用可以部署多个过滤器，这些过滤器组成过一个链（过滤器链）来执行多个操作或者查；

只有当客户端的请求通过这个过滤链的检查后，才能将请求发送到目的组件，如果请求不能通过过滤链中某一个过滤器，那么请求就会被阻止。

过滤器生命周期的各个阶段：

Filter实现步骤：

编写java类实现Filter接口，并实现其doFilter方法。

package com.silvan.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;

 

public class FilterDemo1 implements Filter{

 

     public FilterDemo1() {

         System.out.println("********FilterDemo1 实例化***********");

     }

 

     @Override

     public void destroy() {

         // TODO Auto-generated method stub

         System.out.println("********FilterDemo1 destroy***********");

     }

 

     @Override

     public void doFilter(ServletRequest request, ServletResponse response,

              FilterChain chain) throws IOException, ServletException {

         // TODO Auto-generated method stub

         System.out.println("********FilterDemo1 doFilter chain 前***********");

         // 默认：对目标资源进行了拦截，目标资源没有被访问

         // 如果访问请求调用链下一个资源

         chain.doFilter(request, response);

         System.out.println("********FilterDemo1 doFilter chain 后***********");

     }

 

     @Override

     public void init(FilterConfig filterConfig) throws ServletException {

         // TODO Auto-generated method stub

         System.out.println("********FilterDemo1 init***********");

     }

}

在 web.xml 文件中使用<filter>和<filter-mapping>元素对编写的filter类进行注册，并设置它所能拦截的资源。<url-pattern>/*</url-pattern>表示对所有访问进行拦截。

<filter>

     <filter-name>FilterDemo1</filter-name>

     <filter-class>com.silvan.filter.FilterDemo1</filter-class>

</filter>

 

<filter-mapping>

     <filter-name>FilterDemo1</filter-name>

     <url-pattern>/*</url-pattern>

</filter-mapping>

访问http://localhost:8081/08Servlet/，显示：

 

FilterConfig对象的使用方法：

@Override

         public void init(FilterConfig filterConfig) throws ServletException {

                   // TODO Auto-generated method stub

                   System.out.println("********Filter2 init***********");

                   // 获取过滤器名字

                   String filtername = filterConfig.getFilterName();

                   System.out.println("********Filter2 filtername***********" + filtername);

                   // 功能一：获取配置初始化参数，需要在web.xml中配置

                   String uname = filterConfig.getInitParameter("uname");

                   System.out.println("********Filter2 uname***********" + uname);

                   // 功能二：读取WEB资源文件 必须获取绝对磁盘路径

                   String filePath = filterConfig.getServletContext().getRealPath("/WEB-INF/info.txt");

                   try {

                            BufferedReader reader = new BufferedReader(new FileReader(filePath));

                            System.out.println(reader.readLine());

                            reader.close();

                   } catch (FileNotFoundException e) {

                            e.printStackTrace();

                   } catch (IOException e) {

                            e.printStackTrace();

                   }

         }

案例：

禁止某个IP访问站点

public void doFilter(ServletRequest request, ServletResponse response,

              FilterChain chain) throws IOException, ServletException {

         // TODO Auto-generated method stub

         System.out.println("---------IPFilterDemo1 doFilter");

         // 获取客户端IP地址

         String clientIP = request.getRemoteAddr();

         // 强制类型转换，为了使用跳转方法

         HttpServletResponse httpServletResponse = (HttpServletResponse) response;

         if ("127.0.0.1".equals(clientIP)) {

               //自己创建一个错误输出页面error.jsp

              httpServletResponse.sendRedirect("error.jsp");

         } else {

              chain.doFilter(request, response);

         }

     }

设置字符编码集

@Override

         public void doFilter(ServletRequest request, ServletResponse response,

                            FilterChain chain) throws IOException, ServletException {

                   // TODO Auto-generated method stub

                   System.out.println("---------EncodingFilter doFilter");

                   // 如果用户输入中文，对中文请求内容处理

                   request.setCharacterEncoding("utf-8");

                   // 将中文输出到页面上，设置响应字符集

                   response.setContentType("text/html;charset=utf-8");

                   chain.doFilter(request, response);

         }

第十一章 Servlet MVC模式

MVC模式的核心思想是有效地组合“视图”、“模型”和“控制器”。掌握MVC模式对于设计合理的Web应用框架有着十分重要的意义。

 

JSP开发的两种模型（Model1/Model2)

模型1：

• 使用JSP+JavaBeans将页面显示和业务逻辑处理分开
• JSP实现页面显示，响应请求并将结果返回给客户
• JavaBean对象保存数据和实现业务逻辑

优点：实现了页面显示与业务逻辑的分离

缺点：需要在JSP页面控制流程转向并且调用JavaBean代码；业务逻辑复杂时，JSP编写变得复杂

案例

Jsp+javaBeans模式简单计算器：

Calculator.jsp

<%@ page language="java" contentType="text/html; charset=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>calculator</title>

<script type="text/javascript">

    function checkForm(){

        // 对需要校验字段 添加 id 属性

        var first = document.getElementById("first").value;

        var second = document.getElementById("second").value;

        var operator = document.getElementById("operator").value;

        // 判断参数必须为数字

        if(isNaN(first) || isNaN(second)){ // isNaN is not a number

            alert("输入参数 必须为数字！");

            return false;

        }

        if(second==0 && operator == '/'){

            alert("除数不能为0！");

            return false;

        }

    }

</script>

</head>

<body>

<!-- 计算器页面 -->

 

<!-- 计算结果 -->

<jsp:useBean id="calculator" class="com.silvan.pojo.CalculatorDemo1" scope="page"></jsp:useBean>

<!-- 当用户提交form 自动封装 数据 -->

<jsp:setProperty property="*" name="calculator"/>

 

<h3>计算结果是 ：${calculator.firstNum } ${calculator.operator } ${calculator.secondNum } = ${calculator.result }</h3>

<hr/>

<!-- 计算form表单 -->

<h3>简单的计算器</h3>

<form action="/lesson11/calculator.jsp" method="post" onsubmit="checkForm();">

    <table>

        <tr>

            <td>第一个参数</td>

            <td>

                <!-- 使用 setProperty * form输入项name 必须和 javabean类属性一致 -->

                <input type="text" name="firstNum" id="first"/>

            </td>

        </tr>

        <tr>

            <td>运算符</td>

            <td>

                <select name="operator" id="operator">

                    <option value="+">+</option>

                    <option value="-">-</option>

                    <option value="*">*</option>

                    <option value="/">/</option>

                </select>

            </td>

        </tr>

        <tr>

            <td>第二个参数</td>

            <td>

                <input type="text" name="secondNum" id="second" />

            </td>

        </tr>

        <tr>

            <td colspan="2">

                <input type="submit" value="计算"/>

            </td>

        </tr>

    </table>

</form>

</body>

</html>

  CalculatorDemo1.java

package com.silvan.pojo;

/**

 * 計算類

 * @author Administrator

 */

public class CalculatorDemo1 {

    private String firstNum = "0"; // 参数一

    private String secondNum = "0"; // 参数二

    private String operator = "+"; // 运算符

    private double result; // 运算结果

 

    public String getFirstNum() {

        return firstNum;

    }

 

    public void setFirstNum(String firstNum) {

        this.firstNum = firstNum;

    }

 

    public String getSecondNum() {

        return secondNum;

    }

 

    public void setSecondNum(String secondNum) {

        this.secondNum = secondNum;

    }

 

    public String getOperator() {

        return operator;

    }

 

    public void setOperator(String operator) {

        this.operator = operator;

    }

 

    public double getResult() {

        // 将运算逻辑写到这里

        Double a = Double.parseDouble(firstNum);

        Double b = Double.parseDouble(secondNum);

        Double result = 0.0;

        if (operator.equals("+")) {

            result = a + b;

        } else if (operator.equals("-")) {

            result = a - b;

        } else if (operator.equals("*")) {

            result = a * b;

        } else if (operator.equals("/")) {

            result = a / b;

        }

        return result;

    }

 

    public void setResult(double result) {

        this.result = result;

    }

}

模型2

• 将模型1中JSP嵌入的流程控制和部分逻辑处理代码提取至一个单独的角色：控制器
• 模型2是MVC架构模式在WEB开发中的应用

MVC简介：

MVC是一种设计模式，由Trygve为发展SmallTalk在1978年提出的，出现在GUI设计中。MVC按功能对各种对象进行分割，目的是为了将对象的耦合程度降至最低。

• 模型（Model）——封装了最核心的功能，用于存储数据以及处理用户请求的业务逻辑。
• 视图（View）——系统和用户交互的界面，从模型那获得数据并表现数据，同时将用户请求通知通知器。
• 控制器（Controller）——扮演调度者的角色，，即控制器根据视图提出的请求判断将请求和数据交给那个模型处理，处理后的有关结果交给哪个视图更新显示

JSP中的MVC模式：

• 模型（Model）：一个或多个JavaBean对象，用于存储数据和处理数据；
• 视图（View）：一个或多个JSP页面，为模型提供数据显示，JSP页面主要使用 HTML标记和JavaBean标记来显示数据。
•  控制器（Controller）：一个或多个Servlet对象，根据视图提交的请求进行控制，生成JavaBean实例输出给JSP页面.

模型2实例

JSP中的MVC模式计算器

视图层Calculator.jsp

<%@ page language="java" contentType="text/html; charset=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>calculator</title>

<script type="text/javascript">

    function checkForm(){

        // 对需要校验字段 添加 id 属性

        var first = document.getElementById("first").value;

        var second = document.getElementById("second").value;

        var operator = document.getElementById("operator").value;

        // 判断参数必须为数字

        if(isNaN(first) || isNaN(second)){ // isNaN is not a number

            alert("输入参数 必须为数字！");

            return false;

        }

        if(second==0 && operator == '/'){

            alert("除数不能为0！");

            return false;

        }

    }

</script>

</head>

<body>

<!-- 计算form表单 -->

<h3>简单的计算器</h3>

<form action="/lesson11/CalculatorServletDemo2" method="post" onsubmit="checkForm();">

    <table>

        <tr>

            <td>第一个参数</td>

            <td>

                <!-- 使用 setProperty * form输入项name 必须和 javabean类属性一致 -->

                <input type="text" name="firstNum" id="first"/>

            </td>

        </tr>

        <tr>

            <td>运算符</td>

            <td>

                <select name="operator" id="operator">

                    <option value="+">+</option>

                    <option value="-">-</option>

                    <option value="*">*</option>

                    <option value="/">/</option>

                </select>

            </td>

        </tr>

        <tr>

            <td>第二个参数</td>

            <td>

                <input type="text" name="secondNum" id="second" />

            </td>

        </tr>

        <tr>

            <td colspan="2">

                <input type="submit" value="计算"/>

            </td>

        </tr>

    </table>

</form>

</body>

</html>

控制层CalculatorServletDemo2.java

package com.silvan.servlet;

import java.io.IOException;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import com.silvan.pojo.CalculatorDemo2;

public class CalculatorServletDemo2 extends HttpServlet {

                /**

                 * Constructor of the object.

                 */

                public CalculatorServletDemo2() {

                   super();

                }

                /**

                 * Destruction of the servlet. <br>

                 */

                public void destroy() {

                   super.destroy(); // Just puts "destroy" string in log

                   // Put your code here

                }

                /**

                 * The doGet method of the servlet. <br>

                 *

                 * This method is called when a form has its tag value method equals to get.

                 *

                 * @param request the request send by the client to the server

                 * @param response the response send by the server to the client

                 * @throws ServletException if an error occurred

                 * @throws IOException if an error occurred

                 */

                public void doGet(HttpServletRequest request, HttpServletResponse response)

                            throws ServletException, IOException {

                   //取出计算值

                   double firstNum = Double.parseDouble(request.getParameter("firstNum"));

                   double secondNum = Double.parseDouble(request.getParameter("secondNum"));

                   String operator = request.getParameter("operator");

                   double result = 0;

                   //计算结果

                   if (operator.equals("+")) {

                            result = firstNum + secondNum;

                   } else if (operator.equals("-")) {

                            result = firstNum - secondNum;

                   } else if (operator.equals("*")) {

                            result = firstNum * secondNum;

                   } else if (operator.equals("/")) {

                            result = firstNum / secondNum;

                   }

                   //将数据存入bean中

                   CalculatorDemo2 dataBean = new CalculatorDemo2();

                   dataBean.setFirstNum(firstNum);

                   dataBean.setSecondNum(secondNum);

                   dataBean.setOperator(operator);

                   dataBean.setResult(result);

                   request.setAttribute("bean", dataBean);

                   //跳转到结果显示界面

                   request.getRequestDispatcher("/demo2/showResult.jsp").forward(request, response);

                  

                }

                /**

                 * The doPost method of the servlet. <br>

                 *

                 * This method is called when a form has its tag value method equals to post.

                 *

                 * @param request the request send by the client to the server

                 * @param response the response send by the server to the client

                 * @throws ServletException if an error occurred

                 * @throws IOException if an error occurred

                 */

                public void doPost(HttpServletRequest request, HttpServletResponse response)

                            throws ServletException, IOException {

                   doGet(request,  response);

                }

                /**

                 * Initialization of the servlet. <br>

                 *

                 * @throws ServletException if an error occurs

                 */

                public void init() throws ServletException {

                   // Put your code here

                }

}

模型层CalculatorDemo2.java

package com.silvan.pojo;

public class CalculatorDemo2 {

    private double firstNum; // 参数一

    private double secondNum; // 参数二

    private String operator; // 运算符

    private double result; // 运算结果

 

    public double getFirstNum() {

        return firstNum;

    }

 

    public void setFirstNum(double firstNum) {

        this.firstNum = firstNum;

    }

 

    public double getSecondNum() {

        return secondNum;

    }

 

    public void setSecondNum(double secondNum) {

        this.secondNum = secondNum;

    }

 

    public String getOperator() {

        return operator;

    }

 

    public void setOperator(String operator) {

        this.operator = operator;

    }

 

    public double getResult() {

        return result;

    }

 

    public void setResult(double result) {

        this.result = result;

    }

 

}

视图层showResult.jsp

<%@ page language="java" contentType="text/html; charset=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>calculator</title>

</head>

<body>

<h3>运算结果</h3>

<jsp:useBean id="bean" type="com.silvan.pojo.CalculatorDemo2" scope="request"></jsp:useBean>

<jsp:getProperty property="firstNum" name="bean"/>

<jsp:getProperty property="operator" name="bean"/>

<jsp:getProperty property="secondNum" name="bean"/>

=

<jsp:getProperty property="result" name="bean"/>

</body>

</html>