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-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>

<title>calculator</title>

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>

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

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

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

<hr/>

<h3>简单的计算器</h3>

<table>

<tr>

<td>第一个参数</td>

<td>

</td>

</tr>

<tr>

<td>

</select>

</td>

</tr>

<tr>

<td>第二个参数</td>

<td>

</td>

</tr>

<tr>

</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>

<title>calculator</title>

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>

<h3>简单的计算器</h3>

<table>

<tr>

<td>第一个参数</td>

<td>

</td>

</tr>

<tr>

<td>

</select>

</td>

</tr>

<tr>

<td>第二个参数</td>

<td>

</td>

</tr>

<tr>

</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>

<title>calculator</title>

</head>

<body>

<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>

相关阅读:
css3
css3
npm 安装包无法继续下载？卡住
tcp/ip协议中的SYN, ACK的数值变化
【转】6 Reasons Why JavaScript’s Async/Await Blows Promises Away (Tutorial)
ES6 中 Symbol.split的用法
Why does Typescript use the keyword “export” to make classes and interfaces public?
es6中的import,export浏览器已经支持
Understanding the JavaScript Engine—— two phase
【转】js-ES6学习笔记-Symbol

原文地址：https://www.cnblogs.com/zhouyeqin/p/6743534.html

第十章 过滤器