Servlet详解（下）-个人在线分享

一、Servlet详解
- 1.1、核心接口和类
- - 1.1.1、Servlet接口
  - 1.1.2、GenericServlet
  - 1.1.3、HttpServlet(推荐)
- 1.2、两种配置方法
- - 1.2.1、使用web.xml
  - 1.2.2、使用注解
二、Servlet应用
- 2.1、request对象
- 2.2、request主要方法
- 2.2、response对象
- 2.3、response主要方法
三、转发与重定向
- 3.1、转发
- 3.2、重定向
四、生命周期
- 4.1 实例化
- 4.2 初始化
- 4.3 服务
- 4.4 销毁
五、Servlet线程安全问题
- 5.1、线程安全问题
- 5.2、如何保证线程安全
六、Cookie
- 6.1、什么是Cookie
- 6.2、创建cookie
- 6.3、获取cookie
- 6.4、修改cookie
- 6.5、编码与解码
七、Session
- 7.1、获取Session
- 7.2、Session保存、获取数据
- 7.3、Session移除数据
- 7.4、Session生命周期
八、ServletContext
- 8.1、获取ServletContext对象
- 8.2、ServletContext作用
- 8.3、ServletContext应用场景
九、过滤器
- 9.1、实现过程
- 9.2、过滤器配置
- 9.3、过滤器链和优先级
- 9.4、过滤器应用

一、Servlet详解

在Servlet体系结构中，除了实现Servlet接口，还可以通过继承GenericServlet或HttpServlet类，完成编写。

1.1、核心接口和类

1.1.1、Servlet接口

Servlet详解（下）插图

1.1.2、GenericServlet

提供生命周期方法init和destroy的简单实现，要编写一般的Servlet只需重写抽象service方法

package com.wyy.servlet;

import jakarta.servlet.GenericServlet;
import jakarta.servlet.ServletException;
import jakarta.servlet.ServletRequest;
import jakarta.servlet.ServletResponse;

import java.io.IOException;

public class GenServlet extends GenericServlet {
    @Override
    public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {
        System.out.println("hi~~~");
    }
}

1.1.3、HttpServlet(推荐)

Servlet详解（下）插图(1)

package com.wyy.servlet;

import jakarta.servlet.ServletException;
import jakarta.servlet.ServletRequest;
import jakarta.servlet.ServletResponse;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;

public class httpsServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("get");;
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("post");
    }
}

1.2、两种配置方法

1.2.1、使用web.xml

Servlet详解（下）插图(2)
Servlet详解（下）插图(3)

1.2.2、使用注解

Servlet详解（下）插图(4)

import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;

@WebServlet(value = {"/bs","/bss"})
public class basicServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("get");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("post");
    }
}

二、Servlet应用

2.1、request对象

在Servlet中用来处理客户端请求需要用doGet或doPost方法的request对象
Servlet详解（下）插图(5)

get和post的区别

Servlet详解（下）插图(6)

2.2、request主要方法

Servlet详解（下）插图(7)

HTML

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>登录页面</title>
</head>
<body>
  <form action="/web1_war_exploded/login" method="post">
    用户名：<input type="text" name="username"/><br>
    密码：<input type="password" name="password"/><br>
    <input type="submit" value="登录"/>
  </form>
</body>
</html>

Servlet

package com.wyy.servlet2;

import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;
import java.io.PrintWriter;

@WebServlet(value = "/rs")
public class registerServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //获取用户请求的数据
        String username = req.getParameter("username");
        String password = req.getParameter("password");

        System.out.println("提交的数据: " + username + " " + password);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //对request对象设置统一编码格式
        req.setCharacterEncoding("utf-8");
        //获取用户请求的数据
        String username = req.getParameter("username");
        String password = req.getParameter("password");

        //System.out.println("提交的数据: " + username + " " + password);
        //相应数据给客户端
        resp.setContentType("text/html;charset=utf-8");
        PrintWriter printWriter = resp.getWriter();
        printWriter.println("注册成功");
    }
}

2.2、response对象

response对象用于响应客户请求并向客户端输出信息
Servlet详解（下）插图(8)

2.3、response主要方法

Servlet详解（下）插图(9)
Servlet详解（下）插图(10)

resp.getWriter();//获取字符输出流

       PrintWriter printWriter = resp.getWriter();
        if (admin != null){
            //相应结果成功
            printWriter.println("");
            printWriter.println("");
            printWriter.println("");
            printWriter.println("结果页面");
            printWriter.println("");
            printWriter.println("");
            printWriter.println("登陆成功！！！！
");
            printWriter.println("");
            printWriter.println("");
        }else {
            //相应结果失败
            printWriter.println("");
            printWriter.println("");
            printWriter.println("");
            printWriter.println("结果页面");
            printWriter.println("");
            printWriter.println("");
            printWriter.println("登陆失败
");
            printWriter.println("");
            printWriter.println("");
        }

三、转发与重定向

Servlet详解（下）插图(11)

3.1、转发

转发的作用在服务端，将请求发送给服务器上的其他资源，以共同完成一次请求处理
Servlet详解（下）插图(12)

页面跳转

Servlet详解（下）插图(13)

数据传递

Servlet详解（下）插图(14)

ShowAllAdminController
存数据

req.setAttribute("admins",adminList);

package com.wyy.servletProject.servlet;

import com.wyy.servletProject.entity.Admin;
import com.wyy.servletProject.service.AdminService;
import com.wyy.servletProject.service.imlp.AdminServiceimpl;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;
import java.util.List;

@WebServlet(value = "/showallcontroller")
public class ShowAllAdminController extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //只负责调用业务逻辑
        AdminService adminService = new AdminServiceimpl();
        List<Admin> adminList = adminService.showAllAdmin();

        //request作用域存储数据
        req.setAttribute("admins",adminList);
        //通过转发跳转到显示结果的servlet
        req.getRequestDispatcher("/showalljsp").forward(req,resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

ShowallAdminJSP
取数据

 List<Admin>  adminList = (List<Admin>) req.getAttribute("admins");

package com.wyy.servletProject.servlet;
import com.wyy.servletProject.entity.Admin;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;
@WebServlet(value = "/showalljsp")
public class ShowallAdminJSP extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
List<Admin>  adminList = (List<Admin>) req.getAttribute("admins");
PrintWriter printWriter = resp.getWriter();
if (adminList != null){
printWriter.println("");
printWriter.println("");
printWriter.println("");
printWriter.println("结果页面");
printWriter.println("");
printWriter.println("");
printWriter.println("");
printWriter.println("       username");
printWriter.println("       password");
printWriter.println("       phone");
printWriter.println("       address");
printWriter.println("
");
for (Admin admin :adminList){
printWriter.println("");
printWriter.println("       "+admin.getUsername()+"");
printWriter.println("       "+admin.getPassword()+"");
printWriter.println("       "+admin.getPhone()+"");
printWriter.println("       "+admin.getAddress()+"");
printWriter.println("
");
}
printWriter.println("");
printWriter.println("");
}else {
printWriter.println("");
printWriter.println("");
printWriter.println("");
printWriter.println("结果页面");
printWriter.println("");
printWriter.println("");
printWriter.println("登陆失败
");
printWriter.println("");
printWriter.println("");
}
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}

3.2、重定向

作用在客户端，客户端将请求发送给服务器后，服务器响应给客户端一个新的请求地址，客户端重新发送请求。

页面跳转

Servlet详解（下）插图(15)

数据传输

Servlet详解（下）插图(16)

AServlet
重定向传数据

 resp.sendRedirect("/web1_war_exploded/b?username=Tom"); //只能传String

package com.wyy.servletProject.servlet;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import java.io.IOException;
@WebServlet(value = "/a")
public class AServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//通过request作用域做数据的存储
//        req.setAttribute("username","gavin");
//        req.getRequestDispatcher("/b").forward(req,resp);
resp.sendRedirect("/web1_war_exploded/b?username=Tom");
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}

BServlet
重定向传数据

String username = req.getParameter("username");

package com.wyy.servletProject.servlet;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import java.io.IOException;
@WebServlet(value = "/b")
public class BServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//        String s = (String) req.getAttribute("username");
String username = req.getParameter("username");
System.out.println("B executed ..." + username);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}

当两个Servlet需要传数据时，选择forward转发，不建议使用sendRedirect进行传递

四、生命周期

四个阶段

4.1 实例化

Servlet详解（下）插图(17)

4.2 初始化

Servlet详解（下）插图(18)

4.3 服务

Servlet详解（下）插图(19)

4.4 销毁

Servlet详解（下）插图(20)
Servlet详解（下）插图(21)

package com.wyy.servlet3;
import jakarta.servlet.*;
import jakarta.servlet.annotation.WebServlet;
import java.io.IOException;
@WebServlet(value = "/ls")
public class lifeServlet implements Servlet {
public lifeServlet(){
System.out.println("1、实例化");
}
@Override
public void init(ServletConfig servletConfig) throws ServletException {
System.out.println("2、初始化");
}
@Override
public ServletConfig getServletConfig() {
return null;
}
@Override
public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {
System.out.println("3、接收请求，相应结果");
}
@Override
public String getServletInfo() {
return null;
}
@Override
public void destroy() {
System.out.println("4、销毁");
}
}

Servlet详解（下）插图(22)
Servlet详解（下）插图(23)

五、Servlet线程安全问题

5.1、线程安全问题

Servlet详解（下）插图(24)

5.2、如何保证线程安全

Servlet详解（下）插图(25)

package com.wyy.servlet3;
import jakarta.servlet.ServletException;
import jakarta.servlet.SingleThreadModel;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
public class SafeServlet extends HttpServlet implements SingleThreadModel {
private String massage = "";
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
synchronized (this){
//假设接收参数
//调用业务逻辑，得到登录结果
massage = "登陆成功";
PrintWriter printWriter = resp.getWriter();
printWriter.println(massage);
}
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}

package com.wyy.servlet3;
import jakarta.servlet.ServletException;
import jakarta.servlet.SingleThreadModel;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
public class SafeServlet extends HttpServlet {
// private String massage = "";
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
String massage = "";
//假设接收参数
//调用业务逻辑，得到登录结果
massage = "登陆成功";
PrintWriter printWriter = resp.getWriter();
printWriter.println(massage);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}

六、Cookie

将浏览器与web服务器之间多次交互当作一个整体来处理，并且将多次交互所涉及的数据(即状态)保存下来。

分类：

客户端状态管理技术:将状态保存在客户端。代表性的是Cookie技术。
服务器状态管理技术:将状态保存在服务器端。代表性的是session技术(服务器传递sessionID时需要使用Cookie的方式)

6.1、什么是Cookie

Cookie是在浏览器访问Web服务器某个资源时，由Web服务器在HTTP响应消息头中附带传送给浏览器的一小段数据
一旦Web浏览器保存了某个Cookie，那么它在以后每次访问该Web浏览器时，都应在Http请求头中将这个Cookie回传给Web服务器。
一个Cookies是由标识该信息的名称（name)和值（value）组成。

Servlet详解（下）插图(26)

6.2、创建cookie

Servlet详解（下）插图(27)

package com.wyy.cookies;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.Cookie;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import java.io.IOException;
@WebServlet(value = "/cs")
public class cookieServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doPost(req, resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//服务端创建cookie
Cookie cookie = new Cookie("username","gavin");
Cookie cookie2 = new Cookie("passward","123456");
//设置cookie的访问路径
cookie.setPath("/web1_war_exploded/get");
cookie2.setPath("/web1_war_exploded");
//设置cookie生命周期
cookie.setMaxAge(60*60);
cookie2.setMaxAge(60*60);
//将cookie响应给客户端
resp.addCookie(cookie);
resp.addCookie(cookie2);
}
}

Servlet详解（下）插图(28)

6.3、获取cookie

Servlet详解（下）插图(29)

package com.wyy.cookies;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.Cookie;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import java.io.IOException;
@WebServlet(value = "/get")
public class GetServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//通过request对象获取所有的cookie
Cookie[] cookies = req.getCookies();
//通过循环遍历数组
if (cookies != null){
for (Cookie cookie : cookies){
System.out.println(cookie.getName()+":"+cookie.getValue());
}
}
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}

6.4、修改cookie

Servlet详解（下）插图(30)

package com.wyy.cookies;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.Cookie;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import java.io.IOException;
@WebServlet(value = "/cs2")
public class CookieServlet2 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doPost(req, resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
Cookie cookie = new Cookie("username","aaron");
cookie.setPath("/web1_war_exploded/get");
cookie.setMaxAge(60*60*24*7);
resp.addCookie(cookie);
}
}

如果改变cookie的name有效路径会新建cookie，而改变cookie的值，有效期会覆盖原有的cookie

Servlet详解（下）插图(31)

6.5、编码与解码

Servlet详解（下）插图(32)

编码

URLEncoder.encode("姓名","UTF-8"),URLEncoder.encode("张三","UTF-8")

package com.wyy.cookies;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.Cookie;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.net.URLEncoder;
@WebServlet(value = "/cs3")
public class CookisServlet3 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doPost(req, resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
Cookie cookie = new Cookie(URLEncoder.encode("姓名","UTF-8"),URLEncoder.encode("张三","UTF-8"));
cookie.setPath("/web1_war_exploded/get");
cookie.setMaxAge(600);
resp.addCookie(cookie);
}
}

解码

URLDecoder.decode(cookie.getName(),"UTF-8")+":"+URLDecoder.decode(cookie.getValue(),"UTF-8")

package com.wyy.cookies;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.Cookie;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.net.URLDecoder;
import java.net.URLEncoder;
@WebServlet(value = "/get")
public class GetServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//通过request对象获取所有的cookie
Cookie[] cookies = req.getCookies();
//通过循环遍历数组
if (cookies != null){
for (Cookie cookie : cookies){
System.out.println(URLDecoder.decode(cookie.getName(),"UTF-8")+":"+URLDecoder.decode(cookie.getValue(),"UTF-8"));
}
}
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}

七、Session

概述
Session用于记录用户的状态。Session指的是在一段时间内，单个客户端与Web服务器的一连串相关的交互过程。
在一个Session中，客户可能会多次请求访问同一个资源，也有可能请求访问各种不同的服务器资源。

原理
服务器会为每一次会话分配一个Session对象
同一个浏览器发起的多次请求，同属于- 次会话(Session)
首次使用到Session时，服务器会自动创建Session,并创建Cookie存储Sessionld发送回客户端

使用
Session作用域: 拥有存储数据的空间，作用范围是一次会话有效
一次会话是使用同一浏览器发送的多次请求。一旦浏览器关闭，则结束会话
可以将数据存入Session中，在一次会话的任意位置进行获取
可传递任何数据(基本数据类型、对象、集合、数组)

7.1、获取Session

Servlet详解（下）插图(33)

package com.wyy.Session;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import jakarta.servlet.http.HttpSession;
import java.io.IOException;
@WebServlet(value = "/ss")
public class SessionServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//通过request获取Session对象
HttpSession session = req.getSession();
System.out.println(session.getId());
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}

7.2、Session保存、获取数据

保存

session.setAttribute("username","gavin");

获取

session.getAttribute("username");

package com.wyy.Session;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import jakarta.servlet.http.HttpSession;
import java.io.IOException;
@WebServlet(value = "/getvalue")
public class GetValueServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doPost(req, resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//获取Session对象
HttpSession session = req.getSession();
String s = (String) session.getAttribute("username");
System.out.println("从session中获得了"+s);
}
}

7.3、Session移除数据

session.removeAttribute("username");

package com.wyy.Session;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import jakarta.servlet.http.HttpSession;
import java.io.IOException;
@WebServlet(value = "/remove")
public class RemoveServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doPost(req, resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
HttpSession session = req.getSession();
session.removeAttribute("username");
}
}

request session区别
request是一次请求有效，请求改变，则request改变
session是一次会话有效，浏览器改变，则session改变

7.4、Session生命周期

开始:第一次使用到Session的请求产生，则创建Session
结束:
- 浏览器关闭，则失效
- Session超时，则失效
  - session.setMaxlIactielnterallseconds//设置最大有效时间(单位:秒)
- 手工销毁，则失效
  - session.invalidate/);//登录退出、注销

八、ServletContext

全局对象，也拥有作用域，对应一个Tomcat中的Web应用
当Web服务器启动时，会为每一个Web应用程序创建一块共享的存储区域(ServletContext)。
ServletContext在Web服务器启动时创建，服务器关闭时销毁。

8.1、获取ServletContext对象

GenericServlet提供了getServletContext(）方法。(推荐) this getServletContext（）;
HttpServletRequest提供了getServletContext()方法。(推荐)
HttpSession提供了getServletContext()方法。

package com.wyy.servletProject.servlet.controller;
import jakarta.servlet.ServletContext;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import jakarta.servlet.http.HttpSession;
import java.io.IOException;
@WebServlet(value = "/ctxController")
public class ServletContextController extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doPost(req, resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//方式一 this getServletContext);
ServletContext servletContext = this.getServletContext();
//方式二 request对象获取
ServletContext servletContext1 = req.getServletContext();
//方式三 Session对象获取
HttpSession session = req.getSession();
ServletContext servletContext2 = session.getServletContext();
System.out.println(servletContext);
System.out.println(servletContext1);
System.out.println(servletContext2);
}
}

8.2、ServletContext作用

获取项目的真实路径
```
servletContext.getRealPath("/")
```
获取项目上下文路径
```
servletContext.getContextPath()
```
全局容器(ServletContext拥有作用域，可以存储数据到全局容器中)
- 存储数据: servletContext.setAttribute(“name”,value);
- 获取数据: servletContext getAttrbute(“name”);
- 移除数据: servletContext.removeAttribute(“name”);

package com.wyy.servletProject.servlet.controller;
import jakarta.servlet.ServletContext;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import jakarta.servlet.http.HttpSession;
import java.io.IOException;
@WebServlet(value = "/ctxController")
public class ServletContextController extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doPost(req, resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//方式一 this getServletContext);
ServletContext servletContext = this.getServletContext();
//获取项目的真实路径
System.out.println(servletContext.getRealPath("/"));
//获取项目的上下文路径
System.out.println(servletContext.getContextPath());
//全局容器
servletContext.setAttribute("context","info");
}
}

package com.wyy.servletProject.servlet.controller;
import jakarta.servlet.ServletContext;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import java.io.IOException;
@WebServlet(value = "/showContext")
public class ShowContextController extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doPost(req, resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//先获取ServletContext对象
ServletContext servletContext =  this.getServletContext();
String s = (String) servletContext.getAttribute("context");
System.out.println(s);
}
}

8.3、ServletContext应用场景

HttpServletRequest: 一次请求，请求响应之前有效
HttpSession: 一次会话开始，浏览器不关闭或不超时之前有效
ServletContext: 服务器启动开始，服务器停止之前有效

九、过滤器

处于客户端和服务器目标资源之间的一道过滤技术。
Servlet详解（下）插图(34)
作用：

执行地位在Servlet之前，客户端发送请求时，会先经过Filter, 再到达目标Servlet中;响应时，会根据执行流程再次反向执行Filter
可以解决多个Servlet共性代码的冗余问题(例如:乱码处理、登录验证)

9.1、实现过程

编写Java类实现Filter接口
在doFilter方法中编写拦截逻辑
设置拦截路径

package com.wyy.Filter;
import jakarta.servlet.*;
import jakarta.servlet.annotation.WebFilter;
import java.io.IOException;
@WebFilter(value = "/t")
public class MyFilter implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
Filter.super.init(filterConfig);
}
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
System.out.println("===myfilter====");
//让请求继续
filterChain.doFilter(servletRequest,servletResponse);
System.out.println("====end====");
}
@Override
public void destroy() {
Filter.super.destroy();
}
}

9.2、过滤器配置

注解配置

@WebFilter(value = "/t")

xml配置

Servlet详解（下）插图(35)

package com.wyy.Filter;
import jakarta.servlet.*;
import java.io.IOException;
public class xmlFilter implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
Filter.super.init(filterConfig);
}
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
System.out.println("Web.xml配置过滤器");
filterChain.doFilter(servletRequest,servletResponse);
}
@Override
public void destroy() {
Filter.super.destroy();
}
}

package com.wyy.Filter;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import java.io.IOException;
@WebServlet(value = "/test")
public class TestServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doPost(req, resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
System.out.println("TestServlet");
}
}

   <filter>
<filter-name>xml</filter-name>
<filter-class>com.wyy.Filter.xmlFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>xml</filter-name>
<url-pattern>/test</url-pattern>
</filter-mapping>

拦截路径
Servlet详解（下）插图(36)
后缀拦截

package com.wyy.Filter;
import jakarta.servlet.*;
import jakarta.servlet.annotation.WebFilter;
import jakarta.servlet.http.HttpServlet;
import java.io.IOException;
@WebFilter(value = "*.html")
public class HtmlFilter implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
Filter.super.init(filterConfig);
}
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
System.out.println("拦截html请求");
filterChain.doFilter(servletRequest, servletResponse);
}
@Override
public void destroy() {
Filter.super.destroy();
}
}

通配符拦截

package com.wyy.Filter;
import jakarta.servlet.*;
import jakarta.servlet.annotation.WebFilter;
import java.io.IOException;
@WebFilter(value = "/*")
public class AllFilter implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
Filter.super.init(filterConfig);
}
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
System.out.println("拦截所有请求");
filterChain.doFilter(servletRequest, servletResponse);
}
@Override
public void destroy() {
Filter.super.destroy();
}
}

9.3、过滤器链和优先级

过滤器链
客户端对服务器请求之后，服务器调用Servlet之前会执行一组过滤器(多个过滤器)，那么这组过滤器就称为一条过滤器链。

每个过滤器实现某个特定的功能，当第一个Filter的doFiter方法被调用时，Web服务器会创建一个代表Filter链的ilterChain对象传递给该方法。在doFilter方法中，开发人员如果调用了FilterChain对象的doFiter方法，则Web服务器会检查FilterChain对象中是否还有flter,如果有，则调用第2个filter,如果没有，则调用目标资源。
Servlet详解（下）插图(37)

在一个Web应用中，可以开发编写多个Filter,这些Filter组合起来称之为一个Filter链。优先级:

如果为注解的话，是按照类全名称的字符串顺序决定作用顺序
如果web.xml, 按照filter-mapping注册顺序，从上往下
web.xml配置高于注解方式
如果注解和web.xml同时配置，会创建多个过滤器对象，造成过滤多次。

9.4、过滤器应用

解决编码

package com.wyy.Filter;
import jakarta.servlet.*;
import jakarta.servlet.annotation.WebFilter;
import jakarta.servlet.annotation.WebServlet;
import java.io.IOException;
@WebFilter(value = "/*")
public class EncodingFilter implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
Filter.super.init(filterConfig);
}
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
//统一处理请求和响应的乱码
servletRequest.setCharacterEncoding("UTF-8");
servletResponse.setContentType("text/html;charset=utf-8");
filterChain.doFilter(servletRequest, servletResponse);
}
@Override
public void destroy() {
Filter.super.destroy();
}
}

权限验证

package com.wyy.servletProject.filter;
import com.wyy.servletProject.entity.Manager;
import jakarta.servlet.*;
import jakarta.servlet.annotation.WebFilter;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import jakarta.servlet.http.HttpSession;
import java.io.IOException;
@WebFilter(value = "/showallcontroller")
public class checkfilter implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
Filter.super.init(filterConfig);
}
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
//权限验证 验证管理员是否登录
//向下转型 拆箱
HttpServletRequest request = (HttpServletRequest)servletRequest;
HttpServletResponse response = (HttpServletResponse) servletResponse;
HttpSession session = request.getSession();
Manager mgr = (Manager) session.getAttribute("mgr");
if (mgr != null){
filterChain.doFilter(request,response);
}else {
response.sendRedirect(request.getContextPath()+"/loginMgr.html");
}
}
@Override
public void destroy() {
Filter.super.destroy();
}
}

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