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

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)

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

1.2.2、使用注解

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");
    }
}

1.3、ServletConfig类

ServletConfig类时Servlet程序的配置信息类

注解形式

ServletConfig的三个作用

1. 可以获取Servlet程序的别名servlet-name的值

// 1、可以获取Servlet程序的别名servlet-name的值
   System.out.println("HelloServlet程序的别名是:"+servletConfig.getServletName());

2. 获取初始化参数init-param：可在web.xml中设置多个参数

// 2、获取初始化参数init-param
   System.out.println("初始化参数username的值是："+servletConfig.getInitParameter("username"));
   System.out.println("初始化参数username的值是："+servletConfig.getInitParameter("url"));

3. 获取ServletContext对象

// 3、获取ServletContext对象
   System.out.println(servletConfig.getServletContext());

完整方法代码为：

 @Override
    public void init(ServletConfig servletConfig) throws ServletException {
        System.out.println("2init初始化方法");
//        1、	可以获取Servlet程序的别名servlet-name的值
        System.out.println("HelloServlet程序的别名是:"+servletConfig.getServletName());
//        2、	获取初始化参数init-param
        System.out.println("初始化参数username的值是："+servletConfig.getInitParameter("username"));
        System.out.println("初始化参数username的值是："+servletConfig.getInitParameter("url"));
//        3、	获取ServletContext对象
        System.out.println(servletConfig.getServletContext());
 
 
    }

最后结果显示：

1.4、ServletContext

1.4.1、ServletContext的使用

ServletContext是什么

• ServletContext对象有称呼为上下文对象,或者叫应用域对象(后面统一讲解域对象)
• 容器会为每个app创建一个独立的唯一的ServletContext对象
• ServletContext对象为所有的Servlet所共享
• ServletContext可以为所有的Servlet提供初始配置参数

ServletContext怎么用

• 配置ServletContext参数

<web-app xmlns="https://jakarta.ee/xml/ns/jakartaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="https://jakarta.ee/xml/ns/jakartaee https://jakarta.ee/xml/ns/jakartaee/web-app_5_0.xsd"
         version="5.0">

    <context-param>
        <param-name>paramAparam-name>
        <param-value>valueAparam-value>
    context-param>
    <context-param>
        <param-name>paramBparam-name>
        <param-value>valueBparam-value>
    context-param>
web-app>

• 在Servlet中获取ServletContext并获取参数

package com.atguigu.servlet;

import jakarta.servlet.ServletConfig;
import jakarta.servlet.ServletContext;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;
import java.util.Enumeration;

public class ServletA extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
       
        // 从ServletContext中获取为所有的Servlet准备的参数
        ServletContext servletContext = this.getServletContext();
        String valueA = servletContext.getInitParameter("paramA");
        System.out.println("paramA:"+valueA);
        // 获取所有参数名
        Enumeration<String> initParameterNames = servletContext.getInitParameterNames();
        // 迭代并获取参数名
        while (initParameterNames.hasMoreElements()) {
            String paramaterName = initParameterNames.nextElement();
            System.out.println(paramaterName+":"+servletContext.getInitParameter(paramaterName));
        }
    }
}

1.4.2、 ServletContext其他重要API

获取资源的真实路径

String realPath = servletContext.getRealPath("资源在web目录中的路径");

例如我们的目标是需要获取项目中某个静态资源的路径，不是工程目录中的路径，而是部署目录中的路径；我们如果直接拷贝其在我们电脑中的完整路径的话其实是有问题的，因为如果该项目以后部署到公司服务器上的话，路径肯定是会发生改变的，所以我们需要使用代码动态获取资源的真实路径. 只要使用了servletContext动态获取资源的真实路径，那么无论项目的部署路径发生什么变化，都会动态获取项目运行时候的实际路径，所以就不会发生由于写死真实路径而导致项目部署位置改变引发的路径错误问题

获取项目的上下文路径 项目的访问路径

String contextPath = servletContext.getContextPath();

项目的部署名称,也叫项目的上下文路径,在部署进入tomcat时所使用的路径,该路径是可能发生变化的,通过该API动态获取项目真实的上下文路径,可以帮助我们解决一些后端页面渲染技术或者请求转发和响应重定向中的路径问题

域对象的相关API

• 域对象: 一些用于存储数据和传递数据的对象,传递数据不同的范围,我们称之为不同的域,不同的域对象代表不同的域,共享数据的范围也不同
• ServletContext代表应用,所以ServletContext域也叫作应用域,是webapp中最大的域,可以在本应用内实现数据的共享和传递
• webapp中的三大域对象,分别是应用域,会话域,请求域
• 后续我们会将三大域对象统一进行讲解和演示,三大域对象都具有的API如下

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

get和post的区别

2.2、request主要方法

• 获取请求行信息相关(方式,请求的url,协议及版本)
  

• 获得请求头信息相关
  

• 获得请求参数相关
  

• 其他API
  

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

2.3、response主要方法

• 设置响应行相关
  

• 设置响应头相关
  

• 设置响应体相关
  

• 其他API
  

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("");
            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("");
            printWriter.println("");
            printWriter.println("");
            printWriter.println("
登陆失败
");
            printWriter.println("");
            printWriter.println("");
        }

中文乱码和路径

中文乱码

参考链接

路径

参考链接

三、转发与重定向

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

页面跳转

数据传递

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("");
            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("");
            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

数据传输

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

4.2 初始化

4.3 服务

4.4 销毁

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");
    }
}

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

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。

6.2、创建cookie

访问不同的资源时，可以携带不同的cookie，可以通过cookie的setPath(String path)对cookie的路径进行设置

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的提交路径
        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);
    }
}

6.3、获取cookie

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

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

6.5、编码与解码

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，同属于一次会话(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

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

三大域对象

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。

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

• 创建类 实现Filter接口
• 重写doFilter方法
• 可选择调用放行方法 将请求传下去 ：
  • filterChain.doFilter(servletRequest, servletResponse);
  • 不写此方法 就是不放行请求到目标资源 卡这了
    

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

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>xmlfilter-name>
        <filter-class>com.wyy.Filter.xmlFilterfilter-class>
    filter>
    <filter-mapping>
        <filter-name>xmlfilter-name>
        <url-pattern>/testurl-pattern>
    filter-mapping>

拦截路径

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FilterChain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filter,如果有，则调用第2个filter,如果没有，则调用目标资源。

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();
    }
}

监听器

参考