Servlet学习笔记

笔记地址：https://github.com/userwusir/study-notes

1、环境搭建

1.1、Maven下载配置

下载地址：https://maven.apache.org/download.cgi
配置环境变量

M2_HOME Maven目录下的bin目录，例：C:\Program Files\Environment\apache-maven-3.6.3\bin

MAVEN_HOME Maven的目录，例：C:\Program Files\Environment\apache-maven-3.6.3

在系统Path中配置 %MAVEN_HOME%\bin
查看是否安装成功

mvn -v

配置阿里云镜像

打开conf文件夹下的settings.xml文件，找到<mirrors></mirror>，在其中插入代码

<mirror>
           <id>nexus-aliyun</id>
           <mirrorOf>*,!jeecg,!jeecg-snapshots</mirrorOf>
           <name>Nexus aliyun</name>
           <url>http://maven.aliyun.com/nexus/content/groups/public</url> 
       </mirror>

本地仓库配置

找到<localRepository></localRepository>，默认本地仓库在user/.m2/repository下，可以自己新建文件夹设置为本地仓库，例：<localRepository>C:\Program Files\Environment\apache-maven-3.6.3\maven-repo</localRepository>

1.2、IDEA中Maven的一些操作

pom.xml文件

创建一个Maven的示例webapps项目后
导入jar包

jar包地址：https://mvnrepository.com/

例：需要Servlet的jar包，搜索Servlet，选择自己所需要的jar包，复制这一段内容，在pom.xml中进行配置，Maven会自动配置所需jar包及其所需依赖jar包
配置Tomcat
运行测试

2、HelloServlet

2.1、创建项目

2.2、编写pom.xml

文件中导入Servlet的jar包即可

2.3、编写web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0"
         metadata-complete="true">
    <!--我们写的是JAVA程序，但是要通过浏览器访问，二浏览器需要连接web服务器，
    所以我们需要在web服务中注册我们写的Servlet，还需给它一个浏览器能够访问的路径-->
    <!--注册Servlet-->
    <servlet>
        <servlet-name>hello</servlet-name>
        <servlet-class>com.wll.servlet.HelloServlet</servlet-class>
    </servlet>
    <!--Servlet的请求路径-->
    <servlet-mapping>
        <servlet-name>hello</servlet-name>
        <url-pattern>/hello</url-pattern>
    </servlet-mapping>
</web-app>

2.4、源程序

package com.wll.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

public class HelloServlet extends HttpServlet {
    //get或post只是请求的不同方式，可以互相调用，业务逻辑一样
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        PrintWriter writer = resp.getWriter();
        writer.print("Hello Servlet !");
    }

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

2.5、测试运行

2.6、总结

mapping问题

一个Servlet可以指定一个映射路径

<servlet-mapping>
        <servlet-name>hello</servlet-name>
        <url-pattern>/hello</url-pattern>
</servlet-mapping>

一个Servlet可以指定多个映射路径

<servlet-mapping>
        <servlet-name>hello</servlet-name>
        <url-pattern>/hello</url-pattern>
</servlet-mapping>
<servlet-mapping>
        <servlet-name>hello</servlet-name>
        <url-pattern>/hello1</url-pattern>
</servlet-mapping>
<servlet-mapping>
        <servlet-name>hello</servlet-name>
        <url-pattern>/hello2</url-pattern>
</servlet-mapping>

一个Servlet可以指定通用映射路径

<servlet-mapping>
        <servlet-name>hello</servlet-name>
        <url-pattern>/hello/*</url-pattern>
</servlet-mapping>
<!--默认请求路径-->
<servlet-mapping>
        <servlet-name>hello</servlet-name>
        <url-pattern>/*</url-pattern>
</servlet-mapping>

一个Servlet可以指定一些后缀或前缀

<!--可以自定义后缀实现请求映射，*前面不能加项目映射路径-->
<servlet-mapping>
        <servlet-name>hello</servlet-name>
        <url-pattern>*.wll</url-pattern>
</servlet-mapping>

优先级

指定了固有的映射路径优先级最高（/hello），如果找不到就会走默认的处理请求（/*）

3、Servlet

3.1、 Servlet运行原理图

3.2、ServletContext

web容器在启动的时候，会为每个web程序创建一个对应的ServletContext对象，它代表了当前的web应用

共享数据

我们在这个Servlet中保存的数据，可以在另外一个Servlet中获得，不要存太多，服务器会炸

public class HelloServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    /*
        this.getInitParameter()   初始化参数
        this.getServletConfig()   Servlet配置
        this.getServletContext()  Servlet上下文
     */
        ServletContext servletContext = this.getServletContext();
        String name = "wll";    //数据
        servletContext.setAttribute("name",name);   //保存数据到ServletContext 键：name 值：name

        System.out.println("hello");
    }
}

public class GetServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext servletContext = this.getServletContext();
        String name = (String) servletContext.getAttribute("name");
        System.out.println("名字："+name);
    }

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

<servlet>
    <servlet-name>hello</servlet-name>
    <servlet-class>com.wll.servlet.HelloServlet</servlet-class>
</servlet>

<servlet-mapping>
    <servlet-name>hello</servlet-name>
    <url-pattern>/hello</url-pattern>
</servlet-mapping>

<servlet>
    <servlet-name>getcontext</servlet-name>
    <servlet-class>com.wll.servlet.GetServlet</servlet-class>
</servlet>

<servlet-mapping>
    <servlet-name>getcontext</servlet-name>
    <url-pattern>/getcontext</url-pattern>
</servlet-mapping>

获取初始化参数 getInitParameter

    <!--配置web应用的一些初始化参数-->
    <context-param>
        <param-name>jdbc</param-name>
        <param-value>jdbc:mysql://localhost:3306/mybatis</param-value>
    </context-param>

    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext servletContext = this.getServletContext();
        String jdbc = servletContext.getInitParameter("jdbc");
        resp.getWriter().print(jdbc);
    }

请求转发

    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext servletContext = this.getServletContext();
//        RequestDispatcher getparam = servletContext.getRequestDispatcher("/getparam");   //获取请求转发路径
//        getparam.forward(req,resp); //调用forward实现请求转发
        servletContext.getRequestDispatcher("/getparam").forward(req,resp);
    }

    <servlet>
        <servlet-name>getdispatcher</servlet-name>
        <servlet-class>com.wll.servlet.GetDispatcher</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>getdispatcher</servlet-name>
        <url-pattern>/getdispatcher</url-pattern>
    </servlet-mapping>

Properties

在java目录下新建properties文件，在resources目录下新建properties文件，都被打包到了同一个路径下：classes（classpath）

user=root
password=123123

   protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        InputStream resourceAsStream = this.getServletContext().getResourceAsStream("/WEB-INF/classes/db.properties");
       //InputStream resourceAsStream = this.getServletContext().getResourceAsStream("/WEB-INF/classes/com/wll/servlet/ad.properties");
        Properties properties = new Properties();
        properties.load(resourceAsStream);
        String user = properties.getProperty("user");
        String password = properties.getProperty("password");
        resp.getWriter().print(user+password);
    }

    <servlet>
        <servlet-name>getproperties</servlet-name>
        <servlet-class>com.wll.servlet.GetProperties</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>getproperties</servlet-name>
        <url-pattern>/getproperties</url-pattern>
    </servlet-mapping>

Maven约定大于配置，如果properties写在java目录下无法导出，所以配置pom.xml文件

<build>
    <!--在build中配置resources，来防止我们资源导出失败的问题-->
        <resources>
            <resource>
                <directory>src/main/resources</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
            </resource>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
        </resources>
</build>

3.3、HttpServletRequest

获取前端传递的参数&&请求转发

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Login</title>
</head>
<body>
    <form action="${pageContext.request.contextPath}/login" method="post">
        账号：<input type="text" name="username"> <br>
        密码：<input type="password" name="password"> <br>
        爱好：
        <input type="checkbox" name="hobbies" value="吃饭">吃饭
        <input type="checkbox" name="hobbies" value="睡觉">睡觉
        <input type="checkbox" name="hobbies" value="打游戏">打游戏
        <input type="checkbox" name="hobbies" value="奥力给">奥力给
        <input type="submit">
    </form>
</body>
</html>

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>success</title>
</head>
<body>
    <h1>登录成功</h1>
</body>
</html>

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0"
         metadata-complete="true">
    <welcome-file-list>
        <welcome-file>/login.jsp</welcome-file>
    </welcome-file-list>

    <servlet>
        <servlet-name>request</servlet-name>
        <servlet-class>com.wll.servlet.RequestForward</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>request</servlet-name>
        <url-pattern>/login</url-pattern>
    </servlet-mapping>
</web-app>

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("utf-8");
        resp.setCharacterEncoding("utf-8");

        String username = req.getParameter("username");
        String password = req.getParameter("password");
        //获取checkbox内容
        String[] hobbies = req.getParameterValues("hobbies");
        System.out.println(username);
        System.out.println(password);
        System.out.println(Arrays.toString(hobbies));
        //请求转发	对比ServletContext请求转发
        req.getRequestDispatcher("/success.jsp").forward(req,resp);
    }
    //post调用了get，虽然submit方式是post，但是直接在get里写就行
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }

测试

3.4、HttpServletResponse

向浏览器输出信息

下载文件

获取下载文件的路径
获取下载的文件名
设置办法让浏览器能够支持(Content-Disposition)下载我们需要的东西，中文文件名URLEncoder.encode编码，否则有可能乱码
获取下载文件的输入流
创建缓冲区
获取OutputStream对象
将FileOutputStream流写入到buffer缓冲区，使用OutputStream将缓冲区中的数据输出到客户端
关闭流

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
        //1. 获取下载文件的路径
        String realPath = this.getServletContext().getRealPath("\\WEB-INF\\classes\\a.png");
        //2. 获取下载的文件名，subString：截取父字符串的一部分   lastIndexOf：返回此字符在字符串中最后一次出现的位置
        String fileName = realPath.substring(realPath.lastIndexOf("\\") + 1);
        //3. 设置办法让浏览器能够支持(Content-Disposition)下载我们需要的东西，中文文件名URLEncoder.encode编码，否则有可能乱码
        resp.setHeader("Content-Disposition","attachment;filename="+ URLEncoder.encode(fileName,"UTF-8"));
        //4. 获取下载文件的输入流
        FileInputStream fileInputStream = new FileInputStream(realPath);
        //5. 创建缓冲区
        int len = 0;
        byte[] buffer = new byte[1024];
        //6. 获取OutputStream对象
        ServletOutputStream outputStream = resp.getOutputStream();
        //7. 将FileOutputStream流写入到buffer缓冲区，使用OutputStream将缓冲区中的数据输出到客户端
        while((len=fileInputStream.read(buffer))>0){
            outputStream.write(buffer,0,len);
        }
        //8. 关闭流
        fileInputStream.close();
        outputStream.close();
    }

验证码功能

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //浏览器3秒自动刷新
        resp.setHeader("refresh","3");
        //内存中创建一张图片
        BufferedImage image = new BufferedImage(80, 20, BufferedImage.TYPE_INT_RGB);
        //得到图片
        Graphics2D graphics2D = (Graphics2D)image.getGraphics();    //笔
        //设置图片背景颜色
        graphics2D.setColor(Color.white);
        graphics2D.fillRect(0,0,80,20);
        //给图片写数据
        graphics2D.setColor(Color.blue);
        graphics2D.setFont(new Font(null,Font.BOLD,18));
        graphics2D.drawString(fun(),0,20);

        //告诉浏览器，这个请求用图片方式打开
        resp.setContentType("Image/jpeg");
        //当网站存在缓存，不让浏览器缓存
        resp.setDateHeader("expires",-1);
        resp.setHeader("Cache-Control","no-cache");
        resp.setHeader("Pragma","no-cache");

        //把图片写给浏览器
        ImageIO.write(image,"jpg",resp.getOutputStream());
    }
    //生成随机数
    private String fun(){
        Random random = new Random();
        String s = random.nextInt(99999999) + "";
        StringBuffer buffer = new StringBuffer();
        for (int i = 0; i < 8-s.length(); i++) {
            buffer.append("0");
        }
        //保证一定是八位数
        String s1 = buffer.toString() + s;
        return s1;
    }

实现重定向

一个web资源B收到客户端A请求后，B它会通知客户端去访问另外一个web资源C，这个过程叫重定向

常见场景：

用户登录

public void sendRedirect(String location) throws IOException;

重定向和转发的区别

相同点：页面都会实现跳转 307

不同点：跳转地址url不会变化，重定向会变化 302

<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<html>
<body>
<h2>Hello World!</h2>
<%--这里提交的路径：需要寻找到的项目的路径--%>
<%--${pageContext.request.contextPath}代表当前项目--%>
<form action="${pageContext.request.contextPath}/login" method="post">
    用户名：<input type="username" name="username"><br>
    密码：<input type="password" name="password"><br>
    <input type="submit">
</form>
</body>
</html>

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<body>
<h2>Success</h2>
</body>
</html>

protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        System.out.println(username+" "+password);
        /*
            重定向
            resp.setHeader("location","/response_war/success");
            resp.setStatus(302);
         */
        resp.sendRedirect("/response_war/success.jsp");
    }

3.5、Cookie、Session

一个网站如何判断用户是否来过
- 服务端给客户端一个信件，客户端下次访问服务器带上信件就行了：Cookie（客户端技术）
- 服务器登录用户来过了，下次用户来的时侯服务器匹配用户：Session（服务器技术）

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setContentType("text/html;charset=UTF-8");
        PrintWriter writer = resp.getWriter();
        //从服务器端从客户端获取cookie
        Cookie[] cookies = req.getCookies();
        if (cookies != null) {
            writer.print("你上一次访问的时间是：");
            for (int i = 0; i < cookies.length; i++) {
                Cookie cookie = cookies[i];
                if (cookie.getName().equals("lastLoginTime")) {
                    //获取cookie中的值
                    Long value = Long.parseLong(cookie.getValue());
                    SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
                    writer.print(simpleDateFormat.format(value));
                }
            }
        } else {
            writer.print("这是你第一次访问本网站");
        }
    
        //Cookie lastLoginTime = new Cookie("lastLoginTime", String.valueOf(System.currentTimeMillis()));
        //设置有效期为一天
        //lastLoginTime.setMaxAge(24*60*60);
        //resp.addCookie(lastLoginTime);
    
        //第一次访问服务器给客户端响应一个cookie
        resp.addCookie(new Cookie("lastLoginTime", String.valueOf(System.currentTimeMillis())));
    }

删除cookie：

不设置有效期，关闭浏览器，自动失效
设置有效期时间为0

Session

什么是Session：

服务器会给每一个用户（浏览器）创建一个Session对象
一个Session独占一个浏览器，只要浏览器没关，这个Session就存在
用户登陆后，整个网站都可以访问--->B站个人信息管理

public class Person {
    private String name;
    private int age;
    private String sex;

    public Person(String name, int age, String sex) {
        this.name = name;
        this.age = age;
        this.sex = sex;
    }

    public Person() {
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", sex='" + sex + '\'' +
                '}';
    }
}

SessionTest01

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("utf-8");
        resp.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charset=utf-8");
        //获取Session
        HttpSession session = req.getSession();
        //Session中存东西
        session.setAttribute("person", new Person("jack", 18, "男"));
        //获取Session的id
        String sessionId = session.getId();

        //Session是不是新建
        if (session.isNew()) {
            resp.getWriter().print("Session创建成功，ID：" + sessionId);
        } else {
            resp.getWriter().print("Session已经创建，ID：" + sessionId);
        }
        //Session创建时候干了什么
        //Cookie cookie = new Cookie("JSESSIONID",sessionId);
        //resp.addCookie(cookie);
    }

SessionTest02

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("utf-8");
        resp.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charset=utf-8");
        //获取Session
        HttpSession session = req.getSession();
        //获取session 中的数据
        Object person = session.getAttribute("person");
        resp.getWriter().print(person);
    }

SessionTest03

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //手动注销Session，常见场景：用户注销登录，自动注销Session在web.xml文件中配置
        HttpSession session = req.getSession();
        session.removeAttribute("person");
        session.invalidate();
    }

<servlet>
        <servlet-name>session01</servlet-name>
        <servlet-class>com.wll.servlet.SessionTest01</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>session01</servlet-name>
        <url-pattern>/s1</url-pattern>
    </servlet-mapping>

    <servlet>
        <servlet-name>session02</servlet-name>
        <servlet-class>com.wll.servlet.SessionTest02</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>session02</servlet-name>
        <url-pattern>/s2</url-pattern>
    </servlet-mapping>

    <servlet>
        <servlet-name>session03</servlet-name>
        <servlet-class>com.wll.servlet.SessionTest03</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>session03</servlet-name>
        <url-pattern>/s3</url-pattern>
    </servlet-mapping>

    <!--Session自动注销，1分钟-->
    <session-config>
        <session-timeout>1</session-timeout>
    </session-config>

测试

调用s3后直接访问s2为null、s1中sessionid改变

总结
- Session与Cookie的区别：
  - Cookie是把用户的数据直接写给用户的浏览器，浏览器可以保存（多个）
  - Session把用户的数据写到用户独占的Session中，服务端保存（保存重要的信息，避免服务器资源浪费）
- Session使用场景
  - 保存一个用户的登录信息
  - 购物车信息
  - 在整个网站中经常使用的数据，保存到Session中

posted @ 2021-03-15 20:42 芜湖男酮阅读(100) 评论(0) 收藏举报

刷新页面返回顶部

芜湖男酮

Servlet学习笔记

Servlet学习笔记

1、环境搭建

1.1、Maven下载配置

1.2、IDEA中Maven的一些操作

2、HelloServlet

2.1、创建项目

2.2、编写pom.xml

2.3、编写web.xml

2.4、源程序

2.5、测试运行

2.6、总结

3、Servlet

3.1、 Servlet运行原理图

3.2、ServletContext

3.3、HttpServletRequest

3.4、HttpServletResponse

3.5、Cookie、Session

公告