Servlet基础知识（自学笔记）_webservlet(name="loginservlet",urlpatterns={"---1-

作者：weixin_40725706 | 2024-07-25 22:47:02

踩

webservlet(name="loginservlet",urlpatterns={"---1---"})

使用工具：intellij idea2018版

需准备：

（1）安装intellij idea

（2）安装jdk

（3）安装Tomcat

（4）可以在创建工程之前配置好环境，也可以如下视频在创建过程中配置

1.servlet的简单介绍

servlet全称java Servlet，是用java编写的服务器端程序，其主要功能在于交互式地浏览和修改数据，生成动态web内容。是JavaWeb的三大组件之一（Filter和Listener）

作用：接受客户端发来的请求数据，处理数据，将处理结果通过响应发送给客户端

2.servlet的两种创建方式

（1）servlet3.0之前，通过web.xml部署描述文件，如下视频

第一个servlet.mp4

（2）servlet3.0之后，可以通过注解的方式创建，详细步骤基本同上，区别如下：

a. 在new时选择servlet，然后输入名字即可

b.不用web.xml文件部署，在开头部署，如下标识

剩下的操作和视频1中是基本一样的。

3.request与response


package com.study.servlet;
 
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Enumeration;
 
@WebServlet(name = "RequestServlet",urlPatterns = "/request")
public class RequestServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
 
    }
 
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("接收到get请求");
        //请求行
        System.out.println("请求方式："+request.getMethod());
        System.out.println("URI:"+request.getRequestURI());
        System.out.println("发出请求客户端IP地址："+request.getRemoteAddr());
        System.out.println("服务点请求的IP地址："+request.getLocalAddr());
        System.out.println("访问客户端的端口号"+request.getRemotePort());
        System.out.println("web应用路径："+request.getContextPath());
        System.out.println("http协议和版本："+request.getProtocol());
 
        //获取请求头所有属性信息
        Enumeration<String> headerNames = request.getHeaderNames();
        while (headerNames.hasMoreElements()){
            String element = headerNames.nextElement();
            System.out.println(element+":"+request.getHeader(element));
        }
 
        //请求体，获取请求参数内容
        String name = request.getParameter("name");
        String passWord = request.getParameter("passWord");
        System.out.println("用户名："+name);
        System.out.println("密码："+passWord);
 
        //检验登陆状态方式1
        String result="登陆成功！";
//        ServletOutputStream outputStream = response.getOutputStream();
//        outputStream.write(result.getBytes());
        //检验登陆状态方式2
        response.setContentType("text/html;charset=utf-8");//没有设置这个编码格式，有可能输出结果是乱码
        PrintWriter writer = response.getWriter();
        writer.write(result);
 
    }
}

使用的html文件：action的request对应 urlPatterns = "/request"，意思是当点击提交按钮时，RequestServlet的数据请求可以接收到表单提交的数据


<html>
<head>
    <title>get请求表单</title>
</head>
<body>
<center>
    <h2>发起http get请求</h2>
    <form action="request" method="get">
        <p>账号：<input type="text" name="name" /></p>
        <p>密码：<input type="text" name="passWord" /></p>
        <input type="submit" name="提交" />
    </form>
</center>
</body>
</html>

4.验证码切换


package com.study.servlet;
 
import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;
 
@WebServlet(name = "VerifyCodeServlet",urlPatterns = "/code")
public class VerifyCodeServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
 
    }
 
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        int width=100;
        int height=30;
 
        //定义随机字符
        String data="abcdefghijklmnopqrstuvwxyz0123456789";
        //创建随机对象
        Random random = new Random();
        //创建图片流
        BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_3BYTE_BGR);
 
        //设置图片背景色及形状
        Graphics graphics = image.getGraphics();
        graphics.setColor(Color.gray);
        graphics.fillRect(0,0,width,height);
 
        //设置随机字符数量和颜色、位置及字符
        graphics.setColor(Color.black);
        for(int i=0;i<4;i++){
            int position=random.nextInt(data.length());
            String substring = data.substring(position, position + 1);
            graphics.drawString(substring,width/5*(i+1),15);
        }
 
        //输出请求
        ImageIO.write(image,"jpg",response.getOutputStream());
    }
}

jsp文件


<%--
  Created by IntelliJ IDEA.
  User: shinelon
  Date: 2020/11/23
  Time: 10:41
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>验证码</title>
</head>
<body>
<center>
    <h2>切换验证码</h2>
    <script>
        function changeImageCode() {
            document.getElementById('btn').isDisable=true;
            document.getElementById('identity').src='code?ts='+new Date().getTime();
        }
    </script>
 
    <img src="code" id="identity" onload="btn.disable=false;" style="cursor: pointer;vertical-align: center" />
 
    <input type="button" value="看不清，更换验证码" onclick="changeImageCode()" id="btn" style="vertical-align: center" />
</center>
</body>
</html>

5.servlet的声明周期


package com.study.servlet;
 
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
 
/**
 * servlet是单例设计模式
 * 无论多少次请求都是只有一个servlet实例
 * 多个客户端并发时，服务器则会启动多个线程分别执行servlet的service方法
 */
@WebServlet(name = "LifeServlet", urlPatterns = "/life")
public class LifeServlet extends HttpServlet {
    @Override
    public void init() throws ServletException {//启动服务器，执行该servlet请求只会会执行一次
        System.out.println("初始化过程.....");
    }
 
    //每次请求都会调用
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("服务过程中.....");
        doGet(req,resp);
    }
 
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
 
    }
 
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("doget调用中.....");
    }
 
    //关闭服务器调用
    @Override
    public void destroy() {
        System.out.println("销毁中.....");
    }
}

6.servletConfig和servletContext


package com.study.servlet;
 
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
 
/**
 * servlet是单例设计模式
 * 无论多少次请求都是只有一个servlet实例
 * 多个客户端并发时，服务器则会启动多个线程分别执行servlet的service方法
 */
@WebServlet(name = "LifeServlet", urlPatterns = "/life")
public class LifeServlet extends HttpServlet {
    @Override
    public void init() throws ServletException {//启动服务器，执行该servlet请求只会会执行一次
        System.out.println("初始化过程.....");
    }
 
    //每次请求都会调用
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("服务过程中.....");
        doGet(req,resp);
    }
 
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
 
    }
 
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("doget调用中.....");
    }
 
    //关闭服务器调用
    @Override
    public void destroy() {
        System.out.println("销毁中.....");
    }
}
 
 
package com.study.servlet;
 
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
 
@WebServlet(name = "HelloServlet1",urlPatterns = "/Get")
public class HelloServlet1 extends HttpServlet {
 
 
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("发送请求");
    }
 
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("get请求");
        //获取HelloServlet的发送对象name
        System.out.println(this.getServletContext().getAttribute("name"));
    }
}

7.登陆验证及转发


package com.study.servlet;
 
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
 
/**
 * 请求转发，发送到错误页面
 */
@WebServlet(name = "LoginServlet",urlPatterns = "/login")
public class LoginServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
 
    }
 
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String userName="preston";
        String userPassWord="123456";
 
        //获取登陆页面信息
        String name = request.getParameter("name");
        String passWord = request.getParameter("passWord");
 
        //判断
        if(!name.equals(userName)){
            request.setAttribute("errorMessage","用户名错误");//发送错误信息
            request.getRequestDispatcher("/loginError.jsp").forward(request,response);//转发
 
        }else if(!passWord.equals(userPassWord)){
            request.setAttribute("errorMessage","密码错误");//发送错误信息
            request.getRequestDispatcher("/loginError.jsp").forward(request,response);//转发
 
        }else{
            //重定向方法1
//            response.setStatus(HttpServletResponse.SC_MOVED_TEMPORARILY);
//            response.setHeader("Location","https://www.baidu.com/");
 
            //重定向方法2
            // response.sendRedirect("https://www.baidu.com/");
 
           //跳向自己写的首页
            response.sendRedirect("/hello/index.jsp");
 
 
        }
 
    }
}

8.线程安全


package com.study.servlet;
 
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
 
/**
 * 线程安全问题：
 * 尽量少用成员变量
 *
 */
@WebServlet(name = "ThreadServlet",urlPatterns = "/thread")
public class ThreadServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
 
    }
 
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        int a=0;
        //5秒之后才输出结果
        synchronized (this){
            a++;
            try {
                Thread.sleep(5*1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
 
            response.setContentType("text/html;charset=utf-8");
            response.getWriter().write(a+"");
        }
 
    }
}

9.读取配置文件db.properties


package com.study.servlet;
 
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;
 
/**
 * 读取配置文件db.properties
 */
@WebServlet(name = "ReadDatabaseServlet",urlPatterns = "/data")
public class ReadDatabaseServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
 
    }
 
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        InputStream resourceAsStream = this.getServletContext().getResourceAsStream("/db.properties");
        Properties properties = new Properties();
        properties.load(resourceAsStream);
        String name = properties.getProperty("name");
        String passWord = properties.getProperty("passWord");
        String url = properties.getProperty("url");
        System.out.println(name);
        System.out.println(passWord);
        System.out.println(url);
    }
}

db.properties文件


name=preston
passWord=50095
url=baidu.com

10.自动刷新功能


package com.study.servlet;
 
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
 
/**
 * 自动刷新
 */
@WebServlet(name = "RefreshServlet",urlPatterns = "/refresh")
public class RefreshServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
 
    }
 
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        /**另一种自动刷新方式
         * <meta http-equiv='refresh' content='3;url='>固定格式
         */
        String message="<meta http-equiv='refresh' content='3;url=/hello/index.jsp'>3秒后会自动跳转到首页，如果没有跳转，请点击<a href='/hello/index.jsp'>跳转连接</a>";
        request.setAttribute("message",message);
        request.getRequestDispatcher("/index.jsp").forward(request,response);
    }
 
    private void request() {
        // response.setContentType("text/html;charset=utf-8");
        //自动刷新
//        response.setHeader("refresh","3");
//        response.getWriter().print("3秒后自动刷新");
 
        //3秒后跳转到指定网页
//        response.setHeader("refresh","3;url='/hello/index.jsp'");
//        response.getWriter().print("3秒后自动刷新");
    }
}

11.文件下载


package com.study.servlet;
 
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
 
@WebServlet(name = "DownloadServlet",urlPatterns = "/download")
public class DownloadServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
 
    }
 
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
       //压缩文件直接下载，其它直接打开
 
        //response.getWriter();//输出字节码文件
        String filename = request.getParameter("filename");
        //通知浏览器不要预览，直接下载
        String type = this.getServletContext().getMimeType(filename);
        response.setContentType(type);
        //通知浏览器下载的方式
        response.setHeader("Content-Disposition","attachment;filename="+filename);
 
        //获取文件的绝对路径
        String realPath = this.getServletContext().getRealPath("download/"+filename);
        InputStream in = new FileInputStream(realPath);
        ServletOutputStream outputStream = response.getOutputStream();//输出二进制文件
 
        //文件拷贝
        int len=0;
        byte[] buffer=new byte[1024];
        while ((len=in.read(buffer))>0){
            outputStream.write(buffer,0,len);
        }
        in.close();
    }
}

综合实例链接：https://mp.csdn.net/console/editor/html/110004445

声明：本文内容由网友自发贡献，不代表【wpsshop博客】立场，版权归原作者所有，本站不承担相应法律责任。如您发现有侵权的内容，请联系我们。转载请注明出处：https://www.wpsshop.cn/w/weixin_40725706/article/detail/882325