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javaWeb随笔

前言

javaWeb基础学习

正文

遇到的问题

IDEA创建Maven多模块项目子模块引用不到父模块的pom

个人觉得可能是IDEA的问题，网上说自行修改子项目的pom

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<parent>
    <artifactId>Test3</artifactId>
    <groupId>org.example</groupId>
    <version>1.0-SNAPSHOT</version>	
</parent>

image-20201215220938473

Maven中导入依赖,去仓库搜索需要的依赖

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https://mvnrepository.com/

image-20201215221404910

在父项目中的pom中

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<dependencies>
    <!-- https://mvnrepository.com/artifact/javax.servlet/javax.servlet-api -->
    <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>javax.servlet-api</artifactId>
        <version>4.0.1</version>
        <scope>provided</scope>
    </dependency>
</dependencies>

image-20201215224443423

创建的webapp中的web-xml修改成如下：（这个内容去tomcat的ROOT目录下提取）

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<?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_3_1.xsd"
  version="3.1"
  metadata-complete="true">



</web-app>

Maven资源导出问题

在当前项目中放入如下build

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<!--在build中配置resources，来防止我们资源导出失败的问题-->
    <build>
        <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>

编写一个简单Servlet类

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package com.c0okb.servlet;

import javafx.print.Printer;

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
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        PrintWriter writer = resp.getWriter();
        writer.print("Hello,servlet");
    }
}

（5）编写Servlet映射

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<!--配置Servlet的映射-->
  <!--注册servlet-->
  <servlet>
      <servlet-name>hello</servlet-name>
      <servlet-class>com.c0okb.servlet.helloServlet</servlet-class>
  </servlet>

  <!--注册servlet的请求路径-->
  <servlet-mapping>
    <servlet-name>hello</servlet-name>
    <url-pattern>/hello</url-pattern>
  </servlet-mapping>

</web-app>

配置好Tomcat

image-20201216161606371

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Servlet的运行原理

Servlet是由Web服务器调用，web服务器在收到浏览器之后，会：

image-20201216163306433

Servlet-Mapping问题

1、一个Servlet可以指定一个映射路径

2、一个Servlet可以指定多个映射路径

image-20201216171154201

3、一个Servlet可以指定通用映射路径

image-20201216171322204

4、加指定后缀或前缀

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5、优先级问题

指定固有的映射路径优先级最高，如果找不到就会走默认的处理请求；

image-20201216195524639

image-20201216195606313

image-20201216195707145

ServletContext对象

ServletContext的作用凌驾于该Web应用的所有Servlet之上。web容器在启动时，它会为每一个web程序都创建一个对应的ServletContext对象，它代表了当前的Web应用。

image-20201217121312716

其作用一：数据共享

Servlet1放入ServletContext的数据，Servlet2能够调用该数据，体现数据共享

例子：

image-20201217135300053

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protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    ServletContext servletContext = this.getServletContext();
    String username = (String) servletContext.getAttribute("username");
    resp.setContentType("text/html");
    resp.setCharacterEncoding("utf-8");
    PrintWriter writer = resp.getWriter();
    writer.print("username is:"+username);
}

image-20201217135332424

image-20201217135355963

然后其运行结果

访问

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http://localhost:8080/javaWeb1_war_exploded/helloWorld

将生成username:cookie存入ServletContext

然后访问

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http://localhost:8080/javaWeb1_war_exploded/Context

image-20201217135625175

其作用二：获取初始化参数

例子：

在web.xml中写入

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<context-param>
  <param-name>url</param-name>
  <param-value>http://www.baidu.com</param-value>
</context-param>

创建一个测试类

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package com.c0okb.test2;

import javax.servlet.ServletContext;
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 ParamTest extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext servletContext = this.getServletContext();
        String url = servletContext.getInitParameter("url");
        System.out.println(url);
    }

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

其中

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protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
     ServletContext servletContext = this.getServletContext();
     String url = servletContext.getInitParameter("url");
     System.out.println(url);
 }

image-20201217175533756

在web.xml中注册Servlet

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<servlet>
  <servlet-name>getParam</servlet-name>
  <servlet-class>com.c0okb.test2.ParamTest</servlet-class>
</servlet>
<servlet-mapping>
  <servlet-name>getParam</servlet-name>
  <url-pattern>/getParam</url-pattern>
</servlet-mapping>

image-20201217175744536

其作用三：请求转发

代码：

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protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    ServletContext servletContext = this.getServletContext();
    servletContext.getRequestDispatcher("/getParam").forward(req,resp);
}

注册Servlet

image-20201217184918802

image-20201217184944852

当访问/DisForward时，该请求将会被转发至/getParam

其作用四：读取资源文件 (常用)

读取properties

image-20201217213214043

image-20201217214023598

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    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
        ServletContext servletContext = this.getServletContext();
        //方法一
//        URL url = servletContext.getResource("/WEB-INF/classes/db.properties");
//        InputStream is = url.openStream();
        //方法二
        InputStream is = servletContext.getResourceAsStream("/WEB-INF/classes/db.properties");
        Properties prop = new Properties();
        prop.load(is);
        String username = prop.getProperty("username");
        String password = prop.getProperty("password");
        resp.getWriter().print(username);
        resp.getWriter().print(password);
    }

image-20201217214249820

效果：

image-20201217214855882

HttpServletResponse

web服务器接收到客户端的Http请求，针对这个请求，分别创建一个代表请求的HttpServletRequest对象，代表响应的一个HttpServletResponse;

·如果要获取客户端请求过来的参数：找HttpServletRequest

·如果要给客户端响应一些信息：找HttpServletResponse

下载文件

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package com.c0okb.test2;

import jdk.internal.util.xml.impl.Input;

import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
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;
import java.io.OutputStream;
import java.net.URLEncoder;

public class DownloadFile extends HttpServlet {
    private static final long serialVersionUID = 1L;

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String path = "E:\\javaTest\\Test\\javaWeb1\\Download\\test.jpg";
        System.out.println("文件下载的路径"+path);
        String filename = path.substring(path.lastIndexOf("\\")+1);
        System.out.println(filename);
        resp.setHeader("Content-Disposition", "attachment;filename="+ URLEncoder.encode(filename,"UTF-8"));
        InputStream in = null;
        OutputStream out = null;
        try{
            in = new FileInputStream(path);
            int len = 0;
            byte buffer[] = new byte[1024];
            ServletOutputStream ServletOut = resp.getOutputStream();
            while ((len=in.read(buffer))!=-1){
                ServletOut.write(buffer,0,len);
            }
        } catch (Exception e){
            e.printStackTrace();
        }finally {
            if(in != null){
                in.close();
            }
        }
    }

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

image-20201219145131827

详细参考：Java在上传或下载时header中Content-Disposition的作用以及Content-disposition中Attachment和inline的区别

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1.要获取下载文件的路径
		String path = "E:\\javaTest\\Test\\javaWeb1\\Download\\test.jpg";
		System.out.println("文件下载的路径"+path);
2.下载的文件名是啥?
        String filename = path.substring(path.lastIndexOf("\\")+1);
        System.out.println(filename);
3.设置想办法让浏览器能够支持下截我们需要的东西
		resp.setHeader("Content-Disposition", "attachment;filename="+ 				URLEncoder.encode(filename,"UTF-8"));
4、获取下载文件的输入流
		in = new FileInputStream(path);
5.创建缓冲区
         int len = 0;
         byte buffer[] = new byte[1024];
6.获取OutputStream对象
         ServletOutputStream ServletOut = 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=in.read(buffer))!=-1){
                ServletOut.write(buffer,0,len);}

生成验证码

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package com.c0okb.test2;


import javax.imageio.ImageIO;
import javax.servlet.ServletException;
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;



public class ImageServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setHeader("refresh","3");
        BufferedImage bufferedImage = new BufferedImage(80,20,BufferedImage.TYPE_INT_RGB);
        Graphics2D g = (Graphics2D) bufferedImage.getGraphics();
        g.setColor(Color.white);
        g.fillRect(0,0,80,20);
        //给图片写数据
        g.setColor(Color.BLUE);
        g.setFont(new Font(null,Font.BOLD,20));
        g.drawString(random(),0,20);

        resp.setContentType("image/png");
        ImageIO.write(bufferedImage,"jpg",resp.getOutputStream());
    }


    //生成随机数
    private String random(){
        String str = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
        StringBuilder sb = new StringBuilder(6);
        for(int i=0;i<6;i++){
            char ch = str.charAt(new Random().nextInt(str.length()));
            sb.append(ch);
        }
        return sb.toString();
    }


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

重定向

重定向是指当浏览器向Tomcat服务器发送请求时，由于一个Servlet1类无法完成所有请求响应工作，这时候Servlet1类会通知浏览器重新定向到另一个Servlet2类。浏览器再次发送请求Servlet2,来获得Servlet2的响应。

重定向和转发的相同点和不同点

相同点：页面会实现跳转

不同点：请求转发的时候，url不会产生变化；重定向，url会发生变化

小demo一下：

注册Servlet

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<servlet>
  <servlet-name>Login</servlet-name>
  <servlet-class>com.c0okb.test2.LoginServlet</servlet-class>
</servlet>
<servlet-mapping>
  <servlet-name>Login</servlet-name>
  <url-pattern>/Login</url-pattern>
</servlet-mapping>
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package com.c0okb.test2;



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


public class LoginServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
        System.out.println("进入方法");
        req.setCharacterEncoding("utf-8");
        resp.setContentType("text/html,charset=utf-8");
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        if(("admin").equals(username)&&("root").equals(password)){
            System.out.println("进入welcome方法");
            resp.sendRedirect("/javaWeb1_war_exploded/welcome.jsp");

        }else{
            System.out.println("进入index方法");
            resp.sendRedirect("/javaWeb1_war_exploded/index.jsp");
        }
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws IOException {
        doGet(req, resp);
    }
}
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<%index.jsp%>
<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>Insert title here</title>
</head>
<body>

    <form action="${pageContext.request.contextPath}/Login" method="get">
        username:<input type="text" name="username"><br>
        password:<input type="password" name="password"><br>
        <input type="submit" value="submit">

    </form>

</body>
</html>
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<%welcome.jsp%>
<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>Insert title here</title>
</head>
<body>

welcome

</body>
</html>

​

Author: 我是小吴啦
Link: http://yoursite.com/2020/12/15/javaWeb%E9%9A%8F%E7%AC%94/
Copyright Notice: All articles in this blog are licensed under CC BY-NC-SA 4.0 unless stating additionally.
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