JavaWeb基础学习

1.tomcat的配置

1.下载

tomcat官网下载

解压到你想要的文件夹

进入\bin文件夹,打开startup.bat

访问http://localhost:8080/

成功看到默认

2.去除乱码

我们看到上面的打印是乱码的

打开\conf\logging.properties

标注的地方修改为GBK即可去除乱码

2.下载maven

maven官网下载

解压

1.配置环境变量

MAVEN_HOME

指向maven的根目录如D:\java_web\apache-maven-3.8.1

M2_HOME

指向maven的根目录下的bin目录如D:\java_web\apache-maven-3.8.1\bin

在Path中增加%MAVEN_HOME%\bin

输入mvn -version

配置完成

2.添加镜像仓库

在conf\settings.xml增加如下配置

 <!-- 阿里云中心仓库 -->
<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>

3.添加本地仓库

在conf\settings.xml增加如下配置

3.idea在maven中的操作

项目架构管理工具-maven

Maven: 约定大于配置

有约束不要去违反

Maven会规定你要如何编写我们的代码,必须按照这个规范来

<!--    在build解决maven资源导出(先了解一下)-->
    <resources>
      <resource>
        <directory>src/main/resources</directory>
        <includes>
          <include>**/*.properties</include>
          <include>**/*.xml</include>
        </includes>
        <filtering>false</filtering>
      </resource>
      <resource>
        <directory>src/main/java</directory>
        <includes>
          <include>**/*.properties</include>
          <include>**/*.xml</include>
        </includes>
        <filtering>false</filtering>
      </resource>
    </resources>

1.打开设置

创建新项目

在pom.xml中配置引入jsp的相关jar包

<dependencies>

    <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>javax.servlet-api</artifactId>
        <version>4.0.1</version>
        <scope>provided</scope>
    </dependency>
    <!-- https://mvnrepository.com/artifact/javax.servlet.jsp/javax.servlet.jsp-api -->
    <dependency>
        <groupId>javax.servlet.jsp</groupId>
        <artifactId>javax.servlet.jsp-api</artifactId>
        <version>2.3.3</version>
        <scope>provided</scope>
    </dependency>


</dependencies>

2.配置tomcat

点击右上角

完成

3.手动增加java和resources文件夹

4.Servlet

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">
</web-app>

1 Servlet简介

sun公司开发动态web的一门技术

提供一个接口Servlet

实现Servlet的两个类->HttpServlet和GenericServlet

2 Servlet

编写自己的实现Servlet接口类来处理请求信息并返回相应,一般通过继承HttpServlet来重写doGet等方法.

3 Maping问题

可以指定一个,多个,通配符映射路径

指定了固有的映射路径优先级最高,如果找不到就走默认的请求

4 ServletContext对象

共享数据
- 在这个Servlet中保存的数据,可以在另外一个servlet中拿到

      ServletContext servletContext = this.getServletContext();
      String username = "codelorin";
      // 将一个数据保存在Servlet中
      servletContext.setAttribute("username", username);

ServletContext servletContext = this.getServletContext();
      String username = (String) servletContext.getAttribute("username");
      resp.getWriter().print("username" + ":" + username);

获取初始化参数
请求转化

1 2	ServletContext servletContext = this.getServletContext(); servletContext.getRequestDispatcher("/gp").forward(req,resp);

properties

InputStream resourceAsStream = this.getServletContext().getResourceAsStream("/WEB-INF/classes/db.properties");

Properties properties = new Properties();
properties.load(resourceAsStream);
String user = properties.getProperty("username");

5 HttpServletResponse

web服务器接收到客户端的http请求,针对这个请求,分别创建了一个代表请求的HttpServletRequest对象,代表响应一个了一个HttpServletResponse

5.1.简单分类

发送数据的方法

1
2
3

ServletOutputStream getOutputStream() throws IOException;

PrintWriter getWriter() throws IOException;

5.2.常见应用

输出消息
下载文件
- 下载文件的文件名
- 设置浏览器支持下载的类型
- 获取下载的输入流
- 创建缓冲区
- 获取OutputStream对象
- 将FileOutputStream流写入buffer缓冲区
- 使用OutputStream将缓冲区的数据输出到客户端

//1.获取下载文件的路径
String realPath = "D:\\java\\web-study\\httpres\\src\\main\\resources\\1.jpg";
System.out.println("下载的路径: " + realPath);
//2.下载文件的文件名
String fileName = realPath.substring(realPath.lastIndexOf("\\") + 1);
//3.设置浏览器支持下载的类型
resp.setHeader("Content-disposition", "attachment;filename" + fileName);
//4.获取下载的输入流
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 out = resp.getOutputStream();
//7.将FileOutputStream流写入buffer缓冲区,输出到客户端
while ((len = fileInputStream.read(buffer)) > 0) {
    out.write(buffer, 0, len);
}
fileInputStream.close();
out.close();

验证码

@Override
   protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
       resp.setHeader("refresh", "3");
  
       //创建图片
       BufferedImage bufferedImage = new BufferedImage(80, 20, BufferedImage.TYPE_INT_BGR);
       //得到图片
       Graphics2D graphics = (Graphics2D) bufferedImage.getGraphics();
  
       //设置图片的背景颜色
       graphics.setColor(Color.WHITE);
       //填充背景颜色
       graphics.fillRect(0, 0, 80, 20);
       //给图片写数据
       graphics.setColor(Color.BLUE);
       graphics.setFont(new Font(null, Font.BOLD, 20));
       graphics.drawString(makeNum(), 0, 20);
  
       resp.setContentType("image/jpeg");
       resp.setDateHeader("expires", -1);
       resp.setHeader("Cache-Control", "no-cache");
       resp.setHeader("Pragma", "no-cache");
  
       ImageIO.write(bufferedImage, "jpg", resp.getOutputStream());
   }
  
   private String makeNum() {
       Random random = new Random();
       String num = random.nextInt(9999) + "";
  
       StringBuffer sb = new StringBuffer();
       for (int i = 0; i < 4 - num.length(); i++) {
           sb.append("0");
       }
       String s = sb.toString() + num;
       return num;
   }

5.3.实现重定向

resp.sendRedirect("/image");

//可以分解为以下的代码
resp.setHeader("Location","/image");
resp.setStatus(302);

重定向和转化的区别

相同点

页面会发生跳转

不同点

请求转发的时候,url不会发生变化
重定向时候,url地址栏会发生变化

6 HttpServletRequest

7.cookie和session

保存会话的两种方式

cookie

客户端技术(响应,请求)

req.setCharacterEncoding("utf-8");
       //解决乱码
       resp.setContentType("text/html;charset=utf-8");

       PrintWriter out = resp.getWriter();

       //获取cookies
       Cookie[] cookies = req.getCookies();

       if (cookies != null) {
           for (int i = 0; i < cookies.length; i++) {
               Cookie cookie = cookies[i];
               String name = cookie.getName();
               if (name.equals("lastLoginTime")) {

                   long lastLoginTime = Long.parseLong(cookie.getValue());
                   Date date = new Date(lastLoginTime);
                   out.write("你的最后一次登录时间" + date.toLocaleString());

               }


           }
       } else {
           out.write("这是你第一次访问!");
       }

       Cookie cookie = new Cookie("lastLoginTime", System.currentTimeMillis() + "");
       resp.addCookie(cookie);

session

服务端技术,利用这个技术,可以保存用户的会话信息

package com.codelorin;

import javax.servlet.ServletException;
import javax.servlet.http.*;
import java.io.IOException;


public class sessionStudy extends HttpServlet {
    @Override
    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");

        //得到session
        HttpSession session = req.getSession();

        //往session中存东西
        session.setAttribute("name", new Person("codelorin", 1));

        //获取session的id
        String id = session.getId();

        if (session.isNew()) {
            resp.getWriter().write("session创建成功" + id);
            return;
        }
        resp.getWriter().write("session已经在服务器中存在了" + id);

        //session创建的时候做了什么事情
        Cookie cookie = new Cookie("JSESSIONID", id);
        resp.addCookie(cookie);

    }

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

package com.codelorin;

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



public class sessionStudy2 extends HttpServlet {
    @Override
    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");

        HttpSession session = req.getSession();
        Person name = (Person) session.getAttribute("name");
        System.out.println(name);
        resp.getWriter().write(name.toString());

    }

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

在web.xml可以设置session过期时间

<session-config>
    <!--   15分钟后过期     -->
    <session-timeout>
        15
    </session-timeout>
</session-config>

5.jsp

1.什么是jsp

Java Server Pages: Java服务端页面,也和Servlet一样用于动态web.

2.最大的特点

写JSP就像是在写HTML
区别
- HTML只给用户提供动态数据
- JSP页面可以嵌入JAVA代码,为用户提供动态数据

3.JSP原理

JSP到底怎么执行的

代码层没有任何问题
服务器内部工作
页面转变成java程序

本质是就是Servlet

index_jsp=>HttpJspBase=>HttpServlet

//初始化
public void _jspInit(){
    
}
//销毁
public void _jspDestroy(){
    
}
//JSPService
public void _jspService(){
    
}

判断请求
内置了一些对象

PageContext pageContext;			//页面上下文
HttpSession session;				//session	
ServletContext application;			//applicationContext 
ServletConfig config;				//config
JspWriter out;						//out
Object page = this;					//page:当前
HttpServletRequest request,			//请求
HttpServletResponse response		//相应

以上的对象可以直接在JSP中直接使用

在jsp页面中,java代码原封不动输出,

html代码转化为

1	out.write("<html>\r\n")

这样的格式输出到前端!

4.jsp的依赖

<dependencies>
    <!--Servlet的依赖        -->
    <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>servlet-api</artifactId>
        <version>2.5</version>
    </dependency>
    <!--JSP的依赖        -->
    <dependency>
        <groupId>javax.servlet.jsp</groupId>
        <artifactId>javax.servlet.jsp-api</artifactId>
        <version>2.3.3</version>
    </dependency>
    <!--JSTL的依赖        -->
    <dependency>
        <groupId>javax.servlet.jsp.jstl</groupId>
        <artifactId>jstl-api</artifactId>
        <version>1.2</version>
    </dependency>
    <!--standard标签库的依赖        -->
    <dependency>
        <groupId>taglibs</groupId>
        <artifactId>standard</artifactId>
        <version>1.1.2</version>
    </dependency>
</dependencies>

5.基础语法

JSP表达式

用来将程序的输出到客户端

格式<%= xxx %>

1	<%= new java.util.Date() %>

JSP脚本片段

格式<% xxx %>

<%
int x = 10;
out.println(x);

%>
<p>这是一个JSP文档</p>
<%
int y = 0;
out.println(y);
%>

代码中嵌入HTML元素

格式<% { %> <%}%>

<% for (int i = 0; i < 5; i++) { %>
<h1>by codelorin <%= i %></h1>
<%
}
%>

jsp声明

提高作用域,会被编译到jsp生成的java类中.

其他情况会被编译到_jspServlet方法中

格式:<%!%>

<%!
    static {
        System.out.println("Loading Servlet");
    }
    public void lorin(){
        System.out.println("正在执行方法lorin");
    }
    
%>

jsp的注释不会再客户端显示,html会

6.定制错误页面

jsp中配置

1	<%@page errorPage="Error/500.jsp" %>

web.xml中配置

<error-page>
    <error-code>500</error-code>
    <location>/Error/500.jsp</location>
</error-page>

7.jsp中导包

1	<%@ page import="java.util.Date" %>

8.提取公共页面

变成一个文件

1	<%@include file="Common/header.jsp"%>

代码引用

1	<jsp:include page="Common/header.jsp"/>

9.九大内置对象

PageContext 存东西
Request 存东西
Response
Session 存东西
Application [ServletContext] 存东西
config [Servlet Config]
out
page
exception

简单demo

<%
    pageContext.setAttribute("name","codelorin1");//保存一个页面中有效  
    request.setAttribute("name1","codelorin2");//一次请求有效,请求转发有效 新闻
    session.setAttribute("name2","codelorin3");//保存的数据在一次会话中有效,从打开浏览器到关闭浏览器 购物车
    application.setAttribute("name3","codelorin4");//保存的数据在服务器中有效,从打开服务器到关闭服务器 聊天记录
%>
<%
    String name = (String) pageContext.findAttribute("name");
    String name1 = (String) pageContext.findAttribute("name");
    String name2 = (String) pageContext.findAttribute("name");
    String name3 = (String) pageContext.findAttribute("name");
%>
//el表达式取出值
<h1>取出的值为:</h1>
<h3>${name}</h3>
<h3>${name1}</h3>
<h3>${name2}</h3>
<h3>${name3}</h3>

<h3><%= name %></h3>

1	pageContext.forward("/index")

10.JSP标签,JSTL标签,EL表达式

需要导入包

EL表达式:

获取数据
执行运算
获取web开发的常用对象

JSP标签:

<jsp:forward page="index.jsp">
    <jsp:param name="name" value="codelorin"/>
    <jsp:param name="age" value="18"/>
</jsp:forward>


<%--取出参数--%>
<%= request.getParameter("name")%>
<%= request.getParameter("age")%>

JSTL标签库

HTML的扩展

核心标签

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%--引入--%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<form action="jstl_study.jsp" method="get">
    <input type="text" name="username" value="${param.username}" placeholder="请输入用户名">
    <input type="submit" value="登录">
</form>
<c:if test="${param.username == 'admin'}" var="isAdmin">
    <c:out value="管理员欢迎你!"/>
</c:if>
<c:out value="${isAdmin}"/>
</body>
</html>

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<c:set var="score" value="99"/>
<c:choose>
    <c:when test="${score>=90}">
        你的成绩为优秀
    </c:when>
</c:choose>
</body>
</html>

<%@ page import="java.util.ArrayList" %>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<% ArrayList<String> people = new ArrayList<>();
    people.add(0, "lorin");
    people.add(1, "zou");
    people.add(2, "jjking");
    request.setAttribute("list", people);

%>
<c:forEach var="people" items="${list}">
    <c:out value="${people}"/> <br/>
</c:forEach>
# 遍历变量
<c:forEach var="people" items="${list}" begin="" end="" step=""></c:forEach>
</body>
</html>

11.JavaBean

实体类

JavaBean有特定的写法:

必须要有一个无参构造
属性必须私有化
必须有对应的get/set方法

一般用来和数据库的字段做映射 ORM;

ORM: 对象关系映射

表->类
字段->属性
行->对象

id	name	age	address
1	lorin1	3	广州
2	lorin2	5	广州
3	lorin3	7	广州

package com.codelorin.pojo;

/**
 * @author CodeLorin
 * @date 2021/5/11 11:21
 */
public class People {
    private int id;
    private String name;
    private int age;
    private String address;

    public People() {
    }

    public People(int id, String name, int age, String address) {
        this.id = id;
        this.name = name;
        this.age = age;
        this.address = address;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    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 getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    @Override
    public String toString() {
        return "People{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", age=" + age +
                ", address='" + address + '\'' +
                '}';
    }
}

12.MVC三层架构

MVC: Model view Controller 模型视图控制器

用户可以直接访问控制层,控制层可以直接操作数据库

servlet->CURD->数据库

弊端:程序十分臃肿,不利于维护

servlet:处理请求响应,跳转,jdbc,业务逻辑代码

Model

业务处理:业务逻辑(service)
数据持久层: CRUD (Dao)

View

展示数据
提供链接发起请求 a form

Controller

接受用户请求: (req,session)
交给业务层
控制视图跳转

13.Filter

过滤器,用来过滤网站的数据

处理乱码
登录

package com.codelorin.filter;

import javax.servlet.*;
import java.io.IOException;

/**
 * @author CodeLorin
 * @date 2021/5/19 15:47
 */
public class Demo implements Filter {
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("开始");
    }

    public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws IOException, ServletException {
        req.setCharacterEncoding("utf-8");
        resp.setCharacterEncoding("utf-8");
        resp.setContentType("text/html; charset=UTF-8");
        System.out.println("执行前");
        chain.doFilter(req, resp);//拦截放行
        System.out.println("执行后");
    }

    public void destroy() {
        System.out.println("结束");
    }
}

<!--    页面-->
    <servlet>
        <servlet-name>demo</servlet-name>
        <servlet-class>com.codelorin.Show</servlet-class>
    </servlet>
<!--    两个url 对比-->
    <servlet-mapping>
        <servlet-name>demo</servlet-name>
        <url-pattern>/show</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>demo</servlet-name>
        <url-pattern>/servlet/show</url-pattern>
    </servlet-mapping>
    <filter>
        <filter-name>CharacterEncodingFilter</filter-name>
        <filter-class>com.codelorin.filter.Demo</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>CharacterEncodingFilter</filter-name>
        <url-pattern>/servlet/*</url-pattern>
    </filter-mapping>

14.监听器

package com.codelorin.listener;

import javax.servlet.ServletContext;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

/**
 * @author CodeLorin
 * @date 2021/6/5 14:07
 */
public class Listener implements HttpSessionListener {

    //创建session监听
    public void sessionCreated(HttpSessionEvent se) {

        System.out.println(se.getSession().getId());
        ServletContext ctx = se.getSession().getServletContext();
        Integer count = (Integer) ctx.getAttribute("OnlineCount");
        if (count == null) {
            count = 1;
        } else {

            count = count + 1;
        }
        ctx.setAttribute("OnlineCount", count);
    }

    //销毁session监听
    public void sessionDestroyed(HttpSessionEvent se) {
        ServletContext ctx = se.getSession().getServletContext();
        Integer count = (Integer) ctx.getAttribute("OnlineCount");
        if (count == null) {
            count = 0;
        } else {

            count = count - 1;
        }
        ctx.setAttribute("OnlineCount", count);
    }
}