JSP快速入门、MVC模式和三层架构、EL表达式、JSTL标签

一、概念与作用

● 慨念：Java Server Pages,Java服务端页面
● 一种动态的网页技术，其中既可以定义HTML、JS、CSS等静态内容，还可以定义Jva代码的动态内容
● JSP=HTML +Java
● JSP的作用：简化开发，避免了在Servletr中直接输出HTML标签，本质上就是Servlet

二、JSP快速入门

1.导入JSP坐标

<dependency>
      <groupId>javax.servlet.jsp</groupId>
      <artifactId>jsp-api</artifactId>
      <version>2.2</version>
      <scope>provided</scope>
</dependency>

2.创建JSP文件

3.编写HTML标签和Java代码

<body
<h1>hello jsp~</h1>
<% System.out.printf("jsp hello~"); %>
</body>

三、JSP原理

●概念：Java Server Pages,Java服务端页面

●JSP=HTML+Java,用于简化开发的

●JSP本质上就是一个Servlet

●JSP在被访问时，由SP容器(Tomcat)将其转换为Java文件(Servlet),在由SP容器(Tomcat)将其编译，最终对外提供服务的其实就是这个字节码文件

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四、JSP脚本

● JSP脚本用于在JSP页面内定义Java代码
● SP脚本分类：

1.<%…%>

内容会直接放到_jspService()方法之中

例如：

 public void _jspService(final javax.servlet.http.HttpServletRequest request, final javax.servlet.http.HttpServletResponse response)
        throws java.io.IOException, javax.servlet.ServletException {
    
    

    final javax.servlet.jsp.PageContext pageContext;
    javax.servlet.http.HttpSession session = null;
    final javax.servlet.ServletContext application;
    final javax.servlet.ServletConfig config;
    javax.servlet.jsp.JspWriter out = null;
    final java.lang.Object page = this;
    javax.servlet.jsp.JspWriter _jspx_out = null;
    javax.servlet.jsp.PageContext _jspx_page_context = null;


    try {
    
    
      response.setContentType("text/html;charset=UTF-8");
      pageContext = _jspxFactory.getPageContext(this, request, response,
      			null, true, 8192, true);
      _jspx_page_context = pageContext;
      application = pageContext.getServletContext();
      config = pageContext.getServletConfig();
      session = pageContext.getSession();
      out = pageContext.getOut();
      _jspx_out = out;

      out.write("\r\n");
      out.write("\r\n");
      out.write("\r\n");
      out.write("\r\n");
      out.write("\r\n");
      out.write("\r\n");
      out.write("\r\n");
      out.write("<html>\r\n");
      out.write("<head>\r\n");
      out.write("    <title>Title</title>\r\n");
      out.write("</head>\r\n");
      out.write("<body>\r\n");
      out.write("\r\n");

    //1.接收用户名和密码
    String username = request.getParameter("username");
    String password = request.getParameter("password");
    //2.调用MyBatis完成查询
    //2.1获取SqlSessionFactory对象
	//String resource = "mybatis-config.xml";
	//InputStream inputstream = Resources.getResourceAsStream(resource);
	//SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputstream);
    SqlSessionFactory sqlSessionFactory= SqlSessionFactoryUtils.getSqlSessionFactory();
    //2.2获取SqlSession对象
    SqlSession sqlSession = sqlSessionFactory.openSession();
    //2.3获取Mapper
    UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
    //2.4调用方法
    User user = userMapper.selectById(username, password);
    //2.5释放资源
    sqlSession.close();

2.<%=…%>

内容会放到out.print()中，作为out.print()的参数

例如：

      out.write("\r\n");
      out.write("\r\n");
      out.write("\r\n");
      out.write("\r\n");
      out.write("\r\n");
      out.write("\r\n");
      out.write("\r\n");
      out.write("<html>\r\n");
      out.write("<head>\r\n");
      out.write("    <title>Title</title>\r\n");
      out.write("</head>\r\n");
      out.write("<body>\r\n");
      out.write("\r\n");

3.<%!..%>

内容会放到_spService()方法之外，被类直接包含

public final class login_jsp extends org.apache.jasper.runtime.HttpJspBase
    implements org.apache.jasper.runtime.JspSourceDependent {
    
    


        void show(){
    
    

        }
        String name = "zhangsan";

    
  private static final javax.servlet.jsp.JspFactory _jspxFactory =
          javax.servlet.jsp.JspFactory.getDefaultFactory();

  private static java.util.Map<java.lang.String,java.lang.Long> _jspx_dependants;

4.JSP缺点

由于SP页面内，既可以定义HTML标签，又可以定义ava代a码，造成了以下问题：

1.书写麻烦：特别是复杂的页面

2.阅读麻烦

3.复杂度高：运行需要依赖于各种环境，JRE,JSP容器，JavaEE…

4.占内存和磁盘：JSP会自动生成，java和.class.文件占磁盘，运行的是.class文件占内存

5.调试困难：出错后，需要找到自动生成的.java文件进行调试

6.不利于团队协作：前端人员不会Jva,后端人员不精HTML

7.。。。。

五、EL表达式

Expression Language表达式语言，用于简化JSP页面内的java代码

主要功能：获取数据

语法：${expression}

${brands}

获取域中存储的key为brands的数据

JavaWeb中的四大域对象：

1.page:当前页面有效

2.request::当前请求有效

3.session:当前会话有效

4.application:当前应用有效

表达式获取数据，会依次从这4个域中寻找，直到找到为止

六、JSTL标签

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1.导入jstl，standard依赖

<dependency>
      <groupId>javax.servlet</groupId>
      <artifactId>jstl</artifactId>
      <version>1.2</version>
</dependency>
<dependency>
      <groupId>taglibs</groupId>
      <artifactId>standard</artifactId>
      <version>1.1.2</version>
    </dependency>
<dependency>

2.学习<c:if>\标签,新建jstl-if.jsp文件，引入taglib标签库。

<%--
  Created by IntelliJ IDEA.
  User: 可
  Date: 2022/5/22
  Time: 17:07
  To change this template use File | Settings | File Templates.
--%>
<%@ 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:if test="${status==1}">
        启用
    </c:if>
    <c:if test="${status==0}">
        禁用
    </c:if>
</body>
</html>

3.学习<c:forEach>\标签，新建jstl-foreach.jsp文件，引入taglib标签库。

<%--
  Created by IntelliJ IDEA.
  User: 可
  Date: 2022/5/23
  Time: 10:03
  To change this template use File | Settings | File Templates.
--%>
<%@ 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>
<input type="button" value="新增">
<hr/>
<table border="2" cellspacing="" width="800">
    <tr>
        <th>序号</th>
        <th>品牌名称</th>
        <th>企业名称</th>
        <th>排序</th>
        <th>品牌介绍</th>
        <th>状态</th>
        <th>操作</th>
    </tr>
<c:forEach items="${brands}" var="brand">
            <tr align="center">
                <td>${brand.id}</td>
                <td>${brand.brandName}</td>
                <td>${brand.companyName}</td>
                <td>${brand.ordered}</td>
                <td>${brand.description}</td>
                <td>${brand.status==1 ? "启用" : "禁用"}</td>
                <td><a href="#">修改</a>&nbsp;&nbsp;<a href="#">删除</a></td>
            </tr>
</c:forEach>
</table>
</body>
</html>

4.<c:>标签中varStatus="Nid"属性的设置值${brand.conut}表示从1开始，${Nid.index}表示从0开始

七、MVC模式和三层架构

MVC模式

三层架构

数据访问层又叫dao层，持久层。

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八、案例

1.准备环境

创建新的模块brand-demo,引入坐标

<dependencies>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.5</version>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.47</version>
        </dependency>

        <!--导入jstl-->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>jstl</artifactId>
            <version>1.2</version>
        </dependency>

        <dependency>
            <groupId>taglibs</groupId>
            <artifactId>standard</artifactId>
            <version>1.1.2</version>
        </dependency>

        <!--Servlet-->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>3.1.0</version>
            <scope>provided</scope>
        </dependency>


        <!--JSP-->
        <dependency>
            <groupId>javax.servlet.jsp</groupId>
            <artifactId>jsp-api</artifactId>
            <version>2.2</version>
            <scope>provided</scope>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.tomcat.maven</groupId>
                <artifactId>tomcat7-maven-plugin</artifactId>
                <version>2.2</version>
            </plugin>
        </plugins>
    </build>

创建三层架构的包结构

数据库表tb brand

实体类Brand

MyBatis基础环境

xml文件3版本的标签头：

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">

Mybatis-config.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <typeAliases>
        <!--    起别名    -->
        <package name="cn.itheima.pojo"/>
    </typeAliases>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <!--数据库连接池-->
            <dataSource type="POOLED">
                <!--数据库的连接信息-->
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql:///db1?useSSL=false&amp;useServerPrepStmts=true"/>
                <property name="username" value="root"/>
                <property name="password" value="nigaoxian+0128"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <!-- 扫描mapper -->
        <package name="com.itheima.mapper"/>
    </mappers>
</configuration>