2020-03-21

Mybatis查询所有

前期准备

准备数据库

最终结果：

sql语句:

create table people(
id int(10) primary key auto_increment comment '编号',
name varchar(20) comment '姓名',
age int(3) comment '年龄'
)comment '人员信息表';

insert into people values(default,'张三',21);
insert into people values(default,'李四',22);

准备实体类People


public class People {
	
	private int id;      //和数据库的属性匹配
	private String name;
	private int age;
	
	public int getId() {   //生成所有的set和get方法
		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;
	}
}

搭建环境

*1. 导入mybatis的jar包 + 依赖包 + mysql的jar包 + jstl的jar包 *

2. 搭建全局配置文件

1. 中文chm文档dtd文件找约束
2. 写configuration内容 -- 配置数据库
3. 写mappers的配置 -- 找PeopleMapper.xml(类似于实现类)

<?xml version="1.0" encoding="UTF-8"?>

<!--第一步-->
<!DOCTYPE configuration
  PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
  "http://mybatis.org/dtd/mybatis-3-config.dtd">

<!--第二步-->
<configuration>
	<environments default="default">
		<environment id="default">
			<transactionManager type="JDBC"></transactionManager>
				<dataSource type="POOLED">
					<property name="driver" value="com.mysql.jdbc.Driver"/>
					<property name="url" value="jdbc:mysql://localhost:3306/ssm"/>
					<property name="username" value="root"/>
					<property name="password" value="njdxrjgc7777777."/>
				</dataSource>
		</environment>
	</environments>

<!--第三步-->
	<mappers>
	<mapper resource="com/bjstx/mapper/PeopleMapper.xml"/>
	</mappers>

</configuration>

3. 搭建类似于实现类的xml文件

1. 中文chm文档dtd文件找约束
2. 写mapper配置 -- 里面写sq语句和返回值和方法名等信息

<?xml version="1.0" encoding="UTF-8"?>

<!-- 第一步 -->
<!DOCTYPE mapper
  PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  
<!-- 第二步 -->  
  <mapper namespace="com.bjsxt.mapper.PeopleMapper" >
  	<select id="selAll" resultType="com.bjsxt.pojo.People">
  		select * from people
  	</select>
  </mapper>

准备service层和实现层

PeopleService接口写方法

public interface PeopleService {

	//显示人员
	List<People> show() throws IOException;
}

PeopleServiceImpl类实现PeopleService接口

/*
 *  数据访问层 -- 处理异常和控制器中处理异常    service只是抛出异常 
 */
public class PeopleServiceImpl implements PeopleService{

	@Override
	public List<People> show() throws IOException {
		// 1. 找主配置文件
			InputStream is = Resources.getResourceAsStream("mybatis.xml");
		
		// 2. 使用工厂模式     实例化工厂对象使用构建者模式 (名称标志后面：Builder) 
			//构建者设计模式意义：简化对象实例化过程 (我们这个SqlSessionFactory里面还要很多类很多方法比较麻烦)
			SqlSessionFactory factory=new SqlSessionFactoryBuilder().build(is);
		
		// 3. 创建session 
			SqlSession session=factory.openSession();
			
		//4. 调用xml配置文件中的功能 	
			List<People> list = session.selectList("com.bjsxt.mapper.PeopleMapper.setAll");
			
		//5. 关闭连接
			session.close();
			
		return list;
	}

}

准备Servlet层

@WebServlet("/abc/b/show")  //1.是给默认属性赋值 省略 value=  2.数组是一个值 省略 {}
public class ShowServlet extends HttpServlet {
	//面向接口编程
	    private	PeopleService peopleService=new PeopleServiceImpl();
	
	@Override
	protected void service(HttpServletRequest req,HttpServletResponse resp)throws ServletException,IOException{
		List<People> list = peopleService.show();	
		req.setAttribute("list", list);
		//使用请求转发      这次是相对路径
		req.getRequestDispatcher("/index.jsp").forward(req, resp); //  "/" 全路径(对WebContent目录)    "" 相对路径
	}
}

index.jsp首页

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>   
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>  
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
<table>
	<tr>
		<th>编号</th>
		<th>姓名</th>
		<th>年龄</th>
	</tr>
	<c:forEach items="${list }" var="peo">
		<tr>
			<td>${peo.id}</td>
			<td>${peo.name}</td>
			<td>${peo.age}</td>
		</tr>
	</c:forEach>
</table>
</body>
</html>