01、MyBatis HelloWorld
1. MyBatis简介
1)MyBatis 是支持定制化 SQL、存储过程以及高级映射的优秀的持久层框架
2)MyBatis 避免了几乎所有的 JDBC 代码和手动设置参数以及获取结果集
3)MyBatis可以使用简单的XML或注解用于配置和原始映射,将接口和Java的POJO(Plain Old Java Objects,普通的 Java 对象)映射成数据库中的记录
2. 使用 MyBatis原因
1)JDBC
(1)SQL 夹在 Java 代码块里,耦合度高导致硬编码内伤
(2)维护不易且实际开发需求中 sql 是有变化,频繁修改的情况多见
2)Hibernate 和 JPA
(1)长难复杂 SQL,对于 Hibernate 而言处理也不容易
(2)内部自动生产的 SQL,不容易做特殊优化
(3)基于全映射的全自动框架,大量字段的 POJO 进行部分映射时比较困难。导致数据库性能下降
3)MyBatis
(1)对开发人员而言,核心 sql 还是需要自己优化
(2)sql 和 java 编码分开,功能边界清晰,一个专注业务、一个专注数据
3. MyBatis下载
1)下载网址
https://github.com/mybatis/mybatis-3/
<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE log4j:configuration SYSTEM "log4j.dtd"> <log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/"> <appender name="STDOUT" class="org.apache.log4j.ConsoleAppender"> <param name="Encoding" value="UTF-8" /> <layout class="org.apache.log4j.PatternLayout"> <param name="ConversionPattern" value="%-5p %d{MM-dd HH:mm:ss,SSS} %m (%F:%L) \n" /> </layout> </appender> <logger name="java.sql"> <level value="debug" /> </logger> <logger name="org.apache.ibatis"> <level value="info" /> </logger> <root> <level value="debug" /> <appender-ref ref="STDOUT" /> </root> </log4j:configuration>log4j.xml 2)创建Mysql测试表
-- 创建库 CREATE DATABASE test_mybatis; -- 使用库 USE test_mybatis; -- 创建表 CREATE TABLE tbl_employee( id INT(11) PRIMARY KEY AUTO_INCREMENT, last_name VARCHAR(50), email VARCHAR(50), gender CHAR(1) ); |
3)Employee
使用Employee接收数据库的记录.
public class Employee { private Integer id; private String lastName; private String email; private String gender; public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getLastName() { return lastName; } public void setLastName(String lastName) { this.lastName = lastName; } public String getEmail() { return email; } public void setEmail(String email) { this.email = email; } public String getGender() { return gender; } public void setGender(String gender) { this.gender = gender; } @Override public String toString() { return "Employee [id=" + id + ", lastName=" + lastName + ", email=" + email + ", gender=" + gender + "]"; } }Employee.java
4)配置文件
(1)参考MyBatis官方手册
<?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> <environments default="development"> <environment id="development"> <transactionManager type="JDBC" /> <dataSource type="POOLED"> <property name="driver" value="com.mysql.jdbc.Driver" /> <property name="url" value="jdbc:mysql://localhost:3306/mybatis" /> <property name="username" value="root" /> <property name="password" value="root123" /> </dataSource> </environment> </environments> <!-- !!!!!!!!!非常重要!!!!!!!!!!!! --> <!-- 将我们写好的sql映射文件<EmployeeMapper.xml>一定要注册到全局配置文件中 --> <mappers> <mapper resource="EmployeeMapper.xml" /> </mappers> </configuration>MyBatis-config.xml (2)创建MyBatis的SQL映射文件
<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="com.atguigu.mybatis.EmployeeMapper"> <!-- namespace:名称空间;指定为接口的全类名 id:唯一标识 resultType:返回值类型 #{id}:从传递过来的参数中取出id值 public Employee getEmpById(Integer id); --> <select id="selectEmp" resultType="com.atguigu.mybatis.bean.Employee"> select id,last_name lastName,email,gender from tbl_employee where id = #{id} </select> </mapper>EmployeeMapper.xml 5)测试
(1) 构建 SqlSessionFactory
根据全局配置文件,利用SqlSessionFactoryBuilder创建SqlSessionFactory
public interface EmployeeMapper { public Employee getEmpById(Integer id); }EmployeeMapper.java
@Test public void test1() throws IOException { //1. 获取SQLSessionFactory对象 String resource = "mybatis-config.xml"; InputStream inputStream = Resources.getResourceAsStream(resource); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); //2.获取sqlsession对象 SqlSession openSession = sqlSessionFactory.openSession(); //3.获取接口的实现类对象 接口的类对象会为接口自动的创建一个代理对象,代理对象去执行增删改查方法 try { EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class); Employee employee = mapper.getEmpById(1); System.out.println(mapper.getClass()); System.out.println(employee); } finally { openSession.close(); } }EmployeeTest.java
<select id="getEmpById" resultType="com.atguigu.mybatis.bean.Employee"> select id,last_name lastName,email,gender from tbl_employee where id = #{id} </select>EmployeeMapper.xml 参考文档:https://mybatis.org/mybatis-3/zh/getting-started.html
https://github.com/mybatis/mybatis-3/
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