mybatis入门
1 前言
在一般的程序中,层与层之间的数据传递都是通过实体对象(POJO plain old java objects 普通java对象)。
我们在客户端表单提交数据,到达web层,mvc可以直接把表单数据封装到一个实体中(如:User实体),再把这个User实体对象依次传递,传递到业务层,再业务层传递到dao层。
2 原始jdbc操作的分析
参看我的一篇博客:https://www.cnblogs.com/GumpYan/p/14085000.html
3 什么是mybatis
(1)mybatis是一个优秀的基于java的持久层框架,它内部封装了jdbc,使开发者只需要关注SQL语句本身,而不需要花费精力去处理加载驱动、创建连接、创建statement等繁杂过程
(2)mybatis通过xml或注解的方式将要执行的各种statement配置起来,并通过java对象和statement中SQL的动态参数进行映射生成最终执行的SQL语句
(3)mybatis框架执行SQL并将结果映射为java对象并返回。采用ORM(Object Relation Mapping)思想解决了实体和数据库映射的问题,对jdbc进行了封装,屏蔽了jdbc api底层访问细节,使我们不与jdbc api打交道,就可以完成对数据库的持久化操作
4 mybatis开发步骤
(1)添加MyBatis的坐标
(2)创建user数据表
(3)编写User实体类
(4)编写映射文件UserMapper.xml
(5)编写核心文件SqlMapConfig.xml
(6)编写测试类
案例:
项目结构:
(1)添加mybatis坐标(pom.xml中)
(2)创建user数据表
USE test; create table `user` ( `id` int not null , `username` varchar(40) not null , `password` int not null, primary key (`id`) ) ENGINE = INNODB DEFAULT charset = utf8; insert into user(id, username, password) VALUES (1,'zhangsan',123); insert into user(id, username, password) VALUES (2,'lisi',123); insert into user(id, username, password) VALUES (3,'wangwu',123); insert into user(id, username, password) VALUES (4,'zhaoliu',123); insert into user(id, username, password) VALUES (5,'tianqi',123);
(3)编写User实体
package com.company.domain; public class User { private int id; private String username; private String password; public int getId() { return id; } public void setId(int id) { this.id = id; } public String getUsername() { return username; } public void setUsername(String username) { this.username = username; } public String getPassword() { return password; } public void setPassword(String password) { this.password = password; } @Override public String toString() { return "User{" + "id=" + id + ", username='" + username + '\'' + ", password='" + password + '\'' + '}'; } }
(4)编写映射文件UserMapper.xml
mapping文件约束头
<?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">
完整的UserMapper.xml
<?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="userMapper"> <select id="findAll" resultType="com.company.domain.User"> select * from user </select> </mapper>
(5)编写核心文件SqlMapConfig.xml
核心文件约束头
<?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">
完整的SqlMapConfig.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> <!-- 配置数据源环境--> <environments default="development"> <environment id="development"> <transactionManager type="JDBC"></transactionManager> <dataSource type="POOLED"> <property name="driver" value="com.mysql.jdbc.Driver"/> <property name="url" value="jdbc:mysql://localhost:3306/test"/> <property name="username" value="root"/> <property name="password" value="123456"/> </dataSource> </environment> </environments> <!-- 加载映射文件--> <mappers> <mapper resource="com/company/mapper/UserMapper.xml"></mapper> </mappers> </configuration>
(6)编写测试类
MyBatisTest.java
package com.company.test; import com.company.domain.User; import org.apache.ibatis.io.Resources; import org.apache.ibatis.session.SqlSession; import org.apache.ibatis.session.SqlSessionFactory; import org.apache.ibatis.session.SqlSessionFactoryBuilder; import org.junit.Test; import java.io.IOException; import java.io.InputStream; import java.util.List; public class MyBatisTest { @Test public void test1() throws IOException { // 获得核心配置文件 InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml"); // 获得session工厂对象 SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream); // 获得session会话对象 SqlSession sqlSession = sqlSessionFactory.openSession(); // 执行操作,参数:namespace+id List<User> userList = sqlSession.selectList("userMapper.findAll"); // 打印数据 System.out.println(userList); // 释放资源 sqlSession.close(); } }
运行结果:
完整的pom.xml
<?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>com.company</groupId> <artifactId>mybatis_quick</artifactId> <version>1.0-SNAPSHOT</version> <dependencies> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>5.1.44</version> </dependency> <dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis</artifactId> <version>3.5.6</version> </dependency> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>4.12</version> <scope>test</scope> </dependency> <dependency> <groupId>log4j</groupId> <artifactId>log4j</artifactId> <version>1.2.17</version> </dependency> </dependencies> </project>