十年河东,十年河西,莫欺少年穷
学无止境,精益求精
MyBatis工作原理如下
0、现在MySQl数据库 搞个库并增加一张表,如下:
create database mybatis go use mybatis go CREATE TABLE users ( uid INT PRIMARY KEY, uname VARCHAR ( 20 ), uage INT NOT NULL ) go insert into users(uid,uname,uage) values(1,'jack',22) go insert into users(uid,uname,uage) values(2,'msis',22) go
1、新建java maven项目
2、编辑Mybatis核心配置文件
<?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.one5a</groupId> <artifactId>Test</artifactId> <version>1.0-SNAPSHOT</version> <dependencies> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>8.0.11</version> </dependency> <dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis</artifactId> <version>3.5.4</version> </dependency> <!--junit--> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>4.12</version> <scope>test</scope> </dependency> </dependencies> </project>
添加了三个依赖,分别为MySQL、myBatis核心库,junit单元测试
3、resources中新增数据库属性文件db.properties及myBatis配置文件mybatis-config.xml
db.properties 主要用于存储数据库配置信息,如下:
driver = com.mysql.cj.jdbc.Driver url = jdbc:mysql://localhost:3306/mybatis?useUnicode=true&characterEncoding=utf-8&useSSL=false&serverTimezone=UTC username = root password = chen1234
mybatis-config.xml 用于引入数据库配置信息及用户自定义映射文件
本篇不讲解涉及到缓存、懒加载、开启驼峰相关知识
<?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> <!--引入外部配置文件 --> <properties resource="db.properties"/> <settings> <!--开启全局缓存 默认true--> <setting name="cacheEnabled" value="true"/> <!--开启全局懒加载 默认false--> <setting name="lazyLoadingEnabled" value="true"/> <!--开启关联属性懒加载 默认false--> <setting name="aggressiveLazyLoading" value="true"/> <!--全局开启驼峰映射--> <setting name="mapUnderscoreToCamelCase" value="true"/> </settings> <environments default="development"> <environment id="development"> <transactionManager type="JDBC"/> <dataSource type="POOLED"> <property name="driver" value="${driver}"/> <property name="url" value="${url}"/> <property name="username" value="${username}"/> <property name="password" value="${password}"/> </dataSource> </environment> </environments> <!-- 注册UserMapper.xml --> <mappers> <mapper resource="Mapper/UserMapper.xml"/> </mappers> </configuration>
由于mybatis-config.xml 中引入了用户配置文件 Mapper/UserMapper.xml,需要创建UserMapper.xml
resources中新增目录Mapper,Mapper目录下创建UserMapper.xml
UserMapper.xml 如下
<?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"> <!--namespace=绑定一个指定的Dao/Mapper接口--> <mapper namespace="com.one5a.model.User"> <select id="getUserList" resultType="com.one5a.model.User"> select * from users </select> <select id="getUserbyId" resultType="com.one5a.model.User" parameterType="int"> select * from users where uid=#{id} </select> </mapper>
4、在main/java新建包 com.one5a.model并新增User类
package com.one5a.model; public class User { private int uid; public int getUid() { return uid; } public void setUid(int uid) { this.uid = uid; } public String getUname() { return uname; } public void setUname(String uname) { this.uname = uname; } private String uname; public int getUage() { return uage; } public void setUage(int uage) { this.uage = uage; } private int uage; @Override public String toString() { return "User{" + "uid=" + uid + ", uname='" + uname + '\'' + ", uage=" + uage + '}'; } }
注意包名称及Java类应该和UserMapper.XML中定义的一致,分别为: com.one5a.model 、User
package com.one5a.model; public class User { private int uid; public int getUid() { return uid; } public void setUid(int uid) { this.uid = uid; } public String getUname() { return uname; } public void setUname(String uname) { this.uname = uname; } private String uname; public int getUage() { return uage; } public void setUage(int uage) { this.uage = uage; } private int uage; @Override public String toString() { return "User{" + "uid=" + uid + ", uname='" + uname + '\'' + ", uage=" + uage + '}'; } }
5、书写测试类
创建测试类 UnityTest
package com.one5a.test; import com.one5a.model.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 UnityTest { @Test public void getUserList() throws IOException { String resource = "mybatis-config.xml"; //使用类加载器加载mybatis的配置文件(它也加载关联的映射文件) //InputStream is = Resources.getResourceAsStream(resource); //InputStream is = Tests.class.getClassLoader().getResourceAsStream(resource); InputStream is = Resources.getResourceAsStream(resource); //构建sqlSession的工厂 线程安全 建议使用单列模式 SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(is); //绝对不能将它作为静态对象使用,不可共享 SqlSession session = sessionFactory.openSession(); /** * 映射sql的标识字符串, * com.oumyye.mapping.UserMapping是userMapper.xml文件中mapper标签的namespace属性的值, * getUser是select标签的id属性值,通过select标签的id属性值就可以找到要执行的SQL */ String statement = "com.one5a.model.User.getUserList";//映射sql的标识字符串 //执行查询返回一个唯一user对象的sql List<User> user = session.selectList(statement); for (int i = 0; i < user.size(); i++) { System.out.println(user.toString()); } } @Test public void getUserbyId() throws IOException { String resource = "mybatis-config.xml"; //使用类加载器加载mybatis的配置文件(它也加载关联的映射文件) //InputStream is = Resources.getResourceAsStream(resource); //InputStream is = Tests.class.getClassLoader().getResourceAsStream(resource); InputStream is =Resources.getResourceAsStream(resource); //构建sqlSession的工厂 线程安全 建议使用单列模式 SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(is); //绝对不能将它作为静态对象使用,不可共享 SqlSession session = sessionFactory.openSession(); /** * 映射sql的标识字符串, * com.oumyye.mapping.UserMapping是userMapper.xml文件中mapper标签的namespace属性的值, * getUser是select标签的id属性值,通过select标签的id属性值就可以找到要执行的SQL */ String statement = "com.one5a.model.User.getUserbyId";//映射sql的标识字符串 //执行查询返回一个唯一user对象的sql User user = session.selectOne(statement,1); System.out.println(user); } }
6、测试结果
入门程序,不看也罢
@天才卧龙的博科人