JAVA入门[6]-Mybatis简单示例

初次使用Mybatis,先手写一个hello world级别的例子，即根据id查询商品分类详情。

一、建表

create table Category (
Id INT not null,
Name varchar(80) null,
constraint pk_category primary key (Id)
);

插入测试数据

INSERT INTO category VALUES (1,'Fish');
INSERT INTO category VALUES (2,'Dogs');
INSERT INTO category VALUES (3,'Birds');

二、新建测试项目

新建Maven项目，最终的项目结构如下：

Image(32)

修改pom.xml，引入mybatis相关依赖。

<dependencies><dependency><groupId>org.mybatis</groupId><artifactId>mybatis</artifactId><version>3.4.1</version></dependency><dependency><groupId>org.mybatis.generator</groupId><artifactId>mybatis-generator-core</artifactId><version>1.3.2</version></dependency><dependency><groupId>junit</groupId><artifactId>junit</artifactId><version>4.12</version><scope>test</scope></dependency><!-- Mysql数据库链接jar包 --><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>5.1.21</version><scope>runtime</scope></dependency></dependencies>

三、建立pojo

建立Category对应的实体，这里为了方便测试重写了toString()方法。

public class Category implements Serializable {private int id;private String name;private static final long serialVersionUID = 1L;public int getId() {return id;}public void setId(int id) {this.id= id;}public String getName() {return name;}public void setName(String name) {this.name = name == null ? null : name.trim();}@Overridepublic String toString() {StringBuilder sb = new StringBuilder();sb.append(getClass().getSimpleName());sb.append(" [");sb.append("Hash = ").append(hashCode());sb.append(", id=").append(id);sb.append(", name=").append(name);sb.append("]");return sb.toString();}
}

四、定义数据访问接口

在src/main/cathy.mybatis/mapper包，新增CategoryMapper接口，这里只定义GetById方法。

public interface CategoryMapper {public Category GetById(int id);
}

五、配置mybatis xml文件

1.mybatis的配置都基于XML文件，我们放在resources/config/mybatis-config.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configurationPUBLIC "-//mybatis.org//DTD Config 3.0//EN""http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration><typeAliases><typeAlias type="model.Category" alias="Category" /></typeAliases><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/store" /><property name="username" value="root" /><property name="password" value="root" /></dataSource></environment></environments><mappers><mapper resource="mapper/CategoryMapper.xml" /></mappers>
</configuration>

typeAliases: 类型别名是为 Java 类型设置一个短的名字,用来减少类完全限定名的冗余。
dataSource：使用标准的 JDBC 数据源接口来配置 JDBC 连接对象的资源。
mappers：用来定义SQL映射语句

六、SqlSession工具类

构建SqlSession有多种方式，这里我们先从mybatis-config.xml配置文件构建SqlSessionFactory，然后从SqlSessionFactory获取SqlSession。

public static SqlSession getSqlSession() {SqlSession session = null;try {InputStream stream = Resources.getResourceAsStream(CONFIG_PATH);SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(stream);session = factory.openSession();} catch (Exception e) {e.printStackTrace();}return session;}

七、调用：

public static void main(String[] args) {SqlSession sqlSession=MybatisUtils.getSqlSession();try{CategoryMapper categoryMapper=sqlSession.getMapper(CategoryMapper.class);Category category=categoryMapper.GetById(1);if(category==null){System.out.println("该分类不存在");}else{System.out.println(category.toString());}}catch (Exception e){System.out.println(e.getMessage());}finally {MybatisUtils.closeSession(sqlSession);}}