定义mapping类
MyBatis 有两种定义查询结果到 Java 类的映射关系的方式,一种是通过xml文件定义,一种是通过Java annonation 定义,这里使用第二种方法。
现在我们有一张mysql的表定义如下:
CREATE TABLE `MY_BATIS_TEST` (
`id` varchar(255) NOT NULL DEFAULT '',
`url` varchar(255) DEFAULT NULL
)
首先定义table一条数据在Java中对应的class
public class Redord {
public String url;
}
定义sql查询到Java class 结果集合的映射:
public interface SimpleMapper {
@Select("select url from testdb.MY_BATIS_TEST limit 1;")
Redord selectOneRecord();
@Select("select url from testdb.MY_BATIS_TEST;")
Set<Record> selectRecords();
@Select("select url from testdb.MY_BATIS_TEST where id=#{id};")
Record selectRecordByID(int id);
}
初始化并注册mapping类
Properties properties = new Properties();
properties.setProperty("driver", "com.mysql.jdbc.Driver");
properties.setProperty("url", "jdbc:mysql://127.0.0.1:3306/testdb");
properties.setProperty("username", "the_user_name");
properties.setProperty("password", "the_password");
PooledDataSourceFactory pooledDataSourceFactory = new PooledDataSourceFactory();
pooledDataSourceFactory.setProperties(properties);
DataSource dataSource = pooledDataSourceFactory.getDataSource();
Environment environment = new Environment("development", new JdbcTransactionFactory(), dataSource);
Configuration configuration = new Configuration(environment);
configuration.addMapper(SimpleMapper.class); //注册mapping类
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(configuration);
从mysql中查询数据
SqlSession session = sqlSessionFactory.openSession();
try{
PluginMapper mapper = session.getMapper(PluginMapper.class);
Plugin pl = mapper.selectPluginsByID(1000);
System.out.println(pl.url);
} finally {
session.close();
}
全局唯一以及线程安全
SqlSessionFactory 可以在整个app的生命周期中只创建一次,SqlSession需要在每次执行sql的函数中创建一次并且使用后需要进行关闭:
SqlSession session = sqlSessionFactory.openSession();
try {
// do work
} finally {
session.close();
}
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