Spring中使用JdbcTemplate访问数据库

Spring JDBC是Spring所提供的持久层技术，它的主要目的降低JDBC API的使用难度，以一种更直接、更简洁的方式使用JDBC API。

Spring JDBC中，仅仅需要做那些和业务相关的DML操作的事儿而将获取资源、Statement创建、释放资源以及异常处理等繁杂乏味的工作交给Spring JDBC.

1. 导包 

<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-jdbc</artifactId>
    <version>5.0.8.RELEASE</version>
</dependency>

<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-tx</artifactId>
    <version>5.0.8.RELEASE</version>
</dependency>

2. 核心配置文件 applicationContext.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns:context="http://www.springframework.org/schema/context"
	xmlns:aop="http://www.springframework.org/schema/aop"
	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
		http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.3.xsd
		http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-4.3.xsd">
	
	<!-- 使用注解驱动 自动注册bean  -->
	<context:component-scan base-package="cn.jq.springdemo"></context:component-scan>
	<!-- 导入资源属性文件 -->
	<context:property-placeholder location="classpath:jdbc.properties"/>
	<!-- c3p0 连接池 -->
	<bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource">
		<!-- 类似EL表达式取资源文件的值 -->
		<property name="driverClass" value="${jdbc.driverClass}"></property>
		<property name="jdbcUrl" value="${jdbc.url}"></property>
		<property name="user" value="${jdbc.user}"></property>
		<property name="password" value="${jdbc.password}"></property>
		<property name="initialPoolSize" value="${c3p0.initialPoolSize}"></property>
		<property name="acquireIncrement" value="${c3p0.acquireIncrement}"></property>
		<property name="maxPoolSize" value="${c3p0.maxPoolSize}"></property>
		<property name="minPoolSize" value="${c3p0.minPoolSize}"></property>
		<property name="maxStatements" value="${c3p0.maxStatements}"></property>
		<property name="maxStatementsPerConnection" value="${c3p0.maxStatementsPerConnection}"></property>
	</bean>

	<!-- 配置spring的jdbcTemplate -->
	<bean id="jdbcTemplate" class="org.springframework.jdbc.core.JdbcTemplate">
		<property name="dataSource" ref="dataSource"></property>
	</bean>
	
</beans>

3. 测试类

jdbcTemplate对象的调用方法查看

 1） 增删改 都使用 update 方法

        @Test
	public void test() throws SQLException {
		// 1.初始化ioc容器(装对象的容器)
		ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
	
		//2. 获取jdbcTemplate对象
		JdbcTemplate jdbcTemplate = (JdbcTemplate) context.getBean("jdbcTemplate");
		//增删改
		String sql = "insert into t_user(username,password) values(?,?)";
		jdbcTemplate.update(sql, "lisi","lisi123");

		String sql2 = "update t_user set password=? where id=?";
		jdbcTemplate.update(sql2, "123456",3);

		String sql3 = "delete from t_user where id=3";
		jdbcTemplate.update(sql3);

}

2） 查询一条数据， 返回值为对应对象的集合

        @Test
	public void test() throws SQLException {
		// 1.初始化ioc容器(装对象的容器)
		ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
	
		//2. 获取jdbcTemplate对象
		JdbcTemplate jdbcTemplate = (JdbcTemplate) context.getBean("jdbcTemplate");
				
		String sql = "select * from t_user where id=?";
		RowMapper<User> rowMapper = new BeanPropertyRowMapper<>(User.class);
		User user = jdbcTemplate.queryForObject(sql, rowMapper,1);
		System.out.println(user);
}

3）查询多条数据，返回值为map的集合

        @Test
	public void test() throws SQLException {
		// 1.初始化ioc容器(装对象的容器)
		ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
	
		//2. 获取jdbcTemplate对象
		JdbcTemplate jdbcTemplate = (JdbcTemplate) context.getBean("jdbcTemplate");
		
		//查询多条数据， 
		String sql = "select * from t_user where id>?";
		RowMapper<User> rowMapper = new BeanPropertyRowMapper<>(User.class);
		//List<User> userlist = jdbcTemplate.query(sql,rowMapper,0); //自动映射成对象List集合
		List<Map<String, Object>> userlist = jdbcTemplate.queryForList(sql,0);//自动映射成多个Map对象
		System.out.println(userlist);//[{id=1, username=admin, password=admin123}, {id=2, username=lisi, password=lisi123}]

		//自动映射成单个Map对象, 多个会报错
		String sql2 = "select * from t_user where id=?";
		Map<String, Object> usermap = jdbcTemplate.queryForMap(sql2,1);
		System.out.println(usermap);//{id=1, username=admin, password=admin123}
)

4) 查询一个值，如：某列的一个值，总条数

	@Test
	public void test() throws SQLException {
		// 1.初始化ioc容器(装对象的容器)
		ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
	
		//2. 获取jdbcTemplate对象
		JdbcTemplate jdbcTemplate = (JdbcTemplate) context.getBean("jdbcTemplate");
		
		//查询一个值，如：某列的一个值，总条数
		String sql = "select count(id) from t_user";
		Long count = jdbcTemplate.queryForObject(sql, Long.class); //返回值类型的大CLass
		System.out.println(count);  //2
	}

二， 项目中使用

Dao 类中 注入 jdbcTemplate， 或者写一个util类 提供static方法，通过类名.方法名访问，

@Repository("userDao")
public class UserDaoImpl implements UserDao{
	@Autowired
	private JdbcTemplate jdbcTemplate;

	public User getUser(int id) {
		String sql = "select * from t_user where id=?";
		RowMapper<User> rowMapper = new BeanPropertyRowMapper<>(User.class);
		User user = jdbcTemplate.queryForObject(sql, rowMapper,id);
		return user;
	}
}

测试类 访问DAO类

	@Test
	public void test() throws SQLException {
		// 1.初始化ioc容器(装对象的容器)
		ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
	
		UserDao userDao = (UserDao) context.getBean("userDao");
		User user = userDao.getUser(1);
		System.out.println(user);//User [id=1, username=admin, password=admin123]
	}

参考文章： https://blog.csdn.net/yangshangwei/article/details/78119011?locationNum=1&fps=1