JdbcTemplate（操作数据库-查询返回值）

1.创建数据库

数据库中有3条记录，数据库名是user_db，数据库表是t_book

2.创建实体类

实体类属性对应数据库每一条记录

package org.example.spring.entity;public class Book {private String userId;private String username;public String getUserId() {return userId;}public void setUserId(String userId) {this.userId = userId;}public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}}

3.创建dao层

抽象类：

package org.example.spring.dao;import org.example.spring.entity.Book;public interface BookDao {//查询的方法int selectCount();
}

实现类：

package org.example.spring.dao;import org.example.spring.entity.Book;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.stereotype.Repository;@Repository
public class BookDaoImpl implements BookDao{//注入jdbcTemplate对象@Autowiredprivate JdbcTemplate jdbcTemplate;//    查询@Overridepublic int selectCount() {String sql="select count(*) from t_book";
//        此方法有两个参数//一个参数是sql，一个参数是根据返回值类型而定，如果是String类型就返回String类型，是Int类型就返回Int类型Integer count = jdbcTemplate.queryForObject(sql, Integer.class);return count;}
}

4.创建service层

package org.example.spring.service;import org.example.spring.dao.BookDao;
import org.example.spring.entity.Book;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;@Service
public class BookService {//注入dao@Autowiredprivate BookDao bookDao;//查询表中的记录数public int findCount(){return bookDao.selectCount();}}

5.创建测试类：

package org.example.spring.test;import org.example.spring.entity.Book;
import org.example.spring.service.BookService;
import org.junit.jupiter.api.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;public class TestBook
{@Testpublic void test01(){ApplicationContext context=new ClassPathXmlApplicationContext("bean1.xml");BookService bookService = context.getBean("bookService", BookService.class);//        查询返回某个值int count = bookService.findCount();
//        做输出System.out.println(count);}}

6.xml配置

<?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.xsd
http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd"><!--    开启组件扫描--><context:component-scan base-package="org.example"></context:component-scan>
<!--数据库连接池--><bean id="dataSource" class="com.alibaba.druid.pool.DruidDataSource" destroy-method="close"><property name="url" value="jdbc:mysql://localhost:3306/user_db?useSSL=false&amp;useUnicode=true&amp;characterEncoding=UTF-8"/><property name="username" value="root"/><property name="password" value="sise"/><property name="driverClassName" value="com.mysql.jdbc.Driver"/></bean><!--    创建jdbcTemplate对象--><bean id="jdbcTemplate" class="org.springframework.jdbc.core.JdbcTemplate">
<!--需要注入数据源信息--><property name="dataSource" ref="dataSource"></property></bean>
</beans>