目錄

JdbcTemplate（操作資料庫-查詢返回值）

1.建立資料庫

資料庫中有3條記錄，資料庫名是user_db，資料庫表是t_book

2.建立實體類

實體類屬性對應資料庫每一條記錄

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.建立dao層

抽象類：

package org.example.spring.dao;

import org.example.spring.entity.Book;

public interface BookDao {

    //查詢的方法
    int selectCount();
}

實現類：

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物件
    @Autowired
    private JdbcTemplate jdbcTemplate;


//    查詢
    @Override
    public int selectCount() {
        String sql="select count(*) from t_book";
//        此方法有兩個引數
        //一個引數是sql，一個引數是根據返回值型別而定，如果是String型別就返回String型別，是Int型別就返回Int型別
        Integer count = jdbcTemplate.queryForObject(sql, Integer.class);
        return count;
    }
}
 

4.建立service層

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
    @Autowired
    private BookDao bookDao;


    //查詢表中的記錄數
    public int findCount(){
        return bookDao.selectCount();
    }

}
 

5.建立測試類：

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
{
    @Test
    public void test01(){

        ApplicationContext context=
                new ClassPathXmlApplicationContext("bean1.xml");

        BookService bookService = context.getBean("bookService", BookService.class);


//        查詢返回某個值
        int count = bookService.findCount();
//        做輸出
        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">

<!--    開啟元件掃描-->
    <context:component-scan base-package="org.example">

    </context:component-scan>
<!--資料庫連線池-->
    <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>

<!--    建立jdbcTemplate物件-->
    <bean id="jdbcTemplate" class="org.springframework.jdbc.core.JdbcTemplate">
<!--需要注入資料來源資訊-->
        <property name="dataSource" ref="dataSource">

        </property>
    </bean>
</beans>

7.測試結果：

8.結構示意：