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Spring Boot连接MySQL数据库

目录

上篇 只需两步！Eclipse+Maven 快速构建第一个 Spring Boot 项目 已经构建了一个 Spring Boot 项目，本文在此基础上进行连接 MySQL 数据库的操作。

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1. pom.xml 添加依赖

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>

    &lt;dependency&gt;
        &lt;groupId&gt;mysql&lt;/groupId&gt;
        &lt;artifactId&gt;mysql-connector-java&lt;/artifactId&gt;
    &lt;/dependency&gt;    </pre>

2. application.properties 添加数据库配置

spring.datasource.url=jdbc:mysql://localhost:3306/spring_boot?serverTimezone=GMT%2B8
spring.datasource.username=root
spring.datasource.password=123456
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver

spring.jpa.properties.hibernate.hbm2ddl.auto=update
spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.MySQL5InnoDBDialect
spring.jpa.show-sql= true

 
如果数据库连接写成 spring.datasource.url=jdbc:mysql://localhost:3306/spring_boot ，由于 MySQL 版本的问题，可能会有以下的错误，在后面加上“?serverTimezone=GMT%2B8”，设置下时区，解决。
设置驱动，spring.datasource.driver-class-name=com.mysql.jdbc.Driver 会有下面红色的警告信息。说的是 `com.mysql.jdbc.Driver'被弃用了，要使用新的驱动 `com.mysql.cj.jdbc.Driver'，改成 `com.mysql.cj.jdbc.Driver' 以后一切正常。
Loading class `com.mysql.jdbc.Driver'. This is deprecated. The new driver class is `com.mysql.cj.jdbc.Driver'. The driver is automatically registered via the SPI and manual loading of the driver class is generally unnecessary.

3. 添加实体类

@Entity 代表这是一个实体类，@Table(name=”user”) 用来对应数据库中的 use 表，@Id 用来表达主键，@Column(name=”id”) 表明一个 id 属性。 

@GeneratedValue 使主键自增，如果还有疑问，可参考@GeneratedValue 源码解析。

package com.example.demo.domain;

import java.io.Serializable;


import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;


@Entity
@Table(name = "user")
public class User implements Serializable {


</span><span style="color: rgba(0, 0, 255, 1)">private</span> <span style="color: rgba(0, 0, 255, 1)">static</span> <span style="color: rgba(0, 0, 255, 1)">final</span> <span style="color: rgba(0, 0, 255, 1)">long</span> serialVersionUID = 1L<span style="color: rgba(0, 0, 0, 1)">;

@Id
@GeneratedValue
</span><span style="color: rgba(0, 0, 255, 1)">private</span><span style="color: rgba(0, 0, 0, 1)"> Long id;
@Column(name </span>= "username"<span style="color: rgba(0, 0, 0, 1)">)
</span><span style="color: rgba(0, 0, 255, 1)">private</span><span style="color: rgba(0, 0, 0, 1)"> String userName;
@Column(name </span>= "password"<span style="color: rgba(0, 0, 0, 1)">)
</span><span style="color: rgba(0, 0, 255, 1)">private</span><span style="color: rgba(0, 0, 0, 1)"> String passWord;

</span><span style="color: rgba(0, 0, 255, 1)">public</span><span style="color: rgba(0, 0, 0, 1)"> User() {
    </span><span style="color: rgba(0, 0, 255, 1)">super</span><span style="color: rgba(0, 0, 0, 1)">();
}

</span><span style="color: rgba(0, 0, 255, 1)">public</span><span style="color: rgba(0, 0, 0, 1)"> User(String userName, String passWord) {
    </span><span style="color: rgba(0, 0, 255, 1)">super</span><span style="color: rgba(0, 0, 0, 1)">();
    </span><span style="color: rgba(0, 0, 255, 1)">this</span>.userName =<span style="color: rgba(0, 0, 0, 1)"> userName;
    </span><span style="color: rgba(0, 0, 255, 1)">this</span>.passWord =<span style="color: rgba(0, 0, 0, 1)"> passWord;
}

</span><span style="color: rgba(0, 0, 255, 1)">public</span><span style="color: rgba(0, 0, 0, 1)"> Long getId() {
    </span><span style="color: rgba(0, 0, 255, 1)">return</span><span style="color: rgba(0, 0, 0, 1)"> id;
}

</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> setId(Long id) {
    </span><span style="color: rgba(0, 0, 255, 1)">this</span>.id =<span style="color: rgba(0, 0, 0, 1)"> id;
}

</span><span style="color: rgba(0, 0, 255, 1)">public</span><span style="color: rgba(0, 0, 0, 1)"> String getUserName() {
    </span><span style="color: rgba(0, 0, 255, 1)">return</span><span style="color: rgba(0, 0, 0, 1)"> userName;
}

</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> setUserName(String userName) {
    </span><span style="color: rgba(0, 0, 255, 1)">this</span>.userName =<span style="color: rgba(0, 0, 0, 1)"> userName;
}

</span><span style="color: rgba(0, 0, 255, 1)">public</span><span style="color: rgba(0, 0, 0, 1)"> String getPassWord() {
    </span><span style="color: rgba(0, 0, 255, 1)">return</span><span style="color: rgba(0, 0, 0, 1)"> passWord;
}

</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> setPassWord(String passWord) {
    </span><span style="color: rgba(0, 0, 255, 1)">this</span>.passWord =<span style="color: rgba(0, 0, 0, 1)"> passWord;
}



}

4. 添加 Dao

Dao 层主要用来实现对数据库的增、删、查、改。 dao 只要继承 JpaRepository 类就可以，几乎可以不用写方法，可以根据方法名来自动的生产 SQL，比如 findByUserName 会自动生产一个以 userName 为参数的查询方法。
package com.example.demo.dao;

import org.springframework.data.jpa.repository.JpaRepository;


import com.example.demo.domain.User;


public interface UserRepository extends JpaRepository<User, Long> {


User findByUserName(String userName);



}

5. 添加 Controller

package com.example.demo.controller;

import java.util.ArrayList;
import java.util.List;


import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.RestController;


import com.example.demo.dao.UserRepository;
import com.example.demo.domain.User;


@RestController
@RequestMapping("user")
public class UserController {


@Autowired
</span><span style="color: rgba(0, 0, 255, 1)">private</span><span style="color: rgba(0, 0, 0, 1)"> UserRepository userRepository;

@RequestMapping(</span>"/getAllUser"<span style="color: rgba(0, 0, 0, 1)">)
@ResponseBody
</span><span style="color: rgba(0, 0, 255, 1)">public</span> List&lt;User&gt;<span style="color: rgba(0, 0, 0, 1)"> findAll() {
    List</span>&lt;User&gt; list = <span style="color: rgba(0, 0, 255, 1)">new</span> ArrayList&lt;User&gt;<span style="color: rgba(0, 0, 0, 1)">();
    list </span>=<span style="color: rgba(0, 0, 0, 1)"> userRepository.findAll();
    </span><span style="color: rgba(0, 0, 255, 1)">return</span><span style="color: rgba(0, 0, 0, 1)"> list;
}

@RequestMapping(</span>"/getByUserName"<span style="color: rgba(0, 0, 0, 1)">)
@ResponseBody
</span><span style="color: rgba(0, 0, 255, 1)">public</span><span style="color: rgba(0, 0, 0, 1)"> User getByUserName(String userName) {
    User user </span>=<span style="color: rgba(0, 0, 0, 1)"> userRepository.findByUserName(userName);
    </span><span style="color: rgba(0, 0, 255, 1)">return</span><span style="color: rgba(0, 0, 0, 1)"> user;
}



}

工程添加文件后工程结构图：

6. 新建数据库

新建数据库mysql://localhost:3306/spring_boot ，必须的一个步骤。hibernate 虽然会自动新建表，但是数据库还是要手动建好的。
使用 Navicat 新建本地数据库，连接名上面右键 - > 新建数据库 -> 填写数据库信息 - > 确定。

在 user 表中，插入两条测试数据：

7. 测试

启动项目。用 Postman 发送请求进行测试：
http://localhost:8080//user/getAllUser :

http://localhost:8080//user/getByUserName?userName=Turing :