Spring Boot连接MySQL数据库

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。

1. pom.xml添加依赖

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

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 {

    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue
    private Long id;
    @Column(name = "username")
    private String userName;
    @Column(name = "password")
    private String passWord;

    public User() {
        super();
    }

    public User(String userName, String passWord) {
        super();
        this.userName = userName;
        this.passWord = passWord;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public String getPassWord() {
        return passWord;
    }

    public void setPassWord(String passWord) {
        this.passWord = 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
    private UserRepository userRepository;

    @RequestMapping("/getAllUser")
    @ResponseBody
    public List<User> findAll() {
        List<User> list = new ArrayList<User>();
        list = userRepository.findAll();
        return list;
    }

    @RequestMapping("/getByUserName")
    @ResponseBody
    public User getByUserName(String userName) {
        User user = userRepository.findByUserName(userName);
        return user;
    }

}