Spring Boot集成JPA，分分钟钟搞定。

最近在某项目中用到了关系型数据库mysql的增删改查操作，在查询操作中遇到了一些问题，因为这个本来不是难，或者说这个技术已经在大脑中形成了清晰的操作思想，但是在这次的使用中出了些未知的问题，本想通过查询用户名来判断这个用户名是否在数据库中存在，但是后台总是报错，所以就好好研究了一下JPA，现在问题已经解决，以下是详细的项目结构和源代码。

1、项目结构

2、pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.1.4.RELEASE</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>
	<groupId>com.wyq</groupId>
	<artifactId>jpa</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>jpa</name>
	<description>Demo project for Spring Boot</description>

	<properties>
		<java.version>1.8</java.version>
	</properties>

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

		<dependency>
			<groupId>mysql</groupId>
			<artifactId>mysql-connector-java</artifactId>
			<scope>runtime</scope>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
			<scope>test</scope>
		</dependency>
	</dependencies>

	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>

</project>

3、application.properties

#连接mysql数据库
spring.datasource.url=jdbc:mysql://localhost:3306/test?useSSL=false&characterEncoding=UTF-8&useUnicode=true&serverTimezone=GMT%2B8
spring.datasource.username=root
spring.datasource.password=123456
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
server.tomcat.uri-encoding=UTF-8
 
#JPA Configuration:
spring.jpa.database=mysql
spring.jpa.show-sql=true  
spring.jpa.generate-ddl=true
spring.jpa.hibernate.ddl-auto=update
spring.jpa.database-platform=org.hibernate.dialect.MySQL5Dialect

4、User.class

package com.wyq.entity;

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

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

	@Id
	@GeneratedValue(strategy = GenerationType.AUTO)
	private Integer id;
	
	private Integer age;
	
	private String password;
	
	private String username;
	
	private String phonenum;



	public Integer getId() {
		return id;
	}

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

	public Integer getAge() {
		return age;
	}

	public void setAge(Integer age) {
		this.age = age;
	}

	public String getPassword() {
		return password;
	}

	public void setPassword(String password) {
		this.password = password;
	}
	

	public String getUsername() {
		return username;
	}

	public void setUsername(String username) {
		this.username = username;
	}

	public String getPhonenum() {
		return phonenum;
	}

	public void setPhonenum(String phonenum) {
		this.phonenum = phonenum;
	}

	public User() {}
	
	public User(int id,int age,String username,String password,String phonenum) {
		this.id = id;
		this.age = age;
		this.username = username;
		this.password = password;
		this.phonenum = phonenum;
	}
	
}

5、UserRepository.class

package com.wyq.repository;

import java.util.List;

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

import com.wyq.entity.User;

public interface UserRepository extends JpaRepository<User, Integer>{

	public List<User>  findByUsername(String username);
}

6、UserService.class

package com.wyq.service;

import java.util.List;

import com.wyq.entity.User;

public interface UserService {

	public List<User>  findByUsername(String username);
	
}

7、UserServiceImpl.class

package com.wyq.impl;

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import com.wyq.entity.User;
import com.wyq.repository.UserRepository;
import com.wyq.service.UserService;

@Service("UserService")
public class UserServiceImpl implements UserService{

	@Autowired
	private UserRepository userRepository;
	
	@Override
	public List<User> findByUsername(String username) {
		// TODO Auto-generated method stub
		return this.userRepository.findByUsername(username);
	}
}

8、JpaApplicationTests.class(测试类)

package com.wyq;

import java.util.List;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

import com.wyq.entity.User;
import com.wyq.service.UserService;

@RunWith(SpringRunner.class)
@SpringBootTest
public class JpaApplicationTests {

	@Autowired
	private UserService userService;
	
	@Test
	public void contextLoads() {
		System.out.println("测试程序");
	}
	
	@Test 
	public void jpaTest() {
		
		List<User> testList = this.userService.findByUsername("test");
		
		System.out.println("测试成功"+testList.size());
	}

}

9、需要在test数据库中新建user表，表的字段如图所示。

10、测试结果。
源码地址：https://github.com/lovsw/Spring-Boot-Study
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