使用SpringBoot+JPA的简单案例

简介：

JPA是Java Persistence API的简称，中文名Java持久层API，是JDK 5.0注解或XML描述对象－关系表的映射关系，并将运行期的实体对象持久化到数据库中。

第一步：引入我们需要的POM文件

<dependencies>
    <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
            <version>1.5.1.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.18</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
            <version>2.2.1.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <version>2.2.2.RELEASE</version>
        </dependency>
  </dependencies>

第二步：配置application.yml文件

server:
  port: 8080
spring:
  jpa:
    database-platform: org.hibernate.dialect.MySQL5Dialect
    show-sql: true
  datasource:
    url: jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=utf-8&serverTimezone=GMT%2B8
    driver-class-name: com.mysql.jdbc.Driver
    username: root
    password: root

第三步：创建一个简单的工具类ResponseResult

package com.feicheng.common;

/**
 * 结果返回集
 * @author Lenovo
 */
public class ResponseResult {

    private Integer code;

    private String msg;
    
    public void setCode(Integer code) {
        this.code = code;
    }

    public void setMsg(String msg) {
        this.msg = msg;
    }

    public Integer getCode() {
        return code;
    }

    public String getMsg() {
        return msg;
    }

    public ResponseResult(Integer code, String msg) {
        this.code = code;
        this.msg = msg;
    }
}

第四步：创建一个test数据库和创建一个user表（字段有：id，username）

CREATE DATABASE /*!32312 IF NOT EXISTS*/`test` /*!40100 DEFAULT CHARACTER SET latin1 */;

USE `test`;

/*Table structure for table `user` */

DROP TABLE IF EXISTS `user`;

CREATE TABLE `user` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(50) DEFAULT NULL,
  `password` varchar(64) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=15 DEFAULT CHARSET=utf8;

第五步：创建实体类User

package com.feicheng.entity;
import javax.persistence.*;
/**
 * @author Lenovo
 */
@Table(name = "user")
@Entity
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer id;
	
    private String name;

    private String password;
    
    public Integer getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPassword() {
        return password;
    }

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

第六步：创建UserController

package com.feicheng.controller;

import com.feicheng.common.ResponseResult;
import com.feicheng.entity.User;
import com.feicheng.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.stereotype.Controller;
import org.springframework.util.CollectionUtils;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestMapping;

import java.util.Collections;
import java.util.List;

/**
 * @author Lenovo
 */
@Controller
@RequestMapping("user")
public class UserController {

    @Autowired
    private UserService userService;
    
    /**
     * 查询全部用户
     *
     * @return
     */
    @GetMapping("list")
    public ResponseEntity<List<User>> list() {

        List<User> users = this.userService.select();

        if (CollectionUtils.isEmpty(users)) {

            return ResponseEntity.notFound().build();
        }

        return ResponseEntity.ok(users);
    }

    /**
     * 根据用户名查询用户
     *
     * @param userName
     * @return
     */
    @GetMapping("select/{userName}")
    public ResponseEntity<User> selectUserByName(@PathVariable("userName") String userName) {

        User user = this.userService.selectUserByName(userName);

        if (user == null) {

            return ResponseEntity.status(HttpStatus.NOT_FOUND).build();
        }

        return ResponseEntity.ok(user);
    }

    /**
     * 根据id修改用户
     *
     * @param user
     * @return
     */
    @PostMapping("edit")
    public ResponseEntity<ResponseResult> edit(User user) {

        ResponseResult responseResult = this.userService.edit(user);

        return ResponseEntity.ok(responseResult);
    }

    /**
     * 根据id删除用户
     *
     * @param id
     * @return
     */
    @PostMapping("delete/{id}")
    public ResponseEntity<ResponseResult> delete(@PathVariable("id") Integer id) {

        ResponseResult responseResult = this.userService.delete(id);

        return ResponseEntity.ok(responseResult);
    }
}

第七步：创建UserService

package com.feicheng.service;

import com.feicheng.common.ResponseResult;
import com.feicheng.entity.User;

import java.util.List;

/**
 * @author Lenovo
 */
public interface UserService {

    // 查询全部用户
    List<User> select();

    // 根据用户名查询用户信息
    User selectUserByName(String userName);

    // 根据用户id修改用户
    ResponseResult edit(User user);

    // 根据id删除用户
    ResponseResult delete(Integer id);
}

第八步：创建UserServiceImpl

package com.feicheng.service.impl;

import com.feicheng.common.ResponseResult;
import com.feicheng.entity.User;
import com.feicheng.repository.UserRepository;
import com.feicheng.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.domain.Example;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;
import org.springframework.util.CollectionUtils;

import java.util.List;
import java.util.Optional;

/**
 * @author Lenovo
 */
@Service
public class UserServiceImpl implements UserService {

      @Autowired
    private UserRepository userRepository;
    
    /**
     * 查询全部用户
     *
     * @return
     */
    @Override
    public List<User> select() {

        List<User> users = this.userRepository.findAll();

        if (CollectionUtils.isEmpty(users)) {

            return null;
        }

        return users;
    }

    /**
     * 根据用户名查询用户信息
     *
     * @param userName
     * @return
     */
    @Override
    public User selectUserByName(String userName) {

        User user = new User();

        user.setName(userName);

        Example<User> example = Example.of(user);

        Optional<User> one = this.userRepository.findOne(example);

        user = one.get();

        return user;
    }

    /**
     * 根据用户id修改用户信息
     *
     * @param user
     * @return
     */
    @Override
    public ResponseResult edit(User user) {

        Integer count = this.userRepository.edit(user.getName(), user.getPassword(), user.getId());

        if (count > 0) {

            return new ResponseResult(200, "修改成功");

        }

        return new ResponseResult(500, "修改失败");
    }

    /**
     * 根据id删除用户
     *
     * @param id
     * @return
     */
    @Override
    @Transactional
    public ResponseResult delete(Integer id) {

        try {

            this.userRepository.deleteById(id);

            return new ResponseResult(200, "删除成功");

        } catch (Exception e) {

            e.printStackTrace();

            return new ResponseResult(500, "删除失败");
        }
    }
}

第九步：创建UserRepository

package com.feicheng.repository;

import com.feicheng.entity.User;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Modifying;
import org.springframework.data.jpa.repository.Query;
import org.springframework.data.repository.query.Param;
import org.springframework.stereotype.Repository;
import org.springframework.transaction.annotation.Transactional;

/**
 * @author Lenovo
 */
@Repository
public interface UserRepository extends JpaRepository<User, Integer> {

    @Modifying
    @Transactional
    @Query("update User u set u.name = :name, u.password = :password where u.id = :id")
    Integer edit(@Param("name") String name, @Param("password") String password, @Param("id") Integer id);
}

最后总结：

使用JPA操作数据库比较方便，把我们想要的代码都封装好了
操作起来还是比较简单快捷，容易上手

想继续了解JPA，可以去我的GitHub上做的一个权限管理系统，就是用的JPA来操作的数据库

GitHub地址：github.com/javaenignee…