1.JPA是什么

首先，我們說說JPA是什么？

JPA(java persistence api)，它并不是一個框架，而是一組規(guī)范。我覺得對于任何一個開發(fā)人員來說，理解“規(guī)范”這個詞應該不在話下。其中，Hibernate就實現(xiàn)了這個規(guī)范，而且那是相當成功的（其實TopLink和OpenJPA也都實現(xiàn)了JPA規(guī)范，不過它們被Hinernate的光環(huán)籠罩了）。所以呢，當我們說到JPA的時候，好多人首先想到的就是Hibernate。

2.SpringBootData JPA是什么

SpringData：其實SpringData就是Spring提供了一個操作數(shù)據(jù)的框架。而SpringData JPA只是SpringData框架下的一個基于JPA標準操作數(shù)據(jù)的模塊。
SpringData JPA：基于JPA的標準數(shù)據(jù)進行操作。簡化操作持久層的代碼。只需要編寫接口就可以。

廢話不多說了,直接開始

3.環(huán)境/版本一覽

• 開發(fā)工具：Intellij IDEA 2020.2.3
• springboot：2.3.7.RELEASE
• jdk：1.8.0_211
• maven: 3.6.3

4.工程結構 

5.開始搭建

創(chuàng)建數(shù)據(jù)庫

SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;
-- ----------------------------
-- Table structure for sys_user
-- ----------------------------
DROP TABLE IF EXISTS `sys_user`;
CREATE TABLE `sys_user` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(255) DEFAULT NULL,
  `pwd` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8;
-- ----------------------------
-- Records of sys_user
-- ----------------------------
BEGIN;
INSERT INTO `sys_user` VALUES (1, 'test', '123');
COMMIT;
SET FOREIGN_KEY_CHECKS = 1;

新建項目

pom.xml依賴配置

<?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 https://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>2.3.7.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.niu</groupId>
    <artifactId>datasource</artifactId>
    <version>1.0.0-SNAPSHOT</version>
    <name>datasource</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>1.8</java.version>
    </properties>
    <dependencies>
        <!-- alibaba的druid數(shù)據(jù)庫連接池 -->
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid-spring-boot-starter</artifactId>
            <version>1.1.9</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.39</version>
            <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>

創(chuàng)建配置文件 application.yml

server:
  port: 8080
spring:
  datasource:
    name: main_db
    type: com.alibaba.druid.pool.DruidDataSource
    #druid相關配置
    druid:
      #監(jiān)控統(tǒng)計攔截的filters
      filters: stat
      driver-class-name: com.mysql.jdbc.Driver
      #基本屬性
      url: jdbc:mysql://127.0.0.1:3306/t_user_db?useUnicode=true&characterEncoding=UTF-8&allowMultiQueries=true
      username: root
      password: Abcdef@123456
      #配置初始化大小/最小/最大
      initial-size: 1
      min-idle: 1
      max-active: 20
      #獲取連接等待超時時間
      max-wait: 60000
      #間隔多久進行一次檢測，檢測需要關閉的空閑連接
      time-between-eviction-runs-millis: 60000
      #一個連接在池中最小生存的時間
      min-evictable-idle-time-millis: 300000
      validation-query: SELECT 'x'
      test-while-idle: true
      test-on-borrow: false
      test-on-return: false
      #打開PSCache，并指定每個連接上PSCache的大小。oracle設為true，mysql設為false。分庫分表較多推薦設置為false
      pool-prepared-statements: false
      max-pool-prepared-statement-per-connection-size: 20
  jpa:
    hibernate:
      ddl-auto: update
    show-sql: true

創(chuàng)建model  類多的話可以使用逆向工程創(chuàng)建

@Entity(name = "sys_user") //name值代表數(shù)據(jù)庫對應的表名，如不寫默認按照實體類的駝峰命名法單詞中間加_
@JsonIgnoreProperties(value = { "hibernateLazyInitializer"}) //加這個注解是為了防止本項目把jpa對象直接轉json有空值報錯
public class SysUser {
    @Id
    @GeneratedValue
    private Integer id;
    /**
     *
     *   這里是映射數(shù)據(jù)表字段與實體字段 若數(shù)據(jù)庫表字段為 user_name  這里需要寫成
     *   @Column(name = "user_name") 
     *   private String userName;
     *   如果一致可以不寫   
     */
    @Column(name = "name") 
    private String name;
    private String pwd;
        //get/set省略，記得加上
}

創(chuàng)建Repository

/**
 *  
 * JpaRepository<SysUser,Integer> 參數(shù)1 要映射的實體類
 *                                參數(shù)2 實體類主鍵的數(shù)據(jù)類型
 *  每個dao層接口都要繼承這個類
 **/
@Repository
public interface SysUserRepository  extends JpaRepository<SysUser,Integer> {
}

創(chuàng)建service

@Service
public class UserService {
    @Autowired
    private SysUserRepository sysUserRepository;
    public SysUser getUser(Integer id){
        return  sysUserRepository.getOne(id);
    }
}

創(chuàng)建controller 這里我們讓接口都返回json 使用@RestController注解

@RestController
@RequestMapping("/user")
public class UserController {
    @Autowired
    private UserService userService;
    @GetMapping("/{userId}")
    public SysUser user(@PathVariable  Integer userId){
        return userService.getUser(userId);
    }
}

創(chuàng)建主類

@SpringBootApplication
public class SpringbootJPAApplication {
    public static void main(String[] args) {
        SpringApplication.run(SpringbootJPAApplication.class, args);
    }
}

6.啟動測試

查看下日志：

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.3.7.RELEASE)

2020-12-17 10:05:32.976  INFO 3434 --- [           main] c.n.springboot.SpringbootJPAApplication  : Starting SpringbootJPAApplication on MacBook-Pro.local with PID 3434 (/Users/laoniu/IdeaProjects/datasource/target/classes started by laoniu in /Users/laoniu/IdeaProjects/datasource)
2020-12-17 10:05:32.979  INFO 3434 --- [           main] c.n.springboot.SpringbootJPAApplication  : No active profile set, falling back to default profiles: default
2020-12-17 10:05:33.606  INFO 3434 --- [           main] .s.d.r.c.RepositoryConfigurationDelegate : Bootstrapping Spring Data JPA repositories in DEFAULT mode.
2020-12-17 10:05:33.668  INFO 3434 --- [           main] .s.d.r.c.RepositoryConfigurationDelegate : Finished Spring Data repository scanning in 55ms. Found 1 JPA repository interfaces.
2020-12-17 10:05:34.014  INFO 3434 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2020-12-17 10:05:34.021  INFO 3434 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2020-12-17 10:05:34.021  INFO 3434 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.41]
2020-12-17 10:05:34.096  INFO 3434 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2020-12-17 10:05:34.096  INFO 3434 --- [           main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 1058 ms
2020-12-17 10:05:34.150  INFO 3434 --- [           main] c.a.d.s.b.a.DruidDataSourceAutoConfigure : Init DruidDataSource
Thu Dec 17 10:05:34 CST 2020 WARN: Establishing SSL connection without server's identity verification is not recommended. According to MySQL 5.5.45+, 5.6.26+ and 5.7.6+ requirements SSL connection must be established by default if explicit option isn't set. For compliance with existing applications not using SSL the verifyServerCertificate property is set to 'false'. You need either to explicitly disable SSL by setting useSSL=false, or set useSSL=true and provide truststore for server certificate verification.
2020-12-17 10:05:34.627  INFO 3434 --- [           main] com.alibaba.druid.pool.DruidDataSource   : {dataSource-1} inited
2020-12-17 10:05:34.774  INFO 3434 --- [           main] o.hibernate.jpa.internal.util.LogHelper  : HHH000204: Processing PersistenceUnitInfo [name: default]
2020-12-17 10:05:34.807  INFO 3434 --- [           main] org.hibernate.Version                    : HHH000412: Hibernate ORM core version 5.4.25.Final
2020-12-17 10:05:34.903  INFO 3434 --- [           main] o.hibernate.annotations.common.Version   : HCANN000001: Hibernate Commons Annotations {5.1.2.Final}
2020-12-17 10:05:34.981  INFO 3434 --- [           main] org.hibernate.dialect.Dialect            : HHH000400: Using dialect: org.hibernate.dialect.MySQL57Dialect
2020-12-17 10:05:35.360  INFO 3434 --- [           main] o.h.e.t.j.p.i.JtaPlatformInitiator       : HHH000490: Using JtaPlatform implementation: [org.hibernate.engine.transaction.jta.platform.internal.NoJtaPlatform]
2020-12-17 10:05:35.367  INFO 3434 --- [           main] j.LocalContainerEntityManagerFactoryBean : Initialized JPA EntityManagerFactory for persistence unit 'default'
2020-12-17 10:05:35.580  WARN 3434 --- [           main] JpaBaseConfiguration$JpaWebConfiguration : spring.jpa.open-in-view is enabled by default. Therefore, database queries may be performed during view rendering. Explicitly configure spring.jpa.open-in-view to disable this warning
2020-12-17 10:05:35.680  INFO 3434 --- [           main] o.s.s.concurrent.ThreadPoolTaskExecutor  : Initializing ExecutorService 'applicationTaskExecutor'
2020-12-17 10:05:35.878  INFO 3434 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2020-12-17 10:05:35.890  INFO 3434 --- [           main] c.n.springboot.SpringbootJPAApplication  : Started SpringbootJPAApplication in 3.227 seconds (JVM running for 3.93)
2020-12-17 10:05:49.330  INFO 3434 --- [nio-8080-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring DispatcherServlet 'dispatcherServlet'
2020-12-17 10:05:49.331  INFO 3434 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : Initializing Servlet 'dispatcherServlet'
2020-12-17 10:05:49.335  INFO 3434 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : Completed initialization in 4 ms
Hibernate: select sysuser0_.id as id1_0_0_, sysuser0_.name as name2_0_0_, sysuser0_.pwd as pwd3_0_0_ from sys_user sysuser0_ where sysuser0_.id=?
 

可以看到最后一行是SpringDataJPA為我們生成的查詢語句，我們并沒有寫sql，只是調用的SpringDataJPA自帶的方法，讓我們去看一下SpringDataJPA都為我們提供哪些可用的方法

7.Repository接口的使用

7.1SpringDataJPA提供的方法

按照SpringDataJPA規(guī)范可以讓我們只寫方法就可以進行操作數(shù)據(jù)庫，讓我們試一下

7.2編寫Repository接口方法

//方法名稱必須要遵循駝峰式命名規(guī)則，findBy（關鍵字）+屬性名稱（首字母大寫）+查詢條件（首字母大寫）  
SysUser findByNameAndPwd(String name,String pwd);

這樣就能完成基本的查詢

刪除用deleteBy開頭方法

如果方法不能滿足我的需求呢，我們還可以通過@Query注解手動寫sql

8.@Query基本使用

   /***
     *
     * ?1表示第一個參數(shù)，?2表示第二個參數(shù)
     * 這里的寫法是hql寫法
     * nativeQuery = false 代表使用hql ，默認不設置的話就是false 默認使用的hql
     * 要想使用 原生的sql  改為 true即可
     */
    @Query(value = "from SysUser where name = ?1 and pwd =?2",nativeQuery = false)
    SysUser findByNameAndPwdUseSQL(String name,String pwd);

到此，SpringBoot整合SpringDataJPA基本的使用結束，代碼已經(jīng)推送至github，https://github.com/NiuXiangQian/springboot-jpa

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