JPA全稱為Java Persistence API（Java持久層API），它是Sun公司在JavaEE 5中提出的Java持久化規(guī)范。

它為Java開發(fā)人員提供了一種對象/關聯(lián)映射工具，來管理Java應用中的關系數(shù)據(jù)，JPA吸取了目前Java持久化技術的優(yōu)點，旨在規(guī)范、簡化Java對象的持久化工作。

JPA對于單表的或者簡單的SQL查詢非常友好，甚至可以說非常智能。他為你準備好了大量的拿來即用的持久層操作方法。甚至只要寫findByName這樣一個接口方法，他就能智能的幫你執(zhí)行根據(jù)名稱查找實體類對應的表數(shù)據(jù)，完全不用寫SQL。

它相對于mybatis來說不用寫xml等配置，簡直方便的不行，對于我們開發(fā)者來說，誰更簡單，開發(fā)效率更高，我們就喜歡誰(不喜歡不行，看看產(chǎn)品經(jīng)理手里的菜刀)?。?！

這時候mybatis就不服了，我確實需要寫一大堆亂七八糟的xml，但是也可以用注解啊。

還不是要寫sql，總是一寫增刪改查sql，有沒有把這些常見的增刪改查全部封裝起來，我們直接調用api，sql讓它們自動組裝就好了，說實話我自己封裝了一個基于mybatis的組件，常見的增刪改查，自己組裝成sql去查詢，后來由于沒有oracle，sqlserver的數(shù)據(jù)庫環(huán)境，對這些數(shù)據(jù)庫的時間等等函數(shù)支持不好，又有jpa和mybatisplus這些現(xiàn)有的，我也就偷懶了

好了我們之前有實現(xiàn)過springboot-mybatis

springboot-mybatisplus的整合，現(xiàn)在就來實現(xiàn)一下jpa的，你們看看哪個比較方便好用，可以自己用用看

這是我實現(xiàn)的demo預覽

由于我想看到效果，又不想裝postman來測試，我就集成了swagger

最終效果如上圖

好了，我直接放代碼了

<?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> <groupId>com.zkb</groupId> <artifactId>spring-data-jpa</artifactId> <version>1.0-SNAPSHOT</version> <build> <plugins> <plugin><groupId>org.apache.maven.plugins</groupId><artifactId>maven-compiler-plugin</artifactId><configuration> <source>8</source> <target>8</target></configuration> </plugin> </plugins> </build> <dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> <version>2.1.1.RELEASE</version> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-data-jpa</artifactId> <version>2.1.1.RELEASE</version> </dependency> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>8.0.18</version> </dependency> <dependency> <groupId>org.projectlombok</groupId> <artifactId>lombok</artifactId> <version>1.18.12</version> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-devtools</artifactId> <version>2.0.4.RELEASE</version> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-test</artifactId> <version>2.1.2.RELEASE</version> <scope>test</scope> </dependency> <dependency> <groupId>com.alibaba</groupId> <artifactId>druid</artifactId> <version>1.0.31</version> </dependency> <dependency> <groupId>org.junit.jupiter</groupId> <artifactId>junit-jupiter</artifactId> <version>RELEASE</version> <scope>compile</scope> </dependency> <dependency> <groupId>org.junit.jupiter</groupId> <artifactId>junit-jupiter</artifactId> <version>RELEASE</version> <scope>compile</scope> </dependency> <dependency> <groupId>org.slf4j</groupId> <artifactId>slf4j-api</artifactId> <version>1.7.25</version> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-test</artifactId> <version>2.2.2.RELEASE</version> <scope>compile</scope> </dependency> <dependency> <groupId>io.springfox</groupId> <artifactId>springfox-swagger2</artifactId> <version>2.9.2</version> <exclusions><exclusion> <groupId>io.swagger</groupId> <artifactId>swagger-annotations</artifactId></exclusion><exclusion> <groupId>io.swagger</groupId> <artifactId>swagger-models</artifactId></exclusion> </exclusions> </dependency> <dependency> <groupId>io.swagger</groupId> <artifactId>swagger-annotations</artifactId> <version>1.5.22</version> </dependency> <dependency> <groupId>io.swagger</groupId> <artifactId>swagger-models</artifactId> <version>1.5.22</version> </dependency> <!-- swagger-ui --> <dependency> <groupId>io.springfox</groupId> <artifactId>springfox-swagger-ui</artifactId> <version>2.9.2</version> </dependency> <dependency> <groupId>com.github.xiaoymin</groupId> <artifactId>swagger-bootstrap-ui</artifactId> <version>1.9.1</version> </dependency> </dependencies> </project>

server: port: 5001spring: datasource: type: com.alibaba.druid.pool.DruidDataSource #Druid 是阿里巴巴開源平臺上一個數(shù)據(jù)庫連接池實現(xiàn)，結合了 C3P0、DBCP、PROXOOL 等 DB 池的優(yōu)點，同時加入了日志監(jiān)控 driver-class-name: com.mysql.cj.jdbc.Driver url: jdbc:mysql://localhost:3306/test-demo?useUnicode=true&characterEncoding=utf-8&useSSL=false&serverTimezone=UTC&autoReconnect=true&failOverReadOnly=false&zeroDateTimeBehavior=convertToNull username: root password: root dbcp2: min-idle: 5 initial-size: 5 max-total: 5 max-wait-millis: 200 jpa: database: mysql database-platform: org.hibernate.dialect.MySQL5InnoDBDialect show-sql: true hibernate: ddl-auto: update

package com.zkb.entity; import com.fasterxml.jackson.databind.annotation.JsonSerialize;import com.fasterxml.jackson.databind.ser.std.ToStringSerializer;import io.swagger.annotations.ApiModel;import io.swagger.annotations.ApiModelProperty;import lombok.Data; import javax.persistence.*; /** * 實體類 */@Entity@Table(name = 't_user')@Data@ApiModel(value = '用戶信息', description = '用戶信息')public class User { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) @ApiModelProperty(value = '主鍵') @JsonSerialize(using = ToStringSerializer.class) private Long id; @Column(name = 'username') @ApiModelProperty(value = '用戶名') private String username; @Column(name = 'password') @ApiModelProperty(value = '密碼') private String password; }

package com.zkb.dao; import com.zkb.entity.User;import org.springframework.data.jpa.repository.JpaRepository; public interface UserRepository extends JpaRepository<User,Long> {}

package com.zkb.service; import com.zkb.entity.User; import java.util.List; public interface UserService { public void deleteUser(Long id); List<User> getList();}

package com.zkb.service.impl; import com.zkb.dao.UserRepository;import com.zkb.entity.User;import com.zkb.service.UserService;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.stereotype.Service; import java.util.List; @Servicepublic class UserServiceImpl implements UserService { @Autowired private UserRepository userRepository; @Override public void deleteUser(Long id) { System.out.println(userRepository); userRepository.deleteById(id); } @Override public List<User> getList() { return userRepository.findAll(); }}

package com.zkb.controller; import com.zkb.entity.User;import com.zkb.service.UserService;import io.swagger.annotations.Api;import io.swagger.annotations.ApiOperation;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.web.bind.annotation.PostMapping;import org.springframework.web.bind.annotation.RequestMapping;import org.springframework.web.bind.annotation.RequestParam;import org.springframework.web.bind.annotation.RestController; import java.util.List; @RestController@RequestMapping('/user')@Api(value = 'user',tags = 'user')public class UserController { @Autowired private UserService userService; @PostMapping('/del') @ApiOperation(value='刪除',notes = '刪除') public String delete(@RequestParam('id') Long id){ userService.deleteUser(id); return 'true'; } @PostMapping('/getList') @ApiOperation(value='查詢所有',notes = '查詢所有') public List<User> getList(){ return userService.getList(); }}

package com.zkb.conf; import io.swagger.annotations.ApiOperation;import io.swagger.models.auth.In;import org.springframework.context.annotation.Bean;import org.springframework.context.annotation.Configuration;import springfox.documentation.builders.ApiInfoBuilder;import springfox.documentation.builders.PathSelectors;import springfox.documentation.builders.RequestHandlerSelectors;import springfox.documentation.service.ApiInfo;import springfox.documentation.service.ApiKey;import springfox.documentation.service.Contact;import springfox.documentation.spi.DocumentationType;import springfox.documentation.spring.web.plugins.Docket;import springfox.documentation.swagger2.annotations.EnableSwagger2; import java.util.Arrays;import java.util.List; @Configuration@EnableSwagger2public class SwaggerApp { @Bean public Docket createRestApi1() { return new Docket(DocumentationType.SWAGGER_2).enable(true).apiInfo(apiInfo()).select().apis(RequestHandlerSelectors.withMethodAnnotation(ApiOperation.class)).apis(RequestHandlerSelectors.basePackage('com.zkb.controller')).paths(PathSelectors.any()).build().securitySchemes(apiKeyList()).groupName('接口中心'); } private ApiInfo apiInfo() { return new ApiInfoBuilder().title('API').contact(new Contact('XXXXX', 'http://XXXXXX.XXXX/', '')).version('1.0').description('API 描述').build(); } private List<ApiKey> apiKeyList() { return Arrays.asList(new ApiKey('登錄token', 'token', In.HEADER.name()),new ApiKey('設備類型(android,ios,pc)---必填', 'deviceType', In.HEADER.name())); }}

package com.zkb;import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;import springfox.documentation.swagger2.annotations.EnableSwagger2;@SpringBootApplication@EnableSwagger2public class App { public static void main(String[] args) { SpringApplication.run(App.class,args); }}

CREATE TABLE `t_user` ( `id` bigint NOT NULL AUTO_INCREMENT, `username` varchar(50) COLLATE utf8mb4_general_ci DEFAULT NULL, `password` varchar(50) COLLATE utf8mb4_general_ci DEFAULT NULL, PRIMARY KEY (`id`) USING BTREE) ENGINE=InnoDB AUTO_INCREMENT=1214893367637352451 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci;

非常簡單的一張表，注意數(shù)據(jù)庫名稱

到這里就已經(jīng)實現(xiàn)了一個非常簡單的jpa demo了

當然我這里只是指路，讓知怎么用

補充：SpringBoot使用JPA實現(xiàn)增刪查改

一、運行環(huán)境

SpringBoot2.3.0

JDK1.8

IDEA2020.1.2

MySQL5.7

二、依賴及應用程序配置

<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-validation</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.projectlombok</groupId> <artifactId>lombok</artifactId> <optional>true</optional></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>

1、升級到SpringBoot2.2，spring-boot-starter-test默認使用JUnit 5作為單元測試框架 ，寫單元測試時注解@RunWith(Spring.class)升級為@ExtendWith(SpringExtension.class)

2、升級到SpringBoot2.3，hibernate-validator從spring-boot-starter-web移除，需要單獨引入

3、升級到SpringBoot2.3，MySQL驅動由com.mysql.jdbc.Driver變更為com.mysql.cj.jdbc.Driver;同時，數(shù)據(jù)源url需要添加serverTimezone=UTC&useSSL=false參數(shù)

3、升級到SpringBoot2.x，默認不自動注入HiddenHttpMethodFilter，需要設置spring.mvc.hiddenmethod.filter.enabled=true開啟PUT、DELETE方法支持

應用程序配置如下：

spring.application.name=springbootjpamanagement.endpoints.jmx.exposure.include=*management.endpoints.web.exposure.include=*management.endpoint.health.show-details=always# 應用服務 WEB 訪問端口server.port=8080# Actuator Web 訪問端口management.server.port=8081# mysql settingspring.datasource.driver-class-name=com.mysql.cj.jdbc.Driverspring.datasource.url=jdbc:mysql://localhost:3306/springbootjpa?serverTimezone=UTC&useSSL=falsespring.datasource.username=usernamespring.datasource.password=password# JPA settingspring.jpa.properties.hibernate.hbm2ddl.auto=updatespring.jpa.properties.hibernate.dialect=org.hibernate.dialect.MySQL5InnoDBDialectspring.jpa.show-sql=true# thymeleaf settingspring.thymeleaf.cache=false# delete、put方法支持spring.mvc.hiddenmethod.filter.enabled=true三、定義實體

使用@Entity標記實體類

import lombok.Data;import javax.persistence.*;import javax.validation.constraints.NotEmpty;import java.io.Serializable;@Entity@Datapublic class Article extends BaseEntity implements Serializable { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) private Long id; @Column(nullable = false, unique = true) @NotEmpty(message = '標題不能為空') private String title; @Column(nullable = false) private String body;}

為了自動添加創(chuàng)建日期、修改日期、創(chuàng)建人及修改人，我們把創(chuàng)建、修改信息放到父類中由實體類繼承，并開啟SpringBoot的自動審計功能，將創(chuàng)建/修改信息自動注入

1、定義實體類的父類,@CreatedDate、@LastModifiedDate、@CreatedBy、@LastModifiedBy標注相應字段

import org.hibernate.annotations.Columns;import org.springframework.data.annotation.CreatedBy;import org.springframework.data.annotation.CreatedDate;import org.springframework.data.annotation.LastModifiedBy;import org.springframework.data.annotation.LastModifiedDate;import org.springframework.data.jpa.domain.support.AuditingEntityListener;import javax.persistence.Column;import javax.persistence.EntityListeners;import javax.persistence.MappedSuperclass;@MappedSuperclass@EntityListeners(AuditingEntityListener.class)public class BaseEntity { @CreatedDate private Long createTime; @LastModifiedDate private Long updateTime; @Column(name = 'create_by') @CreatedBy private String createBy; @Column(name = 'lastmodified_by') @LastModifiedBy private String lastmodifiedBy; public Long getCreateTime() { return createTime; } public void setCreateTime(Long createTime) { this.createTime = createTime; } public Long getUpdateTime() { return updateTime; } public void setUpdateTime(Long updateTime) { this.updateTime = updateTime; } public String getCreateBy() { return createBy; } public void setCreateBy(String createBy) { this.createBy = createBy; } public String getLastmodifiedBy() { return lastmodifiedBy; } public void setLastmodifiedBy(String lastmodifiedBy) { this.lastmodifiedBy = lastmodifiedBy; }}@MappedSuperclass注解：

作用于實體類的父類上，父類不生成對應的數(shù)據(jù)庫表

標注@MappedSuperclass的類不能再標注@Entity或@Table注解，也無需實現(xiàn)序列化接口

每個子類（實體類）對應一張數(shù)據(jù)庫表，數(shù)據(jù)庫表包含子類屬性和父類屬性

標注@MappedSuperclass的類可以直接標注@EntityListeners實體監(jiān)聽器

@EntityListeners(AuditingEntityListener.class)注解：

作用范圍僅在標注@MappedSuperclass類的所有繼承類中，并且實體監(jiān)聽器可以被其子類繼承或重載

開啟JPA的審計功能，需要在SpringBoot的入口類標注@EnableJpaAuditing

創(chuàng)建日期、修改日期有默認方法注入值，但創(chuàng)建人和修改人注入則需要手動實現(xiàn)AuditorAware接口:

@Configurationpublic class BaseEntityAuditor implements AuditorAware<String> { @Override public Optional<String> getCurrentAuditor() { return ''; }}四、DAO層實現(xiàn)

JPA支持通過約定方法名進行數(shù)據(jù)庫查詢、修改：

import org.springframework.data.jpa.repository.JpaRepository;import springbootjpa.entity.Article;public interface ArticleRepository extends JpaRepository<Article, Long> { Article findById(long id);}

通過約定方法名查詢，只需實現(xiàn)JpaRepository接口聲明查詢方法而不需要具體實現(xiàn)

此外，可以在方法上標注@Query實現(xiàn)JPQL或原生SQL查詢

JpaRepository<T, ID>,T表示要操作的實體對象，ID表示主鍵。該接口繼承了分頁排序接口PadingAndSortRepository,通過構建Pageable實現(xiàn)分頁查詢：

@Autowiredprivate ArticleRepository articleRepository;@RequestMapping('')public ModelAndView articlelist(@RequestParam(value = 'start', defaultValue = '0') Integer start, @RequestParam(value = 'limit', defaultValue = '5') Integer limit) { start = start < 0 ? 0 : start; Sort sort = Sort.by(Sort.Direction.DESC, 'id'); Pageable pageable = PageRequest.of(start, limit, sort); Page<Article> page = articleRepository.findAll(pageable); ModelAndView modelAndView = new ModelAndView('article/list'); modelAndView.addObject('page', page); return modelAndView;}

如果根據(jù)某一字段排序，可以用Sort.by方法構建Sort對象；如果根據(jù)多個字段排序，首先構建Sort.Order數(shù)組List<Sort.Order>,然后再傳入Sort.by方法構建Sort對象。

PageRequest.of方法生成Pageable對象

五、Contrller 控制器

import org.springframework.beans.factory.annotation.Autowired;import org.springframework.data.domain.Page;import org.springframework.data.domain.PageRequest;import org.springframework.data.domain.Pageable;import org.springframework.data.domain.Sort;import org.springframework.stereotype.Controller;import org.springframework.web.bind.annotation.*;import org.springframework.web.servlet.ModelAndView;import springbootjpa.entity.Article;import springbootjpa.repository.ArticleRepository;@Controller@RequestMapping('/article')public class ArticleController { @Autowired private ArticleRepository articleRepository; @RequestMapping('') public ModelAndView articlelist(@RequestParam(value = 'start', defaultValue = '0') Integer start, @RequestParam(value = 'limit', defaultValue = '5') Integer limit) { start = start < 0 ? 0 : start; Sort sort = Sort.by(Sort.Direction.DESC, 'id'); Pageable pageable = PageRequest.of(start, limit, sort); Page<Article> page = articleRepository.findAll(pageable); ModelAndView modelAndView = new ModelAndView('article/list'); modelAndView.addObject('page', page); return modelAndView; } @RequestMapping('/add') public String addArticle() { return 'article/add'; } @PostMapping('') public String saveArticle(Article article) { articleRepository.save(article); return 'redirect:/article'; } @GetMapping('/{id}') public ModelAndView getArticle(@PathVariable('id') Integer id) { Article article = articleRepository.findById(id); ModelAndView modelAndView = new ModelAndView('article/show'); modelAndView.addObject('article', article); return modelAndView; } @DeleteMapping('/{id}') public String deleteArticle(@PathVariable('id') long id) { System.out.println('put 方法'); articleRepository.deleteById(id); return 'redirect:/article'; } @GetMapping('edit/{id}') public ModelAndView editArticle(@PathVariable('id') Integer id) { Article article = articleRepository.findById(id); ModelAndView modelAndView = new ModelAndView('article/edit'); modelAndView.addObject('article', article); return modelAndView; } @PutMapping('/{id}') public String editArticleSave(Article article, long id) { System.out.println('put 方法'); article.setId(id); articleRepository.save(article); return 'redirect:/article'; }}

因為<form>表單只能發(fā)送GET或POST請求，spring3引入一個監(jiān)聽器HiddenHttpMethodFilter來將POST請求轉換為PUT或POST請求。

SpringBoot2.x開始默認不自動注入HiddenHttpMethodFilter，需要設置spring.mvc.hiddenmethod.filter.enabled=true開啟PUT、DELETE方法支持

配置完后，前端頁面需要在表單中加入隱藏域，表明實際請求方法：

<!-- DELETE 請求 --><form method='POST' action=''><input type='hidden' name='_method' value='delete'></form><!-- PUT 請求 --><form method='POST' action=''><input type='hidden' name='_method' value='put'></form>六、其他th:value和th:field區(qū)別：

th:value解析成html，表現(xiàn)為：value='${th:value}'

th:field解析成html，表現(xiàn)為：name='${th:name}' value='${th:value}'

以上為個人經(jīng)驗，希望能給大家一個參考，也希望大家多多支持好吧啦網(wǎng)。如有錯誤或未考慮完全的地方，望不吝賜教。