一、啥是JPA？
JPA，全英文名叫Java Persistence API，就是java持久化api，是SUN公司推出的一套基于ORM的规范。
持久化想必如雷贯耳，都0202年了，谁还不用个持久化框架啊，举起mybatis。
ORM呢？全英文名为Object-Relational Mapping：对象关系映射，简单来说为了不用JDBC那一套原始方法来操作数据库，ORM框架横空出世（mybatis、hibernate等等）。
然而ORM框架出的太多了，百花齐放，琳琅满目，你一套标准我一套标准，要是想换一套框架实现项目，可能要从头再写。啊这？入土吧。
百度这样介绍SUN的JPA规范：
Sun引入新的JPA ORM规范出于两个原因：
其一，简化现有Java EE和Java SE应用开发工作；
其二，Sun希望整合ORM技术，实现天下归一。
有气魄，我喜欢，学他丫的。
二、Spring-Data-Jpa简介
学jpa哪家强？哪家简单学哪家，spring-data-jpa最简单。介绍如下：
Spring Data JPA是Spring Data家族的一部分，可以轻松实现基于JPA的存储库。 此模块处理对基于JPA的数据访问层的增强支持。 它使构建使用数据访问技术的Spring驱动应用程序变得更加容易。
总的来说JPA是ORM规范，Hibernate、TopLink等是JPA规范的具体实现，这样的好处是开发者可以面向JPA规范进行持久层的开发，而底层的实现则是可以切换的（敲黑板哦）。Spring Data Jpa则是在JPA之上添加另一层抽象（Repository层的实现），极大地简化持久层开发及ORM框架切换的成本。
也就是如下图所示：
三、环境配置
话不多说，使用Maven管理包，使用springboot框架，建个空maven项目就行
1、配置pom.xml
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2、配置application.yml
server:port:8801spring:application:name:user-service datasource:type:com.alibaba.druid.pool.DruidDataSource driverClassName:com.mysql.jdbc.Driver url:jdbc:mysql://10.16.58.21:3306/appt_test username:root password:123456# druid配置项，默认spring-boot不支持，故需要config类来解析 initialSize:5minIdle:5maxActive:20maxWait:60000timeBetweenEvictionRunsMillis:60000minEvictableIdleTimeMillis:300000validationQuery:SELECT1FROM DUAL testWhileIdle:truetestOnBorrow:falsetestOnReturn:falsepoolPreparedStatements:truemaxPoolPreparedStatementPerConnectionSize:20filters:stat,wall,log4j connectionProperties:druid.stat.mergeSql=true;druid.stat.slowSqlMillis=5000jpa:hibernate:ddl-auto:update show-sql:true
3、配置Springboot启动类
@SpringBootApplication@EnableJpaAuditingpublicclassUserServiceApplication{publicstaticvoidmain(String[]args){SpringApplication.run(UserServiceApplication.class,args);}@PostConstructvoidsetDefaultTimeZone(){TimeZone.setDefault(TimeZone.getTimeZone("Asia/Shanghai"));}}
注意：
除了@SpringBootApplication启动注解外，
还有一个注解@EnableJpaAuditing，它是用来启动Jpa的审计功能，比如说在使用建表中经常会加入 版本号、创建时间、修改时间 、创建者、修改者 这五个字段。因此为了简化开发， 我们可以将其交给jpa来自动填充。
4、创建阿里Druid配置类
importcom.alibaba.druid.pool.DruidDataSource;importcom.alibaba.druid.support.http.StatViewServlet;importcom.alibaba.druid.support.http.WebStatFilter;importorg.slf4j.Logger;importorg.slf4j.LoggerFactory;importorg.springframework.beans.factory.annotation.Value;importorg.springframework.boot.web.servlet.FilterRegistrationBean;importorg.springframework.boot.web.servlet.ServletRegistrationBean;importorg.springframework.context.annotation.Bean;importorg.springframework.context.annotation.Configuration;importorg.springframework.context.annotation.Primary;importjavax.sql.DataSource;importjava.sql.SQLException;/**
* 阿里Druid配置类
*
* @author zcc ON 2018/2/11
**/@ConfigurationpublicclassDruidConfig{privatestaticfinal Logger log=LoggerFactory.getLogger(DruidConfig.class);@Value("${spring.datasource.url}")privateString dbUrl;@Value("${spring.datasource.username}")privateString username;@Value("${spring.datasource.password}")privateString password;@Value("${spring.datasource.driverClassName}")privateString driverClassName;@Value("${spring.datasource.initialSize}")privateint initialSize;@Value("${spring.datasource.minIdle}")privateint minIdle;@Value("${spring.datasource.maxActive}")privateint maxActive;@Value("${spring.datasource.maxWait}")privateint maxWait;@Value("${spring.datasource.timeBetweenEvictionRunsMillis}")privateint timeBetweenEvictionRunsMillis;@Value("${spring.datasource.minEvictableIdleTimeMillis}")privateint minEvictableIdleTimeMillis;@Value("${spring.datasource.validationQuery}")privateString validationQuery;@Value("${spring.datasource.testWhileIdle}")privateboolean testWhileIdle;@Value("${spring.datasource.testOnBorrow}")privateboolean testOnBorrow;@Value("${spring.datasource.testOnReturn}")privateboolean testOnReturn;@Value("${spring.datasource.poolPreparedStatements}")privateboolean poolPreparedStatements;@Value("${spring.datasource.maxPoolPreparedStatementPerConnectionSize}")privateint maxPoolPreparedStatementPerConnectionSize;@Value("${spring.datasource.filters}")privateString filters;@Value("{spring.datasource.connectionProperties}")privateString connectionProperties;@Bean @PrimarypublicDataSourcedataSource(){DruidDataSource datasource=newDruidDataSource();log.info("----------- druid datasource ----------");datasource.setUrl(this.dbUrl);datasource.setUsername(username);datasource.setPassword(password);datasource.setDriverClassName(driverClassName);datasource.setInitialSize(initialSize);datasource.setMinIdle(minIdle);datasource.setMaxActive(maxActive);datasource.setMaxWait(maxWait);datasource.setTimeBetweenEvictionRunsMillis(timeBetweenEvictionRunsMillis);datasource.setMinEvictableIdleTimeMillis(minEvictableIdleTimeMillis);datasource.setValidationQuery(validationQuery);datasource.setTestWhileIdle(testWhileIdle);datasource.setTestOnBorrow(testOnBorrow);datasource.setTestOnReturn(testOnReturn);datasource.setPoolPreparedStatements(poolPreparedStatements);datasource.setMaxPoolPreparedStatementPerConnectionSize(maxPoolPreparedStatementPerConnectionSize);try{datasource.setFilters(filters);}catch(SQLExceptione){e.printStackTrace();}datasource.setConnectionProperties(connectionProperties);returndatasource;}@BeanpublicServletRegistrationBeanregistrationBean(){ServletRegistrationBean servletRegistrationBean=newServletRegistrationBean(newStatViewServlet());// 添加初始化参数：initParamsservletRegistrationBean.addUrlMappings("/druid/*");// 白名单servletRegistrationBean.addInitParameter("allow","127.0.0.1");//黑名单 servletRegistrationBean.addInitParameter("deny","192.168.0.101");//登录查看信息的账号密码.servletRegistrationBean.addInitParameter("loginUsername","admin");servletRegistrationBean.addInitParameter("loginPassword","123456");//可重置数据.servletRegistrationBean.addInitParameter("resetEnable","false");returnservletRegistrationBean;}@BeanpublicFilterRegistrationBeanfilterRegistrationBean(){FilterRegistrationBean filterRegistrationBean=newFilterRegistrationBean(newWebStatFilter());//添加过滤规则.filterRegistrationBean.addUrlPatterns("/*");// 添加不需要忽略的格式信息.filterRegistrationBean.addInitParameter("exclusions","*.js,*.gif,*.jpg,*.png,*.css,*.ico,/druid/*");returnfilterRegistrationBean;}}
5、创建repository数据访问层接口，
通过repository接口可以很方便的调用JPA，完成数据库的所有操作，当然包括数据库CRUD
importcom.jacky.userservice.pojo.entity.dvUser;importorg.springframework.data.jpa.repository.JpaRepository;publicinterfacedvUserRepositoryextendsJpaRepository
可以看到，这个接口继承了JpaRepository<实体,ID>，spring-data-jpa只需要这个信息，就可以帮你完成常用的操作：增删查改。
6、创建entity实体类
@Data@Entity@Table(name="dv_user")@EntityListeners(AuditingEntityListener.class)publicclassdvUser{@Id @Column(name="id")@GeneratedValue(strategy=GenerationType.SEQUENCE,generator="JPA_USER_S2")@SequenceGenerator(sequenceName="JPA_USER_S1",name="JPA_USER_S2",allocationSize=1)privateLong id;@Column(name="name")privateString name;@Column(name="object_version")@VersionprivateLong objectVersion;@Column(name="created_by")@CreatedByprivateString createdBy;@Column(name="created_date")@CreatedDate @JsonFormat(pattern="yyyy-MM-dd HH:mm:ss",timezone="GMT+8")privateDate createdDate;@Column(name="last_updated_by")@LastModifiedByprivateString lastUpdatedBy;@Column(name="last_updated_date")@LastModifiedDate @JsonFormat(pattern="yyyy-MM-dd HH:mm:ss",timezone="GMT+8")privateDate lastUpdatedDate;}
7、创建service接口
importcom.jacky.userservice.pojo.entity.dvUser;importjava.util.List;publicinterfacedvUserService{/**
* 新增用户
* @param user 用户对象
*/dvUserinsertUser(dvUser user);/**
* 删除用户
* @param id 删除id
*/voiddeleteUser(Long id);/**
* 修改用户
* @param user 用户信息
*/dvUserupdateUser(dvUser user);/**
* 查询所有用户
*/List
* 通过id查询用户
* @param id 用户id
*/dvUserfindUserById(Long id);}
8、创建service接口实现类
importcom.jacky.userservice.pojo.entity.dvUser;importcom.jacky.userservice.repository.dvUserRepository;importcom.jacky.userservice.service.dvUserService;importorg.springframework.stereotype.Service;importjavax.annotation.Resource;importjava.util.List;@ServicepublicclassdvUserServiceImplimplementsdvUserService{@ResourceprivatedvUserRepository dvUserRepository;@OverridepublicdvUserinsertUser(dvUser user){returndvUserRepository.save(user);}@OverridepublicvoiddeleteUser(Long id){dvUserRepository.deleteById(id);}@OverridepublicdvUserupdateUser(dvUser user){returndvUserRepository.save(user);}@OverridepublicList
9、创建controller访问层
importcom.jacky.userservice.pojo.entity.dvUser;importcom.jacky.userservice.service.dvUserService;importorg.springframework.web.bind.annotation.*;importjavax.annotation.Resource;importjava.util.List;@RestController@RequestMapping("/user")publicclassJpaUserController{@ResourceprivatedvUserService dvUserService;/**
* 新增用户
*/@PostMapping("")publicdvUseraddUser(@RequestBody dvUser user){returndvUserService.insertUser(user);}/**
* 删除用户
*/@DeleteMapping("/{id}")publicvoiddeleteUser(@PathVariable("id")Long id){dvUserService.deleteUser(id);}/**
* 修改用户
*/@PutMapping("")publicdvUserupdateUser(@RequestBody dvUser user){returndvUserService.updateUser(user);}/**
* 全查用户
*/@GetMapping("")publicList
* id查用户
*/@GetMapping("/{id}")publicdvUserfindbyId(@PathVariable("id")Long id){returndvUserService.findUserById(id);}}
四、是实时展示真正的技术了
1、费了老大的劲才把代码敲完，现在是开始见证成果的时候了，让我们使用Post模拟请求
先添加一个用户