JPA全称Java Persistence API.JPA通过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。
JPA 的目标之一是制定一个可以由很多供应商实现的API,并且开发人员可以编码来实现该API,而不是使用私有供应商特有的API。
JPA是需要Provider来实现其功能的,Hibernate就是JPA Provider中很强的一个,应该说无人能出其右。从功能上来说,JPA就是Hibernate功能的一个子集。
创建新项目
pom文件中依赖如下:
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-jdbc</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</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>com.alibaba</groupId>
<artifactId>druid</artifactId>
<version>1.0.29</version>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
修改配置文件:
spring.datasource.driver-class-name=com.mysql.jdbc.Driver
spring.datasource.url=jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=utf8&characterSetResults=utf8
spring.datasource.username=root
spring.datasource.password=root
## jpa configuration
spring.jpa.hibernate.ddl-auto=create
spring.jpa.show-sql=true
==注意:== 如果通过jpa在数据库中建表,将jpa.hibernate,ddl-auto改为create,建完表之后,要改为update,要不然每次重启工程会删除表并新建。
实体类
通过@Entity 表明是一个映射的实体类, @Id表明id, @GeneratedValue 字段自动生成
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
@Entity
public class Account {
@Id
@GeneratedValue
private int id ;
private String name ;
private double money;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public double getMoney() {
return money;
}
public void setMoney(double money) {
this.money = money;
}
}
DAO
数据访问层,通过编写一个继承自 JpaRepository 的接口就能完成数据访问,其中包含了几本的单表查询的方法,非常的方便。值得注意的是,这个Account 对象名,而不是具体的表名,另外Interger是主键的类型,一般为Integer或者Long
public interface AccountDao extends JpaRepository<Account,Integer> {
}
Web层
在这个栗子中简略了service层,在实际开发中,不可省略。新写一个controller,写几个restful api来测试数据的访问。
@RestController
@RequestMapping("/account")
public class AccountController {
@Autowired
AccountDao accountDao;
@RequestMapping(value = "/list", method = RequestMethod.GET)
public List<Account> getAccounts() {
return accountDao.findAll();
}
@RequestMapping(value = "/{id}", method = RequestMethod.GET)
public Account getAccountById(@PathVariable("id") int id) {
return accountDao.findOne(id);
}
@RequestMapping(value = "/{id}", method = RequestMethod.PUT)
public String updateAccount(@PathVariable("id") int id, @RequestParam(value = "name", required = true) String name,
@RequestParam(value = "money", required = true) double money) {
Account account = new Account();
account.setMoney(money);
account.setName(name);
account.setId(id);
Account account1 = accountDao.saveAndFlush(account);
return account1.toString();
}
@RequestMapping(value = "", method = RequestMethod.POST)
public String postAccount(@RequestParam(value = "name") String name,
@RequestParam(value = "money") double money) {
Account account = new Account();
account.setMoney(money);
account.setName(name);
Account account1 = accountDao.save(account);
return account1.toString();
}
}