SpringData JPA接口简单总结
作者:互联网
1 JPA
1.1 整体概念
JPA: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。
ORM呢: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)。
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。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。
![image-20210709084655541](https://www.icode9.com/i/l/?n=20&i=blog/1555060/202111/1555060-20211105203858425-52294775.png)
1.2 JPA实体生命周期
![image-20210709084655541](https://www.icode9.com/i/l/?n=20&i=blog/1555060/202111/1555060-20211105204009575-1793905905.png)
PostLoad
PostPersist
PostRemove
PostUpdate
PrePersist
PreRemove
PreUpdate
import org.springframework.stereotype.Component;
import javax.persistence.PostPersist;
import javax.persistence.PostUpdate;
import javax.persistence.PrePersist;
import javax.persistence.PreUpdate;
public class TestEntityListeners {
@PrePersist
public void PrePersist(Object entity){
System.out.println("开始保存--"+entity.toString());
}
@PreUpdate
public void PreUpdate(Object entity){
System.out.println("开始更新--"+entity.toString());
}
@PostPersist
public void PostPersist(Object entity){
System.out.println("结束保存--"+entity.toString());
}
@PostUpdate
public void PostUpdate(Object entity){
System.out.println("结束更新--"+entity.toString());
}
}
@Entity
@Table(name = "product")
@EntityListeners(value = {TestEntityListeners.class})
public class Product {
private int id;
private String productId;
private String productName;
//getter setter toString()
}
2 JpaEntityInformation
JpaEntityInformation entityInformation = JpaEntityInformationSupport.getEntityInformation(clazz, entityManager);
3 Repository
3.1 Repository
![image-20210708212130010](https://www.icode9.com/i/l/?n=20&i=blog/1555060/202111/1555060-20211105204144882-1187092260.png)
-
JpaRepositoryImplementation<T, ID> extends JpaRepository<T, ID>, JpaSpecificationExecutor<T>
- SPI interface to be implemented by JpaRepository implementations.
- SPI是串行外设接口(Serial Peripheral Interface)的缩写
-
RevisionRepository<T, ID, N extends Number & Comparable<N>> extends Repository<T, ID>
-
A repository which can access entities held in a variety of Revisions.
-
private final JpaEntityInformation<T, ?> entityInformation; private final EntityManager em; private final PersistenceProvider provider;
-
-
public class SimpleJpaRepository<T, ID> implements JpaRepositoryImplementation<T, ID>
-
-
其他子类:
-
-
@NoRepositoryBean
3.2 Optional
示例:
public static void main(String[] args) {
System.out.println("------- 1.get() 若为null会报错");
// Optional<String> empty = Optional.empty();
// System.out.println(empty.get());
/*
public T get() {
if (value == null) {
throw new NoSuchElementException("No value present");
}
return value;
}
*/
System.out.println("------- 2.Optional.of()");
// Optional<Object> empty = Optional.of(null);
// System.out.println(empty.get());
/*
public static <T> Optional<T> of(T value) {
return new Optional<>(value);
}
private Optional(T value) {
this.value = Objects.requireNonNull(value);
}
public static <T> Optional<T> ofNullable(T value) {
return value == null ? empty() : of(value);
}
*/
System.out.println("------- 3.Optional.ofNullable()");
// Optional<Object> empty = Optional.ofNullable(null);
// System.out.println(empty.get());
System.out.println("------- 4.Optional.isPresent()");
Optional<Object> empty = Optional.empty();
System.out.println(empty.isPresent());
System.out.println("------- 5.Optional.ifPresent()");
Optional<String> optional = Optional.of("haha");
optional.ifPresent(str -> System.out.println("参数有值时打印:" + str));
System.out.println("------- 6.Optional.filter()");
boolean present = optional.filter(str -> "hehe".equals(str)).isPresent();
System.out.println(present);
System.out.println("------- 7.Optional.map()");
Optional<String> optional2 = optional.map(str -> str.toUpperCase());
System.out.println(optional2.get());
System.out.println("------- 8.Optional.flatMap()");
Optional<String> s = optional.flatMap(str -> Optional.ofNullable(str.toUpperCase()));
System.out.println(s.get());
System.out.println("------- 9.Optional.orElse()");
Object haha = Optional.empty().orElse("haha");
System.out.println(haha);
System.out.println("------- 10.Optional.orElseGet()");
Object o = Optional.empty().orElseGet(() -> Math.random());
System.out.println(o);
System.out.println("------- 11.Optional.orElseThrow()");
}
3.3 Limit Query
List<User> findFirst10ByLastname(String lastname, Sort sort);
List<User> findTop10ByLastname(String lastname, Pageable pageable);
3.4 Null
![image-20210708214357795](https://www.icode9.com/i/l/?n=20&i=blog/1555060/202111/1555060-20211105204453347-889480303.png)
3.5 Asynchronous Query Results
![image-20210708214357795](https://www.icode9.com/i/l/?n=20&i=blog/1555060/202111/1555060-20211105204520535-1870225084.png)
标签:SpringData,JPA,System,接口,value,println,Optional,empty,out 来源: https://www.cnblogs.com/daheww/p/15515176.html