Spring Data Commons 的 Page 接口为分页结果提供了一个一致的 API，允许在持久化数据存储库中高效地进行分页查询。它通过跟踪页面状态（例如当前页、元素大小）来支持分块结果的检索，并提供一个可扩展的框架来检测新状态以实现连续分页。

Core concepts

Spring Data 存储库抽象中的中心接口是 Repository。它取管理的领域类以及作为类型参数的领域类的标识符类型。此接口主要充当标记接口，用于捕获要处理的类型，并帮助你发现扩展此接口的接口。https://docs.spring.io/spring-data/commons/docs/current/api/org/springframework/data/repository/CrudRepository.html[CrudRepository] 和 ListCrudRepository 接口提供被管理的实体类的复杂 CRUD 功能。

The central interface in the Spring Data repository abstraction is Repository. It takes the domain class to manage as well as the identifier type of the domain class as type arguments. This interface acts primarily as a marker interface to capture the types to work with and to help you to discover interfaces that extend this one. The CrudRepository and ListCrudRepository interfaces provide sophisticated CRUD functionality for the entity class that is being managed.

CrudRepository Interface

public interface CrudRepository<T, ID> extends Repository<T, ID> {

  <S extends T> S save(S entity);      1

  Optional<T> findById(ID primaryKey); 2

  Iterable<T> findAll();               3

  long count();                        4

  void delete(T entity);               5

  boolean existsById(ID primaryKey);   6

  // … more functionality omitted.
}

1	Saves the given entity.
2	Returns the entity identified by the given ID.
3	Returns all entities.
4	Returns the number of entities.
5	Deletes the given entity.
6	Indicates whether an entity with the given ID exists.

在此接口中声明的方法通常称为 CRUD 方法。ListCrudRepository 提供等效方法，但它们在 CrudRepository 方法返回 Iterable 的位置返回 List。

The methods declared in this interface are commonly referred to as CRUD methods. ListCrudRepository offers equivalent methods, but they return List where the CrudRepository methods return an Iterable.

我们还提供了特定于持久化技术的抽象，例如 JpaRepository 或 MongoRepository。这些接口扩展了 CrudRepository，除了相当通用的与持久化技术无关的接口（例如 CrudRepository）之外，还公开了底层持久化技术的功能。

We also provide persistence technology-specific abstractions, such as JpaRepository or MongoRepository. Those interfaces extend CrudRepository and expose the capabilities of the underlying persistence technology in addition to the rather generic persistence technology-agnostic interfaces such as CrudRepository.

除了 CrudRepository 之外，还有 PagingAndSortingRepository 和 ListPagingAndSortingRepository，它们添加了更多方法，可以轻松地对实体进行分页访问：

Additional to the CrudRepository, there are PagingAndSortingRepository and ListPagingAndSortingRepository which add additional methods to ease paginated access to entities:

PagingAndSortingRepository interface

public interface PagingAndSortingRepository<T, ID>  {

  Iterable<T> findAll(Sort sort);

  Page<T> findAll(Pageable pageable);
}

扩展接口受实际存储模块支持。虽然此文档解释了通用方案，但请确保您的存储模块支持您想要使用的接口。

Extension interfaces are subject to be supported by the actual store module. While this documentation explains the general scheme, make sure that your store module supports the interfaces that you want to use.

要按页面大小 20 访问 User 的第二页，可以执行以下操作：

To access the second page of User by a page size of 20, you could do something like the following:

PagingAndSortingRepository<User, Long> repository = // … get access to a bean
Page<User> users = repository.findAll(PageRequest.of(1, 20));

ListPagingAndSortingRepository 提供等效方法，但返回 List，而 PagingAndSortingRepository 方法返回 Iterable。

ListPagingAndSortingRepository offers equivalent methods, but returns a List where the PagingAndSortingRepository methods return an Iterable.

除了查询方法外，还可以使用计数查询和删除查询的查询派生。以下列表显示派生计数查询的接口定义：

In addition to query methods, query derivation for both count and delete queries is available. The following list shows the interface definition for a derived count query:

Derived Count Query

interface UserRepository extends CrudRepository<User, Long> {

  long countByLastname(String lastname);
}

以下列表显示派生删除查询的接口定义：

The following listing shows the interface definition for a derived delete query:

Derived Delete Query

interface UserRepository extends CrudRepository<User, Long> {

  long deleteByLastname(String lastname);

  List<User> removeByLastname(String lastname);
}

Entity State Detection Strategies

@Id-Property 检查（默认）：如果实体的 ID 属性为 null 或 0（对于基本类型），则实体被认为是新的。
@Version-Property 检查：如果带有 @Version 注释的属性存在且为 null，或者对于基本类型的版本属性为 0，则实体被认为是新的。
实现 Persistable：如果实体实现了 Persistable，Spring Data 将委托新检测到实体的 isNew(…) 方法。
提供自定义 EntityInformation 实现：通过创建模块特定存储库工厂的子类并覆盖 getEntityInformation(…) 方法，可以自定义存储库基本实现中使用的 EntityInformation 抽象。

下表描述了 Spring Data 提供的策略，用于检测实体是否新创建：

The following table describes the strategies that Spring Data offers for detecting whether an entity is new:

Table 1. Options for detection whether an entity is new in Spring Data
`@Id`-Property inspection (the default)	By default, Spring Data inspects the identifier property of the given entity. If the identifier property is `null` or `0` in case of primitive types, then the entity is assumed to be new. Otherwise, it is assumed to not be new.
`@Version`-Property inspection	If a property annotated with `@Version` is present and `null`, or in case of a version property of primitive type `0` the entity is considered new. If the version property is present but has a different value, the entity is considered to not be new. If no version property is present Spring Data falls back to inspection of the identifier property.
Implementing `Persistable`	If an entity implements `Persistable`, Spring Data delegates the new detection to the `isNew(…)` method of the entity. See the Javadoc for details. Note: Properties of `Persistable` will get detected and persisted if you use `AccessType.PROPERTY`. To avoid that, use `@Transient`.
Providing a custom `EntityInformation` implementation	You can customize the `EntityInformation` abstraction used in the repository base implementation by creating a subclass of the module specific repository factory and overriding the `getEntityInformation(…)` method. You then have to register the custom implementation of module specific repository factory as a Spring bean. Note that this should rarely be necessary.