使用Spring Data JPA分页和排序

1. Overview

Pagination is often helpful when we have a large dataset and we want to present it to the user in smaller chunks.

Also, we often need to sort that data by some criteria while paging.

In this tutorial, we’ll learn how to easily paginate and sort using Spring Data JPA.

2. Initial Setup

First, let’s say we have a Product entity as our domain class:

@Entity 
public class Product {
    
    @Id
    private long id;
    private String name;
    private double price; 

    // constructors, getters and setters 

}

Each of our Product instances has a unique identifier: id, its name and its price associated with it.

3. Creating a Repository

To access our Products, we’ll need a ProductRepository:

public interface ProductRepository extends PagingAndSortingRepository<Product, Integer> {

    List<Product> findAllByPrice(double price, Pageable pageable);
}

By having it extend PagingAndSortingRepository, we get findAll(Pageable pageable) and findAll(Sort sort) methods for paging and sorting.

Conversely, we could have chosen to extend JpaRepository instead, as it extends PagingAndSortingRepository too.

Once we extend PagingAndSortingRepository, we can add our own methods that take Pageable and Sort as parameters, like we did here with findAllByPrice.

Let’s take a look at how to paginate our Products using our new method.

4. Pagination

Once we have our repository extending from PagingAndSortingRepository, we just need to:

1. Create or obtain a PageRequest object, which is an implementation of the Pageable interface
2. Pass the PageRequest object as an argument to the repository method we intend to use

We can create a PageRequest object by passing in the requested page number and the page size.

Here the page count starts at zero:

Pageable firstPageWithTwoElements = PageRequest.of(0, 2);

Pageable secondPageWithFiveElements = PageRequest.of(1, 5);

In Spring MVC, we can also choose to obtain the Pageable instance in our controller using Spring Data Web Support.

Once we have our PageRequest object, we can pass it in while invoking our repository’s method:

Page<Product> allProducts = productRepository.findAll(firstPageWithTwoElements);

List<Product> allTenDollarProducts = 
  productRepository.findAllByPrice(10, secondPageWithFiveElements);

The findAll(Pageable pageable) method by default returns a Page object.

However, we can choose to return either a Page, a Slice, or a List from any of our custom methods returning paginated data.

A Page instance, in addition to having the list of Products, also knows about the total number of available pages. *It triggers an additional count query to achieve it. To avoid such an overhead cost, we can instead return a Slice or a List.*

A Slice only knows whether the next slice is available or not.

5. Pagination and Sorting

Similarly, to just have our query results sorted, we can simply pass an instance of Sort to the method:

Page<Product> allProductsSortedByName = productRepository.findAll(Sort.by("name"));

However, what if we want to both sort and page our data?

We can do that by passing the sorting details into our PageRequest object itself:

Pageable sortedByName = 
  PageRequest.of(0, 3, Sort.by("name"));

Pageable sortedByPriceDesc = 
  PageRequest.of(0, 3, Sort.by("price").descending());

Pageable sortedByPriceDescNameAsc = 
  PageRequest.of(0, 5, Sort.by("price").descending().and(Sort.by("name")));

Based on our sorting requirements, we can specify the sort fields and the sort direction while creating our PageRequest instance.

As usual, we can then pass this Pageable type instance to the repository’s method.

6. Conclusion

In this article, we learned how to paginate and sort our query results in Spring Data JPA.

As always, the complete code examples used in this article are available over on Github.