What is the role of the Page class in pagination?

Table of Contents

• Introduction
  • The Role of the Page Class
    • 1. Holds the Content of a Page
    • 2. Provides Pagination Metadata
    • 3. Simplifies Pagination Logic
    • 4. Supports Sorting Alongside Pagination
  • Practical Example: Paginated REST API with Spring Data
• Conclusion

Introduction

In Spring Data JPA, the Page class plays a crucial role in handling pagination. When working with large datasets, it’s important to not overwhelm the user or the system with large amounts of data at once. Pagination splits data into smaller, manageable chunks or "pages" that can be loaded separately. The Page class provides a powerful and flexible way to handle paginated data by encapsulating not only the content of the page but also important metadata such as the total number of pages, current page, and total elements.

The Role of the Page Class

The Page class is part of Spring Data's support for pagination and contains several essential features for working with paginated results. Let’s explore the main aspects of the Page class.

1. Holds the Content of a Page

One of the most important roles of the Page class is to hold the content of the current page. The content is typically a list of entities that are fetched from the database based on the current page number and size.

• Content: This is the actual data of the page that is being requested. The content is a list of entities or DTOs (Data Transfer Objects) and can be accessed using the getContent() method.

Example:

In this example:

• The getContent() method returns the list of products on the current page.

2. Provides Pagination Metadata

The Page class doesn’t just contain the content; it also provides useful metadata about the pagination. This allows you to display additional information to the user, such as:

• Total Elements: The total number of records across all pages. This helps you calculate the total number of pages.
• Total Pages: The total number of pages based on the number of records and the page size.
• Current Page: The index of the current page in the pagination sequence.

You can access these metadata properties using the following methods:

• getTotalElements() – returns the total number of elements across all pages.
• getTotalPages() – returns the total number of pages available.
• getNumber() – returns the current page number (starting from 0).
• getSize() – returns the number of elements per page (page size).
• hasNext() – returns true if there is a next page.
• hasPrevious() – returns true if there is a previous page.

Example:

This helps with displaying pagination controls on a front-end interface, such as:

• "Page 1 of 10"
• "Showing 1–10 of 100 products"

3. Simplifies Pagination Logic

By using the Page class, Spring Data JPA simplifies the logic needed for implementing pagination. Instead of manually calculating the total number of pages and handling the content separately, the Page class encapsulates all this functionality in one object.

When you use a Page object, Spring Data handles the necessary calculations behind the scenes, allowing you to focus on using the data and presenting it to the user without worrying about pagination details.

4. Supports Sorting Alongside Pagination

Another key feature of the Page class is that it can work with sorting as well. When you request a page of data, you can specify the sorting criteria (e.g., sort by name, date, etc.), and the Page class will automatically return the data in the specified order.

This is useful when you need paginated data that is also sorted based on certain fields.

Example:

Here, the PageRequest.of() method creates a Pageable object that requests the first page of 10 products, sorted by the price field in ascending order.

Practical Example: Paginated REST API with Spring Data

Here’s a practical example where we use the Page class in a REST API endpoint to return paginated results.

Example: Paginated Product Endpoint

In the ProductService:

• The controller method getProducts() accepts pagination parameters such as page, size, sortBy, and ascending.
• The Page<Product> returned by productService.getProducts() contains both the content (products on the current page) and pagination metadata (total pages, current page, etc.).

Conclusion

The Page class in Spring Data JPA plays a critical role in making pagination simpler and more efficient in your applications. It provides not only the paginated content but also metadata such as the total number of elements, pages, and the current page, which is essential for building responsive and user-friendly applications. By using Page in combination with Pageable, Spring Data JPA handles the heavy lifting of pagination and sorting, allowing you to focus on delivering the right data to your users.