ZetCode

Spring Boot 分页

最后修改于 2023 年 7 月 27 日

在本文中，我们将展示如何在 Spring 应用中对数据进行分页。

Spring 是一个流行的 Java 应用程序框架，而 Spring Boot 是 Spring 的一个演进，它有助于轻松创建独立的、生产级的基于 Spring 的应用程序。

分页

分页是将数据分成合适的块以节省资源的过程。

PagingAndSortingRepository

PagingAndSortingRepository 是 CrudRepository 的扩展，提供额外的使用分页和排序检索实体的方法。

Spring Boot 分页示例

在下面的应用中，我们创建一个简单的 Spring Boot Restful 应用，它允许对数据进行分页。

build.gradle
...
src
├───main
│   ├───java
│   │   └───com
│   │       └───zetcode
│   │           │   Application.java
│   │           ├───controller
│   │           │       MyController.java
│   │           ├───model
│   │           │       Country.java
│   │           ├───repository
│   │           │       CountryRepository.java
│   │           └───service
│   │                   CountryService.java
│   │                   ICountryService.java
│   └───resources
│           application.properties
│           import.sql
└───test
    └───java

这是项目结构。

build.gradle 
plugins {
    id 'org.springframework.boot' version '3.1.1'
    id 'io.spring.dependency-management' version '1.1.0'
    id 'java'
}

group = 'com.zetcode'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = '17'

repositories {
    mavenCentral()
}

dependencies {
    implementation 'org.springframework.boot:spring-boot-starter-web'
    implementation 'org.springframework.boot:spring-boot-starter-data-jpa'
    runtimeOnly 'com.h2database:h2'
}

这是 Gradle 构建文件。h2 依赖项包含 H2 数据库驱动程序。

spring-boot-starter-web 启用 Web 应用，包括经典应用和 RESTful 应用。它使用 Tomcat 作为默认的嵌入式容器。spring-boot-starter-data-jpa 是一个用于将 Spring Data JPA 与 Hibernate 结合使用的启动器。

resources/application.properties 
spring.main.banner-mode=off
spring.jpa.hibernate.ddl-auto=create-drop

在 application.properties 文件中，我们编写了 Spring Boot 应用的各种配置设置。使用 banner-mode 属性，我们关闭了 Spring 横幅。

create-drop 选项会自动创建和删除数据库模式。H2 数据库在内存中运行。

resources/import.sql 
INSERT INTO countries(name, population) VALUES('China', 1382050000);
INSERT INTO countries(name, population) VALUES('India', 1313210000);
INSERT INTO countries(name, population) VALUES('USA', 324666000);
INSERT INTO countries(name, population) VALUES('Indonesia', 260581000);
INSERT INTO countries(name, population) VALUES('Brazil', 207221000);
INSERT INTO countries(name, population) VALUES('Pakistan', 196626000);
INSERT INTO countries(name, population) VALUES('Nigeria', 186988000);
INSERT INTO countries(name, population) VALUES('Bangladesh', 162099000);
INSERT INTO countries(name, population) VALUES('Russia', 146838000);
INSERT INTO countries(name, population) VALUES('Japan', 126830000);
INSERT INTO countries(name, population) VALUES('Mexico', 122273000);
INSERT INTO countries(name, population) VALUES('Philippines', 103738000);
INSERT INTO countries(name, population) VALUES('Ethiopia', 101853000);
INSERT INTO countries(name, population) VALUES('Vietnam', 92700000);
INSERT INTO countries(name, population) VALUES('Egypt', 92641000);
INSERT INTO countries(name, population) VALUES('Germany', 82800000);
INSERT INTO countries(name, population) VALUES('the Congo', 82243000);
INSERT INTO countries(name, population) VALUES('Iran', 82800000);
INSERT INTO countries(name, population) VALUES('Turkey', 79814000);
INSERT INTO countries(name, population) VALUES('Thailand', 68147000);
INSERT INTO countries(name, population) VALUES('France', 66984000);
INSERT INTO countries(name, population) VALUES('United Kingdom', 60589000);
INSERT INTO countries(name, population) VALUES('South Africa', 55908000);
INSERT INTO countries(name, population) VALUES('Myanmar', 51446000);
INSERT INTO countries(name, population) VALUES('South Korea', 68147000);
INSERT INTO countries(name, population) VALUES('Colombia', 49129000);
INSERT INTO countries(name, population) VALUES('Kenya', 47251000);
INSERT INTO countries(name, population) VALUES('Spain', 46812000);
INSERT INTO countries(name, population) VALUES('Argentina', 43850000);
INSERT INTO countries(name, population) VALUES('Ukraine', 42603000);
INSERT INTO countries(name, population) VALUES('Sudan', 41176000);
INSERT INTO countries(name, population) VALUES('Algeria', 40400000);
INSERT INTO countries(name, population) VALUES('Poland', 38439000);
INSERT INTO countries(name, population) VALUES('Canada', 37742154);
INSERT INTO countries(name, population) VALUES('Morocco', 36910560);
INSERT INTO countries(name, population) VALUES('Saudi Arabia', 34813871);
INSERT INTO countries(name, population) VALUES('Uzbekistan', 33469203);
INSERT INTO countries(name, population) VALUES('Peru', 32971854);
INSERT INTO countries(name, population) VALUES('Angola', 32866272);
INSERT INTO countries(name, population) VALUES('Malaysia', 32365999);
INSERT INTO countries(name, population) VALUES('Mozambique', 31255435);
INSERT INTO countries(name, population) VALUES('Ghana', 31072940);
INSERT INTO countries(name, population) VALUES('Yemen', 29825964);
INSERT INTO countries(name, population) VALUES('Nepal', 29136808);
INSERT INTO countries(name, population) VALUES('Venezuela', 28435940);

模式由 Hibernate 自动创建；之后，执行 import.sql 文件以填充表数据。

com/zetcode/model/Country.java 
package com.zetcode.model;

import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.GenerationType;
import jakarta.persistence.Id;
import jakarta.persistence.Table;
import java.util.Objects;

@Entity
@Table(name = "countries")
public class Country {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String name;
    private int population;

    public Country() {
    }

    public Country(Long id, String name, int population) {
        this.id = id;
        this.name = name;
        this.population = population;
    }

    public Long getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getPopulation() {
        return population;
    }

    public void setPopulation(int population) {
        this.population = population;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Country country = (Country) o;
        return population == country.population &&
                Objects.equals(id, country.id) &&
                Objects.equals(name, country.name);
    }

    @Override
    public int hashCode() {
        return Objects.hash(id, name, population);
    }

    @Override
    public String toString() {
        final StringBuilder sb = new StringBuilder("Country{");
        sb.append("id=").append(id);
        sb.append(", name='").append(name).append('\'');
        sb.append(", population=").append(population);
        sb.append('}');
        return sb.toString();
    }
}

这是 Country 实体。每个实体必须至少定义两个注解：@Entity 和 @Id。之前，我们将 ddl-auto 选项设置为 create-drop，这意味着 Hibernate 将从该实体创建表模式。

@Entity
@Table(name = "countries")
public class Country {

@Entity 注解指定该类是一个实体，并映射到一个数据库表。@Table 注解指定用于映射的数据库表的名称。

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;

@Id 注解指定实体的**主键**，而 @GeneratedValue 为主键的值提供了生成策略。

com/zetcode/repository/CountryRepository.java 
package com.zetcode.repository;

import com.zetcode.model.Country;
import org.springframework.data.repository.PagingAndSortingRepository;
import org.springframework.stereotype.Repository;

@Repository
public interface CountryRepository extends PagingAndSortingRepository<Country, Long> {

}

CountryRepository 使用 @Repository 注解进行修饰。通过从 Spring 的 PagingAndSortingRepository 扩展，我们有一些方法可以对数据进行分页。

com/zetcode/service/ICountryService.java 
package com.zetcode.service;

import com.zetcode.model.Country;
import java.util.List;

public interface ICountryService {

    List<Country> findPaginated(int pageNo, int pageSize);
}

ICountryService 包含 findPaginated 契约方法。它包含两个参数：页码和页面大小。

com/zetcode/service/CountryService.java 
package com.zetcode.service;

import com.zetcode.model.Country;
import com.zetcode.repository.CountryRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.PageRequest;
import org.springframework.data.domain.Pageable;
import org.springframework.stereotype.Service;

import java.util.List;

@Service
public class CountryService implements ICountryService {

    private final CountryRepository repository;

    @Autowired
    public CountryService(CountryRepository repository) {
        this.repository = repository;
    }

    @Override
    public List<Country> findPaginated(int pageNo, int pageSize) {

        Pageable paging = PageRequest.of(pageNo, pageSize);
        Page<Country> pagedResult = repository.findAll(paging);

        return pagedResult.toList();
    }
}

CountryService 包含 findPaginated 方法的实现。

private final CountryRepository repository;

@Autowired
public CountryService(CountryRepository repository) {
    this.repository = repository;
}

CountryRepository 被注入到字段中。

Pageable paging = PageRequest.of(pageNo, pageSize);
Page<Country> pagedResult = repository.findAll(paging);

一个 PageRequest 从提供的值创建并传递给 findAll 存储库方法。

com/zetcode/controller/MyController.java 
package com.zetcode.controller;

import com.zetcode.model.Country;
import com.zetcode.service.ICountryService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;

import java.util.List;

@RestController
public class MyController {

    private final ICountryService countryService;

    @Autowired
    public MyController(ICountryService countryService) {
        this.countryService = countryService;
    }

    @GetMapping("/countries/{pageNo}/{pageSize}")
    public List<Country> getPaginatedCountries(@PathVariable int pageNo,
                                               @PathVariable int pageSize) {

        return countryService.findPaginated(pageNo, pageSize);
    }
}

MyController 处理来自客户端的请求。

private final ICountryService countryService;

@Autowired
public MyController(ICountryService countryService) {
    this.countryService = countryService;
}

ICountryService 被注入到 countryService 字段中。

@GetMapping("/countries/{pageNo}/{pageSize}")
public List<Country> getPaginatedCountries(@PathVariable int pageNo, 
        @PathVariable int pageSize) {

    return countryService.findPaginated(pageNo, pageSize);
}

我们提供页码和页面大小作为路径变量。这些值被传递给 findPaginated 服务方法。

com/zetcode/Application.java 
package com.zetcode;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class Application  {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}

Application 是设置 Spring Boot 应用程序的入口点。

$ ./gradlew bootRun

我们运行应用程序。

$ curl localhost:8080/countries/0/5
[{"id":1,"name":"China","population":1382050000},{"id":2,"name":"India","population":1313210000},
{"id":3,"name":"USA","population":324666000},{"id":4,"name":"Indonesia","population":260581000},
{"id":5,"name":"Brazil","population":207221000}]

我们获得第一页的 5 行。索引从 0 开始。

$ curl localhost:8080/countries/1/5
[{"id":6,"name":"Pakistan","population":196626000},{"id":7,"name":"Nigeria","population":186988000},
{"id":8,"name":"Bangladesh","population":162099000},{"id":9,"name":"Russia","population":146838000},
{"id":10,"name":"Japan","population":126830000}]

我们获得下一页。

在本文中，我们展示了如何在 Spring Boot 应用中创建分页。

作者

我叫 Jan Bodnar，是一位充满激情的程序员，拥有丰富的编程经验。自 2007 年以来，我一直在撰写编程文章。到目前为止，我已经撰写了 1,400 多篇文章和 8 本电子书。 我拥有超过十年的编程教学经验。

列出 所有 Spring Boot 教程。