ZetCode

Spring Boot Data JPA 排序

最后修改于 2023 年 7 月 25 日

在本文中，我们将展示如何在 Spring Data JPA 中对查询结果进行排序。查询结果可以通过 `ORDER BY` 子句或 `Sort` 对象进行排序。

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。

Spring Data JPA

Spring Data JPA 是 Spring Data 项目的一部分，该项目使实现基于 JPA 的存储库变得更容易。Spring Data JPA 使用 JPA 将数据存储在关系数据库中。它可以在运行时从存储库接口自动创建存储库实现。

Spring Data JPA 排序

在 Spring Data JPA 中，查询结果可以通过两种方式进行排序

Spring Boot Data JPA 排序示例

以下应用程序检索按升序排序的城市。

build.gradle
...
src
├───main
│   ├───java
│   │   └───com
│   │       └───zetcode
│   │           │   Application.java
│   │           ├───controller
│   │           │       MyController.java
│   │           ├───model
│   │           │       City.java
│   │           ├───repository
│   │           │       CityRepository.java
│   │           └───service
│   │                   CityService.java
│   │                   ICityService.java
│   └───resources
│           application.properties
│           data-h2.sql
│           schema-h2.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.example'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = '17'

repositories {
    mavenCentral()
}

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

这是 Gradle 构建文件。

resources/application.properties 
spring.main.banner-mode=off
spring.sql.init.platform=h2
spring.jpa.hibernate.ddl-auto=none

在主属性文件中，我们使用 `spring.main.banner-mode` 属性关闭 Spring Boot 横幅。`spring.sql.init.platform` 设置为 `h2`，因此数据库名称存在于数据库初始化脚本中。由于我们从 SQL 代码初始化脚本，我们通过将 `spring.jpa.hibernate.ddl-auto` 设置为 `none` 来关闭从实体自动创建表的功能。

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

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

@Entity
@Table(name = "cities")
public class City {

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

    private String name;
    private int population;

    public City() {
    }

    public City(String name, int population) {
        this.name = name;
        this.population = population;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = 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 int hashCode() {
        int hash = 7;
        hash = 79 * hash + Objects.hashCode(this.id);
        hash = 79 * hash + Objects.hashCode(this.name);
        hash = 79 * hash + this.population;
        return hash;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj == null) {
            return false;
        }
        if (getClass() != obj.getClass()) {
            return false;
        }
        final City other = (City) obj;
        if (this.population != other.population) {
            return false;
        }
        if (!Objects.equals(this.name, other.name)) {
            return false;
        }
        return Objects.equals(this.id, other.id);
    }

    @Override
    public String toString() {

        var builder = new StringBuilder();
        builder.append("City{id=").append(id).append(", name=")
                .append(name).append(", population=")
                .append(population).append("}");

        return builder.toString();
    }
}

这是 City 实体。

resources/schema-h2.sql 
CREATE TABLE cities(id INT PRIMARY KEY AUTO_INCREMENT,
    name VARCHAR(255), population INT);

当应用程序启动时，将执行 schema-h2.sql 脚本。它创建一个新的数据库表。

resources/data-h2.sql 
INSERT INTO cities(name, population) VALUES('Bratislava', 432000);
INSERT INTO cities(name, population) VALUES('Budapest', 1759000);
INSERT INTO cities(name, population) VALUES('Prague', 1280000);
INSERT INTO cities(name, population) VALUES('Warsaw', 1748000);
INSERT INTO cities(name, population) VALUES('Los Angeles', 3971000);
INSERT INTO cities(name, population) VALUES('New York', 8550000);
INSERT INTO cities(name, population) VALUES('Edinburgh', 464000);
INSERT INTO cities(name, population) VALUES('Suzhou', 4327066);
INSERT INTO cities(name, population) VALUES('Zhengzhou', 4122087);
INSERT INTO cities(name, population) VALUES('Berlin', 3671000);

稍后，将执行 data-h2.sql 文件。它用数据填充表。

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

import com.zetcode.model.City;

import java.util.List;

public interface ICityService {

    List<City> findAllOrderByPopulationAsc();
    List<City> findAllOrderByNameAsc();
}

`ICityService` 包含两个契约方法。

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

import com.zetcode.model.City;
import com.zetcode.repository.CityRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.domain.Sort;
import org.springframework.stereotype.Service;

import java.util.List;

@Service
public class CityService implements ICityService {

    private final CityRepository repository;

    @Autowired
    public CityService(CityRepository repository) {
        this.repository = repository;
    }

    @Override
    public List<City> findAllOrderByPopulationAsc() {
        return repository.findAllOrderByPopulationAsc();
    }

    @Override
    public List<City> findAllOrderByNameAsc() {

        var sort = Sort.by(Sort.Direction.ASC, "name");
        return repository.findAllOrderByNameAsc(sort);
    }
}

这里我们有两个排序方法的实现。

@Override
public List<City> findAllOrderByNameAsc() {

    var sort = Sort.by(Sort.Direction.ASC, "name");
    return repository.findAllOrderByNameAsc(sort);
}

`Sort.by` 按名称升序对查询结果进行排序。它作为参数传递给 `findAllOrderByNameAsc` 方法。

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

import com.zetcode.model.City;
import org.springframework.data.domain.Sort;
import org.springframework.data.jpa.repository.Query;
import org.springframework.data.repository.CrudRepository;
import org.springframework.stereotype.Repository;

import java.util.List;

@Repository
public interface CityRepository extends CrudRepository<City, Long> {

    @Query("FROM City ORDER BY population ASC")
    List<City> findAllOrderByPopulationAsc();

    @Query("FROM City")
    List<City> findAllOrderByNameAsc(Sort sort);
}

`CityRepository` 有两个排序方法。在第一种情况下，我们使用 `ORDER BY` 子句。在第二种情况下，我们使用 `Sort` 对象。

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

import com.zetcode.model.City;
import com.zetcode.service.ICityService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

import java.util.List;

@RestController
public class MyController {

    private final ICityService cityService;

    @Autowired
    public MyController(ICityService cityService) {
        this.cityService = cityService;
    }

    @GetMapping(value = "/cities")
    public List<City> getCitiesByPopulation() {

        return cityService.findAllOrderByPopulationAsc();
    }

    @GetMapping(value = "/cities2")
    public List<City> getCitiesByName() {

        return cityService.findAllOrderByNameAsc();
    }
}

控制器是 RESTful 的，并以 JSON 格式返回数据。

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。

我们使用 ./gradlew bootRun 运行应用程序。

$ curl localhost:8080/cities
[{"id":1,"name":"Bratislava","population":432000},{"id":7,"name":"Edinburgh","population":464000},
{"id":3,"name":"Prague","population":1280000},{"id":4,"name":"Warsaw","population":1748000},
{"id":2,"name":"Budapest","population":1759000},{"id":10,"name":"Berlin","population":3671000},
{"id":5,"name":"LosAngeles","population":3971000},{"id":9,"name":"Zhengzhou","population":4122087},
{"id":8,"name":"Suzhou","population":4327066},{"id":6,"name":"NewYork","population":8550000}]

在此输出中，城市按人口升序排序。

$ curl localhost:8080/cities2
[{"id":10,"name":"Berlin","population":3671000},{"id":1,"name":"Bratislava","population":432000},
{"id":2,"name":"Budapest","population":1759000},{"id":7,"name":"Edinburgh","population":464000},
{"id":5,"name":"LosAngeles","population":3971000},{"id":6,"name":"NewYork","population":8550000},
{"id":3,"name":"Prague","population":1280000},{"id":8,"name":"Suzhou","population":4327066},
{"id":4,"name":"Warsaw","population":1748000},{"id":9,"name":"Zhengzhou","population":4122087}]

在此输出中，城市按名称升序排序。

本文展示了如何在 Spring Boot Data JPA 中对查询结果进行排序。

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。迄今为止，我撰写了 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。