Spring Boot Data JPA 排序教程展示了如何在 Spring Data JPA 中对查询结果进行排序。 查询结果使用 ORDER BY 子句或 Sort 对象进行排序。
Spring 是流行的 Java 应用框架，而 Spring Boot 是 Spring 的演进，可以帮助轻松地创建独立的，生产级的基于 Spring 的应用。
Spring Data JPA
Spring Data JPA 是伞式 Spring Data 项目的一部分，该项目使实现基于 JPA 的存储库更加容易。 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界面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排序：
在 JPQL 查询中使用 ORDER BY 子句将类型为 Sort 的参数添加到查询方法Spring Boot Data JPA 排序示例
以下应用检索按升序排序的城市。
pom.xmlsrc├───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。
pom.xml
<?xml version="1.0" encoding="UTF-8"?><project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>com.zetcode</groupId> <artifactId>springbootdatajpasort</artifactId> <version>1.0-SNAPSHOT</version> <packaging>jar</packaging> <properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> <maven.compiler.source>11</maven.compiler.source> <maven.compiler.target>11</maven.compiler.target> </properties> <parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>2.1.1.RELEASE</version> </parent> <dependencies> <dependency> <groupId>com.h2database</groupId> <artifactId>h2</artifactId> <scope>runtime</scope> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-data-jpa</artifactId> </dependency> </dependencies> <build> <plugins> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> </plugin> </plugins> </build></project>
这是 Maven pom.xml文件。
resources/application.properties
spring.main.banner-mode=offspring.datasource.platform=h2spring.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.datasource.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，因此通过将spring.jpa.hibernate.ddl-auto设置为none可以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 javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.GenerationType;import javax.persistence.Id;import javax.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);
启动应用时，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);之后，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包含两种签约方法。
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;@Servicepublic class CityService implements ICityService { @Autowired private CityRepository repository; @Override public List<City> findAllOrderByPopulationAsc() { return repository.findAllOrderByPopulationAsc(); } @Override public List<City> findAllOrderByNameAsc() { var sort = new Sort(Sort.Direction.ASC, "name"); return repository.findAllOrderByNameAsc(sort); }}在这里，我们有两种排序方法的实现。
@Overridepublic List<City> findAllOrderByNameAsc() { var sort = new Sort(Sort.Direction.ASC, "name"); return repository.findAllOrderByNameAsc(sort);}Sort对象按名称升序对查询结果进行排序。 Sort作为参数传递给方法。
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;@Repositorypublic 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有两种分类方法。 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;@RestControllerpublic class MyController { @Autowired private ICityService cityService; @GetMapping(value = "/cities") public List<City> getCitiesByPopulation() { return cityService.findAllOrderByPopulationAsc(); } @GetMapping(value = "/cities2") public List<City> getCitiesByName() { return cityService.findAllOrderByNameAsc(); }}控制器为 RESTFul，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;@SpringBootApplicationpublic class Application { public static void main(String[] args) { SpringApplication.run(Application.class, args); }}Application是设置 Spring Boot 应用的入口点。
我们使用mvn -q spring-boot:run运行该应用。
$ 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，城市按人口按升序排序。
$ 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，城市按名称按升序排序。
本教程展示了如何在 Spring Boot Data JPA 中对查询结果进行排序。
