极客教程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.xml
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。
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/4.0.0
http://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=off
spring.datasource.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.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;
@Service
public 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。
@Override
public 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;
@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;
@RestController
public 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;
@SpringBootApplication
public 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。