Spring Boot Data JPA 排序教程

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。

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