Spring Boot JpaRepository 教程|极客教程

SpringBoot JpaRepository 教程展示了如何使用 JpaRepository 在 Spring Boot 应用中管理数据。

Spring 是流行的 Java 应用框架。 Spring Boot 致力于以最小的努力创建独立的，基于生产级别的基于 Spring 的应用。

Spring Data

Spring Data 是用于数据访问的基于 Spring 的编程模型。它减少了使用数据库和数据存储所需的代码量。它由几个模块组成。 Spring Data JPA 简化了使用 JPA 技术的 Spring 应用的开发。

使用 Spring Data，我们为应用中的每个域实体定义了一个存储库接口。存储库包含用于执行 CRUD 操作，对数据进行排序和分页的方法。 @Repository是标记注解，指示基础接口是存储库。通过扩展特定的存储库接口（例如CrudRepository，PagingAndSortingRepository或JpaRepository）来创建存储库。

Spring Data 已与 Spring MVC 控制器进行了高级集成，并提供了从存储库方法名称派生的动态查询。

`JpaRepository`

JpaRepository是Repository的 JPA 特定扩展。它包含CrudRepository和PagingAndSortingRepository的完整 API。因此，它包含用于基本 CRUD 操作的 API，以及用于分页和排序的 API。

Spring Boot `JpaRepository` 示例

以下 Spring Boot 应用使用JpaRepository管理City实体。数据保存在 H2 数据库中。该应用是一个控制台程序。

pom.xml
src
├───main
│   ├───java
│   │   └───com
│   │       └───zetcode
│   │           │   Application.java
│   │           │   MyRunner.java
│   │           ├───model
│   │           │       City.java
│   │           └───repository
│   │                   CityRepository.java
│   └───resources
│           application.properties
└───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>springbootjparepository</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>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>

        <dependency>
            <groupId>com.h2database</groupId>
            <artifactId>h2</artifactId>
            <scope>runtime</scope>
        </dependency>

    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

这是 Maven 构建文件。 spring-boot-starter-data-jpa是将 Spring Data JPA 与 Hibernate 结合使用的入门工具。

resources/application.properties

spring.main.banner-mode=off
logging.pattern.console=%clr(%d{yy-MM-dd E HH:mm:ss.SSS}){blue} %clr(%-5p) %clr(%logger{0}){blue} %clr(%m){faint}%n

application.properties是主要的 Spring Boot 配置文件。使用spring.main.banner-mode属性，我们可以关闭 Spring 标语。 logging.pattern.console定义控制台的日志模式。

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。它包含以下属性：id，name和population。

com/zetcode/repository/CityRepository.java

package com.zetcode.repository;

import com.zetcode.model.City;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

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

}

CityRepository从JpaRepository延伸。它提供了实体的类型及其主键。

Note: In Java enterprise applications it is a good practice to define a service layer that works with repositories. For simplicity reasons, we skip the service layer.

com/zetcode/MyRunner.java

package com.zetcode;

import com.zetcode.model.City;
import com.zetcode.repository.CityRepository;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.data.domain.Sort;
import org.springframework.stereotype.Component;

@Component
public class MyRunner implements CommandLineRunner {

    private static final Logger logger = LoggerFactory.getLogger(MyRunner.class);

    @Autowired
    private CityRepository cityRepository;

    @Override
    public void run(String... args) throws Exception {

        cityRepository.save(new City("Bratislava", 432000));
        cityRepository.save(new City("Budapest", 1759000));
        cityRepository.save(new City("Prague", 1280000));
        cityRepository.save(new City("Warsaw", 1748000));
        cityRepository.save(new City("Los Angeles", 3971000));
        cityRepository.save(new City("New York", 8550000));
        cityRepository.save(new City("Edinburgh", 464000));

        logger.info("# of cities: {}", cityRepository.count());

        logger.info("All cities unsorted:");
        var cities = cityRepository.findAll();
        logger.info("{}", cities);

        logger.info("------------------------");

        logger.info("All cities sorted by name in descending order");
        var sortedCities = cityRepository.findAll(new Sort(Sort.Direction.DESC, "name"));
        logger.info("{}", sortedCities);

        logger.info("------------------------");

        logger.info("Deleting all cities");
        cityRepository.deleteAllInBatch();

        logger.info("# of cities: {}", cityRepository.count());
    }
}

在MyRunner中，我们使用JpaRepository的各种方法。

@Autowired
private CityRepository cityRepository;

我们将CityRepository注入cityRepository字段。

cityRepository.save(new City("Bratislava", 432000));

使用save()插入一个新城市。

logger.info("# of cities: {}", cityRepository.count());

我们用count()计算城市数。

logger.info("All cities unsorted:");
var cities = cityRepository.findAll();
logger.info("{}", cities);

使用findAll()，我们可以到达所有城市。

logger.info("All cities sorted by name in descending order");
var sortedCities = cityRepository.findAll(new Sort(Sort.Direction.DESC, "name"));
logger.info("{}", sortedCities);

通过将Sort对象传递给findAll()方法，我们得到了所有城市的降序排列。

logger.info("Deleting all cities");
cityRepository.deleteAllInBatch();

我们使用deleteAllInBatch()批量删除所有城市。

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设置 Spring Boot 应用。

...
19-06-25 Tue 12:47:14.593 INFO  MyRunner # of cities: 7
19-06-25 Tue 12:47:14.593 INFO  MyRunner All cities unsorted:
19-06-25 Tue 12:47:14.652 INFO  MyRunner [City{id=1, name=Bratislava, population=432000}, City{id=2, name=Budapest, population=1759000}, City{id=3, name=Prague, population=1280000}, City{id=4, name=Warsaw, population=1748000}, City{id=5, name=Los Angeles, population=3971000}, City{id=6, name=New York, population=8550000}, City{id=7, name=Edinburgh, population=464000}]
19-06-25 Tue 12:47:14.652 INFO  MyRunner ------------------------
19-06-25 Tue 12:47:14.652 INFO  MyRunner All cities sorted by name in descending order
19-06-25 Tue 12:47:14.667 INFO  MyRunner [City{id=4, name=Warsaw, population=1748000}, City{id=3, name=Prague, population=1280000}, City{id=6, name=New York, population=8550000}, City{id=5, name=Los Angeles, population=3971000}, City{id=7, name=Edinburgh, population=464000}, City{id=2, name=Budapest, population=1759000}, City{id=1, name=Bratislava, population=432000}]
19-06-25 Tue 12:47:14.668 INFO  MyRunner ------------------------
19-06-25 Tue 12:47:14.668 INFO  MyRunner Deleting all cities
19-06-25 Tue 12:47:14.681 INFO  MyRunner # of cities: 0
...