Spring Boot `CommandLineRunner`教程

原文： http://zetcode.com/springboot/commandlinerunner/

Spring Boot CommandLineRunner教程展示了如何使用CommandLineRunner接口运行 bean。

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。

`CommandLineRunner`

CommandLineRunner是用于指示当 bean 包含在SpringApplication中时应运行的接口。一个 Spring Boot 应用可以有多个实现CommandLineRunner的 bean。可以通过@Order规定。

Spring Boot `CommandLineRunner`示例

以下应用演示了CommandLineRunner的用法。它在 H2 内存数据库中创建城市，然后列出它们。

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>springbootcommandlinerunner</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-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。我们使用 H2 数据库和 Spring Data JPA。

resources/application.properties

spring.main.banner-mode=off

application.properties是 Spring Boot 中的主要配置文件。使用spring.main.banner-mode=off，我们关闭了 Spring 横幅。

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模型，具有以下属性：id，name和population。

com/zetcode/repository/CityRepository.java

package com.zetcode.repository;

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

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

CityRepository在某个城市的存储库中具有一些通用的 CRUD 操作。

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.stereotype.Component;

@Component
public class MyRunner implements CommandLineRunner {

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

    @Autowired
    private CityRepository repository;

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

        repository.save(new City("Bratislava", 432000));
        repository.save(new City("Budapest", 1759000));
        repository.save(new City("Prague", 1280000));

        repository.findAll().forEach((city) -> {
            logger.info("{}", city);
        });
    }
}

通过实现CommandLineRunner，将在应用启动后执行MyRunner类的run()方法。

@Component
public class MyRunner implements CommandLineRunner {

MyRunner也装饰有@Component，因此也会自动检测并注册。

@Autowired
private CityRepository repository;

使用@Autowired注解，我们将CityRepository bean 注入到repository字段中。

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

    repository.save(new City("Bratislava", 432000));
    repository.save(new City("Budapest", 1759000));
    repository.save(new City("Prague", 1280000));

    repository.findAll().forEach((city) -> {
        logger.info("{}", city);
    });

在run()方法中，我们创建三个城市，然后找到所有城市并将其打印到控制台。

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。

我们使用mvn -q spring-boot:run运行该应用。

在本教程中，我们展示了如何使用CommandLineRunner接口创建在应用启动时运行的 bean。您可能也对相关教程感兴趣： Spring Boot @Order教程， Spring Boot @Repository教程， Java 教程或列出了全部 Spring 入门教程。

我们一直在努力

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