自定义一个SpringBoot Starter

简介

官方文档中关于自定义starter的描述

4.29.5. Creating Your Own Starter
Concretely, a custom starter can contain the following:
• The autoconfigure module that contains the auto-configuration code for “acme”.
• The starter module that provides a dependency to the autoconfigure module as well as “acme” and any additional dependencies that are typically useful. In a nutshell, adding the starter should provide everything needed to start using that library.

• autoconfigure module 代码写在此moudle中
• starter module只是一个空的项目，它的唯一目的是提供必要的依赖

如果配置简单，没有可选项，可以把所有东西都写在一个Moudle中

使用Spring Initializr创建一个项目

SpringBoot提供的starter以spring-boot-starter-xxx的方式命名的。官方建议自定义的starter使用xxx-spring-boot-starter命名规则。以区分SpringBoot生态提供的starter。

删掉一些不需要的东西，项目结构和pom如下:

<?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.xgsama</groupId>
    <artifactId>xg-spring-boot-starter</artifactId>
    <version>1.0-SNAPSHOT</version>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.4.1</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-autoconfigure</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-configuration-processor</artifactId>
            <optional>true</optional>
        </dependency>
    </dependencies>
</project>

定义一个配置信息映射类

package com.xgsama.starter.autoconfigure;

import org.springframework.boot.context.properties.ConfigurationProperties;
// 该注解有一个prefix属性，通过指定的前缀，绑定配置文件中的配置
@ConfigurationProperties("xg.hello")
public class HelloProperties {

    private String prefix;

    private String suffix;

    public String getPrefix() {
        return prefix;
    }

    public void setPrefix(String prefix) {
        this.prefix = prefix;
    }

    public String getSuffix() {
        return suffix;
    }

    public void setSuffix(String suffix) {
        this.suffix = suffix;
    }
}

定义一个Service

package com.xgsama.starter.service;

import com.xgsama.starter.autoconfigure.HelloProperties;

import javax.annotation.Resource;

/**
 * HelloService
 *
 * @author xgSama
 * @date 2021/1/10 22:59
 */
public class HelloService {
    @Resource
    HelloProperties properties;

    public String sayHello(String name) {

        return properties.getPrefix() + ":" + name + "!" + properties.getSuffix();
    }
}

定义一个配置类自动装配Service

@EnableConfigurationProperties使 @ConfigurationProperties 注解的类生效
@ConditionalOnMissingBean指定在某个Bean不存在时配置才生效

package com.xgsama.starter.autoconfigure;

import com.xgsama.starter.service.HelloService;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

/**
 * HelloServiceAutoConfiguration
 *
 * @author xgSama
 * @date 2021/1/10 22:59
 */
@Configuration
@EnableConfigurationProperties(HelloProperties.class)
public class HelloServiceAutoConfiguration {

    @Bean
    @ConditionalOnMissingBean(HelloService.class)
    public HelloService helloService() {
        return new HelloService();
    }
}

在spring.factories中指定自动装配的类

在classpath下创建META-INF，新建spring.factories文件

添加以下内容，指定上步骤中定义的配置类为自动装配的配置。

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
com.xgsama.starter.autoconfigure.HelloServiceAutoConfiguration

安装测试

执行maven clean install将自定义的starter安装到本地maven仓库，新建一个Spring Boot测试这个starter
引入依赖

<dependency>
	<groupId>com.xgsama</groupId>
	<artifactId>xg-spring-boot-starter</artifactId>
	<version>1.0-SNAPSHOT</version>
</dependency>

添加配置

server:
  port: 8888
xg:
  hello:
    prefix: hello
    suffix: nice to meet you

编写测试Controller

/**
 * AlphaController
 *
 * @author xgSama
 * @date 2020/12/26 10:44
 */
@RestController
public class AlphaController {

    @Resource
    HelloService helloService;

    @GetMapping("/hello")
    public String hello() {
        String sayHello = helloService.sayHello("玄戈");
        return sayHello;
    }
}

启动项目测试