自定义 Spring Boot Stater

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1 摘要

Spring Boot 以 Stater 的方式将各种组件封装，极大地方便了后台开发者的集成工作。如常用的 Mybatis、webmvc 等，都是直接嵌入就能够使用，无需过多的配置，而原来各种组件需要的配置都在 Stater 中按照默认的方式设定。这也是Java后台开发者在从 SpringMVC 过渡到 Spring Boot 之后感受到配置极大减少的原因。同时，Stater 的配置信息也可以在 Spring Boot 的 yml/properties 配置文件中，从而覆盖默认的配置。本文将基于 Spring Boot 2.3 创建自定义 Spring Boot Stater。

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2 核心 Maven 依赖

./demo-stater/pom.xml

        <dependency>
            <groupId>org.springframework.bootgroupId>
            <artifactId>spring-boot-autoconfigureartifactId>
            <version>${springboot.version}version>
        dependency>

其中 ${springboot.version} 的版本为 2.3.4.RELEASE

完整 pom 文件

<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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0modelVersion>

    <groupId>com.ljq.demo.springbootgroupId>
    <artifactId>demo-staterartifactId>
    <version>1.0.0version>
    <name>demo-statername>
    <packaging>jarpackaging>
    <description>spring boot stater demodescription>

    <properties>
        <springboot.version>2.3.4.RELEASEspringboot.version>
    properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.bootgroupId>
            <artifactId>spring-boot-autoconfigureartifactId>
            <version>${springboot.version}version>
        dependency>

    dependencies>

    <build>
        <finalName>demo-staterfinalName>
    build>

project>

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3 核心代码

3.1 自定义配置

./demo-stater/src/main/java/com/ljq/demo/springboot/stater/config/HelloProperties.java

package com.ljq.demo.springboot.stater.config;

import org.springframework.boot.context.properties.ConfigurationProperties;

/**
 * @Description: 自定义 Spring Boot stater 示例配置信息
 * @Author: junqiang.lu
 * @Date: 2020/10/26
 */
@ConfigurationProperties(prefix = "hello-stater")
public class HelloProperties {

    private static final String DEFAULT_NAME = "helloWorld";

    private String name = DEFAULT_NAME;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

3.2 配置使用类

./demo-stater/src/main/java/com/ljq/demo/springboot/stater/service/HelloService.java

package com.ljq.demo.springboot.stater.service;

/**
 * @Description: spring boot 自定义 stater 示例业务
 * @Author: junqiang.lu
 * @Date: 2020/10/26
 */
public class HelloService {

    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String hello() {
        return "hello," + this.name;
    }

}

3.3 自动配置类

当用户没有在 SpringBoot 的 yml/properties 配置文件中配置对应的属性时，对配置的每一个属性设置默认值，从而实现自动配置

./demo-stater/src/main/java/com/ljq/demo/springboot/stater/config/HelloAutoConfiguration.java

package com.ljq.demo.springboot.stater.config;

import com.ljq.demo.springboot.stater.service.HelloService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
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;

/**
 * @Description: 自定义 Spring Boot Stater 示例配置自动化配置
 * @Author: junqiang.lu
 * @Date: 2020/10/26
 */
@Configuration
@ConditionalOnClass(value = {HelloService.class})
@EnableConfigurationProperties(value = HelloProperties.class)
public class HelloAutoConfiguration {

    @Autowired
    private HelloProperties helloProperties;

    @Bean
    @ConditionalOnMissingBean(HelloService.class)
    public HelloService helloService() {
        HelloService helloService = new HelloService();
        helloService.setName(helloProperties.getName());
        return helloService;
    }
}

3.4 SpringBoot 扫描配置文件

Spring Boot 之所以能够实现自动配置，是因为SpringBoot 在启动时会自动扫描所依赖的包下边的一个配置文件，该配置文件中指定了当前 Stater 中的需要自动配置的类，SpringBoot 读取到配置信息后会执行该类中默认配置的方法，从而在 SpringBoot 项目启动之后，可以直接读取到配置信息。

./demo-stater/src/main/resources/META-INF/spring.factories

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
com.ljq.demo.springboot.stater.config.HelloAutoConfiguration

至此，一个自定义 SpringBoot Stater 就完成了。打包发布就能够直接使用了

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4 使用

4.1 引入自定义 Stater 的依赖

./demo-stater-usage/pom.xml

        
        <dependency>
            <groupId>com.ljq.demo.springbootgroupId>
            <artifactId>demo-staterartifactId>
            <version>${demo.stater.version}version>
        dependency>

其中 ${demo.stater.version} 的版本为 1.0.0

4.2 SpringBoot 配置信息

./demo-stater-usage/src/main/resources/application.yml

## 自定义 stater
hello-stater:
  name: stater-demo-123

4.3 测试类-Controller

./demo-stater-usage/src/main/java/com/ljq/demo/springboot/staterusage/controller/StaterController.java

package com.ljq.demo.springboot.staterusage.controller;

import com.ljq.demo.springboot.stater.service.HelloService;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

/**
 * @Description: 自定义 stater 控制层
 * @Author: junqiang.lu
 * @Date: 2020/10/27
 */
@Slf4j
@RestController
@RequestMapping("/api/stater")
public class StaterController {

    @Autowired
    private HelloService helloService;

    @GetMapping(value = "/hello", produces = {MediaType.APPLICATION_JSON_VALUE})
    public ResponseEntity<String> hello() {
        return ResponseEntity.ok(helloService.hello());
    }
}

4.4 Postman 测试

URL:

http://127.0.0.1:8500/api/stater/hello

返回结果:

hello,stater-demo-123

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5 推荐参考资料

实战|如何自定义SpringBoot Starter

SpringBoot自定义starter及自动配置

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6 Github 源码

Gtihub 源码地址 : https://github.com/Flying9001/springBootDemo

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