start.sping.io代码研读及二次开发

Spring是Java开发者的圣经，https://spring.io官网作为布道场。开发者几乎能在上面找到关于Spring的一切信息，当然也包括官方推荐项目代码规范。其中https://start.spring.io既是官方的手脚架工程，也常被初学者用来生成入门工程。这个站点也是一个开源Spring项目，颇有些自举的骄傲（Git也有这种骄傲）。国内大厂某云平台也发布了定制化版本。

本地构建

国内很多开发者会构建本地版本作为加速镜像，这也是start.spring.io项目最常用的功能。

这项目带有https://start.spring.io前端界面的配置化Spring Initializr 实例。包含下列模块：

start-client: 前端界面
start-site: 后端基础服务和元数据配置
start-site-verification: 元数据测试用例

执行./mvnw clean install生成target/start-site-exec.jar即可运行。值得借鉴的是frontend-maven-plugin插件，通过maven插件来代替shell脚本，更显规范。

<plugin>
	<groupId>com.github.eirslett</groupId>
	<artifactId>frontend-maven-plugin</artifactId>
	<executions>
		<execution>
			<id>install node and yarn</id>
			<goals>
				<goal>install-node-and-yarn</goal>
			</goals>
			<configuration>
				<nodeVersion>v12.13.0</nodeVersion>
				<yarnVersion>v1.22.4</yarnVersion>
			</configuration>
		</execution>
		<execution>
			<id>yarn install</id>
			<goals>
				<goal>yarn</goal>
			</goals>
		</execution>
		<execution>
			<id>yarn build</id>
			<goals>
				<goal>yarn</goal>
			</goals>
			<configuration>
				<arguments>build</arguments>
			</configuration>
		</execution>
	</executions>
</plugin>

start-client项目会将静态资源打包成start-client-0.0.1-SNAPSHOT.jar，然后被start-site项目引入。

代码研读

拜读官方文档可知，start.spring.io项目只是门面，initializr才是里子。initializr文档介绍项目结构：

initializr-actuator: optional module to provide additional information and statistics on project generation.
initializr-bom: provides a Bill of Materials for easier dependency management in your project.
initializr-docs: documentation.
initializr-generator: core project generation library.
initializr-generator-spring: optional module defining the conventions for a typical Spring Boot project. Can be reused or replaced by your own conventions.
initializr-generator-test: test infrastructure for project generation.
initializr-metadata: metadata infrastructure for various aspects of the project.
initializr-service-sample: showcases a basic custom instance.
initializr-version-resolver: optional module to extract version numbers from an arbitrary POM.
initializr-web: web endpoints for third party clients.

为了了解生成原理，主要看 initializr-generator and initializr-generator-spring 。initializr-generator中的ProjectGenerator类是项目生成的单元。

public <T> T generate(ProjectDescription description, ProjectAssetGenerator<T> projectAssetGenerator)
		throws ProjectGenerationException {
    
    
	try (ProjectGenerationContext context = this.contextFactory.get()) {
    
    
		registerProjectDescription(context, description);
		registerProjectContributors(context, description);
		this.contextConsumer.accept(context);
		context.refresh();
		try {
    
    
			return projectAssetGenerator.generate(context);
		}
		catch (IOException ex) {
    
    
			throw new ProjectGenerationException("Failed to generate project", ex);
		}
	}
}

首先在/src/main/resources/META-INF/spring.factories文件注册配置文件，然后通过@ProjectGenerationConfiguration注解扫描获取配置，然后遍历执行其中的配置项生成代码。

二次开发

官方文档预留了丰富的扩展接口，详见6.1.1节。具体实现就是追加或重写配置文件，对于应用级开发直接在start.spring.io项目内开发。
在这里插入图片描述

关键代码

FcsGenerationConfiguration.java

@ProjectGenerationConfiguration
public class FcsGenerationConfiguration {
    
    
	@Bean
	public FcsContributor fcsContributor(ProjectDescription description,TemplateRenderer templateRenderer) {
    
    
		return new FcsContributor(description, templateRenderer);
	}
}

FcsContributor.java

public class FcsContributor implements ProjectContributor {
    
    
	
	private final ProjectDescription description;
	private final TemplateRenderer templateRenderer;
	private final String SOURCE_PATH = "src/main/java/";
	
	public FcsContributor(ProjectDescription description, TemplateRenderer templateRenderer) {
    
    
		this.description = description;
		this.templateRenderer = templateRenderer;
	}

	@Override
	public void contribute(Path projectRoot) throws IOException {
    
    
		Map<String, Object> data = new HashMap<>();
		String groupId = description.getGroupId();
		String artifactId = description.getArtifactId();
		data.put("groupId", groupId);
		data.put("artifactId", artifactId);
		
        Path file = Files.createFile(projectRoot.resolve("README.md"));
        String pre = SOURCE_PATH + groupId.replace(".", "/") + "/" + artifactId;
        Files.createDirectories(projectRoot.resolve(pre+"/controller/"));
        Path codeFile = Files.createFile(projectRoot.resolve(pre+"/controller/DemoController.java"));
        String code = this.templateRenderer.render("code/DemoController.java", data);
        try (
        	PrintWriter writer = new PrintWriter(Files.newBufferedWriter(file));
        	PrintWriter codeWriter = new PrintWriter(Files.newBufferedWriter(codeFile));
        ) {
    
    
            writer.println("README");
            codeWriter.print(code);
        }
	}
}

生成效果

在这里插入图片描述

总结

start.spring.io作为手脚架工程虽说用的次数不多，但作为一个技术风向标值得Java开发者关注。
其打包构建方式，为后续构建流水线提供一个选项。
易于二次开发适配团队的开发风格（配置Maven私有仓库更佳），利于统一团队内的开发架构。