聊聊springboot的EnvironmentPostProcessor

序

本文主要研究一下springboot的EnvironmentPostProcessor

EnvironmentPostProcessor

org/springframework/boot/env/EnvironmentPostProcessor.java

代码语言：javascript复制

@FunctionalInterface
public interface EnvironmentPostProcessor {

	/**
	 * Post-process the given {@code environment}.
	 * @param environment the environment to post-process
	 * @param application the application to which the environment belongs
	 */
	void postProcessEnvironment(ConfigurableEnvironment environment, SpringApplication application);

}

springboot提供了EnvironmentPostProcessor接口，该接口有postProcessEnvironment方法，其中envrionment参数类型为ConfigurableEnvironment，即应用可以通过实现这个接口进行env环境变量的操作

EnvironmentPostProcessorApplicationListener

org/springframework/boot/env/EnvironmentPostProcessorApplicationListener.java

代码语言：javascript复制

/**
 * {@link SmartApplicationListener} used to trigger {@link EnvironmentPostProcessor
 * EnvironmentPostProcessors} registered in the {@code spring.factories} file.
 *
 * @author Phillip Webb
 * @since 2.4.0
 */
public class EnvironmentPostProcessorApplicationListener implements SmartApplicationListener, Ordered {

	/**
	 * The default order for the processor.
	 */
	public static final int DEFAULT_ORDER = Ordered.HIGHEST_PRECEDENCE   10;

	private final DeferredLogs deferredLogs;

	private int order = DEFAULT_ORDER;

	private final EnvironmentPostProcessorsFactory postProcessorsFactory;

	/**
	 * Create a new {@link EnvironmentPostProcessorApplicationListener} with
	 * {@link EnvironmentPostProcessor} classes loaded via {@code spring.factories}.
	 */
	public EnvironmentPostProcessorApplicationListener() {
		this(EnvironmentPostProcessorsFactory
				.fromSpringFactories(EnvironmentPostProcessorApplicationListener.class.getClassLoader()));
	}

	/**
	 * Create a new {@link EnvironmentPostProcessorApplicationListener} with post
	 * processors created by the given factory.
	 * @param postProcessorsFactory the post processors factory
	 */
	public EnvironmentPostProcessorApplicationListener(EnvironmentPostProcessorsFactory postProcessorsFactory) {
		this(postProcessorsFactory, new DeferredLogs());
	}

	EnvironmentPostProcessorApplicationListener(EnvironmentPostProcessorsFactory postProcessorsFactory,
			DeferredLogs deferredLogs) {
		this.postProcessorsFactory = postProcessorsFactory;
		this.deferredLogs = deferredLogs;
	}

	@Override
	public boolean supportsEventType(Class<? extends ApplicationEvent> eventType) {
		return ApplicationEnvironmentPreparedEvent.class.isAssignableFrom(eventType)
				|| ApplicationPreparedEvent.class.isAssignableFrom(eventType)
				|| ApplicationFailedEvent.class.isAssignableFrom(eventType);
	}

	@Override
	public void onApplicationEvent(ApplicationEvent event) {
		if (event instanceof ApplicationEnvironmentPreparedEvent) {
			onApplicationEnvironmentPreparedEvent((ApplicationEnvironmentPreparedEvent) event);
		}
		if (event instanceof ApplicationPreparedEvent) {
			onApplicationPreparedEvent((ApplicationPreparedEvent) event);
		}
		if (event instanceof ApplicationFailedEvent) {
			onApplicationFailedEvent((ApplicationFailedEvent) event);
		}
	}

	private void onApplicationEnvironmentPreparedEvent(ApplicationEnvironmentPreparedEvent event) {
		ConfigurableEnvironment environment = event.getEnvironment();
		SpringApplication application = event.getSpringApplication();
		for (EnvironmentPostProcessor postProcessor : getEnvironmentPostProcessors(event.getBootstrapContext())) {
			postProcessor.postProcessEnvironment(environment, application);
		}
	}

	private void onApplicationPreparedEvent(ApplicationPreparedEvent event) {
		finish();
	}

	private void onApplicationFailedEvent(ApplicationFailedEvent event) {
		finish();
	}

	private void finish() {
		this.deferredLogs.switchOverAll();
	}

	List<EnvironmentPostProcessor> getEnvironmentPostProcessors(ConfigurableBootstrapContext bootstrapContext) {
		return this.postProcessorsFactory.getEnvironmentPostProcessors(this.deferredLogs, bootstrapContext);
	}

	@Override
	public int getOrder() {
		return this.order;
	}

	public void setOrder(int order) {
		this.order = order;
	}

}

EnvironmentPostProcessorApplicationListener用于在接收到ApplicationEnvironmentPreparedEvent事件时触发执行EnvironmentPostProcessor的postProcessEnvironment方法

代码语言：javascript复制

# Application Listeners
org.springframework.context.ApplicationListener=
org.springframework.boot.ClearCachesApplicationListener,
org.springframework.boot.builder.ParentContextCloserApplicationListener,
org.springframework.boot.context.FileEncodingApplicationListener,
org.springframework.boot.context.config.AnsiOutputApplicationListener,
org.springframework.boot.context.config.DelegatingApplicationListener,
org.springframework.boot.context.logging.LoggingApplicationListener,
org.springframework.boot.env.EnvironmentPostProcessorApplicationListener,
org.springframework.boot.liquibase.LiquibaseServiceLocatorApplicationListener

示例

代码语言：javascript复制

public class EnvironmentPostProcessorExample implements EnvironmentPostProcessor {

	private final YamlPropertySourceLoader loader = new YamlPropertySourceLoader();

	@Override
	public void postProcessEnvironment(ConfigurableEnvironment environment, SpringApplication application) {
		Resource path = new ClassPathResource("com/example/myapp/config.yml");
		PropertySource<?> propertySource = loadYaml(path);
		environment.getPropertySources().addLast(propertySource);
	}

	private PropertySource<?> loadYaml(Resource path) {
		if (!path.exists()) {
			throw new IllegalArgumentException("Resource "   path   " does not exist");
		}
		try {
			return this.loader.load("custom-resource", path).get(0);
		}
		catch (IOException ex) {
			throw new IllegalStateException("Failed to load yaml configuration from "   path, ex);
		}
	}

}

EnvironmentPostProcessorExample实现了postProcessEnvironment方法，它额外加载com/example/myapp/config.yml里头的配置最为最后的propertySource

小结

springboot的EnvironmentPostProcessor提供了一个environment的扩展接口，方便应用去做environment的扩展，比如扩展propertySource等

springboot

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