原始碼分析

本文程式碼基於 Springboot 2.1.0

package org.springframework.boot.web.context;

import java.util.HashMap;
import java.util.Map;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.web.server.WebServer;
import org.springframework.context.ApplicationContext;
 

import org.springframework.context.ApplicationContextInitializer;
import org.springframework.context.ApplicationListener;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.core.env.ConfigurableEnvironment;
import org.springframework.core.env.Environment;
import
 
 org.springframework.core.env.MapPropertySource;
import org.springframework.core.env.MutablePropertySources;
import org.springframework.core.env.PropertySource;
import org.springframework.util.StringUtils;

/**
 * ApplicationContextInitializer that sets Environment properties for the
 * ports that WebServer servers are actually listening on. The property
 * "local.server.port" can be injected directly into tests using
 * Value @Value or obtained via the Environment.
 * 
 * 即是一個ApplicationContextInitializer也是一個ApplicationListener，應用上下文
 * 初始化時將自己作為一個ApplicationListener註冊到應用上下文，關注事件WebServerInitializedEvent,
 * 在該事件發生時向環境屬性物件中新增一個屬性物件"local.server.port",值是
 * WebServer當前使用的監聽埠。這樣的話，"local.server.port"就可以通過註解@Value
 * 的方式直接注入到測試中，或者通過Environment物件獲得：
 * environment.getProperty("local.server.port")
 * 
 * If the WebServerInitializedEvent has a
 * WebServerApplicationContext#getServerNamespace() server namespace , it will be
 * used to construct the property name. For example, the "management" actuator context
 * will have the property name "local.management.port".
 * 
 * Properties are automatically propagated up to any parent context.
 *
 * @author Dave Syer
 * @author Phillip Webb
 * @since 2.0.0
 */
 

public class ServerPortInfoApplicationContextInitializer
		implements ApplicationContextInitializer<ConfigurableApplicationContext>,
		ApplicationListener<WebServerInitializedEvent> {

	@Override
	public void initialize(ConfigurableApplicationContext applicationContext) {
		// 應用上下文初始化過程中將自己作為一個ApplicationListener註冊到應用上下文,
		// 關注的事件是WebServerInitializedEvent
		applicationContext.addApplicationListener(this);
	}

	@Override
	public void onApplicationEvent(WebServerInitializedEvent event) {
		// 作為ApplicationListener時的任務:WebServerInitializedEvent 事件發生時,
		// 將當前Web伺服器監聽埠設定到環境屬性local.server.port(通常是這個名字，從下面
		的程式碼來看，也有可能是其他名字)
		String propertyName = "local." + getName(event.getApplicationContext()) + ".port";
		setPortProperty(event.getApplicationContext(), propertyName,
				event.getWebServer().getPort());
	}

	private String getName(WebServerApplicationContext context) {
		// 如果制定了名字使用指定的名字否則使用預設名稱 server
		String name = context.getServerNamespace();
		return StringUtils.hasText(name) ? name : "server";
	}

	private void setPortProperty(ApplicationContext context, String propertyName,
			int port) {
		if (context instanceof ConfigurableApplicationContext) {
			// 將埠資訊設定到應用上下文的環境屬性中去
			setPortProperty(((ConfigurableApplicationContext) context).getEnvironment(),
					propertyName, port);
		}
		if (context.getParent() != null) {
			// 如果當前應用上下文的雙親應用上下文存在，則把該屬性設定向上傳播
			setPortProperty(context.getParent(), propertyName, port);
		}
	}

	@SuppressWarnings("unchecked")
	private void setPortProperty(ConfigurableEnvironment environment, String propertyName,
			int port) {
		// 獲取環境物件environment中的屬性源server.ports,如果不存在則先建立它	
		MutablePropertySources sources = environment.getPropertySources();
		PropertySource<?> source = sources.get("server.ports");
		if (source == null) {
			source = new MapPropertySource("server.ports", new HashMap<>());
			sources.addFirst(source);
		}
		// 將埠名稱/值設定到環境物件environment的屬性源server.ports中去
		((Map<String, Object>) source.getSource()).put(propertyName, port);
	}

}

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