判断改类是否在项目中加载

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# 判断改类是否在项目中加载
boolean present = ClassUtils.isPresent("ch.qos.logback.access.db.DBAppender", null);

springboot 源码 入口：this.webApplicationType = WebApplicationType.*deduceFromClasspath*();

springboot 会判断 他是否是

  1. 反应式web应用程序运行，并应启动嵌入式反应式web服务器
  2. 为基于servlet的web应用程序运行，并且应该启动嵌入式servlet web服务器
  3. 程序不应作为web应用程序运行，也不应启动嵌入式web服务器
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private static final String WEBMVC_INDICATOR_CLASS = "org.springframework.web.servlet.DispatcherServlet";

private static final String WEBFLUX_INDICATOR_CLASS = "org.springframework.web.reactive.DispatcherHandler";

private static final String JERSEY_INDICATOR_CLASS = "org.glassfish.jersey.servlet.ServletContainer";

static WebApplicationType deduceFromClasspath() {
	if (ClassUtils.isPresent(WEBFLUX_INDICATOR_CLASS, null) && !ClassUtils.isPresent(WEBMVC_INDICATOR_CLASS, null)
			&& !ClassUtils.isPresent(JERSEY_INDICATOR_CLASS, null)) {
		return WebApplicationType.REACTIVE;
	}
	for (String className : SERVLET_INDICATOR_CLASSES) {
		if (!ClassUtils.isPresent(className, null)) {
			return WebApplicationType.NONE;
		}
	}
	return WebApplicationType.SERVLET;
}

设置初始化器(Initializer)

setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));

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public static final String *FACTORIES_RESOURCE_LOCATION* = "META-INF/spring.factories";

Enumeration<URL> urls = classLoader.getResources(FACTORIES_RESOURCE_LOCATION);
while (urls.hasMoreElements()) {
	URL url = urls.nextElement();
	UrlResource resource = new UrlResource(url);
	Properties properties = PropertiesLoaderUtils.loadProperties(resource);
	for (Map.Entry<?, ?> entry : properties.entrySet()) {
		String factoryTypeName = ((String) entry.getKey()).trim();
		String[] factoryImplementationNames =
				StringUtils.commaDelimitedListToStringArray((String) entry.getValue());
		for (String factoryImplementationName : factoryImplementationNames) {
			result.computeIfAbsent(factoryTypeName, key -> new ArrayList<>())
					.add(factoryImplementationName.trim());
		}
	}
}