springboot中 加载初始化器的三种方式 ApplicationContextInitializer

程序猿欧文 2020-11-10 18:08:24
SpringBoot 初始化 加载 初始 三种


ApplicationContextInitializer主要用于初始化 spring上下文 ConfigurableApplicationContext, 所有的初始化器将在spring创建完ConfigurableApplicationContext之后紧接着执行.并且在ConfigurableApplicationContext#refresh()方法之前.

通常用于配置环境 ConfigurableApplicationContext#getEnvironment(), 或者注册各种前置处理器context.addBeanFactoryPostProcessor()等. 

/** * Callback interface for initializing a Spring {@link ConfigurableApplicationContext} * prior to being {@linkplain ConfigurableApplicationContext#refresh() refreshed}. * * <p>Typically used within web applications that require some programmatic initialization * of the application context. For example, registering property sources or activating * profiles against the {@linkplain ConfigurableApplicationContext#getEnvironment() * context's environment}. See {@code ContextLoader} and {@code FrameworkServlet} support * for declaring a "contextInitializerClasses" context-param and init-param, respectively. * * <p>{@code ApplicationContextInitializer} processors are encouraged to detect * whether Spring's {@link org.springframework.core.Ordered Ordered} interface has been * implemented or if the @{@link org.springframework.core.annotation.Order Order} * annotation is present and to sort instances accordingly if so prior to invocation. * * @author Chris Beams * @since 3.1 * @param <C> the application context type * @see org.springframework.web.context.ContextLoader#customizeContext * @see org.springframework.web.context.ContextLoader#CONTEXT_INITIALIZER_CLASSES_PARAM * @see org.springframework.web.servlet.FrameworkServlet#setContextInitializerClasses * @see org.springframework.web.servlet.FrameworkServlet#applyInitializers */public interface ApplicationContextInitializer<C extends ConfigurableApplicationContext> { /** * Initialize the given application context. * @param applicationContext the application to configure */ void initialize(C applicationContext);}

 

下面是注册初始化器的三种方式:

 

1.通过在项目中建立 META-INF/spring.factories 文件 并在文件中添加类信息:

# Application Context Initializersorg.springframework.context.ApplicationContextInitializer=\org.springframework.boot.context.ConfigurationWarningsApplicationContextInitializer,\org.springframework.boot.context.ContextIdApplicationContextInitializer,\org.springframework.boot.context.config.DelegatingApplicationContextInitializer,\org.springframework.boot.web.context.ServerPortInfoApplicationContextInitializer

ps: springboot在启动的时候会自动全项目(包括引入的所有jar包)扫描 META-INF目录下的spring.factories文件, 然后一次性全部读取到 缓存中 ,根据ClassLoader,进行区分不同缓存. 然后会执行无参构造函数进行实例化, 排序 存储在org.springframework.boot.SpringApplication#initializers变量中.

* The location to look for factories. * <p>Can be present in multiple JAR files. */ public static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories";
// 缓存 private static final Map<ClassLoader, MultiValueMap<Strin.........
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