《这是知识点》之ApplicationContextInitializer源码和简单使用

一、 ApplicationContextInitializer 介绍

首先看下spring官方说明

源码

package org.springframework.context;

/**
 * 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);

}

简单说明一下：

用于spring上下文初始化的回调函数在上下文（ConfigurableApplicationContext）刷新（refresh）之前调用。
通常被用作web应用，在一些程序设计在spring容器初始化使用。比如说注册一些熟悉配置或者激活一些配置文件针对（ConfigurableApplicationContext的getEnvironment()方法）。参考ContextLoader和FrameworkServlet支持定义一个”contextInitializerClasses”上下文参数或者初始化参数。
可排序的（实现Ordered接口，或者添加@Order注解）

二、 ApplicationContextInitializer实现方式

首先新建一个类 MyApplicationContextInitializer 并实现 ApplicationContextInitializer 接口

SpringBoot的main方法添加

@SpringBootApplication
public class Application {
    public static void main(String[] args) {
        SpringApplication application = new SpringApplication(Application.class);
        application.addInitializers(new MyApplicationContextInitializer());
        application.run(args);
    }
}