SpringBoot之SpringApplication

2021-07-06 09:50:25

简介

可以用于从java主方法中引导和启动Spring应用程序的类，在默认情况下，通过以下步骤来启动应用：

  • 创建一个ApplicationContext实例
  • 注册CommandLinePropertySource用来暴露命令行参数作为spring的属性
  • refresh applicationContext，加载所有的singleton bean
  • 触发任何CommandLineRunner bean

自定义SpringApplication

默认的启动方式，代码如下，不做深入介绍

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SpringApplication.run(AppBoot1.class, args);

当然也可以做一些定制，如在Banner里面介绍的自定义banner，还有添加Listener等诸多设置，格式如下：

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SpringApplication app = new SpringApplication(MySpringConfiguration.class);
	app.setBannerMode(Banner.Mode.OFF);
	app.run(args);

使用Fluent Builder API进行构建

先上代码，如下：

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new SpringApplicationBuilder()
                .sources(ParentConfig.class)
                .child(Child1Config.class)
                .sibling(Child2Config.class)
                .banner(new AppBanner())
                .logStartupInfo(false)
                .run(args);
                


//@Configuration

@PropertySource("classpath:/parent.properties")
public class  {
}

// Child1Config.class


@PropertySource("classpath:/child1.properties")
public class Child1Config {

}

// Child2Config.class


@PropertySource("classpath:/child2.properties")
public class Child2Config {

}

使用SpringApplicationBuilder在构建分层的ApplicationContext应用的时候非常便利，但是官网给的代码示例很简单，对于一些初次介入的人可能理解上不是那么透彻。就上面的代码做一些简单的介绍

  • .sources(ParentConfig.class)该方法是用来配置父配置，或主配置的。但是有坑!!!!请看上面的ParentConfig的代码，注解我使用的是@SpringBootApplication，如果你使用的是springboot的1.x的版本，那么你会很顺利，如果你正在研究springboot 2.x的版本，你会发现无论如何也无法启动成功（我被坑的好惨）…。聪明的人也许看到我的注释，没错换成@Configuration之后就可以正常工作。但是很抱歉，这是为什么暂时还没找到原因，在github上请教暂时也没得到正确的结果，后面继续研究，如果有人发现了其中的原因，请通知我一下
  • .child(Child1Config.class)那么通过名字就可以看到是子环境了，Child1Config就是child1的配置文件。也许你的应用里有多个child，那么你可能会想用多个child().child()，那么这样你的第二个child不是parent的child，而是第一个child的child，parent的孙子。想要实现多个同级的孩子，可以使用代码中的.sibling(Child2Config.class)方法。这里同样存在一个springboot的版本改动问题，那就是如果你要在配置文件里面为child1配置一个context path，那么在版本1里面的方法是server.contextPath=child1，但是如果使用版本2的朋友就需要做一点小改动了，改为server.servlet.contextPath=child1

可以参照github上的代码进行详细的理解github

事件和监听器

spring里面的监听器有三种实现方式：

  • @EventListener注解方式
  • 实现ApplicationListener接口
  • 实现SmartApplicationListener接口

上面三种方式代码分别为

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@Component
public class AnnotationRegisterListener {

    @EventListener
    public void register(UserRegisterEvent event) {
        User user = event.getUser();

        System.out.println("AnnotationRegisterListener " + user.getName() + ", " + user.getPassword());
    }
}
 
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@Component
public class RegisterListener implements ApplicationListener<UserRegisterEvent>{

    @Override
    public void onApplicationEvent(UserRegisterEvent event) {

        User user = event.getUser();

        System.out.println("RegisterListener " + user.getName() + ", " + user.getPassword());
    }
}
 
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@Component
public class UserRegisterListener implements SmartApplicationListener {

    /**
     * 该方法返回true&supportsSourceType同样返回true时，才会调用该监听内的onApplicationEvent方法
     * @param eventType
     * @return
     */
    @Override
    public boolean supportsEventType(Class<? extends ApplicationEvent> eventType) {
        return UserRegisterEvent.class.isAssignableFrom(eventType);
    }

    /**
     * 该方法返回true&supportsEventType同样返回true时，才会调用该监听内的onApplicationEvent方法
     * @param sourceType
     * @return
     */
    @Override
    public boolean supportsSourceType(@Nullable Class<?> sourceType) {
        return UserService.class.isAssignableFrom(sourceType);
    }

    @Override
    public void onApplicationEvent(ApplicationEvent event) {
        UserRegisterEvent userRegisterEvent = (UserRegisterEvent) event;
        User user = userRegisterEvent.getUser();
        System.out.println("UserRegisterListener " + user.getName() + ", " + user.getPassword());
    }

    /**
     * 同步情况下监听执行的顺序
     * @return
     */
    @Override
    public int getOrder() {
        return 3;
    }
}

前两种实现方式比较简单，稍微介绍一下第三种，这种实现方式必须在supportsEventType和supportsSourceType同时返回true的情况下才会执行事件，具体如何返回true和false就看你自己的业务实现。在这里我使用了jdk的isAssignableFrom方法来判断父子关系的。
上面两种方式事件的执行顺序是无序的，第三种提供了一种指定属性的方法getOrder()

具体的isAssignableFrom是如何使用的，请看如下代码：

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public class Animal {
}

public class Bird 大专栏  SpringBoot之SpringApplicationn class="keyword">extends Animal implements Fly {
}

public class Dove extends Bird {
}

public class Penguin extends Bird {
}

public interface Fly {
}

public class Demo03 {
	public static void main(String[] args) {

		assignOut(Animal.class, Animal.class);
		assignOut(Animal.class, Bird.class);
		assignOut(Bird.class, Animal.class);
		assignOut(Animal.class, Dove.class);
		assignOut(Penguin.class, Dove.class);
		assignOut(Fly.class, Bird.class);
		assignOut(Fly.class, Dove.class);


	}

	static void assignOut(Class cls1, Class cls2) {
		System.out.println(cls1.getSimpleName() + " isAssignableFrom " + cls2.getSimpleName() + " : " + cls1.isAssignableFrom(cls2));
	}
}

// 输出结果
Animal isAssignableFrom Animal : true
Animal isAssignableFrom Bird : true
Bird isAssignableFrom Animal : false
Animal isAssignableFrom Dove : true
Penguin isAssignableFrom Dove : false
Fly isAssignableFrom Bird : true
Fly isAssignableFrom Dove : true

SpringBoot启动过程中的事件及监听器

  • ApplicationStartingEvent 应用开始启动时执行，在初始化listeners and initializers之前执行
  • ApplicationEnvironmentPreparedEvent 环境准备好开始执行，上下文创建之前执行
  • ApplicationPreparedEvent 应用准备好开始执行，即所有bean都已经加载完毕之后，在refresh方法执行之前执行
  • ApplicationStartedEvent 应用启动后开始执行，即上下文被refreshed之后，任何的application和command-line runners调用前执行
  • ApplicationReadyEvent 应用启动完毕开始执行，任何的application和command-line runners调用后执行，从此后可以服务request了
  • ApplicationFailedEvent 启动时遇到异常执行

Listener的写法很简单，只以ApplicationStartingEvent为例，其他类似

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public class MyApplicationStartedListener implements ApplicationListener<ApplicationStartedEvent> {
	@Override
	public void onApplicationEvent(ApplicationStartedEvent applicationStartedEvent) {
		System.out.println("MyApplicationStartedListener...");
	}
}

在main方法注入
SpringApplicationBuilder builder = new SpringApplicationBuilder();
        builder.listeners(new MyApplicationStartingListener());
        builder.listeners(new MyApplicationEnvironmentPreparedListener());
        builder.listeners(new MyApplicationPreparedListener());
        builder.listeners(new MyApplicationStartedListener());
//        builder.listeners(new MyApplicationReadyListener());
        builder.sources(AppBoot.class);
        builder.run(args);
或者可以在META-INF/spring.factories中配置
org.springframework.context.ApplicationListener=com.smxknife.springboot.v2.ex03.listener.MyApplicationReadyListener

看一下输出结果

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2018-03-03 01:24:06.387  INFO 5399 --- [  restartedMain] .ConditionEvaluationDeltaLoggingListener : Condition evaluation unchanged
2018-03-03 01:28:58.909  INFO 5399 --- [      Thread-28] ConfigServletWebServerApplicationContext : Closing org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext@58c49e73: startup date [Sat Mar 03 01:24:05 CST 2018]; root of context hierarchy
2018-03-03 01:28:58.913  INFO 5399 --- [      Thread-28] o.s.j.e.a.AnnotationMBeanExporter        : Unregistering JMX-exposed beans on shutdown
MyApplicationStartingListener...
MyApplicationEnvironmentPreparedListener...

  .   ____          _            __ _ _
 /\ / ___'_ __ _ _(_)_ __  __ _    
( ( )___ | '_ | '_| | '_ / _` |    
 \/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |___, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::            (v2.0.0.RC2)

2018-03-03 01:28:59.534  INFO 5399 --- [  restartedMain] com.smxknife.springboot.v2.ex03.AppBoot  : Starting AppBoot on ShaoYundeMacBook-Pro.local with PID 5399 (/Users/ShaoYun/local/workstation/programs/smxknife/spring-boot/spring-boot-v2/spring-boot-v2-web/target/classes started by ShaoYun in /Users/ShaoYun/local/workstation/programs/smxknife/spring-boot)
2018-03-03 01:28:59.536  INFO 5399 --- [  restartedMain] com.smxknife.springboot.v2.ex03.AppBoot  : No active profile set, falling back to default profiles: default
MyApplicationPreparedListener...
2018-03-03 01:28:59.539  INFO 5399 --- [  restartedMain] ConfigServletWebServerApplicationContext : Refreshing org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext@45b78eb1: startup date [Sat Mar 03 01:28:59 CST 2018]; root of context hierarchy
2018-03-03 01:29:00.304  INFO 5399 --- [  restartedMain] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 10101 (http)
2018-03-03 01:29:00.305  INFO 5399 --- [  restartedMain] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2018-03-03 01:29:00.305  INFO 5399 --- [  restartedMain] org.apache.catalina.core.StandardEngine  : Starting Servlet Engine: Apache Tomcat/8.5.28
2018-03-03 01:29:00.316  INFO 5399 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2018-03-03 01:29:00.317  INFO 5399 --- [ost-startStop-1] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 778 ms
2018-03-03 01:29:00.338  INFO 5399 --- [ost-startStop-1] o.s.b.w.servlet.ServletRegistrationBean  : Servlet dispatcherServlet mapped to [/]
2018-03-03 01:29:00.338  INFO 5399 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'characterEncodingFilter' to: [/*]
2018-03-03 01:29:00.338  INFO 5399 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'hiddenHttpMethodFilter' to: [/*]
2018-03-03 01:29:00.338  INFO 5399 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'httpPutFormContentFilter' to: [/*]
2018-03-03 01:29:00.338  INFO 5399 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'requestContextFilter' to: [/*]
2018-03-03 01:29:00.492  INFO 5399 --- [  restartedMain] s.w.s.m.m.a.RequestMappingHandlerAdapter : Looking for @ControllerAdvice: org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext@45b78eb1: startup date [Sat Mar 03 01:28:59 CST 2018]; root of context hierarchy
2018-03-03 01:29:00.529  INFO 5399 --- [  restartedMain] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/register]}" onto public java.lang.String com.smxknife.springboot.v2.ex03.web.controller.UserController.register(com.smxknife.springboot.v2.ex03.domain.User)
2018-03-03 01:29:00.533  INFO 5399 --- [  restartedMain] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/error]}" onto public org.springframework.http.ResponseEntity<java.util.Map<java.lang.String, java.lang.Object>> org.springframework.boot.autoconfigure.web.servlet.error.BasicErrorController.error(javax.servlet.http.HttpServletRequest)
2018-03-03 01:29:00.534  INFO 5399 --- [  restartedMain] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/error],produces=[text/html]}" onto public org.springframework.web.servlet.ModelAndView org.springframework.boot.autoconfigure.web.servlet.error.BasicErrorController.errorHtml(javax.servlet.http.HttpServletRequest,javax.servlet.http.HttpServletResponse)
2018-03-03 01:29:00.555  INFO 5399 --- [  restartedMain] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/webjars/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2018-03-03 01:29:00.555  INFO 5399 --- [  restartedMain] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2018-03-03 01:29:00.591  INFO 5399 --- [  restartedMain] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/**/favicon.ico] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2018-03-03 01:29:00.648  INFO 5399 --- [  restartedMain] o.s.b.d.a.OptionalLiveReloadServer       : LiveReload server is running on port 35729
2018-03-03 01:29:00.720  INFO 5399 --- [  restartedMain] o.s.j.e.a.AnnotationMBeanExporter        : Registering beans for JMX exposure on startup
2018-03-03 01:29:00.738  INFO 5399 --- [  restartedMain] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 10101 (http) with context path ''
2018-03-03 01:29:00.739  INFO 5399 --- [  restartedMain] com.smxknife.springboot.v2.ex03.AppBoot  : Started AppBoot in 1.585 seconds (JVM running for 3711.163)
MyApplicationStartedListener...
MyApplicationReadyListener...
2018-03-03 01:29:00.741  INFO 5399 --- [  restartedMain] .ConditionEvaluationDeltaLoggingListener : Condition evaluation unchanged

Listener的相关代码可以参照 github

SpringBoot之SpringApplication

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