SpringBoot之SpringApplication _Application

业无高卑志当坚，男儿有求安得闲？这篇文章主要讲述SpringBoot之SpringApplication相关的知识，希望能为你提供帮助。
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

1	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 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 01:24:06.387INFO 5399 --- [restartedMain] .ConditionEvaluationDeltaLoggingListener : Condition evaluation unchanged
2018-03-03 01:28:58.909INFO 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 01:28:58.913INFO 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 01:28:59.534INFO 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 01:28:59.536INFO 5399 --- [restartedMain] com.smxknife.springboot.v2.ex03.AppBoot: No active profile set, falling back to default profiles: default
MyApplicationPreparedListener...
2018-03-03 01:28:59.539INFO 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 01:29:00.304INFO 5399 --- [restartedMain] o.s.b.w.embedded.tomcat.TomcatWebServer: Tomcat initialized with port(s): 10101 (http)
2018-03-03 01:29:00.305INFO 5399 --- [restartedMain] o.apache.catalina.core.StandardService: Starting service [Tomcat]
2018-03-03 01:29:00.305INFO 5399 --- [restartedMain] org.apache.catalina.core.StandardEngine: Starting Servlet Engine: Apache Tomcat/8.5.28
2018-03-03 01:29:00.316INFO 5399 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/]: Initializing Spring embedded WebApplicationContext
2018-03-03 01:29:00.317INFO 5399 --- [ost-startStop-1] o.s.web.context.ContextLoader: Root WebApplicationContext: initialization completed in 778 ms
2018-03-03 01:29:00.338INFO 5399 --- [ost-startStop-1] o.s.b.w.servlet.ServletRegistrationBean: Servlet dispatcherServlet mapped to [/]
2018-03-03 01:29:00.338INFO 5399 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean: Mapping filter: ' characterEncodingFilter' to: [/*]
2018-03-03 01:29:00.338INFO 5399 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean: Mapping filter: ' hiddenHttpMethodFilter' to: [/*]
2018-03-03 01:29:00.338INFO 5399 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean: Mapping filter: ' httpPutFormContentFilter' to: [/*]
2018-03-03 01:29:00.338INFO 5399 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean: Mapping filter: ' requestContextFilter' to: [/*]
2018-03-03 01:29:00.492INFO 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 01:29:00.529INFO 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 01:29:00.533INFO 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 01:29:00.534INFO 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 01:29:00.555INFO 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 01:29:00.555INFO 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 01:29:00.591INFO 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 01:29:00.648INFO 5399 --- [restartedMain] o.s.b.d.a.OptionalLiveReloadServer: LiveReload server is running on port 35729
2018-03-03 01:29:00.720INFO 5399 --- [restartedMain] o.s.j.e.a.AnnotationMBeanExporter: Registering beans for JMX exposure on startup
2018-03-03 01:29:00.738INFO 5399 --- [restartedMain] o.s.b.w.embedded.tomcat.TomcatWebServer: Tomcat started on port(s): 10101 (http) with context path ' '
2018-03-03 01:29:00.739INFO 5399 --- [restartedMain] com.smxknife.springboot.v2.ex03.AppBoot: Started AppBoot in 1.585 seconds (JVM running for 3711.163)
MyApplicationStartedListener...
MyApplicationReadyListener...
2018-03-03 01:29:00.741INFO 5399 --- [restartedMain] .ConditionEvaluationDeltaLoggingListener : Condition evaluation unchanged