SpringBoot 之 SpringApplication

小鱼儿 2022-05-14 00:53 211阅读 0赞

# 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

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：

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：

new SpringApplicationBuilder()
                    .sources(ParentConfig.class)
                    .child(Child1Config.class)
                    .sibling(Child2Config.class)
                    .banner(new AppBanner())
                    .logStartupInfo(false)
                    .run(args);
    
    // ParentConfig.class
    
    //@Configuration
    @SpringBootApplication
    @PropertySource("classpath:/parent.properties")
    public class ParentConfig {
    }
    
    // Child1Config.class
    
    @SpringBootApplication
    @PropertySource("classpath:/child1.properties")
    public class Child1Config {
    
    }
    
    // Child2Config.class
    
    @SpringBootApplication
    @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

@Component
    public class AnnotationRegisterListener {
    
        @EventListener
        public void register(UserRegisterEvent event) {
            User user = event.getUser();
    
            System.out.println("AnnotationRegisterListener " + user.getName() + ", " + user.getPassword());
        }
    }

@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());
        }
    }

@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：

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

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

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

转载链接：https://www.imooc.com/article/23628

项目地址：[https://github.com/smxknife/smxknife/tree/master/spring-boot/spring-boot-v2/spring-boot-v2-web/src/main/java/com/smxknife/springboot/v2/ex03][https_github.com_smxknife_smxknife_tree_master_spring-boot_spring-boot-v2_spring-boot-v2-web_src_main_java_com_smxknife_springboot_v2_ex03]

[github]: https://github.com/smxknife/smxknife/tree/master/spring-boot/spring-boot-v2/spring-boot-v2-web/src/main/java/com/smxknife/springboot/v2/ex02
[https_github.com_smxknife_smxknife_tree_master_spring-boot_spring-boot-v2_spring-boot-v2-web_src_main_java_com_smxknife_springboot_v2_ex03]: https://github.com/smxknife/smxknife/tree/master/spring-boot/spring-boot-v2/spring-boot-v2-web/src/main/java/com/smxknife/springboot/v2/ex03