Spring Boot 的 @SpringBootApplication 注解与 SpringApplication 类

2 年 ago
科, 雅
8 minutes

Spring Boot的@SpringBootApplication注解

Spring Boot的@SpringBootApplication注解用于标记一个配置类，该类声明了一个或多个@Bean方法，并触发自动配置和组件扫描。它与声明一个带有@Configuration、@EnableAutoConfiguration和@ComponentScan注解的类是相同的。

Spring Boot的SpringApplication类

Spring Boot的SpringApplication类用于从Java的main方法引导并启动一个Spring应用。这个类会自动从类路径上创建ApplicationContext，扫描配置类并启动应用程序。使用Spring Boot，这个类对于启动Spring MVC或Spring REST应用程序非常有帮助。

SpringBootApplication 和 SpringApplication 示例

在上次的Spring RestController教程中，我们创建了一个Spring RESTful web服务并将其部署到Tomcat上。我们需要创建web.xml和Spring上下文文件，还需要手动添加Spring MVC依赖项并管理它们的版本。这里我们将把项目改为以Spring Boot应用程序运行，并摒弃配置文件。这将有助于快速测试我们的应用逻辑，因为我们不需要手动构建和部署项目到外部Tomcat服务器中。

你应该查看我们的GitHub仓库中现有的项目，在接下来的部分中，我们将对项目文件进行必要的更改。

SpringBootApplication and SpringApplication Example

添加Spring Boot Maven依赖

第一步是清理pom.xml文件并为Spring Boot进行配置。由于它是一个REST网络服务，我们只需要spring-boot-starter-web依赖。然而，我们需要保留JAXB依赖，因为我们在Java 10上运行并且需要支持XML请求和响应。我们还需要添加spring-boot-maven-plugin插件，该插件允许我们将简单的Java应用程序作为Spring Boot应用程序运行。以下是我们更新后的pom.xml文件。

<project xmlns="https://maven.apache.org/POM/4.0.0"
	xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="https://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>Spring-RestController</groupId>
	<artifactId>Spring-RestController</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<packaging>war</packaging>

	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.0.2.RELEASE</version>
		<relativePath /> <!-- lookup parent from repository -->
	</parent>
	<properties>
		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
		<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
		<java.version>10</java.version>
	</properties>
	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>

		<!-- JAXB for XML Response needed to explicitly define from Java 9 onwards -->

		<dependency>
			<groupId>javax.xml.bind</groupId>
			<artifactId>jaxb-api</artifactId>
		</dependency>
		<dependency>
			<groupId>org.glassfish.jaxb</groupId>
			<artifactId>jaxb-runtime</artifactId>
			<version>2.3.0</version>
			<scope>runtime</scope>
		</dependency>
		<dependency>
			<groupId>javax.activation</groupId>
			<artifactId>javax.activation-api</artifactId>
			<version>1.2.0</version>
		</dependency>
	</dependencies>

	<build>
		<!-- added to remove Version from WAR file -->
		<finalName>${project.artifactId}</finalName>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>
</project>

我们可以删除WebContent目录，也可以保留它，因为它不会被我们的Spring Boot应用程序使用。

Spring Boot应用程序类

现在我们需要创建一个带有主方法的Java类，用@SpringBootApplication注解标记它，并调用SpringApplication.run()方法。

package com.Olivia.spring;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class SpringBootRestApplication {

	public static void main(String[] args) {
		SpringApplication.run(SpringBootRestApplication.class, args);
	}
}

只需将该类作为Java应用程序运行，它将产生以下输出。我已删除一些我们在这里不关心的日志记录器。该应用程序将不会退出并等待客户端请求。

2018-06-18 14:33:51.276  INFO 3830 --- [           main] c.j.spring.SpringBootRestApplication     : Starting SpringBootRestApplication on Olivia with PID 3830 (/Users/Olivia/Documents/eclipse-jee-workspace/Spring-RestController/target/classes started by Olivia in /Users/Olivia/Documents/eclipse-jee-workspace/Spring-RestController)
2018-06-18 14:33:51.280  INFO 3830 --- [           main] c.j.spring.SpringBootRestApplication     : No active profile set, falling back to default profiles: default
2018-06-18 14:33:51.332  INFO 3830 --- [           main] ConfigServletWebServerApplicationContext : Refreshing org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext@38467116: startup date [Mon Jun 18 14:33:51 IST 2018]; root of context hierarchy
2018-06-18 14:33:52.311  INFO 3830 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2018-06-18 14:33:52.344  INFO 3830 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2018-06-18 14:33:52.344  INFO 3830 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet Engine: Apache Tomcat/8.5.31
2018-06-18 14:33:52.453  INFO 3830 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2018-06-18 14:33:52.453  INFO 3830 --- [ost-startStop-1] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 1127 ms
2018-06-18 14:33:52.564  INFO 3830 --- [ost-startStop-1] o.s.b.w.servlet.ServletRegistrationBean  : Servlet dispatcherServlet mapped to [/]
2018-06-18 14:33:52.927  INFO 3830 --- [           main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/rest/employee/get/{id}],methods=[GET]}" onto public com.Olivia.spring.model.Employee com.Olivia.spring.controller.EmployeeRestController.getEmployeeByID(int)
2018-06-18 14:33:52.928  INFO 3830 --- [           main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/rest/employee/getAll],methods=[GET]}" onto public java.util.List<com.Olivia.spring.model.Employee> com.Olivia.spring.controller.EmployeeRestController.getAllEmployees()
2018-06-18 14:33:52.929  INFO 3830 --- [           main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/rest/employee/create],methods=[POST]}" onto public com.Olivia.spring.model.Employee com.Olivia.spring.controller.EmployeeRestController.createEmployee(com.Olivia.spring.model.Employee)
2018-06-18 14:33:52.929  INFO 3830 --- [           main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/rest/employee/search/{name}],methods=[GET]}" onto public com.Olivia.spring.model.Employee com.Olivia.spring.controller.EmployeeRestController.getEmployeeByName(java.lang.String)
2018-06-18 14:33:52.929  INFO 3830 --- [           main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/rest/employee/delete/{id}],methods=[DELETE]}" onto public com.Olivia.spring.model.Employee com.Olivia.spring.controller.EmployeeRestController.deleteEmployeeByID(int)
2018-06-18 14:33:53.079  INFO 3830 --- [           main] o.s.j.e.a.AnnotationMBeanExporter        : Registering beans for JMX exposure on startup
2018-06-18 14:33:53.118  INFO 3830 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2018-06-18 14:33:53.124  INFO 3830 --- [           main] c.j.spring.SpringBootRestApplication     : Started SpringBootRestApplication in 2.204 seconds (JVM running for 2.633)

从日志中我们可以得出一些重要的观点。

    Spring Boot应用程序的进程ID为3830。
    Spring Boot应用程序正在端口8080上启动Tomcat。
    我们的应用程序上下文路径为空。这意味着在调用我们的API时，我们不需要提供Servlet上下文。
    记录器打印所有已配置的API，例如消息Mapped “{[/rest/employee/get/{id}],methods=[GET]}”等。
Spring Boot Application Example

@SpringBootApplication 扫描基础包名

默认情况下，SpringApplication会扫描配置类包及其所有子包。因此，如果我们的SpringBootRestApplication类位于com.Olivia.spring.main包中，则不会扫描com.Olivia.spring.controller包。我们可以使用@SpringBootApplication注解的scanBasePackages属性来解决这个问题。

@SpringBootApplication(scanBasePackages="com.Olivia.spring")
public class SpringBootRestApplication {
}

Spring Boot自动配置的Bean

由于Spring Boot提供了自动配置功能，因此它会配置许多bean。我们可以使用下面的代码片段获取这些bean的列表。

ApplicationContext ctx = SpringApplication.run(SpringBootRestApplication.class, args);
String[] beans = ctx.getBeanDefinitionNames();
for(String s : beans) System.out.println(s);

以下是我们的Spring Boot应用程序配置的豆子列表。

org.springframework.context.annotation.internalConfigurationAnnotationProcessor
org.springframework.context.annotation.internalAutowiredAnnotationProcessor
org.springframework.context.annotation.internalRequiredAnnotationProcessor
org.springframework.context.annotation.internalCommonAnnotationProcessor
org.springframework.context.event.internalEventListenerProcessor
org.springframework.context.event.internalEventListenerFactory
springBootRestApplication
org.springframework.boot.autoconfigure.internalCachingMetadataReaderFactory
employeeRestController
employeeRepository
org.springframework.boot.autoconfigure.AutoConfigurationPackages
org.springframework.boot.autoconfigure.context.PropertyPlaceholderAutoConfiguration
org.springframework.boot.autoconfigure.condition.BeanTypeRegistry
propertySourcesPlaceholderConfigurer
org.springframework.boot.autoconfigure.websocket.servlet.WebSocketServletAutoConfiguration$TomcatWebSocketConfiguration
websocketContainerCustomizer
org.springframework.boot.autoconfigure.websocket.servlet.WebSocketServletAutoConfiguration
org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryConfiguration$EmbeddedTomcat
tomcatServletWebServerFactory
org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration
servletWebServerFactoryCustomizer
tomcatServletWebServerFactoryCustomizer
server-org.springframework.boot.autoconfigure.web.ServerProperties
org.springframework.boot.context.properties.ConfigurationPropertiesBindingPostProcessor
org.springframework.boot.context.properties.ConfigurationBeanFactoryMetadata
webServerFactoryCustomizerBeanPostProcessor
errorPageRegistrarBeanPostProcessor
org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration$DispatcherServletConfiguration
dispatcherServlet
mainDispatcherServletPathProvider
spring.mvc-org.springframework.boot.autoconfigure.web.servlet.WebMvcProperties
org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration$DispatcherServletRegistrationConfiguration
dispatcherServletRegistration
org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration
org.springframework.boot.autoconfigure.validation.ValidationAutoConfiguration
defaultValidator
methodValidationPostProcessor
org.springframework.boot.autoconfigure.web.servlet.error.ErrorMvcAutoConfiguration$WhitelabelErrorViewConfiguration
error
beanNameViewResolver
org.springframework.boot.autoconfigure.web.servlet.error.ErrorMvcAutoConfiguration$DefaultErrorViewResolverConfiguration
conventionErrorViewResolver
org.springframework.boot.autoconfigure.web.servlet.error.ErrorMvcAutoConfiguration
errorAttributes
basicErrorController
errorPageCustomizer
preserveErrorControllerTargetClassPostProcessor
spring.resources-org.springframework.boot.autoconfigure.web.ResourceProperties
org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration$WebMvcAutoConfigurationAdapter$FaviconConfiguration
faviconHandlerMapping
faviconRequestHandler
org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration$EnableWebMvcConfiguration
requestMappingHandlerAdapter
requestMappingHandlerMapping
mvcConversionService
mvcValidator
mvcContentNegotiationManager
mvcPathMatcher
mvcUrlPathHelper
viewControllerHandlerMapping
beanNameHandlerMapping
resourceHandlerMapping
mvcResourceUrlProvider
defaultServletHandlerMapping
mvcUriComponentsContributor
httpRequestHandlerAdapter
simpleControllerHandlerAdapter
handlerExceptionResolver
mvcViewResolver
mvcHandlerMappingIntrospector
org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration$WebMvcAutoConfigurationAdapter
defaultViewResolver
viewResolver
welcomePageHandlerMapping
requestContextFilter
org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration
hiddenHttpMethodFilter
httpPutFormContentFilter
org.springframework.boot.autoconfigure.jmx.JmxAutoConfiguration
mbeanExporter
objectNamingStrategy
mbeanServer
org.springframework.boot.autoconfigure.context.ConfigurationPropertiesAutoConfiguration
org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration$Jackson2ObjectMapperBuilderCustomizerConfiguration
standardJacksonObjectMapperBuilderCustomizer
spring.jackson-org.springframework.boot.autoconfigure.jackson.JacksonProperties
org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration$JacksonObjectMapperBuilderConfiguration
jacksonObjectMapperBuilder
org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration$ParameterNamesModuleConfiguration
parameterNamesModule
org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration$JacksonObjectMapperConfiguration
jacksonObjectMapper
org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration
jsonComponentModule
org.springframework.boot.autoconfigure.http.HttpMessageConvertersAutoConfiguration$StringHttpMessageConverterConfiguration
stringHttpMessageConverter
spring.http.encoding-org.springframework.boot.autoconfigure.http.HttpEncodingProperties
org.springframework.boot.autoconfigure.http.JacksonHttpMessageConvertersConfiguration$MappingJackson2HttpMessageConverterConfiguration
mappingJackson2HttpMessageConverter
org.springframework.boot.autoconfigure.http.JacksonHttpMessageConvertersConfiguration
org.springframework.boot.autoconfigure.http.HttpMessageConvertersAutoConfiguration
messageConverters
org.springframework.boot.autoconfigure.http.codec.CodecsAutoConfiguration$JacksonCodecConfiguration
jacksonCodecCustomizer
org.springframework.boot.autoconfigure.http.codec.CodecsAutoConfiguration
org.springframework.boot.autoconfigure.info.ProjectInfoAutoConfiguration
spring.info-org.springframework.boot.autoconfigure.info.ProjectInfoProperties
org.springframework.boot.autoconfigure.security.reactive.ReactiveSecurityAutoConfiguration
spring.security-org.springframework.boot.autoconfigure.security.SecurityProperties
org.springframework.boot.autoconfigure.web.client.RestTemplateAutoConfiguration
restTemplateBuilder
org.springframework.boot.autoconfigure.web.embedded.EmbeddedWebServerFactoryCustomizerAutoConfiguration$TomcatWebServerFactoryCustomizerConfiguration
tomcatWebServerFactoryCustomizer
org.springframework.boot.autoconfigure.web.embedded.EmbeddedWebServerFactoryCustomizerAutoConfiguration
org.springframework.boot.autoconfigure.web.servlet.HttpEncodingAutoConfiguration
characterEncodingFilter
localeCharsetMappingsCustomizer
org.springframework.boot.autoconfigure.web.servlet.MultipartAutoConfiguration
multipartConfigElement
multipartResolver
spring.servlet.multipart-org.springframework.boot.autoconfigure.web.servlet.MultipartProperties

这是一个庞大的清单，有许多我们没有使用的自动配置的bean。我们可以通过使用@SpringBootApplication的排除或排除名称属性来优化我们的Spring Boot应用程序。下面的代码片段将禁用JMX和Multipart自动配置。

@SpringBootApplication(scanBasePackages = "com.Olivia.spring", exclude = {
org.springframework.boot.autoconfigure.web.servlet.MultipartAutoConfiguration.class, org.springframework.boot.autoconfigure.jmx.JmxAutoConfiguration.class })
public class SpringBootRestApplication {
}

请注意，如果我们尝试排除任何非自动配置类，将会出现错误，并且我们的应用程序将无法启动。

@SpringBootApplication(scanBasePackages = "com.Olivia.spring", exclude = {com.Olivia.spring.controller.EmployeeRestController.class })
public class SpringBootRestApplication {
}

上述代码片段将会抛出以下错误：

2018-06-18 15:10:43.602 ERROR 3899 --- [main] o.s.boot.SpringApplication: Application run failed

java.lang.IllegalStateException: The following classes could not be excluded because they are not auto-configuration classes:
	- com.Olivia.spring.controller.EmployeeRestController

SpringBootApplication注解和SpringApplication示例就介绍到这里。

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