《Spring Boot极简教程》第3章 一键启动应用程序

第3章 一键启动应用程序

3.1 SpringBoot版的Restful Hello,World

3.1.1 Spring Boot CLI groovy版Hello World

首先安装Spring Boot CLI，参考文档：http://docs.spring.io/spring-boot/docs/current-SNAPSHOT/reference/htmlsingle/#getting-started-installing-the-cli

在命令行验证spring环境安装成功：

$ spring --versionSpring CLI v1.3.6.RELEASE

随便打开编辑器，敲入如下代码：

 @Controller class HelloController{      @RequestMapping("/hello")      @ResponseBody      String hello(){          return "Hello World!"      } }

然后在命令行执行：

$ spring run HelloController.groovy

你将看到如下输出日志：

  .   ____          _            __ _ _ /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \ \\/  ___)| |_)| | | | | || (_| |  ) ) ) )  '  |____| .__|_| |_|_| |_\__, | / / / / =========|_|==============|___/=/_/_/_/ :: Spring Boot ::        (v1.3.6.RELEASE)2017-04-04 21:37:29.685  INFO 87317 --- [       runner-0] o.s.boot.SpringApplication               : Starting application on jacks-MacBook-Air.local with PID 87317 (/Users/jack/.m2/repository/org/springframework/boot/spring-boot/1.3.6.RELEASE/spring-boot-1.3.6.RELEASE.jar started by jack in /Users/jack/book)2017-04-04 21:37:29.699  INFO 87317 --- [       runner-0] o.s.boot.SpringApplication               : No active profile set, falling back to default profiles: default2017-04-04 21:37:30.367  INFO 87317 --- [       runner-0] ationConfigEmbeddedWebApplicationContext : Refreshing org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@30cc0018: startup date [Tue Apr 04 21:37:30 CST 2017]; root of context hierarchy2017-04-04 21:37:33.757  INFO 87317 --- [       runner-0] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat initialized with port(s): 8080 (http)2017-04-04 21:37:33.790  INFO 87317 --- [       runner-0] o.apache.catalina.core.StandardService   : Starting service Tomcat2017-04-04 21:37:33.793  INFO 87317 --- [       runner-0] org.apache.catalina.core.StandardEngine  : Starting Servlet Engine: Apache Tomcat/8.0.362017-04-04 21:37:33.986  INFO 87317 --- [ost-startStop-1] org.apache.catalina.loader.WebappLoader  : Unknown loader org.springframework.boot.cli.compiler.ExtendedGroovyClassLoader$DefaultScopeParentClassLoader@67cc18dd class org.springframework.boot.cli.compiler.ExtendedGroovyClassLoader$DefaultScopeParentClassLoader2017-04-04 21:37:34.037  INFO 87317 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext2017-04-04 21:37:34.038  INFO 87317 --- [ost-startStop-1] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 3673 ms2017-04-04 21:37:34.538  INFO 87317 --- [ost-startStop-1] o.s.b.c.e.ServletRegistrationBean        : Mapping servlet: 'dispatcherServlet' to [/]2017-04-04 21:37:34.552  INFO 87317 --- [ost-startStop-1] o.s.b.c.embedded.FilterRegistrationBean  : Mapping filter: 'characterEncodingFilter' to: [/*]2017-04-04 21:37:34.553  INFO 87317 --- [ost-startStop-1] o.s.b.c.embedded.FilterRegistrationBean  : Mapping filter: 'hiddenHttpMethodFilter' to: [/*]2017-04-04 21:37:34.553  INFO 87317 --- [ost-startStop-1] o.s.b.c.embedded.FilterRegistrationBean  : Mapping filter: 'httpPutFormContentFilter' to: [/*]2017-04-04 21:37:34.553  INFO 87317 --- [ost-startStop-1] o.s.b.c.embedded.FilterRegistrationBean  : Mapping filter: 'requestContextFilter' to: [/*]2017-04-04 21:37:35.309  INFO 87317 --- [       runner-0] s.w.s.m.m.a.RequestMappingHandlerAdapter : Looking for @ControllerAdvice: org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@30cc0018: startup date [Tue Apr 04 21:37:30 CST 2017]; root of context hierarchy2017-04-04 21:37:35.482  INFO 87317 --- [       runner-0] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/hello]}" onto public java.lang.String HelloController.hello()2017-04-04 21:37:35.485  INFO 87317 --- [       runner-0] 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.BasicErrorController.error(javax.servlet.http.HttpServletRequest)2017-04-04 21:37:35.486  INFO 87317 --- [       runner-0] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/error],produces=[text/html]}" onto public org.springframework.web.servlet.ModelAndView org.springframework.boot.autoconfigure.web.BasicErrorController.errorHtml(javax.servlet.http.HttpServletRequest,javax.servlet.http.HttpServletResponse)2017-04-04 21:37:35.523  INFO 87317 --- [       runner-0] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/webjars/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]2017-04-04 21:37:35.524  INFO 87317 --- [       runner-0] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]2017-04-04 21:37:35.606  INFO 87317 --- [       runner-0] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/**/favicon.ico] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]2017-04-04 21:37:36.225  INFO 87317 --- [       runner-0] o.s.j.e.a.AnnotationMBeanExporter        : Registering beans for JMX exposure on startup2017-04-04 21:37:36.397  INFO 87317 --- [       runner-0] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat started on port(s): 8080 (http)2017-04-04 21:37:36.403  INFO 87317 --- [       runner-0] o.s.boot.SpringApplication               : Started application in 8.263 seconds (JVM running for 12.897)

一个极简的Restful Hello World就搞定了。浏览器访问：http://localhost:8080/hello（或者curl http://localhost:8080/hello）

你会看到输出：

Hello World!

3.1.2 常规的Java版的Hello World

1.命令行输入：

$ spring init -dweb --build gradleUsing service at https://start.spring.ioContent saved to 'demo.zip'

2.解压zip，导入idea中

你将看到如下一个Demo Application

.├── build.gradle├── gradle│   └── wrapper│       ├── gradle-wrapper.jar│       └── gradle-wrapper.properties├── gradlew├── gradlew.bat└── src    ├── main    │   ├── java    │   │   └── com    │   │       └── example    │   │           └── DemoApplication.java    │   └── resources    │       ├── application.properties    │       ├── static    │       └── templates    └── test        └── java            └── com                └── example                    └── DemoApplicationTests.java14 directories, 8 files

其中DemoApplication.java代码如下：

package com.example;import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;@SpringBootApplicationpublic class DemoApplication {    public static void main(String[] args) {        SpringApplication.run(DemoApplication.class, args);    }}

build.gradle配置文件如下：

buildscript {    ext {        springBootVersion = '1.5.2.RELEASE'    }    repositories {        mavenCentral()    }    dependencies {        classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}")    }}apply plugin: 'java'apply plugin: 'eclipse'apply plugin: 'org.springframework.boot'version = '0.0.1-SNAPSHOT'sourceCompatibility = 1.8repositories {    mavenCentral()}dependencies {    compile('org.springframework.boot:spring-boot-starter-web')    testCompile('org.springframework.boot:spring-boot-starter-test')}

OK,我们直接Run

Run

同样的，你讲看到如下日志：

  .   ____          _            __ _ _ /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \ \\/  ___)| |_)| | | | | || (_| |  ) ) ) )  '  |____| .__|_| |_|_| |_\__, | / / / / =========|_|==============|___/=/_/_/_/ :: Spring Boot ::        (v1.5.2.RELEASE)2017-04-04 22:51:58.995  INFO 89676 --- [           main] com.example.DemoApplication              : Starting DemoApplication on jacks-MacBook-Air.local with PID 89676 (/Users/jack/book/demo/build/classes/main started by jack in /Users/jack/book/demo)2017-04-04 22:51:58.998  INFO 89676 --- [           main] com.example.DemoApplication              : No active profile set, falling back to default profiles: default2017-04-04 22:51:59.191  INFO 89676 --- [           main] ationConfigEmbeddedWebApplicationContext : Refreshing org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@6950e31: startup date [Tue Apr 04 22:51:59 CST 2017]; root of context hierarchy2017-04-04 22:52:02.718  INFO 89676 --- [           main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat initialized with port(s): 8080 (http)2017-04-04 22:52:02.750  INFO 89676 --- [           main] o.apache.catalina.core.StandardService   : Starting service Tomcat2017-04-04 22:52:02.754  INFO 89676 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet Engine: Apache Tomcat/8.5.112017-04-04 22:52:02.974  INFO 89676 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext2017-04-04 22:52:02.974  INFO 89676 --- [ost-startStop-1] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 3788 ms2017-04-04 22:52:03.173  INFO 89676 --- [ost-startStop-1] o.s.b.w.servlet.ServletRegistrationBean  : Mapping servlet: 'dispatcherServlet' to [/]2017-04-04 22:52:03.198  INFO 89676 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'characterEncodingFilter' to: [/*]2017-04-04 22:52:03.199  INFO 89676 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'hiddenHttpMethodFilter' to: [/*]2017-04-04 22:52:03.199  INFO 89676 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'httpPutFormContentFilter' to: [/*]2017-04-04 22:52:03.200  INFO 89676 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'requestContextFilter' to: [/*]2017-04-04 22:52:03.758  INFO 89676 --- [           main] s.w.s.m.m.a.RequestMappingHandlerAdapter : Looking for @ControllerAdvice: org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@6950e31: startup date [Tue Apr 04 22:51:59 CST 2017]; root of context hierarchy2017-04-04 22:52:03.931  INFO 89676 --- [           main] 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.BasicErrorController.error(javax.servlet.http.HttpServletRequest)2017-04-04 22:52:03.932  INFO 89676 --- [           main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/error],produces=[text/html]}" onto public org.springframework.web.servlet.ModelAndView org.springframework.boot.autoconfigure.web.BasicErrorController.errorHtml(javax.servlet.http.HttpServletRequest,javax.servlet.http.HttpServletResponse)2017-04-04 22:52:03.986  INFO 89676 --- [           main] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/webjars/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]2017-04-04 22:52:03.987  INFO 89676 --- [           main] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]2017-04-04 22:52:04.076  INFO 89676 --- [           main] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/**/favicon.ico] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]2017-04-04 22:52:04.334  INFO 89676 --- [           main] o.s.j.e.a.AnnotationMBeanExporter        : Registering beans for JMX exposure on startup2017-04-04 22:52:04.447  INFO 89676 --- [           main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat started on port(s): 8080 (http)2017-04-04 22:52:04.455  INFO 89676 --- [           main] com.example.DemoApplication              : Started DemoApplication in 6.41 seconds (JVM running for 7.608)

通过日志，我们可以看到SpringBootApplication大致的启动流程。这个过程中，很大一部分工作是在做Spring应用的初始化。

Initializing Spring embedded WebApplicationContext

同时，嵌入式的servlet容器tomcat的启动，org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext是关键类。对细节感兴趣的可以直接debug一下源码。

上面的代码虽然看不出什么效果。但SpringBootApplication的基本架构流程已经基本在里面了。SpringBoot通过注解@SpringBootApplication，完成了自动配置的工作。(源码参见： org.springframework.boot.autoconfigure.SpringBootApplication)

3.写个HelloWorldController

package com.example.controller;import java.util.Date;import org.springframework.web.bind.annotation.RequestMapping;import org.springframework.web.bind.annotation.RestController;/** * Created by jack on 2017/4/4. */@RestControllerpublic class HelloWorldController {    @RequestMapping("hello")    String hello() {        return "Hello World! " + new Date();    }}

直接Run DemoApplication，我们可以看到有如下的日志：

...Mapped "{[/hello]}" onto java.lang.String com.example.controller.HelloWorldController.hello()...

浏览器访问：http://localhost:8080/hello

我们将看到如下输出：

Hello World! Tue Apr 04 23:08:33 CST 2017

另外，如果是在命令行运行，使用SpringBoot gradle插件的执行：

$gradle bootRun

使用SpringBoot maven插件的执行：

$mvn spring-boot:run

3.2 启动Springboot的自动配置@EnableAutoConfiguration

SpringBoot AutoConfiguration的原理是通过Spring的@Conditional注解实现。@Conditional以编程的方式确定的bean的状态，来决定哪些bean是要初始化到容器中（根据外界条件注册不同Bean）。

@EnableAutoConfiguration的意思是启用Spring应用程序上下文的自动配置，通过扫描CLASSPATH里面所有的组件，然后基于条件来决定是否注册bean来使得Spring的ApplicationContext自动配置。

比如说，Spring检测jdbcTemplate是否在classpath？if true, 看看bean容器里面是否有DataSource ? if true, 配置一个JdbcTemplate的Bean到容器中。

看EnableAutoConfiguration源码：

package org.springframework.boot.autoconfigure;import java.lang.annotation.Documented;import java.lang.annotation.ElementType;import java.lang.annotation.Inherited;import java.lang.annotation.Retention;import java.lang.annotation.RetentionPolicy;import java.lang.annotation.Target;import org.springframework.context.annotation.Import;@Target({ElementType.TYPE})@Retention(RetentionPolicy.RUNTIME)@Documented@Inherited@AutoConfigurationPackage@Import({EnableAutoConfigurationImportSelector.class})public @interface EnableAutoConfiguration {    String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";    Class<?>[] exclude() default {};    String[] excludeName() default {};}

可以发现，这里Import了EnableAutoConfigurationImportSelector。
Import主要是配合Configuration来使用的，用来导出更多的Configuration类，ConfigurationClassPostProcessor会读取Import的内容来实现具体的逻辑。
EnableAutoConfigurationImportSelector实现了DeferredImportSelector接口,并实现了selectImports方法，用来导出Configuration类。

String[] selectImports(AnnotationMetadata importingClassMetadata);
导出的类是通过SpringFactoriesLoader.loadFactoryNames()读取了ClassPath下面的META-INF/spring.factories文件，这个文件内容大致如下：

# Auto Configureorg.springframework.boot.autoconfigure.EnableAutoConfiguration=\org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\......org.springframework.boot.autoconfigure.websocket.WebSocketAutoConfiguration,\org.springframework.boot.autoconfigure.websocket.WebSocketMessagingAutoConfiguration,\org.springframework.boot.autoconfigure.webservices.WebServicesAutoConfiguration

其中EmbeddedServletContainerAutoConfiguration是实现web服务的主要的配置类。这个类会根据当前存在的类的信息注入必要的EmbeddedServletContainerFactory类。
spring-boot-starter-tomcat引入了tomcat的依赖，所以EmbeddedServletContainerAutoConfiguration发现存在Tomcat.class就会注入TomcatEmbeddedServletContainerFactory来内置web容器。

当然，如果你想排除一些bean的自动注入，你可以用Class<?>[] exclude() 或者String[] excludeName()。

SpringBoot在spring-boot-autoconfigure-{版本号}.jar里面提供了很多AutoConfiguration的类来负责注册各种不同的组件。这些组件几乎涵盖了Spring开发中需要的绝大部分的配置。

本章源代码

https://github.com/EasySpringBoot/HelloWorld/tree/hello_world_2017.4.4