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 --version
Spring 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: default
2017-04-04 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 hierarchy
2017-04-04 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 Tomcat
2017-04-04 21:37:33.793 INFO 87317 --- [ runner-0] org.apache.catalina.core.StandardEngine : Starting Servlet Engine: Apache Tomcat/8.0.36
2017-04-04 21:37:33.986 INFO 87317 --- [ost-startStop-1] org.apache.catalina.loader.WebappLoader : Unknown loader org.springframework.boot.cli.compiler.ExtendedGroovyClassLoader$DefaultScopeParentClassLoader@67cc18dd class org.springframework.boot.cli.compiler.ExtendedGroovyClassLoader$DefaultScopeParentClassLoader
2017-04-04 21:37:34.037 INFO 87317 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext
2017-04-04 21:37:34.038 INFO 87317 --- [ost-startStop-1] o.s.web.context.ContextLoader : Root WebApplicationContext: initialization completed in 3673 ms
2017-04-04 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 hierarchy
2017-04-04 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 startup
2017-04-04 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 gradle
Using service at https://start.spring.io
Content 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.java
14 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;
@SpringBootApplication
public 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 = 1.8
repositories {
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: default
2017-04-04 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 hierarchy
2017-04-04 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 Tomcat
2017-04-04 22:52:02.754 INFO 89676 --- [ main] org.apache.catalina.core.StandardEngine : Starting Servlet Engine: Apache Tomcat/8.5.11
2017-04-04 22:52:02.974 INFO 89676 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext
2017-04-04 22:52:02.974 INFO 89676 --- [ost-startStop-1] o.s.web.context.ContextLoader : Root WebApplicationContext: initialization completed in 3788 ms
2017-04-04 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 hierarchy
2017-04-04 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 startup
2017-04-04 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.
*/
@RestController
public 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 Configure
org.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
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