SpringBoot的@Enable*注解的使用介绍

@EnableAsync或@EnableConfigurationProperties背后的运行原理，是使用了@Import注解。

@Import({User.class,Role.class,MyConfiguration.class})，@Import里面可以存放数组类型的。

@Import用来导入一个或多个类（bean被spring容器托管）、或者配置类（配置类里面的Bean都会被spring容器托管）。

@Enable*其实就是使用了@Import，@Import其实就是导入了配置类。

1、以如何将配置文件里面的配置注入到bean中。之前贴过了，这里再贴一下，权当自己熟悉了。

 package com.bie.enable;

 import org.springframework.boot.context.properties.ConfigurationProperties;
 import org.springframework.stereotype.Component;

 /**
  *
  * @Description TODO
  * @author biehl
  * @Date 2018年12月31日 下午1:13:07
  *
  */
 @Component
 @ConfigurationProperties(prefix = "tomcat")
 public class TomcatProperties {

     private String hosts;
     private String ports;
     public String getHosts() {
         return hosts;
     }
     public void setHosts(String hosts) {
         this.hosts = hosts;
     }
     public String getPorts() {
         return ports;
     }
     public void setPorts(String ports) {
         this.ports = ports;
     }
     @Override
     public String toString() {
         return "TomcatProperties [hosts=" + hosts + ", ports=" + ports + "]";
     }

 }

然后在配置文件里面进行配置：

tomcat.hosts=192.168.11.12
tomcat.ports=

然后写一个主运行类来进行运行：

可以看到正常运行了。运行效果就不粘贴了。

package com.bie.enable;

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

/**
 *
 * @Description TODO
 * @author biehl
 * @Date 2018年12月31日 下午1:15:27
 *
 */
@SpringBootApplication
public class TomcatApplication {

    public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(TomcatApplication.class, args);
        System.out.println("------------------------------------------------------------");
        System.out.println(context.getEnvironment().getProperty("tomcat.hosts"));//从容器中获取到对象tomcat.hosts
        System.out.println(context.getEnvironment().getProperty("tomcat.ports"));//从容器中获取到对象tomcat.ports
        System.out.println("------------------------------------------------------------");
        context.close();
    }
}

2、ctrl键和鼠标左键点开@SpringBootApplication注解，其实可以发现，注解里面主要使用了如此注解@EnableAutoConfiguration和@ComponentScan来实现的功能的。

注意1：@SpringBootConfiguration注解和Spring的@Configuration注解的作用是一样的。

注意2：@EnableConfigurationProperties注解是替代@EnableAutoConfiguration，发挥作用的是@EnableConfigurationProperties注解。

然后呢，你会发现，使用这两个注解和使用@SpringBootApplication注解的作用是一样的。

package com.bie.enable;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.ComponentScan;

/**
 *
 * @Description TODO
 * @author biehl
 * @Date 2018年12月31日 下午1:15:27
 *
 */
//@SpringBootApplication
@EnableAutoConfiguration
@ComponentScan
public class TomcatApplication {

    public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(TomcatApplication.class, args);
        System.out.println("------------------------------------------------------------");
        System.out.println(context.getEnvironment().getProperty("tomcat.hosts"));
        System.out.println(context.getEnvironment().getProperty("tomcat.ports"));
        System.out.println("------------------------------------------------------------");
        context.close();
    }
}

运行效果如下所示：

上面说了发挥作用的@EnableConfigurationProperties，然而我测试的时候发现如下所示：

   .   ____          _            __ _ _
  /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
 ( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
  \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
   '  |____| .__|_| |_|_| |_\__, | / / / /
  =========|_|==============|___/=/_/_/_/
  :: Spring Boot ::       (v1.5.10.RELEASE)

 -- ::18.515  INFO  --- [           main] com.bie.enable.TomcatApplication         : Starting TomcatApplication on DESKTOP-T450s with PID  (E:\eclipeswork\guoban\spring-boot-hello\target\classes started by Aiyufei in E:\eclipeswork\guoban\spring-boot-hello)
 -- ::18.521  INFO  --- [           main] com.bie.enable.TomcatApplication         : No active profile set, falling back to default profiles: default
 -- ::18.600  INFO  --- [           main] ationConfigEmbeddedWebApplicationContext : Refreshing org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@101df177: startup date [Mon Dec  :: CST ]; root of context hierarchy
 -- ::18.932  WARN  --- [           main] ationConfigEmbeddedWebApplicationContext : Exception encountered during context initialization - cancelling refresh attempt: org.springframework.context.ApplicationContextException: Unable to start embedded container; nested exception is org.springframework.context.ApplicationContextException: Unable to start EmbeddedWebApplicationContext due to missing EmbeddedServletContainerFactory bean.
 -- ::19.423 ERROR  --- [           main] o.s.boot.SpringApplication               : Application startup failed

 org.springframework.context.ApplicationContextException: Unable to start embedded container; nested exception is org.springframework.context.ApplicationContextException: Unable to start EmbeddedWebApplicationContext due to missing EmbeddedServletContainerFactory bean.
     at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.onRefresh(EmbeddedWebApplicationContext.java:) ~[spring-boot-1.5..RELEASE.jar:1.5..RELEASE]
     at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:) ~[spring-context-4.3..RELEASE.jar:4.3..RELEASE]
     at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh(EmbeddedWebApplicationContext.java:) ~[spring-boot-1.5..RELEASE.jar:1.5..RELEASE]
     at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:) [spring-boot-1.5..RELEASE.jar:1.5..RELEASE]
     at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:) [spring-boot-1.5..RELEASE.jar:1.5..RELEASE]
     at org.springframework.boot.SpringApplication.run(SpringApplication.java:) [spring-boot-1.5..RELEASE.jar:1.5..RELEASE]
     at org.springframework.boot.SpringApplication.run(SpringApplication.java:) [spring-boot-1.5..RELEASE.jar:1.5..RELEASE]
     at org.springframework.boot.SpringApplication.run(SpringApplication.java:) [spring-boot-1.5..RELEASE.jar:1.5..RELEASE]
     at com.bie.enable.TomcatApplication.main(TomcatApplication.java:) [classes/:na]
 Caused by: org.springframework.context.ApplicationContextException: Unable to start EmbeddedWebApplicationContext due to missing EmbeddedServletContainerFactory bean.
     at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.getEmbeddedServletContainerFactory(EmbeddedWebApplicationContext.java:) ~[spring-boot-1.5..RELEASE.jar:1.5..RELEASE]
     at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.createEmbeddedServletContainer(EmbeddedWebApplicationContext.java:) ~[spring-boot-1.5..RELEASE.jar:1.5..RELEASE]
     at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.onRefresh(EmbeddedWebApplicationContext.java:) ~[spring-boot-1.5..RELEASE.jar:1.5..RELEASE]
     ...  common frames omitted

然而就百度呗，发现并没有很清晰说这个问题怎么解决的。

在https://stackoverflow.com/questions/37114076/exception-in-thread-main-org-springframework-context-applicationcontextexcepti发现了一段话，还挺有意思的。如是说，丢失注解，其实是依赖不对的问题，哈哈哈，然后看看自己的依赖。发现了问题所在。

我一开始是使用的<artifactId>spring-boot-starter-web</artifactId>，这种web的依赖，修改为了<artifactId>spring-boot-starter</artifactId>普通项目的依赖，这样使用@EnableConfigurationProperties注解是替代@EnableAutoConfiguration运行就没有问题了。

@EnableConfigurationProperties注解是用来启用一个特性的，这个特性就是，可以把配置文件注入到bean里面去。一般是要和@ConfigurationProperties一起使用。

2、SpringBoot中如何启用一个异步，看看SpringBoot如何对异步进行支持的。

 package com.bie.enable;

 import java.util.concurrent.TimeUnit;

 import org.springframework.scheduling.annotation.Async;
 import org.springframework.stereotype.Component;

 /**
  *
  * @Description TODO
  * @author biehl
  * @Date 2018年12月31日 下午2:08:52
  * 1、实现Runnable接口的类要实现run的方法
  */
 @Component //添加到容器中
 public class SyncRunnable implements Runnable {

     //@Async注解实现，异步执行
     @Async
     public void run() {
         try {
             for (int i = ; i < ; i++) {
                 System.out.println("-------------------" + i);
                 TimeUnit.SECONDS.sleep();
             }
         } catch (InterruptedException e) {
             e.printStackTrace();
         }

     }

 }

然后写主运行类，如下所示：

 package com.bie.enable;

 import org.springframework.boot.SpringApplication;
 import org.springframework.boot.autoconfigure.SpringBootApplication;
 import org.springframework.context.ConfigurableApplicationContext;
 import org.springframework.scheduling.annotation.EnableAsync;

 /**
  *
  * @Description TODO
  * @author biehl
  * @Date 2018年12月31日 下午2:11:52
  *
  */
 @SpringBootApplication
 @EnableAsync //启用异步注解
 public class SyncApplication {

     public static void main(String[] args) {
         ConfigurableApplicationContext context = SpringApplication.run(SyncApplication.class, args);
         SyncRunnable bean = context.getBean(SyncRunnable.class);
         System.out.println(bean);
         bean.run();
         System.out.println("-----------end-----------");

         //关闭
         context.close();
     }
 }

如果使用上面的会报错，如下所示：

   .   ____          _            __ _ _
  /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
 ( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
  \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
   '  |____| .__|_| |_|_| |_\__, | / / / /
  =========|_|==============|___/=/_/_/_/
  :: Spring Boot ::       (v1.5.10.RELEASE)

 -- ::34.676  INFO  --- [           main] com.bie.enable.SyncApplication           : Starting SyncApplication on DESKTOP-T450s with PID  (E:\eclipeswork\guoban\spring-boot-hello\target\classes started by Aiyufei in E:\eclipeswork\guoban\spring-boot-hello)
 -- ::34.682  INFO  --- [           main] com.bie.enable.SyncApplication           : No active profile set, falling back to default profiles: default
 -- ::34.991  INFO  --- [           main] s.c.a.AnnotationConfigApplicationContext : Refreshing org.springframework.context.annotation.AnnotationConfigApplicationContext@103f852: startup date [Mon Dec  :: CST ]; root of context hierarchy
 -- ::38.523  INFO  --- [           main] o.s.j.e.a.AnnotationMBeanExporter        : Registering beans for JMX exposure on startup
 -- ::38.623  INFO  --- [           main] com.bie.enable.SyncApplication           : Started SyncApplication in 5.1 seconds (JVM running for 5.898)
 Exception in thread "main" org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'com.bie.enable.SyncRunnable' available
     at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBean(DefaultListableBeanFactory.java:)
     at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBean(DefaultListableBeanFactory.java:)
     at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:)
     at com.bie.enable.SyncApplication.main(SyncApplication.java:)
 -- ::38.663  INFO  --- [       Thread-] s.c.a.AnnotationConfigApplicationContext : Closing org.springframework.context.annotation.AnnotationConfigApplicationContext@103f852: startup date [Mon Dec  :: CST ]; root of context hierarchy
 -- ::38.670  INFO  --- [       Thread-] o.s.j.e.a.AnnotationMBeanExporter        : Unregistering JMX-exposed beans on shutdown

百度了一下，参考链接：https://www.cnblogs.com/javJoker/p/7281688.html

修改为了如下所示，参考链接的问题，确实也问住我了，需要深思一下吧。

@EnableAsync //启用异步注解，一般是和@Async一起使用。来实现异步的功能。

 package com.bie.enable;

 import org.springframework.boot.SpringApplication;
 import org.springframework.boot.autoconfigure.SpringBootApplication;
 import org.springframework.context.ConfigurableApplicationContext;
 import org.springframework.scheduling.annotation.EnableAsync;

 /**
  *
  * @Description TODO
  * @author biehl
  * @Date 2018年12月31日 下午2:11:52
  *
  */
 @SpringBootApplication
 @EnableAsync //启用异步注解
 public class SyncApplication {

     public static void main(String[] args) {
         ConfigurableApplicationContext context = SpringApplication.run(SyncApplication.class, args);
         Runnable bean = context.getBean(Runnable.class);
         System.out.println(bean);
         bean.run();
         System.out.println("-----------end-----------");

         //关闭
         context.close();
     }
 }

运行结果如下所示：

待续......