一、@Enable* 启用某个特性的注解

1、EnableConfigurationProperties

回顾属性装配

application.properties中添加

tomcat.host=192.168.2.1
tomcat.port=8080

增加属性类TomcatProperties

package com.lhx.spring.springboot_enable;

import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.stereotype.Component; @Component
@ConfigurationProperties(prefix = "tomcat")
public class TomcatProperties {
private String host;
private String port; public String getHost() {
return host;
} public void setHost(String host) {
this.host = host;
} public String getPort() {
return port;
} public void setPort(String port) {
this.port = port;
} @Override
public String toString() {
return "TomcatProperties [host=" + host + ", port=" + port + "]";
} }

在App中添加代码

@SpringBootApplication
public class App {
public static void main(String[] args) {
ConfigurableApplicationContext context = SpringApplication.run(App.class, args);
System.out.println(context.getBean(TomcatProperties.class));
context.close();
}
}

查看注解SpringBootApplication,其中使其起作用的是@EnableAutoConfiguration,继续追踪代码,其实生效的是:@EnableConfigurationProperties

故以上代码配置

@ComponentScan
@EnableConfigurationProperties
public class App {
public static void main(String[] args) {
ConfigurableApplicationContext context = SpringApplication.run(App.class, args);
System.out.println(context.getBean(TomcatProperties.class));
context.close();
}
}

注解:是用来启用一个特性的,特性可以把配置文件的属性注入到Bean类中,一般和@ConfigurationProperties一起使用

2、EnableAsync

增加一个异步打印类

package com.lhx.spring.springboot_enable;

import java.util.concurrent.TimeUnit;

import org.springframework.stereotype.Component;

@Component
public class Jeep implements Runnable { @Override
public void run() {
try {
for (int i = 0; i < 10; i++) {
System.out.println("---------------"+i);
TimeUnit.SECONDS.sleep(1);
}
} catch (Exception e) {
e.printStackTrace();
} } }

在App中调用

@ComponentScan
@EnableConfigurationProperties
public class App {
public static void main(String[] args) {
ConfigurableApplicationContext context = SpringApplication.run(App.class, args);
System.out.println(context.getBean(TomcatProperties.class));
context.getBean(Runnable.class).run();
System.out.println("------end------");
context.close();
}
}

发现此时并没有异步执行

需要在异步打印类中启用@EnableAsync,并在具体方法上标注@Async即可

package com.lhx.spring.springboot_enable;

import java.util.concurrent.TimeUnit;

import org.springframework.scheduling.annotation.Async;
import org.springframework.scheduling.annotation.EnableAsync;
import org.springframework.stereotype.Component; @Component
@EnableAsync
public class Jeep implements Runnable { @Override
@Async
public void run() {
try {
for (int i = 0; i < 10; i++) {
System.out.println("---------------"+i);
TimeUnit.SECONDS.sleep(1);
}
} catch (Exception e) {
e.printStackTrace();
} } }

这时在调用App方法即可异步

注解:启用异步,一般和Async一起使用

二、原理

1、注解Import

  跟踪EnableAsync或EnableConfigurationProperties进入发现,共同注解@Import。  

/*
* Copyright 2002-2016 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/ package org.springframework.context.annotation; import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target; /**
* Indicates one or more {@link Configuration @Configuration} classes to import.
*
* <p>Provides functionality equivalent to the {@code <import/>} element in Spring XML.
* Allows for importing {@code @Configuration} classes, {@link ImportSelector} and
* {@link ImportBeanDefinitionRegistrar} implementations, as well as regular component
* classes (as of 4.2; analogous to {@link AnnotationConfigApplicationContext#register}).
*
* <p>{@code @Bean} definitions declared in imported {@code @Configuration} classes should be
* accessed by using {@link org.springframework.beans.factory.annotation.Autowired @Autowired}
* injection. Either the bean itself can be autowired, or the configuration class instance
* declaring the bean can be autowired. The latter approach allows for explicit, IDE-friendly
* navigation between {@code @Configuration} class methods.
*
* <p>May be declared at the class level or as a meta-annotation.
*
* <p>If XML or other non-{@code @Configuration} bean definition resources need to be
* imported, use the {@link ImportResource @ImportResource} annotation instead.
*
* @author Chris Beams
* @author Juergen Hoeller
* @since 3.0
* @see Configuration
* @see ImportSelector
* @see ImportResource
*/
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Import { /**
* {@link Configuration}, {@link ImportSelector}, {@link ImportBeanDefinitionRegistrar}
* or regular component classes to import.
*/
Class<?>[] value(); }

  import作用:Indicates one or more {@link Configuration @Configuration} classes to 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

示例

新建一个User类

package com.lhx.spring.springboot_enable;

public class User {

}

新建一个Role类

package com.lhx.spring.springboot_enable;

public class Role {

}

使用Import在App中导入

package com.lhx.spring.springboot_enable;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Import; @ComponentScan
@Import(User.class)
public class App2 {
public static void main(String[] args) {
ConfigurableApplicationContext context = SpringApplication.run(App2.class, args);
System.out.println(context.getBean(User.class));
System.out.println(context.getBean(Role.class));
context.close();
}
}

可以看到导入一个,另一个会失败

也可以导入配置类

package com.lhx.spring.springboot_enable;

import org.springframework.context.annotation.Bean;

public class MyConfiguration {
@Bean
public Runnable createRunnable() {
return () -> {
};
} @Bean
public Runnable createRunnable2() {
return () -> {
};
}
}

导入

@Import({User.class,Role.class,MyConfiguration.class})  

2、ImportSelector接口

作用:方法selectImports的返回值,必须是一个class(全称),改class会被Spring容器托管

/*
* Copyright 2002-2013 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/ package org.springframework.context.annotation; import org.springframework.core.type.AnnotationMetadata; /**
* Interface to be implemented by types that determine which @{@link Configuration}
* class(es) should be imported based on a given selection criteria, usually one or more
* annotation attributes.
*
* <p>An {@link ImportSelector} may implement any of the following
* {@link org.springframework.beans.factory.Aware Aware} interfaces, and their respective
* methods will be called prior to {@link #selectImports}:
* <ul>
* <li>{@link org.springframework.context.EnvironmentAware EnvironmentAware}</li>
* <li>{@link org.springframework.beans.factory.BeanFactoryAware BeanFactoryAware}</li>
* <li>{@link org.springframework.beans.factory.BeanClassLoaderAware BeanClassLoaderAware}</li>
* <li>{@link org.springframework.context.ResourceLoaderAware ResourceLoaderAware}</li>
* </ul>
*
* <p>ImportSelectors are usually processed in the same way as regular {@code @Import}
* annotations, however, it is also possible to defer selection of imports until all
* {@code @Configuration} classes have been processed (see {@link DeferredImportSelector}
* for details).
*
* @author Chris Beams
* @since 3.1
* @see DeferredImportSelector
* @see Import
* @see ImportBeanDefinitionRegistrar
* @see Configuration
*/
public interface ImportSelector { /**
* Select and return the names of which class(es) should be imported based on
* the {@link AnnotationMetadata} of the importing @{@link Configuration} class.
*/
String[] selectImports(AnnotationMetadata importingClassMetadata); }

示例

创建一个MyImportSelector

package com.lhx.spring.springboot_enable;

import org.springframework.context.annotation.ImportSelector;
import org.springframework.core.type.AnnotationMetadata; public class MyImportSelector implements ImportSelector { @Override
public String[] selectImports(AnnotationMetadata importingClassMetadata) {
return new String[] {"com.lhx.spring.springboot_enable.User",Role.class.getName(),MyConfiguration.class.getName()};
} }

在App中使用

package com.lhx.spring.springboot_enable;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Import;
import org.springframework.context.annotation.ImportSelector; @ComponentScan
@Import(MyImportSelector.class)
public class App3 {
public static void main(String[] args) {
ConfigurableApplicationContext context = SpringApplication.run(App3.class, args);
System.out.println(context.getBean(User.class));
System.out.println(context.getBean(Role.class));
System.out.println(context.getBeansOfType(Runnable.class)); context.close();
}
}

增加一个Enable开头的注解,可以结合注解使用

增加一个注解EnableLog

package com.lhx.spring.springboot_enable;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
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
@Import(MyImportSelector2.class)
public @interface EnableLog {
String name();
}

增加一个ImportSelector实现MyImportSelector2

package com.lhx.spring.springboot_enable;

import org.springframework.context.annotation.ImportSelector;
import org.springframework.core.type.AnnotationMetadata; public class MyImportSelector2 implements ImportSelector { @Override
public String[] selectImports(AnnotationMetadata importingClassMetadata) {
System.out.println(importingClassMetadata.getAllAnnotationAttributes(EnableLog.class.getName()));
return new String[] { "com.lhx.spring.springboot_enable.User", Role.class.getName(),
MyConfiguration.class.getName() };
} }

使用

package com.lhx.spring.springboot_enable;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Import;
import org.springframework.context.annotation.ImportSelector; @ComponentScan
@EnableLog(name="my annon")
public class App4 {
public static void main(String[] args) {
ConfigurableApplicationContext context = SpringApplication.run(App4.class, args);
System.out.println(context.getBean(User.class));
System.out.println(context.getBean(Role.class));
System.out.println(context.getBeansOfType(Runnable.class)); context.close();
}
}

3、ImportBeanDefinitionRegistrar

作用:方法的参数有一个BeanDefinitionRegistry,BeanDefinitionRegistry可以用来网Spring容器中注入Bean,如此,就可以动态注入bean

/*
* Copyright 2002-2013 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/ package org.springframework.context.annotation; import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.BeanDefinitionRegistryPostProcessor;
import org.springframework.core.type.AnnotationMetadata; /**
* Interface to be implemented by types that register additional bean definitions when
* processing @{@link Configuration} classes. Useful when operating at the bean definition
* level (as opposed to {@code @Bean} method/instance level) is desired or necessary.
*
* <p>Along with {@code @Configuration} and {@link ImportSelector}, classes of this type
* may be provided to the @{@link Import} annotation (or may also be returned from an
* {@code ImportSelector}).
*
* <p>An {@link ImportBeanDefinitionRegistrar} may implement any of the following
* {@link org.springframework.beans.factory.Aware Aware} interfaces, and their respective
* methods will be called prior to {@link #registerBeanDefinitions}:
* <ul>
* <li>{@link org.springframework.context.EnvironmentAware EnvironmentAware}</li>
* <li>{@link org.springframework.beans.factory.BeanFactoryAware BeanFactoryAware}
* <li>{@link org.springframework.beans.factory.BeanClassLoaderAware BeanClassLoaderAware}
* <li>{@link org.springframework.context.ResourceLoaderAware ResourceLoaderAware}
* </ul>
*
* <p>See implementations and associated unit tests for usage examples.
*
* @author Chris Beams
* @since 3.1
* @see Import
* @see ImportSelector
* @see Configuration
*/
public interface ImportBeanDefinitionRegistrar { /**
* Register bean definitions as necessary based on the given annotation metadata of
* the importing {@code @Configuration} class.
* <p>Note that {@link BeanDefinitionRegistryPostProcessor} types may <em>not</em> be
* registered here, due to lifecycle constraints related to {@code @Configuration}
* class processing.
* @param importingClassMetadata annotation metadata of the importing class
* @param registry current bean definition registry
*/
public void registerBeanDefinitions(
AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry); }

自定义实现MyImportBeanDefinitionRegistrar

package com.lhx.spring.springboot_enable;

import org.springframework.beans.factory.support.AbstractBeanDefinition;
import org.springframework.beans.factory.support.BeanDefinitionBuilder;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.context.annotation.ImportBeanDefinitionRegistrar;
import org.springframework.core.type.AnnotationMetadata; public class MyImportBeanDefinitionRegistrar implements ImportBeanDefinitionRegistrar { @Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
registry.registerBeanDefinition("user",
BeanDefinitionBuilder.rootBeanDefinition(User.class).getBeanDefinition()); registry.registerBeanDefinition("role",
BeanDefinitionBuilder.rootBeanDefinition(Role.class).getBeanDefinition());
registry.registerBeanDefinition(MyConfiguration.class.getName(),
BeanDefinitionBuilder.rootBeanDefinition(MyConfiguration.class).getBeanDefinition()); } }

此时就可以在EnableLog上使用

package com.lhx.spring.springboot_enable;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
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
//@Import(MyImportSelector2.class)
@Import(MyImportBeanDefinitionRegistrar.class)
public @interface EnableLog {
String name();
}

示例

代码地址:https://github.com/bjlhx15/spring-boot.git 中的 springboot-enable即可

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