作者：whisper

链接：http://proprogrammar.com:443/article/329

声明：请尊重原作者的劳动，如需转载请注明出处

package com.atguigu;


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


/**
 *  @SpringBootApplication 来标注一个主程序类，说明这是一个Spring Boot应用
 */
@SpringBootApplication
public class HelloWorldMainApplication {

    public static void main(String[] args) {

        // Spring应用启动起来
        SpringApplication.run(HelloWorldMainApplication.class,args);
    }
}

　　@SpringBootApplication: Spring Boot应用标注在某个类上说明这个类是SpringBoot的主配置类，SpringBoot就应该运行这个类的main方法来启动SpringBoot应用；

/*
 * Copyright 2012-2017 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.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.boot.SpringBootConfiguration;
import org.springframework.boot.context.TypeExcludeFilter;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.ComponentScan.Filter;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.FilterType;
import org.springframework.core.annotation.AliasFor;

/**
 * Indicates a {@link Configuration configuration} class that declares one or more
 * {@link Bean @Bean} methods and also triggers {@link EnableAutoConfiguration
 * auto-configuration} and {@link ComponentScan component scanning}. This is a convenience
 * annotation that is equivalent to declaring {@code @Configuration},
 * {@code @EnableAutoConfiguration} and {@code @ComponentScan}.
 *
 * @author Phillip Webb
 * @author Stephane Nicoll
 * @since 1.2.0
 */
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = {
        @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
        @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
public @interface SpringBootApplication {

    /**
     * Exclude specific auto-configuration classes such that they will never be applied.
     * @return the classes to exclude
     */
    @AliasFor(annotation = EnableAutoConfiguration.class, attribute = "exclude")
    Class<?>[] exclude() default {};

    /**
     * Exclude specific auto-configuration class names such that they will never be
     * applied.
     * @return the class names to exclude
     * @since 1.3.0
     */
    @AliasFor(annotation = EnableAutoConfiguration.class, attribute = "excludeName")
    String[] excludeName() default {};

    /**
     * Base packages to scan for annotated components. Use {@link #scanBasePackageClasses}
     * for a type-safe alternative to String-based package names.
     * @return base packages to scan
     * @since 1.3.0
     */
    @AliasFor(annotation = ComponentScan.class, attribute = "basePackages")
    String[] scanBasePackages() default {};

    /**
     * Type-safe alternative to {@link #scanBasePackages} for specifying the packages to
     * scan for annotated components. The package of each class specified will be scanned.
     * <p>
     * Consider creating a special no-op marker class or interface in each package that
     * serves no purpose other than being referenced by this attribute.
     * @return base packages to scan
     * @since 1.3.0
     */
    @AliasFor(annotation = ComponentScan.class, attribute = "basePackageClasses")
    Class<?>[] scanBasePackageClasses() default {};

}

　　@SpringBootConfiguration:Spring Boot的配置类；标注在某个类上，表示这是一个Spring Boot的配置类；

 * Copyright 2012-2016 the original author or authors.

package org.springframework.boot;

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.Configuration;

/**
 * Indicates that a class provides Spring Boot application
 * {@link Configuration @Configuration}. Can be used as an alternative to the Spring's
 * standard {@code @Configuration} annotation so that configuration can be found
 * automatically (for example in tests).
 * <p>
 * Application should only ever include <em>one</em> {@code @SpringBootConfiguration} and
 * most idiomatic Spring Boot applications will inherit it from
 * {@code @SpringBootApplication}.
 *
 * @author Phillip Webb
 * @since 1.4.0
 */
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Configuration
public @interface SpringBootConfiguration {

}

　　@Configuration:配置类上来标注这个注解；配置类 ----- 配置文件；配置类也是容器中的一个组件；@Component

/*
 * Copyright 2002-2017 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;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

/**
 * Indicates that a class declares one or more {@link Bean @Bean} methods and
 * may be processed by the Spring container to generate bean definitions and
 * service requests for those beans at runtime, for example:
 *
 * <pre class="code">
 * @Configuration
 * public class AppConfig {
 *
 *     @Bean
 *     public MyBean myBean() {
 *         // instantiate, configure and return bean ...
 *     }
 * }</pre>
 *
 * <h2>Bootstrapping {@code @Configuration} classes</h2>
 *
 * <h3>Via {@code AnnotationConfigApplicationContext}</h3>
 *
 * {@code @Configuration} classes are typically bootstrapped using either
 * {@link AnnotationConfigApplicationContext} or its web-capable variant,
 * {@link org.springframework.web.context.support.AnnotationConfigWebApplicationContext
 * AnnotationConfigWebApplicationContext}. A simple example with the former follows:
 *
 * <pre class="code">
 * AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
 * ctx.register(AppConfig.class);
 * ctx.refresh();
 * MyBean myBean = ctx.getBean(MyBean.class);
 * // use myBean ...
 * </pre>
 *
 * See {@link AnnotationConfigApplicationContext} Javadoc for further details and see
 * {@link org.springframework.web.context.support.AnnotationConfigWebApplicationContext
 * AnnotationConfigWebApplicationContext} for {@code web.xml} configuration instructions.
 *
 * <h3>Via Spring {@code <beans>} XML</h3>
 *
 * <p>As an alternative to registering {@code @Configuration} classes directly against an
 * {@code AnnotationConfigApplicationContext}, {@code @Configuration} classes may be
 * declared as normal {@code <bean>} definitions within Spring XML files:
 * <pre class="code">
 * {@code
 * <beans>
 *    <context:annotation-config/>
 *    <bean class="com.acme.AppConfig"/>
 * </beans>}</pre>
 *
 * In the example above, {@code <context:annotation-config/>} is required in order to
 * enable {@link ConfigurationClassPostProcessor} and other annotation-related
 * post processors that facilitate handling {@code @Configuration} classes.
 *
 * <h3>Via component scanning</h3>
 *
 * <p>{@code @Configuration} is meta-annotated with {@link Component @Component}, therefore
 * {@code @Configuration} classes are candidates for component scanning (typically using
 * Spring XML's {@code <context:component-scan/>} element) and therefore may also take
 * advantage of {@link Autowired @Autowired}/{@link javax.inject.Inject @Inject}
 * like any regular {@code @Component}. In particular, if a single constructor is present
 * autowiring semantics will be applied transparently:
 *
 * <pre class="code">
 * @Configuration
 * public class AppConfig {
 *     private final SomeBean someBean;
 *
 *     public AppConfig(SomeBean someBean) {
 *         this.someBean = someBean;
 *     }
 *
 *     // @Bean definition using "SomeBean"
 *
 * }</pre>
 *
 * <p>{@code @Configuration} classes may not only be bootstrapped using
 * component scanning, but may also themselves <em>configure</em> component scanning using
 * the {@link ComponentScan @ComponentScan} annotation:
 *
 * <pre class="code">
 * @Configuration
 * @ComponentScan("com.acme.app.services")
 * public class AppConfig {
 *     // various @Bean definitions ...
 * }</pre>
 *
 * See the {@link ComponentScan @ComponentScan} javadoc for details.
 *
 * <h2>Working with externalized values</h2>
 *
 * <h3>Using the {@code Environment} API</h3>
 *
 * Externalized values may be looked up by injecting the Spring
 * {@link org.springframework.core.env.Environment} into a {@code @Configuration}
 * class the usual (e.g. using the {@code @Autowired} annotation):
 *
 * <pre class="code">
 * @Configuration
 * public class AppConfig {
 *
 *     @Autowired Environment env;
 *
 *     @Bean
 *     public MyBean myBean() {
 *         MyBean myBean = new MyBean();
 *         myBean.setName(env.getProperty("bean.name"));
 *         return myBean;
 *     }
 * }</pre>
 *
 * Properties resolved through the {@code Environment} reside in one or more "property
 * source" objects, and {@code @Configuration} classes may contribute property sources to
 * the {@code Environment} object using
 * the {@link org.springframework.core.env.PropertySources @PropertySources} annotation:
 *
 * <pre class="code">
 * @Configuration
 * @PropertySource("classpath:/com/acme/app.properties")
 * public class AppConfig {
 *
 *     @Inject Environment env;
 *
 *     @Bean
 *     public MyBean myBean() {
 *         return new MyBean(env.getProperty("bean.name"));
 *     }
 * }</pre>
 *
 * See {@link org.springframework.core.env.Environment Environment}
 * and {@link PropertySource @PropertySource} Javadoc for further details.
 *
 * <h3>Using the {@code @Value} annotation</h3>
 *
 * Externalized values may be 'wired into' {@code @Configuration} classes using
 * the {@link Value @Value} annotation:
 *
 * <pre class="code">
 * @Configuration
 * @PropertySource("classpath:/com/acme/app.properties")
 * public class AppConfig {
 *
 *     @Value("${bean.name}") String beanName;
 *
 *     @Bean
 *     public MyBean myBean() {
 *         return new MyBean(beanName);
 *     }
 * }</pre>
 *
 * This approach is most useful when using Spring's
 * {@link org.springframework.context.support.PropertySourcesPlaceholderConfigurer
 * PropertySourcesPlaceholderConfigurer}, usually enabled via XML with
 * {@code <context:property-placeholder/>}.  See the section below on composing
 * {@code @Configuration} classes with Spring XML using {@code @ImportResource},
 * see {@link Value @Value} Javadoc, and see {@link Bean @Bean} Javadoc for details on working with
 * {@code BeanFactoryPostProcessor} types such as
 * {@code PropertySourcesPlaceholderConfigurer}.
 *
 * <h2>Composing {@code @Configuration} classes</h2>
 *
 * <h3>With the {@code @Import} annotation</h3>
 *
 * <p>{@code @Configuration} classes may be composed using the {@link Import @Import} annotation,
 * not unlike the way that {@code <import>} works in Spring XML. Because
 * {@code @Configuration} objects are managed as Spring beans within the container,
 * imported configurations may be injected the usual way (e.g. via constructor injection):
 *
 * <pre class="code">
 * @Configuration
 * public class DatabaseConfig {
 *
 *     @Bean
 *     public DataSource dataSource() {
 *         // instantiate, configure and return DataSource
 *     }
 * }
 *
 * @Configuration
 * @Import(DatabaseConfig.class)
 * public class AppConfig {
 *
 *     private final DatabaseConfig dataConfig;
 *
 *     public AppConfig(DatabaseConfig dataConfig) {
 *         this.dataConfig = dataConfig;
 *     }
 *
 *     @Bean
 *     public MyBean myBean() {
 *         // reference the dataSource() bean method
 *         return new MyBean(dataConfig.dataSource());
 *     }
 * }</pre>
 *
 * Now both {@code AppConfig} and the imported {@code DatabaseConfig} can be bootstrapped
 * by registering only {@code AppConfig} against the Spring context:
 *
 * <pre class="code">
 * new AnnotationConfigApplicationContext(AppConfig.class);</pre>
 *
 * <h3>With the {@code @Profile} annotation</h3>
 *
 * {@code @Configuration} classes may be marked with the {@link Profile @Profile} annotation to
 * indicate they should be processed only if a given profile or profiles are <em>active</em>:
 *
 * <pre class="code">
 * @Profile("development")
 * @Configuration
 * public class EmbeddedDatabaseConfig {
 *
 *     @Bean
 *     public DataSource dataSource() {
 *         // instantiate, configure and return embedded DataSource
 *     }
 * }
 *
 * @Profile("production")
 * @Configuration
 * public class ProductionDatabaseConfig {
 *
 *     @Bean
 *     public DataSource dataSource() {
 *         // instantiate, configure and return production DataSource
 *     }
 * }</pre>
 *
 * Alternatively, you may also declare profile conditions at the {@code @Bean} method level,
 * e.g. for alternative bean variants within the same configuration class:
 *
 * <pre class="code">
 * @Configuration
 * public class ProfileDatabaseConfig {
 *
 *     @Bean("dataSource")
 *     @Profile("development")
 *     public DataSource embeddedDatabase() { ... }
 *
 *     @Bean("dataSource")
 *     @Profile("production")
 *     public DataSource productionDatabase() { ... }
 * }</pre>
 *
 * See the {@link Profile @Profile} and {@link org.springframework.core.env.Environment}
 * javadocs for further details.
 *
 * <h3>With Spring XML using the {@code @ImportResource} annotation</h3>
 *
 * As mentioned above, {@code @Configuration} classes may be declared as regular Spring
 * {@code <bean>} definitions within Spring XML files. It is also possible to
 * import Spring XML configuration files into {@code @Configuration} classes using
 * the {@link ImportResource @ImportResource} annotation. Bean definitions imported from
 * XML can be injected the usual way (e.g. using the {@code Inject} annotation):
 *
 * <pre class="code">
 * @Configuration
 * @ImportResource("classpath:/com/acme/database-config.xml")
 * public class AppConfig {
 *
 *     @Inject DataSource dataSource; // from XML
 *
 *     @Bean
 *     public MyBean myBean() {
 *         // inject the XML-defined dataSource bean
 *         return new MyBean(this.dataSource);
 *     }
 * }</pre>
 *
 * <h3>With nested {@code @Configuration} classes</h3>
 *
 * {@code @Configuration} classes may be nested within one another as follows:
 *
 * <pre class="code">
 * @Configuration
 * public class AppConfig {
 *
 *     @Inject DataSource dataSource;
 *
 *     @Bean
 *     public MyBean myBean() {
 *         return new MyBean(dataSource);
 *     }
 *
 *     @Configuration
 *     static class DatabaseConfig {
 *         @Bean
 *         DataSource dataSource() {
 *             return new EmbeddedDatabaseBuilder().build();
 *         }
 *     }
 * }</pre>
 *
 * When bootstrapping such an arrangement, only {@code AppConfig} need be registered
 * against the application context. By virtue of being a nested {@code @Configuration}
 * class, {@code DatabaseConfig} <em>will be registered automatically</em>. This avoids
 * the need to use an {@code @Import} annotation when the relationship between
 * {@code AppConfig} {@code DatabaseConfig} is already implicitly clear.
 *
 * <p>Note also that nested {@code @Configuration} classes can be used to good effect
 * with the {@code @Profile} annotation to provide two options of the same bean to the
 * enclosing {@code @Configuration} class.
 *
 * <h2>Configuring lazy initialization</h2>
 *
 * <p>By default, {@code @Bean} methods will be <em>eagerly instantiated</em> at container
 * bootstrap time.  To avoid this, {@code @Configuration} may be used in conjunction with
 * the {@link Lazy @Lazy} annotation to indicate that all {@code @Bean} methods declared within
 * the class are by default lazily initialized. Note that {@code @Lazy} may be used on
 * individual {@code @Bean} methods as well.
 *
 * <h2>Testing support for {@code @Configuration} classes</h2>
 *
 * The Spring <em>TestContext framework</em> available in the {@code spring-test} module
 * provides the {@code @ContextConfiguration} annotation, which as of Spring 3.1 can
 * accept an array of {@code @Configuration} {@code Class} objects:
 *
 * <pre class="code">
 * @RunWith(SpringJUnit4ClassRunner.class)
 * @ContextConfiguration(classes={AppConfig.class, DatabaseConfig.class})
 * public class MyTests {
 *
 *     @Autowired MyBean myBean;
 *
 *     @Autowired DataSource dataSource;
 *
 *     @Test
 *     public void test() {
 *         // assertions against myBean ...
 *     }
 * }</pre>
 *
 * See TestContext framework reference documentation for details.
 *
 * <h2>Enabling built-in Spring features using {@code @Enable} annotations</h2>
 *
 * Spring features such as asynchronous method execution, scheduled task execution,
 * annotation driven transaction management, and even Spring MVC can be enabled and
 * configured from {@code @Configuration}
 * classes using their respective "{@code @Enable}" annotations. See
 * {@link org.springframework.scheduling.annotation.EnableAsync @EnableAsync},
 * {@link org.springframework.scheduling.annotation.EnableScheduling @EnableScheduling},
 * {@link org.springframework.transaction.annotation.EnableTransactionManagement @EnableTransactionManagement},
 * {@link org.springframework.context.annotation.EnableAspectJAutoProxy @EnableAspectJAutoProxy},
 * and {@link org.springframework.web.servlet.config.annotation.EnableWebMvc @EnableWebMvc}
 * for details.
 *
 * <h2>Constraints when authoring {@code @Configuration} classes</h2>
 *
 * <ul>
 * <li>Configuration classes must be provided as classes (i.e. not as instances returned
 * from factory methods), allowing for runtime enhancements through a generated subclass.
 * <li>Configuration classes must be non-final.
 * <li>Configuration classes must be non-local (i.e. may not be declared within a method).
 * <li>Any nested configuration classes must be declared as {@code static}.
 * <li>{@code @Bean} methods may not in turn create further configuration classes
 * (any such instances will be treated as regular beans, with their configuration
 * annotations remaining undetected).
 * </ul>
 *
 * @author Rod Johnson
 * @author Chris Beams
 * @since 3.0
 * @see Bean
 * @see Profile
 * @see Import
 * @see ImportResource
 * @see ComponentScan
 * @see Lazy
 * @see PropertySource
 * @see AnnotationConfigApplicationContext
 * @see ConfigurationClassPostProcessor
 * @see org.springframework.core.env.Environment
 * @see org.springframework.test.context.ContextConfiguration
 */
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
public @interface Configuration {

    /**
     * Explicitly specify the name of the Spring bean definition associated
     * with this Configuration class. If left unspecified (the common case),
     * a bean name will be automatically generated.
     * <p>The custom name applies only if the Configuration class is picked up via
     * component scanning or supplied directly to a {@link AnnotationConfigApplicationContext}.
     * If the Configuration class is registered as a traditional XML bean definition,
     * the name/id of the bean element will take precedence.
     * @return the suggested component name, if any (or empty String otherwise)
     * @see org.springframework.beans.factory.support.DefaultBeanNameGenerator
     */
    String value() default "";

}

　　@EnableAutoConfiguration：开启自动配置功能；以前我们需要配置的东西，Spring Boot帮我们自动配置；@EnableAutoConfiguration告诉SpringBoot开启自动配置功能；这样自动配置才能生效；

/*
 * Copyright 2012-2017 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.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.boot.autoconfigure.condition.ConditionalOnBean;
import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.boot.context.embedded.EmbeddedServletContainerFactory;
import org.springframework.boot.context.embedded.tomcat.TomcatEmbeddedServletContainerFactory;
import org.springframework.context.annotation.Conditional;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;
import org.springframework.core.io.support.SpringFactoriesLoader;

/**
 * Enable auto-configuration of the Spring Application Context, attempting to guess and
 * configure beans that you are likely to need. Auto-configuration classes are usually
 * applied based on your classpath and what beans you have defined. For example, If you
 * have {@code tomcat-embedded.jar} on your classpath you are likely to want a
 * {@link TomcatEmbeddedServletContainerFactory} (unless you have defined your own
 * {@link EmbeddedServletContainerFactory} bean).
 * <p>
 * When using {@link SpringBootApplication}, the auto-configuration of the context is
 * automatically enabled and adding this annotation has therefore no additional effect.
 * <p>
 * Auto-configuration tries to be as intelligent as possible and will back-away as you
 * define more of your own configuration. You can always manually {@link #exclude()} any
 * configuration that you never want to apply (use {@link #excludeName()} if you don't
 * have access to them). You can also exclude them via the
 * {@code spring.autoconfigure.exclude} property. Auto-configuration is always applied
 * after user-defined beans have been registered.
 * <p>
 * The package of the class that is annotated with {@code @EnableAutoConfiguration},
 * usually via {@code @SpringBootApplication}, has specific significance and is often used
 * as a 'default'. For example, it will be used when scanning for {@code @Entity} classes.
 * It is generally recommended that you place {@code @EnableAutoConfiguration} (if you're
 * not using {@code @SpringBootApplication}) in a root package so that all sub-packages
 * and classes can be searched.
 * <p>
 * Auto-configuration classes are regular Spring {@link Configuration} beans. They are
 * located using the {@link SpringFactoriesLoader} mechanism (keyed against this class).
 * Generally auto-configuration beans are {@link Conditional @Conditional} beans (most
 * often using {@link ConditionalOnClass @ConditionalOnClass} and
 * {@link ConditionalOnMissingBean @ConditionalOnMissingBean} annotations).
 *
 * @author Phillip Webb
 * @author Stephane Nicoll
 * @see ConditionalOnBean
 * @see ConditionalOnMissingBean
 * @see ConditionalOnClass
 * @see AutoConfigureAfter
 * @see SpringBootApplication
 */
@SuppressWarnings("deprecation")
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import(EnableAutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {

    String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";

    /**
     * Exclude specific auto-configuration classes such that they will never be applied.
     * @return the classes to exclude
     */
    Class<?>[] exclude() default {};

    /**
     * Exclude specific auto-configuration class names such that they will never be
     * applied.
     * @return the class names to exclude
     * @since 1.3.0
     */
    String[] excludeName() default {};

}

　　@AutoConfigurationPackage：自动配置包

​      　　 @Import(AutoConfigurationPackages.Registrar.class)：

​ 　　　　Spring的底层注解@Import，给容器中导入一个组件；导入的组件由AutoConfigurationPackages.Registrar.class；

　　　　将主配置类（@SpringBootApplication标注的类）的所在包及下面所有子包里面的所有组件扫描到Spring容器；

/*
 * Copyright 2012-2015 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.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;

/**
 * Indicates that the package containing the annotated class should be registered with
 * {@link AutoConfigurationPackages}.
 *
 * @author Phillip Webb
 * @since 1.3.0
 * @see AutoConfigurationPackages
 */
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import(AutoConfigurationPackages.Registrar.class)
public @interface AutoConfigurationPackage {

}

　　@Import(EnableAutoConfigurationImportSelector.class)；给容器中导入组件

​ 　　EnableAutoConfigurationImportSelector：导入哪些组件的选择器；

​ 　　将所有需要导入的组件以全类名的方式返回；这些组件就会被添加到容器中；

/*
 * Copyright 2012-2017 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.boot.autoconfigure;

import org.springframework.context.annotation.DeferredImportSelector;
import org.springframework.core.type.AnnotationMetadata;

/**
 * {@link DeferredImportSelector} to handle {@link EnableAutoConfiguration
 * auto-configuration}. This class can also be subclassed if a custom variant of
 * {@link EnableAutoConfiguration @EnableAutoConfiguration}. is needed.
 *
 * @deprecated as of 1.5 in favor of {@link AutoConfigurationImportSelector}
 * @author Phillip Webb
 * @author Andy Wilkinson
 * @author Stephane Nicoll
 * @author Madhura Bhave
 * @since 1.3.0
 * @see EnableAutoConfiguration
 */
@Deprecated
public class EnableAutoConfigurationImportSelector
        extends AutoConfigurationImportSelector {

    @Override
    protected boolean isEnabled(AnnotationMetadata metadata) {
        if (getClass().equals(EnableAutoConfigurationImportSelector.class)) {
            return getEnvironment().getProperty(
                    EnableAutoConfiguration.ENABLED_OVERRIDE_PROPERTY, Boolean.class,
                    true);
        }
        return true;
    }

}

/*
 * Copyright 2012-2017 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.boot.autoconfigure;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashSet;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.TimeUnit;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.Aware;
import org.springframework.beans.factory.BeanClassLoaderAware;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.BeanFactoryAware;
import org.springframework.beans.factory.NoSuchBeanDefinitionException;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.boot.bind.RelaxedPropertyResolver;
import org.springframework.context.EnvironmentAware;
import org.springframework.context.ResourceLoaderAware;
import org.springframework.context.annotation.DeferredImportSelector;
import org.springframework.core.Ordered;
import org.springframework.core.annotation.AnnotationAttributes;
import org.springframework.core.env.ConfigurableEnvironment;
import org.springframework.core.env.Environment;
import org.springframework.core.io.ResourceLoader;
import org.springframework.core.io.support.SpringFactoriesLoader;
import org.springframework.core.type.AnnotationMetadata;
import org.springframework.core.type.classreading.CachingMetadataReaderFactory;
import org.springframework.core.type.classreading.MetadataReaderFactory;
import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;
import org.springframework.util.StringUtils;

/**
 * {@link DeferredImportSelector} to handle {@link EnableAutoConfiguration
 * auto-configuration}. This class can also be subclassed if a custom variant of
 * {@link EnableAutoConfiguration @EnableAutoConfiguration}. is needed.
 *
 * @author Phillip Webb
 * @author Andy Wilkinson
 * @author Stephane Nicoll
 * @author Madhura Bhave
 * @since 1.3.0
 * @see EnableAutoConfiguration
 */
public class AutoConfigurationImportSelector
        implements DeferredImportSelector, BeanClassLoaderAware, ResourceLoaderAware,
        BeanFactoryAware, EnvironmentAware, Ordered {

    private static final String[] NO_IMPORTS = {};

    private static final Log logger = LogFactory
            .getLog(AutoConfigurationImportSelector.class);

    private ConfigurableListableBeanFactory beanFactory;

    private Environment environment;

    private ClassLoader beanClassLoader;

    private ResourceLoader resourceLoader;

    @Override
    public String[] selectImports(AnnotationMetadata annotationMetadata) {
        if (!isEnabled(annotationMetadata)) {
            return NO_IMPORTS;
        }
        try {
            AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader
                    .loadMetadata(this.beanClassLoader);
            AnnotationAttributes attributes = getAttributes(annotationMetadata);
            List<String> configurations = getCandidateConfigurations(annotationMetadata,
                    attributes);
            configurations = removeDuplicates(configurations);
            configurations = sort(configurations, autoConfigurationMetadata);
            Set<String> exclusions = getExclusions(annotationMetadata, attributes);
            checkExcludedClasses(configurations, exclusions);
            configurations.removeAll(exclusions);
            configurations = filter(configurations, autoConfigurationMetadata);
            fireAutoConfigurationImportEvents(configurations, exclusions);
            return configurations.toArray(new String[configurations.size()]);
        }
        catch (IOException ex) {
            throw new IllegalStateException(ex);
        }
    }

    protected boolean isEnabled(AnnotationMetadata metadata) {
        return true;
    }

    /**
     * Return the appropriate {@link AnnotationAttributes} from the
     * {@link AnnotationMetadata}. By default this method will return attributes for
     * {@link #getAnnotationClass()}.
     * @param metadata the annotation metadata
     * @return annotation attributes
     */
    protected AnnotationAttributes getAttributes(AnnotationMetadata metadata) {
        String name = getAnnotationClass().getName();
        AnnotationAttributes attributes = AnnotationAttributes
                .fromMap(metadata.getAnnotationAttributes(name, true));
        Assert.notNull(attributes,
                "No auto-configuration attributes found. Is " + metadata.getClassName()
                        + " annotated with " + ClassUtils.getShortName(name) + "?");
        return attributes;
    }

    /**
     * Return the source annotation class used by the selector.
     * @return the annotation class
     */
    protected Class<?> getAnnotationClass() {
        return EnableAutoConfiguration.class;
    }

    /**
     * Return the auto-configuration class names that should be considered. By default
     * this method will load candidates using {@link SpringFactoriesLoader} with
     * {@link #getSpringFactoriesLoaderFactoryClass()}.
     * @param metadata the source metadata
     * @param attributes the {@link #getAttributes(AnnotationMetadata) annotation
     * attributes}
     * @return a list of candidate configurations
     */
    protected List<String> getCandidateConfigurations(AnnotationMetadata metadata,
            AnnotationAttributes attributes) {
        List<String> configurations = SpringFactoriesLoader.loadFactoryNames(
                getSpringFactoriesLoaderFactoryClass(), getBeanClassLoader());
        Assert.notEmpty(configurations,
                "No auto configuration classes found in META-INF/spring.factories. If you "
                        + "are using a custom packaging, make sure that file is correct.");
        return configurations;
    }

    /**
     * Return the class used by {@link SpringFactoriesLoader} to load configuration
     * candidates.
     * @return the factory class
     */
    protected Class<?> getSpringFactoriesLoaderFactoryClass() {
        return EnableAutoConfiguration.class;
    }

    private void checkExcludedClasses(List<String> configurations,
            Set<String> exclusions) {
        List<String> invalidExcludes = new ArrayList<String>(exclusions.size());
        for (String exclusion : exclusions) {
            if (ClassUtils.isPresent(exclusion, getClass().getClassLoader())
                    && !configurations.contains(exclusion)) {
                invalidExcludes.add(exclusion);
            }
        }
        if (!invalidExcludes.isEmpty()) {
            handleInvalidExcludes(invalidExcludes);
        }
    }

    /**
     * Handle any invalid excludes that have been specified.
     * @param invalidExcludes the list of invalid excludes (will always have at least one
     * element)
     */
    protected void handleInvalidExcludes(List<String> invalidExcludes) {
        StringBuilder message = new StringBuilder();
        for (String exclude : invalidExcludes) {
            message.append("\t- ").append(exclude).append(String.format("%n"));
        }
        throw new IllegalStateException(String
                .format("The following classes could not be excluded because they are"
                        + " not auto-configuration classes:%n%s", message));
    }

    /**
     * Return any exclusions that limit the candidate configurations.
     * @param metadata the source metadata
     * @param attributes the {@link #getAttributes(AnnotationMetadata) annotation
     * attributes}
     * @return exclusions or an empty set
     */
    protected Set<String> getExclusions(AnnotationMetadata metadata,
            AnnotationAttributes attributes) {
        Set<String> excluded = new LinkedHashSet<String>();
        excluded.addAll(asList(attributes, "exclude"));
        excluded.addAll(Arrays.asList(attributes.getStringArray("excludeName")));
        excluded.addAll(getExcludeAutoConfigurationsProperty());
        return excluded;
    }

    private List<String> getExcludeAutoConfigurationsProperty() {
        if (getEnvironment() instanceof ConfigurableEnvironment) {
            RelaxedPropertyResolver resolver = new RelaxedPropertyResolver(
                    this.environment, "spring.autoconfigure.");
            Map<String, Object> properties = resolver.getSubProperties("exclude");
            if (properties.isEmpty()) {
                return Collections.emptyList();
            }
            List<String> excludes = new ArrayList<String>();
            for (Map.Entry<String, Object> entry : properties.entrySet()) {
                String name = entry.getKey();
                Object value = entry.getValue();
                if (name.isEmpty() || name.startsWith("[") && value != null) {
                    excludes.addAll(new HashSet<String>(Arrays.asList(StringUtils
                            .tokenizeToStringArray(String.valueOf(value), ","))));
                }
            }
            return excludes;
        }
        RelaxedPropertyResolver resolver = new RelaxedPropertyResolver(getEnvironment(),
                "spring.autoconfigure.");
        String[] exclude = resolver.getProperty("exclude", String[].class);
        return (Arrays.asList(exclude == null ? new String[0] : exclude));
    }

    private List<String> sort(List<String> configurations,
            AutoConfigurationMetadata autoConfigurationMetadata) throws IOException {
        configurations = new AutoConfigurationSorter(getMetadataReaderFactory(),
                autoConfigurationMetadata).getInPriorityOrder(configurations);
        return configurations;
    }

    private List<String> filter(List<String> configurations,
            AutoConfigurationMetadata autoConfigurationMetadata) {
        long startTime = System.nanoTime();
        String[] candidates = configurations.toArray(new String[configurations.size()]);
        boolean[] skip = new boolean[candidates.length];
        boolean skipped = false;
        for (AutoConfigurationImportFilter filter : getAutoConfigurationImportFilters()) {
            invokeAwareMethods(filter);
            boolean[] match = filter.match(candidates, autoConfigurationMetadata);
            for (int i = 0; i < match.length; i++) {
                if (!match[i]) {
                    skip[i] = true;
                    skipped = true;
                }
            }
        }
        if (!skipped) {
            return configurations;
        }
        List<String> result = new ArrayList<String>(candidates.length);
        for (int i = 0; i < candidates.length; i++) {
            if (!skip[i]) {
                result.add(candidates[i]);
            }
        }
        if (logger.isTraceEnabled()) {
            int numberFiltered = configurations.size() - result.size();
            logger.trace("Filtered " + numberFiltered + " auto configuration class in "
                    + TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - startTime)
                    + " ms");
        }
        return new ArrayList<String>(result);
    }

    protected List<AutoConfigurationImportFilter> getAutoConfigurationImportFilters() {
        return SpringFactoriesLoader.loadFactories(AutoConfigurationImportFilter.class,
                this.beanClassLoader);
    }

    private MetadataReaderFactory getMetadataReaderFactory() {
        try {
            return getBeanFactory().getBean(
                    SharedMetadataReaderFactoryContextInitializer.BEAN_NAME,
                    MetadataReaderFactory.class);
        }
        catch (NoSuchBeanDefinitionException ex) {
            return new CachingMetadataReaderFactory(this.resourceLoader);
        }
    }

    protected final <T> List<T> removeDuplicates(List<T> list) {
        return new ArrayList<T>(new LinkedHashSet<T>(list));
    }

    protected final List<String> asList(AnnotationAttributes attributes, String name) {
        String[] value = attributes.getStringArray(name);
        return Arrays.asList(value == null ? new String[0] : value);
    }

    private void fireAutoConfigurationImportEvents(List<String> configurations,
            Set<String> exclusions) {
        List<AutoConfigurationImportListener> listeners = getAutoConfigurationImportListeners();
        if (!listeners.isEmpty()) {
            AutoConfigurationImportEvent event = new AutoConfigurationImportEvent(this,
                    configurations, exclusions);
            for (AutoConfigurationImportListener listener : listeners) {
                invokeAwareMethods(listener);
                listener.onAutoConfigurationImportEvent(event);
            }
        }
    }

    protected List<AutoConfigurationImportListener> getAutoConfigurationImportListeners() {
        return SpringFactoriesLoader.loadFactories(AutoConfigurationImportListener.class,
                this.beanClassLoader);
    }

    private void invokeAwareMethods(Object instance) {
        if (instance instanceof Aware) {
            if (instance instanceof BeanClassLoaderAware) {
                ((BeanClassLoaderAware) instance)
                        .setBeanClassLoader(this.beanClassLoader);
            }
            if (instance instanceof BeanFactoryAware) {
                ((BeanFactoryAware) instance).setBeanFactory(this.beanFactory);
            }
            if (instance instanceof EnvironmentAware) {
                ((EnvironmentAware) instance).setEnvironment(this.environment);
            }
            if (instance instanceof ResourceLoaderAware) {
                ((ResourceLoaderAware) instance).setResourceLoader(this.resourceLoader);
            }
        }
    }

    @Override
    public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
        Assert.isInstanceOf(ConfigurableListableBeanFactory.class, beanFactory);
        this.beanFactory = (ConfigurableListableBeanFactory) beanFactory;
    }

    protected final ConfigurableListableBeanFactory getBeanFactory() {
        return this.beanFactory;
    }

    @Override
    public void setBeanClassLoader(ClassLoader classLoader) {
        this.beanClassLoader = classLoader;
    }

    protected ClassLoader getBeanClassLoader() {
        return this.beanClassLoader;
    }

    @Override
    public void setEnvironment(Environment environment) {
        this.environment = environment;
    }

    protected final Environment getEnvironment() {
        return this.environment;
    }

    @Override
    public void setResourceLoader(ResourceLoader resourceLoader) {
        this.resourceLoader = resourceLoader;
    }

    protected final ResourceLoader getResourceLoader() {
        return this.resourceLoader;
    }

    @Override
    public int getOrder() {
        return Ordered.LOWEST_PRECEDENCE - 1;
    }

}

　　说一下AutoConfigurationImportSelector

　　有了自动配置类，免去了我们手动编写配置注入功能组件等的工作；以前我们需要自己配置的东西，自动配置类都帮我们；

　　J2EE的整体整合解决方案和自动配置都在spring-boot-autoconfigure-1.5.9.RELEASE.jar；

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