深入浅析SpringBoot中的自动装配

一、自动装配过程分析
二、何时进行自动装配
三、总结

SpringBoot的自动装配是拆箱即用的基础，也是微服务化的前提。这次主要的议题是，来看看它是怎么样实现的，我们透过源代码来把握自动装配的来龙去脉。

一、自动装配过程分析

1.1、关于@SpringBootApplication

　　我们在编写SpringBoot项目时，@SpringBootApplication是最常见的注解了，我们可以看一下源代码：

				?

									/*

									 * 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 {};

									}

　　这里面包含了@SpringBootConfiguration，@EnableAutoConfiguration，@ComponentScan，此处@ComponentScan由于没有指定扫描包，因此它默认扫描的是与该类同级的类或者同级包下的所有类，另外@SpringBootConfiguration，通过源码得知它是一个@Configuration:

				?

									/*

									 * Copyright 2012-2016 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.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 {

									}

　　由此我们可以推断出@SpringBootApplication等同于@Configuration @ComponentScan @EnableAutoConfiguration

1.2、@EnableAutoConfiguration

　　一旦加上此注解，那么将会开启自动装配功能，简单点讲，Spring会试图在你的classpath下找到所有配置的Bean然后进行装配。当然装配Bean时，会根据若干个(Conditional)定制规则来进行初始化。我们看一下它的源码：

				?

									/*

									 * 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 {};

									}

　　虽然根据文档注释的说明它指点我们去看EnableAutoConfigurationImportSelector。但是该类在SpringBoot1.5.X版本已经过时了，因此我们看一下它的父类AutoConfigurationImportSelector：

				?

									/*

									 * 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;

									 }

									}

　　首先该类实现了DeferredImportSelector接口，这个接口继承了ImportSelector:

				?

									/*

									 * 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);

									}

　　该接口主要是为了导入@Configuration的配置项，而DeferredImportSelector是延期导入，当所有的@Configuration都处理过后才会执行。

　　回过头来我们看一下AutoConfigurationImportSelector的selectImport方法：

				?

									@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);

									 }

									 }

　　该方法刚开始会先判断是否进行自动装配，而后会从META-INF/spring-autoconfigure-metadata.properties读取元数据与元数据的相关属性，紧接着会调用getCandidateConfigurations方法：

				?

									/**

									 * 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;

									 }

　　在这里又遇到我们的老熟人了--SpringFactoryiesLoader, 它会读取META-INF/spring.factories下的EnableAutoConfiguration的配置，紧接着在进行排除与过滤，进而得到需要装配的类。最后让所有配置在META-INF/spring.factories下的AutoConfigurationImportListener执行AutoConfigurationImportEvent事件，代码如下：

				?

									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);

									 }

二、何时进行自动装配

　　在前面的环节里只是最终要确定哪些类需要被装配，在SpringBoot时何时处理这些自动装配的类呢？下面我们简要的分析一下：

2.1、AbstractApplicationContext的refresh方法：

　　这个方法老生常谈了其中请大家关注一下这个方法：

				?

									// Invoke factory processors registered as beans in the context.

									 invokeBeanFactoryPostProcessors(beanFactory);

　　在这里是处理BeanFactoryPostProcessor的，那么我们在来看一下这个接口BeanDefinitionRegistryPostProcessor:

				?

									/*

									 * Copyright 2002-2010 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.beans.factory.support;

									import org.springframework.beans.BeansException;

									import org.springframework.beans.factory.config.BeanFactoryPostProcessor;

									/**

									 * Extension to the standard {@link BeanFactoryPostProcessor} SPI, allowing for

									 * the registration of further bean definitions <i>before</i> regular

									 * BeanFactoryPostProcessor detection kicks in. In particular,

									 * BeanDefinitionRegistryPostProcessor may register further bean definitions

									 * which in turn define BeanFactoryPostProcessor instances.

									 *

									 * @author Juergen Hoeller

									 * @since 3.0.1

									 * @see org.springframework.context.annotation.ConfigurationClassPostProcessor

									 */

									public interface BeanDefinitionRegistryPostProcessor extends BeanFactoryPostProcessor {

									 /**

									 * Modify the application context's internal bean definition registry after its

									 * standard initialization. All regular bean definitions will have been loaded,

									 * but no beans will have been instantiated yet. This allows for adding further

									 * bean definitions before the next post-processing phase kicks in.

									 * @param registry the bean definition registry used by the application context

									 * @throws org.springframework.beans.BeansException in case of errors

									 */

									 void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException;

									}

　　该接口继承了BeanFactoryPostProcessor。

2.2、ConfigurationClassPostProcessor 类

　　该类主要处理@Configuration注解的，它实现了BeanDefinitionRegistryPostProcessor, 那么也间接实现了BeanFactoryPostProcessor，关键代码如下：

				?

									@Override

									 public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {

									 int factoryId = System.identityHashCode(beanFactory);

									 if (this.factoriesPostProcessed.contains(factoryId)) {

									  throw new IllegalStateException(

									   "postProcessBeanFactory already called on this post-processor against " + beanFactory);

									 }

									 this.factoriesPostProcessed.add(factoryId);

									 if (!this.registriesPostProcessed.contains(factoryId)) {

									  // BeanDefinitionRegistryPostProcessor hook apparently not supported...

									  // Simply call processConfigurationClasses lazily at this point then.

									  processConfigBeanDefinitions((BeanDefinitionRegistry) beanFactory);

									 }

									 enhanceConfigurationClasses(beanFactory);

									 beanFactory.addBeanPostProcessor(new ImportAwareBeanPostProcessor(beanFactory));

									 }

									/**

									 * Build and validate a configuration model based on the registry of

									 * {@link Configuration} classes.

									 */

									 public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) {

									 //.....省略部分代码

									 // Parse each @Configuration class

									 ConfigurationClassParser parser = new ConfigurationClassParser(

									  this.metadataReaderFactory, this.problemReporter, this.environment,

									  this.resourceLoader, this.componentScanBeanNameGenerator, registry);

									 Set<BeanDefinitionHolder> candidates = new LinkedHashSet<BeanDefinitionHolder>(configCandidates);

									 Set<ConfigurationClass> alreadyParsed = new HashSet<ConfigurationClass>(configCandidates.size());

									 do {

									  parser.parse(candidates);

									  parser.validate();

									  Set<ConfigurationClass> configClasses = new LinkedHashSet<ConfigurationClass>(parser.getConfigurationClasses());

									  configClasses.removeAll(alreadyParsed);

									  // Read the model and create bean definitions based on its content

									  if (this.reader == null) {

									  this.reader = new ConfigurationClassBeanDefinitionReader(

									   registry, this.sourceExtractor, this.resourceLoader, this.environment,

									   this.importBeanNameGenerator, parser.getImportRegistry());

									  }

									  this.reader.loadBeanDefinitions(configClasses);

									  alreadyParsed.addAll(configClasses);

									  candidates.clear();

									  if (registry.getBeanDefinitionCount() > candidateNames.length) {

									  String[] newCandidateNames = registry.getBeanDefinitionNames();

									  Set<String> oldCandidateNames = new HashSet<String>(Arrays.asList(candidateNames));

									  Set<String> alreadyParsedClasses = new HashSet<String>();

									  for (ConfigurationClass configurationClass : alreadyParsed) {

									   alreadyParsedClasses.add(configurationClass.getMetadata().getClassName());

									  }

									  for (String candidateName : newCandidateNames) {

									   if (!oldCandidateNames.contains(candidateName)) {

									   BeanDefinition bd = registry.getBeanDefinition(candidateName);

									   if (ConfigurationClassUtils.checkConfigurationClassCandidate(bd, this.metadataReaderFactory) &&

									    !alreadyParsedClasses.contains(bd.getBeanClassName())) {

									    candidates.add(new BeanDefinitionHolder(bd, candidateName));

									   }

									   }

									  }

									  candidateNames = newCandidateNames;

									  }

									 }

									 while (!candidates.isEmpty());

									　　　　// ....省略部分代码

									 }

其实这里注释已经很清楚了，我们可以清楚的看到解析每一个@ConfigurationClass的关键类是：ConfigurationClassParser，那么我们继续看一看这个类的parse方法：

				?

									public void parse(Set<BeanDefinitionHolder> configCandidates) {

									 this.deferredImportSelectors = new LinkedList<DeferredImportSelectorHolder>();

									 for (BeanDefinitionHolder holder : configCandidates) {

									  BeanDefinition bd = holder.getBeanDefinition();

									  try {

									  if (bd instanceof AnnotatedBeanDefinition) {

									   parse(((AnnotatedBeanDefinition) bd).getMetadata(), holder.getBeanName());

									  }

									  else if (bd instanceof AbstractBeanDefinition && ((AbstractBeanDefinition) bd).hasBeanClass()) {

									   parse(((AbstractBeanDefinition) bd).getBeanClass(), holder.getBeanName());

									  }

									  else {

									   parse(bd.getBeanClassName(), holder.getBeanName());

									  }

									  }

									  catch (BeanDefinitionStoreException ex) {

									  throw ex;

									  }

									  catch (Throwable ex) {

									  throw new BeanDefinitionStoreException(

									   "Failed to parse configuration class [" + bd.getBeanClassName() + "]", ex);

									  }

									 }

									 processDeferredImportSelectors();

									 }

　　在这里大家留意一下最后一句processDeferredImportSelectors方法，在这里将会对DeferredImportSelector进行处理，这样我们就和AutoConfigurationSelectImporter结合到一起了：

				?

									private void processDeferredImportSelectors() {

									 List<DeferredImportSelectorHolder> deferredImports = this.deferredImportSelectors;

									 this.deferredImportSelectors = null;

									 Collections.sort(deferredImports, DEFERRED_IMPORT_COMPARATOR);

									 for (DeferredImportSelectorHolder deferredImport : deferredImports) {

									  ConfigurationClass configClass = deferredImport.getConfigurationClass();

									  try {

									  String[] imports = deferredImport.getImportSelector().selectImports(configClass.getMetadata());

									  processImports(configClass, asSourceClass(configClass), asSourceClasses(imports), false);

									  }

									  catch (BeanDefinitionStoreException ex) {

									  throw ex;

									  }

									  catch (Throwable ex) {

									  throw new BeanDefinitionStoreException(

									   "Failed to process import candidates for configuration class [" +

									   configClass.getMetadata().getClassName() + "]", ex);

									  }

									 }

									 }

请大家关注这句代码：String[] imports = deferredImport.getImportSelector().selectImports(configClass.getMetadata());在这里deferredImport的类型为DeferredImportSelectorHolder：

				?

									private static class DeferredImportSelectorHolder {

									 private final ConfigurationClass configurationClass;

									 private final DeferredImportSelector importSelector;

									 public DeferredImportSelectorHolder(ConfigurationClass configClass, DeferredImportSelector selector) {

									  this.configurationClass = configClass;

									  this.importSelector = selector;

									 }

									 public ConfigurationClass getConfigurationClass() {

									  return this.configurationClass;

									 }

									 public DeferredImportSelector getImportSelector() {

									  return this.importSelector;

									 }

									 }

　　在这个内部类里持有了一个DeferredImportSelector的引用，至此将会执行自动装配的所有操作

三、总结

　　1）自动装配还是利用了SpringFactoriesLoader来加载META-INF/spring.factoires文件里所有配置的EnableAutoConfgruation，它会经过exclude和filter等操作，最终确定要装配的类

　　2) 处理@Configuration的核心还是ConfigurationClassPostProcessor，这个类实现了BeanFactoryPostProcessor, 因此当AbstractApplicationContext执行refresh方法里的invokeBeanFactoryPostProcessors(beanFactory)方法时会执行自动装配

以上所述是小编给大家介绍的SpringBoot中的自动装配，希望对大家有所帮助，如果大家有任何疑问欢迎给我留言，小编会及时回复大家的！

原文链接：http://www.cnblogs.com/niechen/p/9027804.html