1.简单的示例：
@Configuration
@EnableConfigurationProperties({DemoProperties.class})
public class DemoConfiguration { @Bean
public Book getBook(){
return new Book();
}
}
Configuration
@Autowired Book book;
@Test
public void testBook(){
System.out.println(book.toString());
}
单元测试
结果打印出book对象，证明Book已经被注入到Spring 容器中了。
2.@Configuration配置的bean是如何注入到Spring容器中的呢？
首先先来简单介绍下通过BeanDefinitionRegistry注入bean
@Autowired
public void registBeanDefinition(BeanFactory factory){
if(factory instanceof BeanDefinitionRegistry) {
BeanDefinitionRegistry registry = (BeanDefinitionRegistry)factory;
BeanDefinition beanDefinition = BeanDefinitionBuilder.rootBeanDefinition(Book.class).getBeanDefinition();
registry.registerBeanDefinition("mybook", beanDefinition);
}
}
@Autowired @Qualifier("mybook") Book book2;
@Test
public void testBook2(){
System.out.println(book2);
}
单元测试
结果同样打印出book对象，这里，笔者将beanFactory强转为BenDefinitionRegistry,因为笔者的Demo中使用的是默认BeanFactory,----DefaultListableBeanFactory,他实现了BeanDefinitionRegistry接口。
3.入口，下图为ApplicaitonContext refresh方法的简化，只保留了BeandefinitionRegistry注册bean部分功能。
然，似乎并没什么用？此处会调用BeanDefinitionRegistryPostProcessor的postProcessBeanDefinitionRegistry方法。要解决的一个问题是，BeanDefinitionRegistryPostProcessor类型的bean是如何注入的。以SpringBoot初始化为例。
注意到，ApplicationContext的构造方法：
public AnnotationConfigEmbeddedWebApplicationContext() {
this.reader = new AnnotatedBeanDefinitionReader(this);
this.scanner = new ClassPathBeanDefinitionScanner(this);
}
ApplicationContext构造
public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry) {
this(registry, getOrCreateEnvironment(registry));
}
public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry, Environment environment) {
Assert.notNull(registry, "BeanDefinitionRegistry must not be null");
Assert.notNull(environment, "Environment must not be null");
this.registry = registry;
this.conditionEvaluator = new ConditionEvaluator(registry, environment, null);
AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);
}
public static Set<BeanDefinitionHolder> registerAnnotationConfigProcessors(
BeanDefinitionRegistry registry, Object source) { DefaultListableBeanFactory beanFactory = unwrapDefaultListableBeanFactory(registry);
if (beanFactory != null) {
if (!(beanFactory.getDependencyComparator() instanceof AnnotationAwareOrderComparator)) {
beanFactory.setDependencyComparator(AnnotationAwareOrderComparator.INSTANCE);
}
if (!(beanFactory.getAutowireCandidateResolver() instanceof ContextAnnotationAutowireCandidateResolver)) {
beanFactory.setAutowireCandidateResolver(new ContextAnnotationAutowireCandidateResolver());
}
} Set<BeanDefinitionHolder> beanDefs = new LinkedHashSet<BeanDefinitionHolder>(4);
//注解@Configuration处理
if (!registry.containsBeanDefinition(CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(ConfigurationClassPostProcessor.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME));
} .......//省略部分代码 return beanDefs;
}
注意到对@Configuration的处理为ConfigurationClassPostProcessor。
注意到ConfigurationClassPostProcessor实现了BeanDefinitionRegistryPostProcessor接口，显然关键方法为postProcessBeanDefinitionRegistry。ConfigurationClassPostProcessor的postProcessBeanDefinitionRegistry会调用ConfirgurationClassParser的parse方法。会依次解析注解，我们一步一步查看对各个注解的解析。
（1）@PropertySources和@PropertySource
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface PropertySources { PropertySource[] value(); }
PropertySources定义
最终都是处理@PropertySource,@PropertySources仅仅只是包含多个@PropertySource,@PropertySource注解的主要功能是引入配置文件，将配置的属性键值对与环境变量中的配置合并。其中最关键的类为MutablePropertySources
public class MutablePropertySources implements PropertySources {
private final Log logger;
private final List<PropertySource<?>> propertySourceList = new CopyOnWriteArrayList<PropertySource<?>>();
......
}
显然MutablePropertySources中包含有一个PropertySource列表。MutablePropertySources仅仅是封装了迭代器功能。可以理解成PropertySources是PropertySource的集合，增加了常用的集合操作。
（2）@ComponentScan
定义自动扫描的包。简化的序列图如下：
其最关键的方法为doScan方法，会注册BeanDefinition到容器中。
protected Set<BeanDefinitionHolder> doScan(String... basePackages) {
Assert.notEmpty(basePackages, "At least one base package must be specified");
Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<BeanDefinitionHolder>();
for (String basePackage : basePackages) {
Set<BeanDefinition> candidates = findCandidateComponents(basePackage);
for (BeanDefinition candidate : candidates) {
ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);
candidate.setScope(scopeMetadata.getScopeName());
String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);
if (candidate instanceof AbstractBeanDefinition) {
postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName);
}
if (candidate instanceof AnnotatedBeanDefinition) {
AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);
}
if (checkCandidate(beanName, candidate)) {
BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);
definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
beanDefinitions.add(definitionHolder);
registerBeanDefinition(definitionHolder, this.registry);
}
}
}
return beanDefinitions;
}
doScan方法
registerBeanDefinition(definitionHolder, this.registry);能说明一切。
（3）@Import
@Import注解可以配置需要引入的class(假设配置为A,可以是数组),有三种方式。其流程图如下：
如果A为ImportSelector的子类，调用selectImports()方法，返回class类名数组，循环解析每一个import的类，如果A为BeanDefinitionRegistrar则直接调用registerBeanDefinition直接注入bean到容器中。如果A为普通的类（非前面提到的两种类型），则将A当做@Configuration配置的类，重新解析Configuration.
（4）@ImportSource
主要功能为引入资源文件。
（5）@Bean，比较简单，童FactoryMethod一样
// Process individual @Bean methods
Set<MethodMetadata> beanMethods = sourceClass.getMetadata().getAnnotatedMethods(Bean.class.getName());
for (MethodMetadata methodMetadata : beanMethods) {
configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));
} // Process default methods on interfaces
for (SourceClass ifc : sourceClass.getInterfaces()) {
beanMethods = ifc.getMetadata().getAnnotatedMethods(Bean.class.getName());
for (MethodMetadata methodMetadata : beanMethods) {
if (!methodMetadata.isAbstract()) {
// A default method or other concrete method on a Java 8+ interface...
configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));
}
}
}
@Bean解析
最后真实加载beanDefinition是loadBeanDefinitionsForConfigurationClass方法：
private void loadBeanDefinitionsForConfigurationClass(ConfigurationClass configClass,
TrackedConditionEvaluator trackedConditionEvaluator) { if (trackedConditionEvaluator.shouldSkip(configClass)) {
String beanName = configClass.getBeanName();
if (StringUtils.hasLength(beanName) && this.registry.containsBeanDefinition(beanName)) {
this.registry.removeBeanDefinition(beanName);
}
this.importRegistry.removeImportingClassFor(configClass.getMetadata().getClassName());
return;
} if (configClass.isImported()) {
registerBeanDefinitionForImportedConfigurationClass(configClass);
}
for (BeanMethod beanMethod : configClass.getBeanMethods()) {
loadBeanDefinitionsForBeanMethod(beanMethod);
}
loadBeanDefinitionsFromImportedResources(configClass.getImportedResources());
loadBeanDefinitionsFromRegistrars(configClass.getImportBeanDefinitionRegistrars());
}