簡明易理解的@SpringBootApplication註解原始碼分析
@SpringBootApplication
public class MicroServiceApplication {
public static void main(String[] args) {
SpringApplication.run(MicroServiceApplication.class, args);
}
}
我們進入@SpringBootApplication註解，發現它等價於三個註解：@SpringBootConfiguration @EnableAutoConfiguration @ComponentScan
@SpringBootConfiguration @EnableAutoConfiguration @ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class), @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) }) public @interface SpringBootApplication { ... }
1） @SpringBootConfiguration 就相當於 @Configuration
@Configuration
public @interface SpringBootConfiguration {
}
2） @EnabelAutoConfiguration 相當於將這兩個類的例項加入到容器中AutoConfigurationImportSelector.class AutoConfigurationPackages.Registrar.class
@AutoConfigurationPackage @Import(AutoConfigurationImportSelector.class) public @interface EnableAutoConfiguration { ... }
@Import(AutoConfigurationPackages.Registrar.class)
public @interface AutoConfigurationPackage {
}
-
AutoConfigurationImportSelector.class的作用是，注入spring.factories檔案中EnableAutoConfiguration對應的類的例項，當然要經過spring.factories檔案中AutoConfigurationImportFilter對應的過濾器（OnBeanCondition、OnClassCondition、OnWebApplicationCondition等等）的過濾。還要排除掉@EnableAutoConfiguration中的exclude和excludeName具體見
ConfigurationClassParser的getImports方法，其中呼叫了AutoConfigurationImportSelector的process方法和selectImports方法。public Iterable<group.entry> getImports() { for (DeferredImportSelectorHolder deferredImport : this.deferredImports) { this.group.process(deferredImport.getConfigurationClass().getMetadata(), deferredImport.getImportSelector()); } return this.group.selectImports(); }AutoConfigurationImportSelector實現了DeferredImportSelector，所以它是解析@Configuration的最後一步。DeferredImportSelector可以和@Order搭配使用。AutoConfigurationImportSelector的意義在於引入其他包時，可以直接注入其他包的@Configuration，當然需要在其他包的resources資料夾下，新建META-INF目錄，在META-INF目錄下新建spring.factories檔案，加入org.springframework.boot.autoconfigure.EnableAutoConfiguration = @Configuration標註的類的路徑 -
AutoConfigurationPackages.Registrar.class的作用是，注入一個名稱為AutoConfigurationPackages的BasePackages.class例項。這個例項的作用在於儲存自動掃描的包路徑，供以後使用（比如JPA 的entity掃描）public static void register(BeanDefinitionRegistry registry, String... packageNames) { if (registry.containsBeanDefinition(BEAN)) { BeanDefinition beanDefinition = registry.getBeanDefinition(BEAN); ConstructorArgumentValues constructorArguments = beanDefinition .getConstructorArgumentValues(); constructorArguments.addIndexedArgumentValue(0, addBasePackages(constructorArguments, packageNames)); } else { GenericBeanDefinition beanDefinition = new GenericBeanDefinition(); beanDefinition.setBeanClass(BasePackages.class); beanDefinition.getConstructorArgumentValues().addIndexedArgumentValue(0, packageNames); beanDefinition.setRole(BeanDefinition.ROLE_INFRASTRUCTURE); registry.registerBeanDefinition(BEAN, beanDefinition); } } private static String[] addBasePackages( ConstructorArgumentValues constructorArguments, String[] packageNames) { String[] existing = (String[]) constructorArguments .getIndexedArgumentValue(0, String[].class).getValue(); Set<string> merged = new LinkedHashSet<>(); merged.addAll(Arrays.asList(existing)); merged.addAll(Arrays.asList(packageNames)); return StringUtils.toStringArray(merged); }
3） @ComponentScan 當然是將路徑下合適的類載入到容器中
Q：它為什麼要用到TypeExcludeFilter.class 和AutoConfigurationExcludeFilter.class 這兩個過濾器
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = {
@Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
public @interface SpringBootApplication {
...
}
-
這兩個過濾器在
ComponentScanAnnotationParser的parse方法中，被加入public Set<beandefinitionholder> parse(AnnotationAttributes componentScan, final String declaringClass) { //此處加入了三個預設的includeFilter，一個用來篩選@Componment標記的類，一個用來篩選javax.annotation.ManagedBean標記的類，一個用來篩選JSR-330中javax.inject.Named標記的類（如果引入了JSR-330依賴注入標準的話，即引入javax.inject包） ClassPathBeanDefinitionScanner scanner = new ClassPathBeanDefinitionScanner(this.registry, componentScan.getBoolean("useDefaultFilters"), this.environment, this.resourceLoader); ... for (AnnotationAttributes filter : componentScan.getAnnotationArray("excludeFilters")) { for (TypeFilter typeFilter : typeFiltersFor(filter)) { scanner.addExcludeFilter(typeFilter); } } ... scanner.addExcludeFilter(new AbstractTypeHierarchyTraversingFilter(false, false) { @Override protected boolean matchClassName(String className) { return declaringClass.equals(className); } }); return scanner.doScan(StringUtils.toStringArray(basePackages)); }**也是在parse這個方法裡呼叫了 typeFiltersFor方法，對`TypeFilter.class`的實現類進行了例項化**。（也就是說`TypeExcludeFilter.class` `AutoConfigurationExcludeFilter.class` `AbstractTypeHierarchyTraversingFilter.class`都在這裡進行了例項化，但是沒有加入spring的bean池）private List<typefilter> typeFiltersFor(AnnotationAttributes filterAttributes) { List<typefilter> typeFilters = new ArrayList<>(); FilterType filterType = filterAttributes.getEnum("type"); for (Class<!--?--> filterClass : filterAttributes.getClassArray("classes")) { switch (filterType) { case ANNOTATION: Assert.isAssignable(Annotation.class, filterClass, "@ComponentScan ANNOTATION type filter requires an annotation type"); @SuppressWarnings("unchecked") Class<annotation> annotationType = (Class<annotation>) filterClass; typeFilters.add(new AnnotationTypeFilter(annotationType)); break; case ASSIGNABLE_TYPE: typeFilters.add(new AssignableTypeFilter(filterClass)); break; case CUSTOM: Assert.isAssignable(TypeFilter.class, filterClass, "@ComponentScan CUSTOM type filter requires a TypeFilter implementation"); TypeFilter filter = BeanUtils.instantiateClass(filterClass, TypeFilter.class); ParserStrategyUtils.invokeAwareMethods( filter, this.environment, this.resourceLoader, this.registry); typeFilters.add(filter); break; default: throw new IllegalArgumentException("Filter type not supported with Class value: " + filterType); } } for (String expression : filterAttributes.getStringArray("pattern")) { switch (filterType) { case ASPECTJ: typeFilters.add(new AspectJTypeFilter(expression, this.resourceLoader.getClassLoader())); break; case REGEX: typeFilters.add(new RegexPatternTypeFilter(Pattern.compile(expression))); break; default: throw new IllegalArgumentException("Filter type not supported with String pattern: " + filterType); } } return typeFilters; }ComponentScanAnnotationParser的parse方法中，scanner最後為什麼又加了一個AbstractTypeHierarchyTraversingFilter呢？我們看一下它的match方法，發現是過濾掉啟動類，不讓它作為@configuration標記的候選類，避免再一次解析啟動類上的各種註解（因為它的兩個引數considerInherited和considerInterfaces在scanner.addExcludeFilter這條語句中，設定成了false，導致下面的判斷語句不生效）。public boolean match(MetadataReader metadataReader, MetadataReaderFactory metadataReaderFactory) throws IOException { ... ClassMetadata metadata = metadataReader.getClassMetadata(); if (matchClassName(metadata.getClassName())) { return true; } if (this.considerInherited) { ... } if (this.considerInterfaces) { ... } return false; }注：啟動類本身還是會注入到spring的bean池中的，具體見
SpringApplication的load方法 -
ExcludeFilter在
ClassPathScanningCandidateComponentProvider的isCandidateComponent方法中被使用。protected boolean isCandidateComponent(MetadataReader metadataReader) throws IOException { for (TypeFilter tf : this.excludeFilters) { if (tf.match(metadataReader, getMetadataReaderFactory())) { return false; } } for (TypeFilter tf : this.includeFilters) { if (tf.match(metadataReader, getMetadataReaderFactory())) { return isConditionMatch(metadataReader); } } return false; } -
AutoConfigurationExcludeFilter的作用是過濾掉會自動配置的配置類，避免重複@Override public boolean match(MetadataReader metadataReader, MetadataReaderFactory metadataReaderFactory) throws IOException { //如果這個類被@Configuration標註，且屬於自動載入的配置，那麼過濾它，避免重複 return isConfiguration(metadataReader) && isAutoConfiguration(metadataReader); } private boolean isConfiguration(MetadataReader metadataReader) { return metadataReader.getAnnotationMetadata() .isAnnotated(Configuration.class.getName()); } private boolean isAutoConfiguration(MetadataReader metadataReader) { return getAutoConfigurations() .contains(metadataReader.getClassMetadata().getClassName()); } protected List<string> getAutoConfigurations() { if (this.autoConfigurations == null) { /** 從META-INF/spring.factories檔案中，找出EnableAutoConfiguration.class 多個jar包中，都存在spring.factories檔案 其中包含EnableAutoConfiguration.class的spring.factories檔案，位於spring-boot-autoconfigure **/ this.autoConfigurations = SpringFactoriesLoader.loadFactoryNames( EnableAutoConfiguration.class, this.beanClassLoader); } return this.autoConfigurations; } -
TypeExcludeFilter的作用是載入spring bean池中所有針對TypeExcludeFilter的擴充套件，並迴圈遍歷這些擴充套件類呼叫其match方法public boolean match(MetadataReader metadataReader, MetadataReaderFactory metadataReaderFactory) throws IOException { if (this.beanFactory instanceof ListableBeanFactory && getClass() == TypeExcludeFilter.class) { //載入spring bean池中所有針對TypeExcludeFilter的拓展 Collection<typeexcludefilter> delegates = ((ListableBeanFactory) this.beanFactory) .getBeansOfType(TypeExcludeFilter.class).values(); // 迴圈遍歷，呼叫其match方法 for (TypeExcludeFilter delegate : delegates) { if (delegate.match(metadataReader, metadataReaderFactory)) { return true; } } } return false; }
</typeexcludefilter></string></annotation></annotation></typefilter></typefilter></beandefinitionholder></string>