spring 掃描BeanDefinition詳解以及TypeFilter擴充套件點
摘要：
前言
本篇主要講解
在指定的基礎包中執行掃描註冊BeanDefinition: doscan(String... basePackages)
方法以及掃描過濾，匹配。
解析
主要方法：ClassPat...
前言
本篇主要講解 在指定的基礎包中執行掃描註冊BeanDefinition: doscan(String... basePackages) 方法以及掃描過濾，匹配。
解析
主要方法：ClassPathBeanDefinitionScanner#doScan(String... basePackages)在指定的基礎包中執行掃描，返回已註冊的bean定義。
protected Set<BeanDefinitionHolder> doScan(String... basePackages) {
Assert.notEmpty(basePackages, "At least one base package must be specified");
Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<>();
for (String basePackage : basePackages) {
//掃描候選元件的類路徑
Set<BeanDefinition> candidates = findCandidateComponents(basePackage);
for (BeanDefinition candidate : candidates) {
ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);
candidate.setScope(scopeMetadata.getScopeName());
//生成bean名稱
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);
//註冊bean定義
registerBeanDefinition(definitionHolder, this.registry);
}
}
}
return beanDefinitions;
}複製程式碼
1、ClassPathScanningCandidateComponentProvider#findCandidateComponents(basePackage)， 掃描候選元件的類路徑
public Set<BeanDefinition> findCandidateComponents(String basePackage) {
if (this.componentsIndex != null && indexSupportsIncludeFilters()) {
//根據索引獲得bean定義，配合spring-context-indexer使用,有興趣得自己去了解一下，這裡不做具體得解析
return addCandidateComponentsFromIndex(this.componentsIndex, basePackage);
}
else {
//掃描獲得bean定義
return scanCandidateComponents(basePackage);
}
}複製程式碼
2、ClassPathScanningCandidateComponentProvider#scanCandidateComponents(String basePackage)
private Set<BeanDefinition> scanCandidateComponents(String basePackage) {
Set<BeanDefinition> candidates = new LinkedHashSet<>();
try {
//classpath*:com/zxj/***/service/**/*.classant path模式串
String packageSearchPath = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX +
resolveBasePackage(basePackage) + '/' + this.resourcePattern;
//用ant path獲取到檔案內容，檔案和path(class檔案)
Resource[] resources = getResourcePatternResolver().getResources(packageSearchPath);
boolean traceEnabled = logger.isTraceEnabled();
boolean debugEnabled = logger.isDebugEnabled();
for (Resource resource : resources) {
if (traceEnabled) {
logger.trace("Scanning " + resource);
}
if (resource.isReadable()) {
try {
//讀取源資訊
MetadataReader metadataReader = getMetadataReaderFactory().getMetadataReader(resource);
//過濾匹配排除excludeFilters排除過濾器(可以沒有),包含includeFilter中的包含過濾器（至少包含一個）。
if (isCandidateComponent(metadataReader)) {
ScannedGenericBeanDefinition sbd = new ScannedGenericBeanDefinition(metadataReader);
sbd.setResource(resource);
sbd.setSource(resource);
//判斷是否是合格的bean定義
if (isCandidateComponent(sbd)) {
if (debugEnabled) {
logger.debug("Identified candidate component class: " + resource);
}
candidates.add(sbd);
} else {
if (debugEnabled) {
logger.debug("Ignored because not a concrete top-level class: " + resource);
}
}
} else {
if (traceEnabled) {
logger.trace("Ignored because not matching any filter: " + resource);
}
}
} catch (Throwable ex) {
throw new BeanDefinitionStoreException(
"Failed to read candidate component class: " + resource, ex);
}
} else {
if (traceEnabled) {
logger.trace("Ignored because not readable: " + resource);
}
}
}
} catch (IOException ex) {
throw new BeanDefinitionStoreException("I/O failure during classpath scanning", ex);
}
return candidates;
}
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3、ClassPathScanningCandidateComponentProvider#isCandidateComponent(MetadataReader metadataReader)
protected boolean isCandidateComponent(MetadataReader metadataReader) throws IOException {
//排除的
for (TypeFilter tf : this.excludeFilters) {
if (tf.match(metadataReader, getMetadataReaderFactory())) {
return false;
}
}
//包含的
for (TypeFilter tf : this.includeFilters) {
if (tf.match(metadataReader, getMetadataReaderFactory())) {
return isConditionMatch(metadataReader);
}
}
return false;
}
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excludeFilters和includeFilters有那幾種定義呢？
|
過濾器型別 |
示例表達 |
描述 |
|---|---|---|
|
annotation (default) |
|
要在目標元件中的型別級別出現的註釋。 |
|
assignable |
|
目標元件可分配給（擴充套件或實現）的類（或介面）。 |
|
aspectj |
|
要由目標元件匹配的AspectJ型別表示式。 |
|
regex |
|
要由目標元件類名匹配的正則表示式。 |
|
custom |
|
org.springframework.core.type .TypeFilter
介面的自定義實現 。 |
例如：
@Configuration
@ComponentScan(basePackages = "org.example",
includeFilters = @Filter(type = FilterType.REGEX, pattern = ".*Stub.*Repository"),
excludeFilters = @Filter(Repository.class))
public class AppConfig {
...
}複製程式碼
預設註冊的ClassPathScanningCandidateComponentProvider#registerDefaultFilters包含過濾器AnnotationTypeFilter(Component.class)。 作用：@Component及其子類都會匹配到。
@Component子類：@ Repository @ Controller @service
protected void registerDefaultFilters() {
this.includeFilters.add(new AnnotationTypeFilter(Component.class));
ClassLoader cl = ClassPathScanningCandidateComponentProvider.class.getClassLoader();
try {
this.includeFilters.add(new AnnotationTypeFilter(
((Class<? extends Annotation>) ClassUtils.forName("javax.annotation.ManagedBean", cl)), false));
logger.trace("JSR-250 'javax.annotation.ManagedBean' found and supported for component scanning");
} catch (ClassNotFoundException ex) {
// JSR-250 1.1 API (as included in Java EE 6) not available - simply skip.
}
try {
this.includeFilters.add(new AnnotationTypeFilter(
((Class<? extends Annotation>) ClassUtils.forName("javax.inject.Named", cl)), false));
logger.trace("JSR-330 'javax.inject.Named' annotation found and supported for component scanning");
} catch (ClassNotFoundException ex) {
// JSR-330 API not available - simply skip.
}
}複製程式碼
這裡就體現了一個擴充套件點，例如我自己定義一個@myservice註解，在匹配的時候就會匹配到，就能夠被掃描進bean定義容器。
@Target({ ElementType.TYPE })
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
public @interface MyService {
String value() default "";
}
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4、具體的匹配方法：
1、AbstractTypeHierarchyTraversingFilter#match(MetadataReader metadataReader, MetadataReaderFactory metadataReaderFactory)
//
@Override
public boolean match(MetadataReader metadataReader, MetadataReaderFactory metadataReaderFactory)
throws IOException {
// This method optimizes avoiding unnecessary creation of ClassReaders
// as well as visiting over those readers.
//匹配自己
if (matchSelf(metadataReader)) {
return true;
}
ClassMetadata metadata = metadataReader.getClassMetadata();
if (matchClassName(metadata.getClassName())) {
return true;
}
if (this.considerInherited) {
String superClassName = metadata.getSuperClassName();
if (superClassName != null) {
// Optimization to avoid creating ClassReader for super class.
Boolean superClassMatch = matchSuperClass(superClassName);
if (superClassMatch != null) {
if (superClassMatch.booleanValue()) {
return true;
}
}
else {
// Need to read super class to determine a match...
try {
if (match(metadata.getSuperClassName(), metadataReaderFactory)) {
return true;
}
}
catch (IOException ex) {
logger.debug("Could not read super class [" + metadata.getSuperClassName() +
"] of type-filtered class [" + metadata.getClassName() + "]");
}
}
}
}}
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2、AnnotationTypeFilter#matchSelf(MetadataReader metadataReader)
@Override
//父類定義的鉤子方法，子類實現。 匹配註解
protected boolean matchSelf(MetadataReader metadataReader) {
AnnotationMetadata metadata = metadataReader.getAnnotationMetadata();
//metadata.hasAnnotation(this.annotationType.getName()) 例如如果當前類上的註解為@Service,那麼元註解的annotationSet屬性則為Service 自己
return metadata.hasAnnotation(this.annotationType.getName()) ||
//metadata.hasMetaAnnotation(this.annotationType.getName())例如如果當前類上的註解為@Service，那麼元註解的metaAnotationMap則有@Service和@Component,自己和父類
(this.considerMetaAnnotations && metadata.hasMetaAnnotation(this.annotationType.getName()));
}複製程式碼
裡面的擴充套件還有：org.springframework.core.type .TypeFilter 介面的自定義實現，去匹配註解，或者其他，匹配完成後註冊bean定義。例如：
public class MyTypeFilter implements TypeFilter {
@Override
public boolean match(MetadataReader metadataReader, MetadataReaderFactory metadataReaderFactory)
throws IOException {
// 使用metadataReader中的類資訊、註解資訊來進行你的過濾判斷邏輯
return metadataReader.getClassMetadata().getClassName().equals(Abean.class.getName());
}
}
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