Spring原始碼深度解析(郝佳)-學習-原始碼解析-基於註解注入（二）
在Spring原始碼深度解析(郝佳)-學習-原始碼解析-基於註解bean解析(一)部落格中，己經對有註解的類進行了解析，得到了BeanDefinition，但是我們看到屬性並沒有封裝到BeanDefinition（關於BeanDefinition的定義，這裡不做過多的解釋了，就是定義了Bean的屬性，比如單例，多例，依賴，工廠方法，是否使用代理，等，而Bean的建立，是基於Bean的定義來的）中，而Bean建立的時候，是如何注入的呢？今天，我們帶著這個問題，繼續來跟蹤基於註解的屬性是如何注入。
先上示例。
Car.java
@Component
@Data
public class Car {
private String color = "red";
}
Dog.java
@Component
public class Dog {
}
MyRequestAnnotation.java
@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Service
public @interface MyRequestAnnotation {
String value() default "";
}
MyTestAnnotation.java
@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
@Mapping
@MyRequestAnnotation
public @interface MyTestAnnotation {
String name() default "";
@AliasFor("path")
String[] value() default {};
RequestMethod[] method() default {};
}
User.java
@Service("xxxx")
@MyTestAnnotation("/user/info")
public class User {
@Autowired
private Car car;
@Autowired
private Dog dog;
public void drive(){
System.out.println(car);
}
}
spring35_resource_inject_1.xml
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:p="http://www.springframework.org/schema/p" xmlns:oxm="http://www.springframework.org/schema/oxm"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/oxm http://www.springframework.org/schema/oxm/spring-oxm.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">
<context:component-scan base-package="com.spring_1_100.test_31_40.test35_resource_inject.anno"/>
</beans>
測試：
public static void main(String[] args) {
ApplicationContext ac = new ClassPathXmlApplicationContext("classpath:spring_1_100/config_31_40/spring35_resource_inject_1.xml");
User user = (User) ac.getBean("xxxx");
user.drive();
}
結果輸出：
而本篇部落格的主要目的就是研究User物件中的car是如何注入的。
我們知道屬性注入都是在Spring原始碼中的populateBean這個方法，那我們來測試一下，在這個方法之前和在這個方法之後打斷點，看屬性car有沒有被注入進去。
在方法呼叫前，car和，dog都是空
方法呼叫後，car 和dog 都被例項化了。那我們就來重點分析 populateBean方法，其實Spring無論是xml配置的屬性，還是通過註解依賴注入的屬性，都是通過這個方法（populateBean）來進行屬性填充的。
經過我不斷的打斷點，尋尋覓覓，竟然是通過AutowiredAnnotationBeanPostProcessor的postPropertyValues方法進行屬性注入的。而AutowiredAnnotationBeanPostProcessor又是如何儲存到AbstractBeanFactory的beanPostProcessors裡的呢（因為在populateBean方法中呼叫了getBeanPostProcessors()方法，才得到所有的BeanPostProcessor，而getBeanPostProcessors()方法獲取BeanPostProcessor是直接從AbstractBeanFactory的beanPostProcessors集合中取出來的）？帶著好奇，我們來探索一番。因此，通過全域性查詢發現AutowiredAnnotationBeanPostProcessor.class關鍵字只在AnnotationConfigUtils的registerAnnotationConfigProcessors方法和AutowiredAnnotationBeanPostProcessor的建構函式中出現過，如下圖所示，因此分別在這兩處打上斷點。
最終，我們發現AutowiredAnnotationBeanPostProcessor的BeanDefinition定義是在ComponentScanBeanDefinitionParser類的registerComponents方法處呼叫的。如下圖，而ComponentScanBeanDefinitionParser這個類主要是Bean的註解解析時呼叫。
而AutowiredAnnotationBeanPostProcessor是在哪裡呼叫建立的呢？繼續跟蹤斷點。終於到了AutowiredAnnotationBeanPostProcessor的建構函式中。
從下圖中可以看出，AutowiredAnnotationBeanPostProcessor的例項化是在refresh()方法的註冊bean的處理器方法中呼叫。
PostProcessorRegistrationDelegate.java
private static void registerBeanPostProcessors(
ConfigurableListableBeanFactory beanFactory, List postProcessors) {
for (BeanPostProcessor postProcessor : postProcessors) {
beanFactory.addBeanPostProcessor(postProcessor);
}
}
AbstractBeanFactory.java
public void addBeanPostProcessor(BeanPostProcessor beanPostProcessor) {
Assert.notNull(beanPostProcessor, "BeanPostProcessor must not be null");
this.beanPostProcessors.remove(beanPostProcessor);
this.beanPostProcessors.add(beanPostProcessor);
if (beanPostProcessor instanceof InstantiationAwareBeanPostProcessor) {
this.hasInstantiationAwareBeanPostProcessors = true;
}
if (beanPostProcessor instanceof DestructionAwareBeanPostProcessor) {
this.hasDestructionAwareBeanPostProcessors = true;
}
}
通過程式碼，最終，我們看到AutowiredAnnotationBeanPostProcessor被加入到beanPostProcessors中。到這裡，我們知道了，在populateBean方法中，呼叫getBeanPostProcessors()方法時，能獲取到AutowiredAnnotationBeanPostProcessor物件了。通過上面的鋪墊，下面，我們來正式分析Spring是如何通過註解來進行屬性注入的。
AutowiredAnnotationBeanPostProcessor.java
public PropertyValues postProcessPropertyValues(
PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName) throws BeansException {
InjectionMetadata metadata = findAutowiringMetadata(beanName, bean.getClass(), pvs);
try {
metadata.inject(bean, beanName, pvs);
}
catch (Throwable ex) {
throw new BeanCreationException(beanName, "Injection of autowired dependencies failed", ex);
}
return pvs;
}
private InjectionMetadata findAutowiringMetadata(String beanName, Class<?> clazz, PropertyValues pvs) {
//從快取中獲取
String cacheKey = (StringUtils.hasLength(beanName) ? beanName : clazz.getName());
InjectionMetadata metadata = this.injectionMetadataCache.get(cacheKey);
if (InjectionMetadata.needsRefresh(metadata, clazz)) {
synchronized (this.injectionMetadataCache) {
metadata = this.injectionMetadataCache.get(cacheKey);
if (InjectionMetadata.needsRefresh(metadata, clazz)) {
if (metadata != null) {
metadata.clear(pvs);
}
try {
//快取中不存在，直接構建metadata
metadata = buildAutowiringMetadata(clazz);
this.injectionMetadataCache.put(cacheKey, metadata);
}
catch (NoClassDefFoundError err) {
throw new IllegalStateException("Failed to introspect bean class [" + clazz.getName() +
"] for autowiring metadata: could not find class that it depends on", err);
}
}
}
}
return metadata;
}
private InjectionMetadata buildAutowiringMetadata(final Class<?> clazz) {
LinkedList<InjectionMetadata.InjectedElement> elements = new LinkedList<InjectionMetadata.InjectedElement>();
Class<?> targetClass = clazz;
do {
final LinkedList<InjectionMetadata.InjectedElement> currElements =
new LinkedList<InjectionMetadata.InjectedElement>();
ReflectionUtils.doWithLocalFields(targetClass, new ReflectionUtils.FieldCallback() {
@Override
public void doWith(Field field) throws IllegalArgumentException, IllegalAccessException {
//找到當前屬性的所有註解資訊
AnnotationAttributes ann = findAutowiredAnnotation(field);
if (ann != null) {
if (Modifier.isStatic(field.getModifiers())) {
if (logger.isWarnEnabled()) {
logger.warn("Autowired annotation is not supported on static fields: " + field);
}
return;
}
boolean required = determineRequiredStatus(ann);
currElements.add(new AutowiredFieldElement(field, required));
}
}
});
ReflectionUtils.doWithLocalMethods(targetClass, new ReflectionUtils.MethodCallback() {
@Override
public void doWith(Method method) throws IllegalArgumentException, IllegalAccessException {
Method bridgedMethod = BridgeMethodResolver.findBridgedMethod(method);
if (!BridgeMethodResolver.isVisibilityBridgeMethodPair(method, bridgedMethod)) {
return;
}
AnnotationAttributes ann = findAutowiredAnnotation(bridgedMethod);
if (ann != null && method.equals(ClassUtils.getMostSpecificMethod(method, clazz))) {
if (Modifier.isStatic(method.getModifiers())) {
if (logger.isWarnEnabled()) {
logger.warn("Autowired annotation is not supported on static methods: " + method);
}
return;
}
if (method.getParameterTypes().length == 0) {
if (logger.isWarnEnabled()) {
logger.warn("Autowired annotation should be used on methods with parameters: " + method);
}
}
boolean required = determineRequiredStatus(ann);
PropertyDescriptor pd = BeanUtils.findPropertyForMethod(bridgedMethod, clazz);
currElements.add(new AutowiredMethodElement(method, required, pd));
}
}
});
elements.addAll(0, currElements);
targetClass = targetClass.getSuperclass();
}
while (targetClass != null && targetClass != Object.class);
return new InjectionMetadata(clazz, elements);
}
private AnnotationAttributes findAutowiredAnnotation(AccessibleObject ao) {
for (Class<? extends Annotation> type : this.autowiredAnnotationTypes) {
AnnotationAttributes attributes = AnnotatedElementUtils.getMergedAnnotationAttributes(ao, type);
if (attributes != null) {
return attributes;
}
}
return null;
}
ReflectionUtils.java
public static void doWithLocalFields(Class<?> clazz, FieldCallback fc) {
//獲取類的所有的屬性
for (Field field : getDeclaredFields(clazz)) {
try {
fc.doWith(field);
}
catch (IllegalAccessException ex) {
throw new IllegalStateException("Not allowed to access field '" + field.getName() + "': " + ex);
}
}
}
AutowiredAnnotationBeanPostProcessor.java
private AnnotationAttributes findAutowiredAnnotation(AccessibleObject ao) { //autowiredAnnotationTypes中是@Autowired和@Value註解，在AutowiredAnnotationBeanPostProcessor例項化時加入其中的 for (Class<? extends Annotation> type : this.autowiredAnnotationTypes) { AnnotationAttributes attributes = AnnotatedElementUtils.getMergedAnnotationAttributes(ao, type); if (attributes != null) { return attributes; } } return null; }
AnnotatedElementUtils.java
public static AnnotationAttributes getMergedAnnotationAttributes(AnnotatedElement element, Class<? extends Annotation> annotationType) {
Assert.notNull(annotationType, "annotationType must not be null");
return getMergedAnnotationAttributes(element, annotationType.getName());
}
public static AnnotationAttributes getMergedAnnotationAttributes(AnnotatedElement element, String annotationName) {
return getMergedAnnotationAttributes(element, annotationName, false, false);
}
public static AnnotationAttributes getMergedAnnotationAttributes(AnnotatedElement element, String annotationName,
boolean classValuesAsString, boolean nestedAnnotationsAsMap) {
AnnotationAttributes attributes = searchWithGetSemantics(element, annotationName,
new MergedAnnotationAttributesProcessor(annotationName, classValuesAsString, nestedAnnotationsAsMap));
AnnotationUtils.postProcessAnnotationAttributes(element, attributes, classValuesAsString,
nestedAnnotationsAsMap);
return attributes;
}
private static T searchWithGetSemantics(AnnotatedElement element, String annotationName, Processor processor) {
try {
return searchWithGetSemantics(element, annotationName, processor, new HashSet(), 0);
}
catch (Throwable ex) {
AnnotationUtils.rethrowAnnotationConfigurationException(ex);
throw new IllegalStateException("Failed to introspect annotations on " + element, ex);
}
}
private static <T> T searchWithGetSemantics(AnnotatedElement element, String annotationName,
Processor<T> processor, Set<AnnotatedElement> visited, int metaDepth) {
Assert.notNull(element, "AnnotatedElement must not be null");
Assert.hasText(annotationName, "annotationName must not be null or empty");
//註解去重
if (visited.add(element)) {
try {
//獲取屬性上的所有註解
List<Annotation> declaredAnnotations = Arrays.asList(element.getDeclaredAnnotations());
T result = searchWithGetSemanticsInAnnotations(element, declaredAnnotations, annotationName, processor,
visited, metaDepth);
if (result != null) {
return result;
}
List<Annotation> inheritedAnnotations = new ArrayList<Annotation>();
for (Annotation annotation : element.getAnnotations()) {
if (!declaredAnnotations.contains(annotation)) {
inheritedAnnotations.add(annotation);
}
}
// Continue searching within inherited annotations
result = searchWithGetSemanticsInAnnotations(element, inheritedAnnotations, annotationName, processor,
visited, metaDepth);
if (result != null) {
return result;
}
}
catch (Exception ex) {
AnnotationUtils.handleIntrospectionFailure(element, ex);
}
}
return null;
}
private static <T> T searchWithGetSemanticsInAnnotations(AnnotatedElement annotatedElement, List<Annotation> annotations,
String annotationName, Processor<T> processor, Set<AnnotatedElement> visited, int metaDepth) {
//遞迴遍歷所有的註解
for (Annotation annotation : annotations) {
//非java.lang.annotation包開頭的註解，並且註解的名稱為Autowired或者Value
if (!AnnotationUtils.isInJavaLangAnnotationPackage(annotation)
&& (annotation.annotationType().getName().equals(annotationName) || metaDepth > 0)) {
T result = processor.process(annotatedElement, annotation, metaDepth);
if (result != null) {
return result;
}
}
}
//主要是遞迴查詢，比如Car car 屬性配置了@MyAutowired註解，但是@MyAutowired又配置了@Autowired註解
for (Annotation annotation : annotations) {
if (!AnnotationUtils.isInJavaLangAnnotationPackage(annotation)) {
T result = searchWithGetSemantics(annotation.annotationType(), annotationName, processor, visited,
metaDepth + 1);
if (result != null) {
processor.postProcess(annotatedElement, annotation, result);
return result;
}
}
}
return null;
}
MergedAnnotationAttributesProcessor.java
public AnnotationAttributes process(AnnotatedElement annotatedElement, Annotation annotation, int metaDepth) {
boolean found = annotation.annotationType().getName().equals(this.annotationName);
return (found ? AnnotationUtils.getAnnotationAttributes(annotatedElement, annotation,
this.classValuesAsString, this.nestedAnnotationsAsMap, true) : null);
}
AnnotationUtils.java
static AnnotationAttributes getAnnotationAttributes(AnnotatedElement annotatedElement, Annotation annotation,
boolean classValuesAsString, boolean nestedAnnotationsAsMap, boolean mergeMode) {
if (!mergeMode) {
annotation = synthesizeAnnotation(annotation, annotatedElement);
}
Class<? extends Annotation> annotationType = annotation.annotationType();
AnnotationAttributes attrs = new AnnotationAttributes(annotationType);
//獲取註解的所有方法並遍歷
for (Method method : getAttributeMethods(annotationType)) {
try {
//通過反射，獲取註解配置的值
Object value = method.invoke(annotation);
//獲取註解配置的預設值
Object defaultValue = method.getDefaultValue();
if (mergeMode && (defaultValue != null)) {
if (ObjectUtils.nullSafeEquals(value, defaultValue)) {
//將值設定為Spring的預設值
value = DEFAULT_VALUE_PLACEHOLDER;
}
}
attrs.put(method.getName(),
adaptValue(annotatedElement, value, classValuesAsString, nestedAnnotationsAsMap));
}
catch (Exception ex) {
if (ex instanceof InvocationTargetException) {
Throwable targetException = ((InvocationTargetException) ex).getTargetException();
rethrowAnnotationConfigurationException(targetException);
}
throw new IllegalStateException("Could not obtain annotation attribute value for " + method, ex);
}
}
return attrs;
}
當這個方法執行完畢後，我們得到Spring result是AnnotationAttributes。
我們再回到AnnotatedElementUtils的getMergedAnnotationAttributes方法中。
AnnotationUtils.java
static void postProcessAnnotationAttributes(AnnotatedElement element, AnnotationAttributes attributes, boolean classValuesAsString, boolean nestedAnnotationsAsMap) { //屬性是不是為空 if (attributes == null) { return; } Class<? extends Annotation> annotationType = attributes.annotationType(); //值是不是被替換 Set<String> valuesAlreadyReplaced = new HashSet<String>(); //註解的屬性方法是否有別名 Map<String, List<String>> aliasMap = getAttributeAliasMap(annotationType); //如果有別名，將做別名相關的處理 for (String attributeName : aliasMap.keySet()) { if (valuesAlreadyReplaced.contains(attributeName)) { continue; } Object value = attributes.get(attributeName); boolean valuePresent = (value != null && value != DEFAULT_VALUE_PLACEHOLDER); for (String aliasedAttributeName : aliasMap.get(attributeName)) { if (valuesAlreadyReplaced.contains(aliasedAttributeName)) { continue; } Object aliasedValue = attributes.get(aliasedAttributeName); boolean aliasPresent = (aliasedValue != null && aliasedValue != DEFAULT_VALUE_PLACEHOLDER); // Something to validate or replace with an alias? if (valuePresent || aliasPresent) { if (valuePresent && aliasPresent) { // Since annotation attributes can be arrays, we must use ObjectUtils.nullSafeEquals(). if (!ObjectUtils.nullSafeEquals(value, aliasedValue)) { String elementAsString = (element != null ? element.toString() : "unknown element"); String msg = String.format("In AnnotationAttributes for annotation [%s] declared on [%s], " + "attribute [%s] and its alias [%s] are declared with values of [%s] and [%s], " + "but only one declaration is permitted.", annotationType.getName(), elementAsString, attributeName, aliasedAttributeName, ObjectUtils.nullSafeToString(value), ObjectUtils.nullSafeToString(aliasedValue)); throw new AnnotationConfigurationException(msg); } } else if (aliasPresent) { // Replace value with aliasedValue attributes.put(attributeName, adaptValue(element, aliasedValue, classValuesAsString, nestedAnnotationsAsMap)); valuesAlreadyReplaced.add(attributeName); } else { // Replace aliasedValue with value attributes.put(aliasedAttributeName, adaptValue(element, value, classValuesAsString, nestedAnnotationsAsMap)); valuesAlreadyReplaced.add(aliasedAttributeName); } } } } //將註解屬性方法的值是<SPRING DEFAULT VALUE PLACEHOLDER>替換成屬性方法的預設值，如@Autowired的required的預設值是true for (String attributeName : attributes.keySet()) { if (valuesAlreadyReplaced.contains(attributeName)) { continue; } Object value = attributes.get(attributeName); if (value == DEFAULT_VALUE_PLACEHOLDER) { attributes.put(attributeName, adaptValue(element, getDefaultValue(annotationType, attributeName), classValuesAsString, nestedAnnotationsAsMap)); } } }
經過漫長枯燥的解析，我們終於得到了Car 的@Autowired註解的required屬性的預設值是true 。經過上面的分析，我們得到了InjectionMetadata物件，下面，我們來繼續分析屬性的注入。
InjectionMetadata.java
public void inject(Object target, String beanName, PropertyValues pvs) throws Throwable { Collection<InjectedElement> elementsToIterate = (this.checkedElements != null ? this.checkedElements : this.injectedElements); if (!elementsToIterate.isEmpty()) { boolean debug = logger.isDebugEnabled(); for (InjectedElement element : elementsToIterate) { if (debug) { logger.debug("Processing injected element of bean '" + beanName + "': " + element); } element.inject(target, beanName, pvs); } } }
AutowiredFieldElement.java
protected void inject(Object bean, String beanName, PropertyValues pvs) throws Throwable { Field field = (Field) this.member; try { Object value; if (this.cached) { value = resolvedCachedArgument(beanName, this.cachedFieldValue); } else { //建立屬性的描述器 DependencyDescriptor desc = new DependencyDescriptor(field, this.required); //設定屬性的bean 的class desc.setContainingClass(bean.getClass()); Set<String> autowiredBeanNames = new LinkedHashSet<String>(1); //獲取工廠bean的型別轉換器 TypeConverter typeConverter = beanFactory.getTypeConverter(); //獲取到屬性的具體值，比如Car物件 value = beanFactory.resolveDependency(desc, beanName, autowiredBeanNames, typeConverter); synchronized (this) { if (!this.cached) { if (value != null || this.required) { this.cachedFieldValue = desc; //註冊bean之間的依賴關係，也就是User中有屬性Car， Car 在User中使用過等，這樣的資訊 registerDependentBeans(beanName, autowiredBeanNames); if (autowiredBeanNames.size() == 1) { String autowiredBeanName = autowiredBeanNames.iterator().next(); if (beanFactory.containsBean(autowiredBeanName)) { // 名稱是否匹配 if (beanFactory.isTypeMatch(autowiredBeanName, field.getType())) { // 建立bean的引用 this.cachedFieldValue = new RuntimeBeanReference(autowiredBeanName); } } } } else { this.cachedFieldValue = null; } this.cached = true; } } } if (value != null) { // 通過反射將屬性值設定到bean中 ReflectionUtils.makeAccessible(field); field.set(bean, value); } } catch (Throwable ex) { throw new BeanCreationException("Could not autowire field: " + field, ex); } }
DefaultListableBeanFactory.java
public Object resolveDependency(DependencyDescriptor descriptor, String beanName,
Set<String> autowiredBeanNames, TypeConverter typeConverter) throws BeansException {
descriptor.initParameterNameDiscovery(getParameterNameDiscoverer());
if (descriptor.getDependencyType().equals(javaUtilOptionalClass)) {
return new OptionalDependencyFactory().createOptionalDependency(descriptor, beanName);
}
else if (ObjectFactory.class == descriptor.getDependencyType()) {
return new DependencyObjectFactory(descriptor, beanName);
}
else if (javaxInjectProviderClass == descriptor.getDependencyType()) {
return new DependencyProviderFactory().createDependencyProvider(descriptor, beanName);
}
else {
//如果屬性是延遲初始化，做相應的處理
Object result = getAutowireCandidateResolver().getLazyResolutionProxyIfNecessary(descriptor, beanName);
if (result == null) {
//真正的解析bean
result = doResolveDependency(descriptor, beanName, autowiredBeanNames, typeConverter);
}
return result;
}
}
public Object doResolveDependency(DependencyDescriptor descriptor, String beanName,
Set<String> autowiredBeanNames, TypeConverter typeConverter) throws BeansException {
Class<?> type = descriptor.getDependencyType();
Object value = getAutowireCandidateResolver().getSuggestedValue(descriptor);
if (value != null) {
if (value instanceof String) {
String strVal = resolveEmbeddedValue((String) value);
BeanDefinition bd = (beanName != null && containsBean(beanName) ? getMergedBeanDefinition(beanName) : null);
value = evaluateBeanDefinitionString(strVal, bd);
}
TypeConverter converter = (typeConverter != null ? typeConverter : getTypeConverter());
return (descriptor.getField() != null ?
converter.convertIfNecessary(value, type, descriptor.getField()) :
converter.convertIfNecessary(value, type, descriptor.getMethodParameter()));
}
if (type.isArray()) {
Class<?> componentType = type.getComponentType();
DependencyDescriptor targetDesc = new DependencyDescriptor(descriptor);
targetDesc.increaseNestingLevel();
Map<String, Object> matchingBeans = findAutowireCandidates(beanName, componentType, targetDesc);
if (matchingBeans.isEmpty()) {
if (descriptor.isRequired()) {
raiseNoSuchBeanDefinitionException(componentType, "array of " + componentType.getName(), descriptor);
}
return null;
}
if (autowiredBeanNames != null) {
autowiredBeanNames.addAll(matchingBeans.keySet());
}
TypeConverter converter = (typeConverter != null ? typeConverter : getTypeConverter());
Object result = converter.convertIfNecessary(matchingBeans.values(), type);
if (getDependencyComparator() != null && result instanceof Object[]) {
Arrays.sort((Object[]) result, adaptDependencyComparator(matchingBeans));
}
return result;
}
else if (Collection.class.isAssignableFrom(type) && type.isInterface()) {
Class<?> elementType = descriptor.getCollectionType();
if (elementType == null) {
if (descriptor.isRequired()) {
throw new FatalBeanException("No element type declared for collection [" + type.getName() + "]");
}
return null;
}
DependencyDescriptor targetDesc = new DependencyDescriptor(descriptor);
targetDesc.increaseNestingLevel();
Map<String, Object> matchingBeans = findAutowireCandidates(beanName, elementType, targetDesc);
if (matchingBeans.isEmpty()) {
if (descriptor.isRequired()) {
raiseNoSuchBeanDefinitionException(elementType, "collection of " + elementType.getName(), descriptor);
}
return null;
}
if (autowiredBeanNames != null) {
autowiredBeanNames.addAll(matchingBeans.keySet());
}
TypeConverter converter = (typeConverter != null ? typeConverter : getTypeConverter());
Object result = converter.convertIfNecessary(matchingBeans.values(), type);
if (getDependencyComparator() != null && result instanceof List) {
Collections.sort((List<?>) result, adaptDependencyComparator(matchingBeans));
}
return result;
}
else if (Map.class.isAssignableFrom(type) && type.isInterface()) {
Class<?> keyType = descriptor.getMapKeyType();
if (String.class != keyType) {
if (descriptor.isRequired()) {
throw new FatalBeanException("Key type [" + keyType + "] of map [" + type.getName() +
"] must be [java.lang.String]");
}
return null;
}
Class<?> valueType = descriptor.getMapValueType();
if (valueType == null) {
if (descriptor.isRequired()) {
throw new FatalBeanException("No value type declared for map [" + type.getName() + "]");
}
return null;
}
DependencyDescriptor targetDesc = new DependencyDescriptor(descriptor);
targetDesc.increaseNestingLevel();
Map<String, Object> matchingBeans = findAutowireCandidates(beanName, valueType, targetDesc);
if (matchingBeans.isEmpty()) {
if (descriptor.isRequired()) {
raiseNoSuchBeanDefinitionException(valueType, "map with value type " + valueType.getName(), descriptor);
}
return null;
}
if (autowiredBeanNames != null) {
autowiredBeanNames.addAll(matchingBeans.keySet());
}
return matchingBeans;
}
else {
Map<String, Object> matchingBeans = findAutowireCandidates(beanName, type, descriptor);
if (matchingBeans.isEmpty()) {
//如果autowired的required為true,但是容器中並沒有這個bean，則丟擲異常
if (descriptor.isRequired()) {
raiseNoSuchBeanDefinitionException(type, "", descriptor);
}
return null;
}
//如果通過名稱獲取到多個bean物件
if (matchingBeans.size() > 1) {
String primaryBeanName = determineAutowireCandidate(matchingBeans, descriptor);
//如果沒有設定@Primary註解，則直接丟擲異常
if (primaryBeanName == null) {
throw new NoUniqueBeanDefinitionException(type, matchingBeans.keySet());
}
if (autowiredBeanNames != null) {
//如果設定了@Primary，則取設定了@Primary的作為注入值
autowiredBeanNames.add(primaryBeanName);
}
return matchingBeans.get(primaryBeanName);
}
Map.Entry<String, Object> entry = matchingBeans.entrySet().iterator().next();
if (autowiredBeanNames != null) {
autowiredBeanNames.add(entry.getKey());
}
//返回屬性值
return entry.getValue();
}
}
protected Map<String, Object> findAutowireCandidates(
String beanName, Class<?> requiredType, DependencyDescriptor descriptor) {
String[] candidateNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(
this, requiredType, true, descriptor.isEager());
Map<String, Object> result = new LinkedHashMap<String, Object>(candidateNames.length);
for (Class<?> autowiringType : this.resolvableDependencies.keySet()) {
if (autowiringType.isAssignableFrom(requiredType)) {
Object autowiringValue = this.resolvableDependencies.get(autowiringType);
autowiringValue = AutowireUtils.resolveAutowiringValue(autowiringValue, requiredType);
if (requiredType.isInstance(autowiringValue)) {
result.put(ObjectUtils.identityToString(autowiringValue), autowiringValue);
break;
}
}
}
for (String candidateName : candidateNames) {
//不是自己引用自己，包括類物件是否引用了自己的工廠方法。
if (!isSelfReference(beanName, candidateName) && isAutowireCandidate(candidateName, descriptor)) {
//到這裡，我們終於看到了關鍵方法，通過getBean獲取car的bean物件
result.put(candidateName, getBean(candidateName));
}
}
if (result.isEmpty()) {
DependencyDescriptor fallbackDescriptor = descriptor.forFallbackMatch();
for (String candidateName : candidateNames) {
if (!candidateName.equals(beanName) && isAutowireCandidate(candidateName, fallbackDescriptor)) {
result.put(candidateName, getBean(candidateName));
}
}
}
return result;
}
到這裡，我們己經得到了屬性的具體值。我們再次回到屬性注入方法，inject ，我們到這裡，己經將屬性的注入分析完了，我們還是來總結一下吧。
- 獲取到註解的所有的屬性。
- 檢視註解中是否包含@Autowired註解或者@Value註解
- 如果有@Autowired註解，獲取@Autowired註解的屬性方法required的值
- 呼叫getBean()方法，獲取屬性物件
- 通過反射將屬性值注入物件
到這裡，己經將User 的Car 屬性注入解析完成，Dog物件，也是相同的解析辦法，這裡將不再做過多的綴述了。
本文的 github 地址是
https://github.com/quyixiao/spring_tiny/tree/master/src/main/java/com/spring_1_100/test_31_40/test35_resource_inject
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