版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/wxb880114/article/details/83898206
现象描述
在开发过程中，遇到一种情况，当某种条件下才创建beanA，而这个beanA恰好又被另外一个beanB引用了，当beanA为null的时候beanB初始化失败,代码如下
@Autowired
private ProducerBean producer;抛出异常如下：
nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'aliMqService':
Unsatisfied dependency expressed through field 'producer'; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type
'com.aliyun.openservices.ons.api.bean.ProducerBean' available: expected at least 1 bean
which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}解决方式比较简单
查看源码@Autowired中有个required属性，设置为false，就不会报错了
原理分析
先找到源码路径
Autowired.class对应着AutowiredAnnotationBeanPostProcessor.class
默认required为true
public class AutowiredAnnotationBeanPostProcessor extends InstantiationAwareBeanPostProcessorAdapter
implements MergedBeanDefinitionPostProcessor, PriorityOrdered, BeanFactoryAware {
protected final Log logger = LogFactory.getLog(getClass());
private final Set<Class<? extends Annotation>> autowiredAnnotationTypes =
new LinkedHashSet<Class<? extends Annotation>>();
private String requiredParameterName = "required";
private boolean requiredParameterValue = true;
private int order = Ordered.LOWEST_PRECEDENCE - 2;
// bean工厂类
private ConfigurableListableBeanFactory beanFactory;
private final Set<String> lookupMethodsChecked =
Collections.newSetFromMap(new ConcurrentHashMap<String, Boolean>(256));
private final Map<Class<?>, Constructor<?>[]> candidateConstructorsCache =
new ConcurrentHashMap<Class<?>, Constructor<?>[]>(256);
private final Map<String, InjectionMetadata> injectionMetadataCache =
new ConcurrentHashMap<String, InjectionMetadata>(256);
// 构造函数
/**
* Create a new AutowiredAnnotationBeanPostProcessor
* for Spring's standard {@link Autowired} annotation.
* <p>Also supports JSR-330's {@link javax.inject.Inject} annotation, if available.
*/
@SuppressWarnings("unchecked")
public AutowiredAnnotationBeanPostProcessor() {
this.autowiredAnnotationTypes.add(Autowired.class);
this.autowiredAnnotationTypes.add(Value.class);
try {
this.autowiredAnnotationTypes.add((Class<? extends Annotation>)
ClassUtils.forName("javax.inject.Inject", AutowiredAnnotationBeanPostProcessor.class.getClassLoader()));
logger.info("JSR-330 'javax.inject.Inject' annotation found and supported for autowiring");
}
catch (ClassNotFoundException ex) {
// JSR-330 API not available - simply skip.
}
}
// 在constructors, fields，settter方法，属性配置方法 上设置 ‘autowired’
/**
* Set the 'autowired' annotation type, to be used on constructors, fields,
* setter methods and arbitrary config methods.
* <p>The default autowired annotation type is the Spring-provided
* {@link Autowired} annotation, as well as {@link Value}.
* <p>This setter property exists so that developers can provide their own
* (non-Spring-specific) annotation type to indicate that a member is
* supposed to be autowired.
*/
public void setAutowiredAnnotationType(Class<? extends Annotation> autowiredAnnotationType) {
Assert.notNull(autowiredAnnotationType, "'autowiredAnnotationType' must not be null");
this.autowiredAnnotationTypes.clear();
this.autowiredAnnotationTypes.add(autowiredAnnotationType);
}
/**
* Set the 'autowired' annotation types, to be used on constructors, fields,
* setter methods and arbitrary config methods.
* <p>The default autowired annotation type is the Spring-provided
* {@link Autowired} annotation, as well as {@link Value}.
* <p>This setter property exists so that developers can provide their own
* (non-Spring-specific) annotation types to indicate that a member is
* supposed to be autowired.
*/
public void setAutowiredAnnotationTypes(Set<Class<? extends Annotation>> autowiredAnnotationTypes) {
Assert.notEmpty(autowiredAnnotationTypes, "'autowiredAnnotationTypes' must not be empty");
this.autowiredAnnotationTypes.clear();
this.autowiredAnnotationTypes.addAll(autowiredAnnotationTypes);
}
/**
* Set the name of a parameter of the annotation that specifies
* whether it is required.
* @see #setRequiredParameterValue(boolean)
*/
public void setRequiredParameterName(String requiredParameterName) {
this.requiredParameterName = requiredParameterName;
}
//设置required 为true 或者false
/**
* Set the boolean value that marks a dependency as required
* <p>For example if using 'required=true' (the default),
* this value should be {@code true}; but if using
* 'optional=false', this value should be {@code false}.
* @see #setRequiredParameterName(String)
*/
public void setRequiredParameterValue(boolean requiredParameterValue) {
this.requiredParameterValue = requiredParameterValue;
}
public void setOrder(int order) {
this.order = order;
}
@Override
public int getOrder() {
return this.order;
}
// bean工厂类
@Override
public void setBeanFactory(BeanFactory beanFactory) {
if (!(beanFactory instanceof ConfigurableListableBeanFactory)) {
throw new IllegalArgumentException(
"AutowiredAnnotationBeanPostProcessor requires a ConfigurableListableBeanFactory: " + beanFactory);
}
this.beanFactory = (ConfigurableListableBeanFactory) beanFactory;
}
@Override
public void postProcessMergedBeanDefinition(RootBeanDefinition beanDefinition, Class<?> beanType, String beanName) {
if (beanType != null) {
InjectionMetadata metadata = findAutowiringMetadata(beanName, beanType, null);
metadata.checkConfigMembers(beanDefinition);
}
}
@Override
public Constructor<?>[] determineCandidateConstructors(Class<?> beanClass, final String beanName)
throws BeanCreationException {
// Let's check for lookup methods here..
if (!this.lookupMethodsChecked.contains(beanName)) {
try {
ReflectionUtils.doWithMethods(beanClass, new ReflectionUtils.MethodCallback() {
@Override
public void doWith(Method method) throws IllegalArgumentException, IllegalAccessException {
Lookup lookup = method.getAnnotation(Lookup.class);
if (lookup != null) {
LookupOverride override = new LookupOverride(method, lookup.value());
try {
RootBeanDefinition mbd = (RootBeanDefinition) beanFactory.getMergedBeanDefinition(beanName);
mbd.getMethodOverrides().addOverride(override);
}
catch (NoSuchBeanDefinitionException ex) {
throw new BeanCreationException(beanName,
"Cannot apply @Lookup to beans without corresponding bean definition");
}
}
}
});
}
catch (IllegalStateException ex) {
throw new BeanCreationException(beanName, "Lookup method resolution failed", ex);
}
catch (NoClassDefFoundError err) {
throw new BeanCreationException(beanName, "Failed to introspect bean class [" + beanClass.getName() +
"] for lookup method metadata: could not find class that it depends on", err);
}
this.lookupMethodsChecked.add(beanName);
}
// Quick check on the concurrent map first, with minimal locking.
Constructor<?>[] candidateConstructors = this.candidateConstructorsCache.get(beanClass);
if (candidateConstructors == null) {
// Fully synchronized resolution now...
synchronized (this.candidateConstructorsCache) {
candidateConstructors = this.candidateConstructorsCache.get(beanClass);
if (candidateConstructors == null) {
Constructor<?>[] rawCandidates;
try {
rawCandidates = beanClass.getDeclaredConstructors();
}
catch (Throwable ex) {
throw new BeanCreationException(beanName,
"Resolution of declared constructors on bean Class [" + beanClass.getName() +
"] from ClassLoader [" + beanClass.getClassLoader() + "] failed", ex);
}
List<Constructor<?>> candidates = new ArrayList<Constructor<?>>(rawCandidates.length);
Constructor<?> requiredConstructor = null;
Constructor<?> defaultConstructor = null;
for (Constructor<?> candidate : rawCandidates) {
AnnotationAttributes ann = findAutowiredAnnotation(candidate);
if (ann == null) {
Class<?> userClass = ClassUtils.getUserClass(beanClass);
if (userClass != beanClass) {
try {
Constructor<?> superCtor =
userClass.getDeclaredConstructor(candidate.getParameterTypes());
ann = findAutowiredAnnotation(superCtor);
}
catch (NoSuchMethodException ex) {
// Simply proceed, no equivalent superclass constructor found...
}
}
}
if (ann != null) {
if (requiredConstructor != null) {
throw new BeanCreationException(beanName,
"Invalid autowire-marked constructor: " + candidate +
". Found constructor with 'required' Autowired annotation already: " +
requiredConstructor);
}
boolean required = determineRequiredStatus(ann);
if (required) {
if (!candidates.isEmpty()) {
throw new BeanCreationException(beanName,
"Invalid autowire-marked constructors: " + candidates +
". Found constructor with 'required' Autowired annotation: " +
candidate);
}
requiredConstructor = candidate;
}
candidates.add(candidate);
}
else if (candidate.getParameterTypes().length == 0) {
defaultConstructor = candidate;
}
}
if (!candidates.isEmpty()) {
// Add default constructor to list of optional constructors, as fallback.
if (requiredConstructor == null) {
if (defaultConstructor != null) {
candidates.add(defaultConstructor);
}
else if (candidates.size() == 1 && logger.isWarnEnabled()) {
logger.warn("Inconsistent constructor declaration on bean with name '" + beanName +
"': single autowire-marked constructor flagged as optional - " +
"this constructor is effectively required since there is no " +
"default constructor to fall back to: " + candidates.get(0));
}
}
candidateConstructors = candidates.toArray(new Constructor<?>[candidates.size()]);
}
else if (rawCandidates.length == 1 && rawCandidates[0].getParameterTypes().length > 0) {
candidateConstructors = new Constructor<?>[] {rawCandidates[0]};
}
else {
candidateConstructors = new Constructor<?>[0];
}
this.candidateConstructorsCache.put(beanClass, candidateConstructors);
}
}
}
return (candidateConstructors.length > 0 ? candidateConstructors : null);
}
@Override
public PropertyValues postProcessPropertyValues(
PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName) throws BeanCreationException {
InjectionMetadata metadata = findAutowiringMetadata(beanName, bean.getClass(), pvs);
try {
metadata.inject(bean, beanName, pvs);
}
catch (BeanCreationException ex) {
throw ex;
}
catch (Throwable ex) {
throw new BeanCreationException(beanName, "Injection of autowired dependencies failed", ex);
}
return pvs;
}
/**
* 'Native' processing method for direct calls with an arbitrary target instance,
* resolving all of its fields and methods which are annotated with {@code @Autowired}.
* @param bean the target instance to process
* @throws BeanCreationException if autowiring failed
*/
public void processInjection(Object bean) throws BeanCreationException {
Class<?> clazz = bean.getClass();
InjectionMetadata metadata = findAutowiringMetadata(clazz.getName(), clazz, null);
try {
metadata.inject(bean, null, null);
}
catch (BeanCreationException ex) {
throw ex;
}
catch (Throwable ex) {
throw new BeanCreationException(
"Injection of autowired dependencies failed for class [" + clazz + "]", ex);
}
}
private InjectionMetadata findAutowiringMetadata(String beanName, Class<?> clazz, PropertyValues pvs) {
// Fall back to class name as cache key, for backwards compatibility with custom callers.
String cacheKey = (StringUtils.hasLength(beanName) ? beanName : clazz.getName());
// Quick check on the concurrent map first, with minimal locking.
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 {
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 {
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 only 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) {
if (ao.getAnnotations().length > 0) {
for (Class<? extends Annotation> type : this.autowiredAnnotationTypes) {
AnnotationAttributes attributes = AnnotatedElementUtils.getMergedAnnotationAttributes(ao, type);
if (attributes != null) {
return attributes;
}
}
}
return null;
}
/**
* Determine if the annotated field or method requires its dependency.
* <p>A 'required' dependency means that autowiring should fail when no beans
* are found. Otherwise, the autowiring process will simply bypass the field
* or method when no beans are found.
* @param ann the Autowired annotation
* @return whether the annotation indicates that a dependency is required
*/
protected boolean determineRequiredStatus(AnnotationAttributes ann) {
return (!ann.containsKey(this.requiredParameterName) ||
this.requiredParameterValue == ann.getBoolean(this.requiredParameterName));
}
/**
* Obtain all beans of the given type as autowire candidates.
* @param type the type of the bean
* @return the target beans, or an empty Collection if no bean of this type is found
* @throws BeansException if bean retrieval failed
*/
protected <T> Map<String, T> findAutowireCandidates(Class<T> type) throws BeansException {
if (this.beanFactory == null) {
throw new IllegalStateException("No BeanFactory configured - " +
"override the getBeanOfType method or specify the 'beanFactory' property");
}
return BeanFactoryUtils.beansOfTypeIncludingAncestors(this.beanFactory, type);
}
/**
* Register the specified bean as dependent on the autowired beans.
*/
private void registerDependentBeans(String beanName, Set<String> autowiredBeanNames) {
if (beanName != null) {
for (String autowiredBeanName : autowiredBeanNames) {
if (this.beanFactory.containsBean(autowiredBeanName)) {
this.beanFactory.registerDependentBean(autowiredBeanName, beanName);
}
if (logger.isDebugEnabled()) {
logger.debug("Autowiring by type from bean name '" + beanName +
"' to bean named '" + autowiredBeanName + "'");
}
}
}
}
/**
* Resolve the specified cached method argument or field value.
*/
private Object resolvedCachedArgument(String beanName, Object cachedArgument) {
if (cachedArgument instanceof DependencyDescriptor) {
DependencyDescriptor descriptor = (DependencyDescriptor) cachedArgument;
return this.beanFactory.resolveDependency(descriptor, beanName, null, null);
}
else {
return cachedArgument;
}
}
/**
* Class representing injection information about an annotated field.
*/
private class AutowiredFieldElement extends InjectionMetadata.InjectedElement {
private final boolean required;
private volatile boolean cached = false;
private volatile Object cachedFieldValue;
public AutowiredFieldElement(Field field, boolean required) {
super(field, null);
this.required = required;
}
@Override
protected void inject(Object bean, String beanName, PropertyValues pvs) throws Throwable {
Field field = (Field) this.member;
Object value;
if (this.cached) {
value = resolvedCachedArgument(beanName, this.cachedFieldValue);
}
else {
DependencyDescriptor desc = new DependencyDescriptor(field, this.required);
desc.setContainingClass(bean.getClass());
Set<String> autowiredBeanNames = new LinkedHashSet<String>(1);
TypeConverter typeConverter = beanFactory.getTypeConverter();
try {
value = beanFactory.resolveDependency(desc, beanName, autowiredBeanNames, typeConverter);
}
catch (BeansException ex) {
throw new UnsatisfiedDependencyException(null, beanName, new InjectionPoint(field), ex);
}
synchronized (this) {
if (!this.cached) {
if (value != null || this.required) {
this.cachedFieldValue = desc;
registerDependentBeans(beanName, autowiredBeanNames);
if (autowiredBeanNames.size() == 1) {
String autowiredBeanName = autowiredBeanNames.iterator().next();
if (beanFactory.containsBean(autowiredBeanName)) {
if (beanFactory.isTypeMatch(autowiredBeanName, field.getType())) {
this.cachedFieldValue = new ShortcutDependencyDescriptor(
desc, autowiredBeanName, field.getType());
}
}
}
}
else {
this.cachedFieldValue = null;
}
this.cached = true;
}
}
}
if (value != null) {
ReflectionUtils.makeAccessible(field);
field.set(bean, value);
}
}
}
/**
* Class representing injection information about an annotated method.
*/
private class AutowiredMethodElement extends InjectionMetadata.InjectedElement {
private final boolean required;
private volatile boolean cached = false;
private volatile Object[] cachedMethodArguments;
public AutowiredMethodElement(Method method, boolean required, PropertyDescriptor pd) {
super(method, pd);
this.required = required;
}
@Override
protected void inject(Object bean, String beanName, PropertyValues pvs) throws Throwable {
if (checkPropertySkipping(pvs)) {
return;
}
Method method = (Method) this.member;
Object[] arguments;
if (this.cached) {
// Shortcut for avoiding synchronization...
arguments = resolveCachedArguments(beanName);
}
else {
Class<?>[] paramTypes = method.getParameterTypes();
arguments = new Object[paramTypes.length];
DependencyDescriptor[] descriptors = new DependencyDescriptor[paramTypes.length];
Set<String> autowiredBeans = new LinkedHashSet<String>(paramTypes.length);
TypeConverter typeConverter = beanFactory.getTypeConverter();
for (int i = 0; i < arguments.length; i++) {
MethodParameter methodParam = new MethodParameter(method, i);
DependencyDescriptor currDesc = new DependencyDescriptor(methodParam, this.required);
currDesc.setContainingClass(bean.getClass());
descriptors[i] = currDesc;
try {
Object arg = beanFactory.resolveDependency(currDesc, beanName, autowiredBeans, typeConverter);
if (arg == null && !this.required) {
arguments = null;
break;
}
arguments[i] = arg;
}
catch (BeansException ex) {
throw new UnsatisfiedDependencyException(null, beanName, new InjectionPoint(methodParam), ex);
}
}
synchronized (this) {
if (!this.cached) {
if (arguments != null) {
this.cachedMethodArguments = new Object[paramTypes.length];
for (int i = 0; i < arguments.length; i++) {
this.cachedMethodArguments[i] = descriptors[i];
}
registerDependentBeans(beanName, autowiredBeans);
if (autowiredBeans.size() == paramTypes.length) {
Iterator<String> it = autowiredBeans.iterator();
for (int i = 0; i < paramTypes.length; i++) {
String autowiredBeanName = it.next();
if (beanFactory.containsBean(autowiredBeanName)) {
if (beanFactory.isTypeMatch(autowiredBeanName, paramTypes[i])) {
this.cachedMethodArguments[i] = new ShortcutDependencyDescriptor(
descriptors[i], autowiredBeanName, paramTypes[i]);
}
}
}
}
}
else {
this.cachedMethodArguments = null;
}
this.cached = true;
}
}
}
if (arguments != null) {
try {
ReflectionUtils.makeAccessible(method);
method.invoke(bean, arguments);
}
catch (InvocationTargetException ex){
throw ex.getTargetException();
}
}
}
private Object[] resolveCachedArguments(String beanName) {
if (this.cachedMethodArguments == null) {
return null;
}
Object[] arguments = new Object[this.cachedMethodArguments.length];
for (int i = 0; i < arguments.length; i++) {
arguments[i] = resolvedCachedArgument(beanName, this.cachedMethodArguments[i]);
}
return arguments;
}
}
/**
* DependencyDescriptor variant with a pre-resolved target bean name.
*/
@SuppressWarnings("serial")
private static class ShortcutDependencyDescriptor extends DependencyDescriptor {
private final String shortcut;
private final Class<?> requiredType;
public ShortcutDependencyDescriptor(DependencyDescriptor original, String shortcut, Class<?> requiredType) {
super(original);
this.shortcut = shortcut;
this.requiredType = requiredType;
}
@Override
public Object resolveShortcut(BeanFactory beanFactory) {
return resolveCandidate(this.shortcut, this.requiredType, beanFactory);
}
}
}