技术标签: spring spring boot java SpringBoot相关 Autowired Resource
目录
不能将所有的@Resource无脑替换成@Autowired
结合源码分析Autowire vs Resource 性能比较
org.springframework.beans.factory.support.DefaultListableBeanFactory#doGetBeanNamesForType:
org.springframework.beans.factory.support.AbstractBeanFactory#isFactoryBean(java.lang.String)
org.springframework.context.annotation.CommonAnnotationBeanPostProcessor#autowireResource:
@Autowired和@Resource之间的区别?表格对比版
@Resource性能比@Autowire好很多,尤其是在bean个数较多的场景下。简单的说,@Resource相当于O(1),@Autowire相当于O(n) 。
@Resource注解的工作方式是首先按名称进行装配,如果没有找到对应的bean,那么再按类型进行装配。默认情况下,它在字段或者方法上,取字段名或者getter方法的属性名作为bean的名称。这种方式在大多数情况下都能正常工作,但在某些特殊情况下可能会导致查找失败。
以下是一些可能导致@Resource查找失败的情况:
因此,虽然@Resource在大多数情况下都能正常工作,但在某些特殊情况下可能会导致查找失败。在使用@Resource时,需要注意这些潜在的问题,并根据具体的情况进行适当的处理。
@Override
protected void inject(Object bean, @Nullable String beanName, @Nullable 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<>(paramTypes.length);
Assert.state(beanFactory != null, "No BeanFactory available");
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) {
Object[] cachedMethodArguments = new Object[paramTypes.length];
System.arraycopy(descriptors, 0, cachedMethodArguments, 0, arguments.length);
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) &&
beanFactory.isTypeMatch(autowiredBeanName, paramTypes[i])) {
cachedMethodArguments[i] = new ShortcutDependencyDescriptor(
descriptors[i], autowiredBeanName, paramTypes[i]);
}
}
}
this.cachedMethodArguments = cachedMethodArguments;
}
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 String[] doGetBeanNamesForType(ResolvableType type, boolean includeNonSingletons, boolean allowEagerInit) {
List<String> result = new ArrayList<>();
// Check all bean definitions.
for (String beanName : this.beanDefinitionNames) {
// Only consider bean as eligible if the bean name
// is not defined as alias for some other bean.
if (!isAlias(beanName)) {
try {
RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
// Only check bean definition if it is complete.
if (!mbd.isAbstract() && (allowEagerInit ||
(mbd.hasBeanClass() || !mbd.isLazyInit() || isAllowEagerClassLoading()) &&
!requiresEagerInitForType(mbd.getFactoryBeanName()))) {
// In case of FactoryBean, match object created by FactoryBean.
boolean isFactoryBean = isFactoryBean(beanName, mbd);
BeanDefinitionHolder dbd = mbd.getDecoratedDefinition();
boolean matchFound =
(allowEagerInit || !isFactoryBean ||
(dbd != null && !mbd.isLazyInit()) || containsSingleton(beanName)) &&
(includeNonSingletons ||
(dbd != null ? mbd.isSingleton() : isSingleton(beanName))) &&
isTypeMatch(beanName, type);
if (!matchFound && isFactoryBean) {
// In case of FactoryBean, try to match FactoryBean instance itself next.
beanName = FACTORY_BEAN_PREFIX + beanName;
matchFound = (includeNonSingletons || mbd.isSingleton()) && isTypeMatch(beanName, type);
}
if (matchFound) {
result.add(beanName);
}
}
}
catch (CannotLoadBeanClassException ex) {
if (allowEagerInit) {
throw ex;
}
// Probably a class name with a placeholder: let's ignore it for type matching purposes.
if (logger.isTraceEnabled()) {
logger.trace("Ignoring bean class loading failure for bean '" + beanName + "'", ex);
}
onSuppressedException(ex);
}
catch (BeanDefinitionStoreException ex) {
if (allowEagerInit) {
throw ex;
}
// Probably some metadata with a placeholder: let's ignore it for type matching purposes.
if (logger.isTraceEnabled()) {
logger.trace("Ignoring unresolvable metadata in bean definition '" + beanName + "'", ex);
}
onSuppressedException(ex);
}
}
}
// Check manually registered singletons too.
for (String beanName : this.manualSingletonNames) {
try {
// In case of FactoryBean, match object created by FactoryBean.
if (isFactoryBean(beanName)) {
if ((includeNonSingletons || isSingleton(beanName)) && isTypeMatch(beanName, type)) {
result.add(beanName);
// Match found for this bean: do not match FactoryBean itself anymore.
continue;
}
// In case of FactoryBean, try to match FactoryBean itself next.
beanName = FACTORY_BEAN_PREFIX + beanName;
}
// Match raw bean instance (might be raw FactoryBean).
if (isTypeMatch(beanName, type)) {
result.add(beanName);
}
}
catch (NoSuchBeanDefinitionException ex) {
// Shouldn't happen - probably a result of circular reference resolution...
if (logger.isTraceEnabled()) {
logger.trace("Failed to check manually registered singleton with name '" + beanName + "'", ex);
}
}
}
return StringUtils.toStringArray(result);
}
@Override
public boolean isFactoryBean(String name) throws NoSuchBeanDefinitionException {
String beanName = transformedBeanName(name);
Object beanInstance = getSingleton(beanName, false);
if (beanInstance != null) {
return (beanInstance instanceof FactoryBean);
}
// No singleton instance found -> check bean definition.
if (!containsBeanDefinition(beanName) && getParentBeanFactory() instanceof ConfigurableBeanFactory) {
// No bean definition found in this factory -> delegate to parent.
return ((ConfigurableBeanFactory) getParentBeanFactory()).isFactoryBean(name);
}
return isFactoryBean(beanName, getMergedLocalBeanDefinition(beanName));
}
@Override
protected Object getResourceToInject(Object target, @Nullable String requestingBeanName) {
return (this.lazyLookup ? buildLazyResourceProxy(this, requestingBeanName) :
getResource(this, requestingBeanName));
}
protected Object autowireResource(BeanFactory factory, LookupElement element, @Nullable String requestingBeanName)
throws NoSuchBeanDefinitionException {
Object resource;
Set<String> autowiredBeanNames;
String name = element.name;
if (factory instanceof AutowireCapableBeanFactory) {
AutowireCapableBeanFactory beanFactory = (AutowireCapableBeanFactory) factory;
DependencyDescriptor descriptor = element.getDependencyDescriptor();
if (this.fallbackToDefaultTypeMatch && element.isDefaultName && !factory.containsBean(name)) {
autowiredBeanNames = new LinkedHashSet<>();
resource = beanFactory.resolveDependency(descriptor, requestingBeanName, autowiredBeanNames, null);
if (resource == null) {
throw new NoSuchBeanDefinitionException(element.getLookupType(), "No resolvable resource object");
}
}
else {
resource = beanFactory.resolveBeanByName(name, descriptor);
autowiredBeanNames = Collections.singleton(name);
}
}
else {
resource = factory.getBean(name, element.lookupType);
autowiredBeanNames = Collections.singleton(name);
}
if (factory instanceof ConfigurableBeanFactory) {
ConfigurableBeanFactory beanFactory = (ConfigurableBeanFactory) factory;
for (String autowiredBeanName : autowiredBeanNames) {
if (requestingBeanName != null && beanFactory.containsBean(autowiredBeanName)) {
beanFactory.registerDependentBean(autowiredBeanName, requestingBeanName);
}
}
}
return resource;
}
@Autowired可用于:构造函数、成员变量、Setter方法;
同 |
两者都可以写在字段和setter方法上;两者如果都写在字段上,那么就不需要再写setter方法; |
同 |
@Resource和@Autowired都是做bean的注入时使用; |
@Autowired |
@Resource |
|
注入方式 |
@Autowired默认是按照类型 (byType) 装配注入的,默认情况下它要求依赖对象必须存在 (可以设置它required属性为false); 这会有什么问题呢? 当一个接口存在多个实现类的话,byType这种方式就无法正确注入对象了,因为这个时候 Spring 会同时找到多个满足条件的选择,默认情况下它自己不知道选择哪一个; 想使用按照名称 (byName) 来装配,可以结合@Qualifier注解一起使用; |
@Resource默认是按照名称 (byName) 来装配注入的,只有当找不到与名称匹配的bean才会按照类型来装配注入; @Resource装配顺序:
@Resource的作用相当于@Autowired,只不过@Autowired按照byType自动注入; |
来源 |
@Autowired为Spring提供的注解,需要导入包org.springframework.beans.factory.annotation.Autowired; |
@Resource并不是Spring的注解,它的包是javax.annotation.Resource,需要导入,但是Spring支持该注解的注入; |
作用域 |
字段或属性的方法上; |
字段或属性的方法上; |
性能 |
@Autowired查找Bean的时间复杂度为O(n):
|
@Resource查找Bean的时间复杂度为O(1):
|
@Resource有两个重要的属性:name和 type,而Spring将@Resource注解的name属性解析为bean的名字,而type属性则解析为bean的类型;
|
||
当我们在使用@Autowired注解的时候,默认required=true,表示注入的时候bean必须存在,否则注入失败; @Autowired(required=false) |
不支持可选依赖 |
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