代码在文件\spring-beans\src\main\java\org\springframework\beans\factory\support\AbstractAutowireCapableBeanFactory.java
/** * Create a new instance for the specified bean, using an appropriate instantiation strategy: * factory method, constructor autowiring, or simple instantiation. * 为指定的bean创建一个新实例，使用适当的实例化策略:工厂方法、构造函数自动装配或简单实例化。 * @param beanName the name of the bean * @param mbd the bean definition for the bean * @param args explicit arguments to use for constructor or factory method invocation * @return a BeanWrapper for the new instance 新实例的bean包装 * @see #obtainFromSupplier 从这开始，下面是四个函数，当前函数会调用到的 * @see #instantiateUsingFactoryMethod * @see #autowireConstructor * @see #instantiateBean */ protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) { // Make sure bean class is actually resolved at this point. Class<?> beanClass = resolveBeanClass(mbd, beanName); if (beanClass != null && !Modifier.isPublic(beanClass.getModifiers()) && !mbd.isNonPublicAccessAllowed()) { throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Bean class isn't public, and non-public access not allowed: " + beanClass.getName()); } Supplier<?> instanceSupplier = mbd.getInstanceSupplier(); if (instanceSupplier != null) { return obtainFromSupplier(instanceSupplier, beanName); } if (mbd.getFactoryMethodName() != null) {//如果工厂方法不为空，则使用工厂方法初始化策略 return instantiateUsingFactoryMethod(beanName, mbd, args); } // Shortcut when re-creating the same bean... boolean resolved = false; boolean autowireNecessary = false; if (args == null) { synchronized (mbd.constructorArgumentLock) { //一个类有多个构造函数，每个构造函数都有不同的参数，所以调用前需要先根据参数锁定构造函数或对应的工厂方法 if (mbd.resolvedConstructorOrFactoryMethod != null) { resolved = true; autowireNecessary = mbd.constructorArgumentsResolved; } } } if (resolved) {//如果已经解析过则使用解析好的构造函数方法不需要再次锁定 if (autowireNecessary) { //构造函数自动注入 return autowireConstructor(beanName, mbd, null, null); } else { //使用默认构造函数构造 return instantiateBean(beanName, mbd); } } // Candidate constructors for autowiring? //需要根据参数解析构造函数 Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName); if (ctors != null || mbd.getResolvedAutowireMode() == AUTOWIRE_CONSTRUCTOR || mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) { return autowireConstructor(beanName, mbd, ctors, args);//构造函数自动注入 } // Preferred constructors for default construction? ctors = mbd.getPreferredConstructors(); if (ctors != null) { return autowireConstructor(beanName, mbd, ctors, null); } // No special handling: simply use no-arg constructor. return instantiateBean(beanName, mbd);//使用默认构造函数构造 }上面那个函数的调用是从AbstractBeanFactory中的函数调用链传递过来的： AbstractBeanFactory：getBean() ->AbstractBeanFactory:doGetBean()->DefaultSingletonBeanRegistry:getSingleton()-> 在DefaultSingletonBeanRegistry:getSingleton()函数中会创建一个匿名内部类实现ObjectFactory接口，并且在接口的getObject()方法内会调用AbstractBeanFactory的createBean方法，但是AbstractBeanFactory类没有实现该方法，所以会根据运行时调用相应的实现了该方法的类，这里就是上面的AbstractAutowireCapableBeanFactory类，实现了createBean()方法。 在DefaultSingletonBeanRegistry:getSingleton()内部会调用ObjectFactory的getObject方法也就会调用createBean方法了。 AbstractAutowireCapableBeanFactory：createBean()->doCreateBean()->createBeanInstance 在书中没有obtainFromSupplier这个函数，上面的代码是5.2.x版本，书中的是3.x版本。 函数解析： 1.如果在RootBeanDefinition中存在factoryMethodName属性，或者说在配置文件中配置了factory-method，那么Spring会尝试使用instantiateUsingFactoryMethod(beanName,mbd,args)方法根据RootBeanDefinition中的配置生成bean实例。 2.解析构造函数并进行构造函数的实例化。因为一个bean对应类中可能会有多个构造函数，而每个构造函数的参数不同，Spring在根据参数及类型去判断最终会使用那个构造函数进行实例化。但是，判断过程是个比较消耗性能的步骤，所以采用缓存机制，如果已经解析过则不需要重复解析而是直接从RootBeanDefinition中的属性resolvedConstructorOrFactoryMethod缓存的值去取，否则需要再次解析，并将解析的结果添加至RootBeanDefinition中的属性resolvedConstructorOrFactoryMethod中。 上面的这个函数在类层次上如下图：
所以接下来就看解析构造函数的那个函数autowireConstructor(final String beanName,final RootBeanDefinition mbd,final Constructor[] chosenCtors,final Object[] explicitArgs)。函数在D:\IDEAProject\spring-source\spring-beans\src\main\java\org\springframework\beans\factory\support\ConstructorResolver.java文件中。 要进入这个autowireConstructor函数，需要配置下面一个类：
@Component public class ConstructParam { int year; public ConstructParam(int year) { this.year = year; } }这个类会由于解析构造函数失败而抛出异常，本博客记录下代码执行过程。 解析构造函数的代码(在AbstractAutowireCapableBeanFactory的createBeanInstance方法中存在以下代码进行构造函数的解析)：
Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);这个函数会循环遍历Spring中所有的后处理器，寻找SmartInstantiationAwareBeanPostProcessor后处理器，调用后处理器(SmartInstantiationAwareBeanPostProcessor)进行构造函数的解析：
/** * Determine candidate constructors to use for the given bean, checking all registered * {@link SmartInstantiationAwareBeanPostProcessor SmartInstantiationAwareBeanPostProcessors}. * @param beanClass the raw class of the bean * @param beanName the name of the bean * @return the candidate constructors, or {@code null} if none specified * @throws org.springframework.beans.BeansException in case of errors * @see org.springframework.beans.factory.config.SmartInstantiationAwareBeanPostProcessor#determineCandidateConstructors */ @Nullable protected Constructor<?>[] determineConstructorsFromBeanPostProcessors(@Nullable Class<?> beanClass, String beanName) throws BeansException { if (beanClass != null && hasInstantiationAwareBeanPostProcessors()) { for (BeanPostProcessor bp : getBeanPostProcessors()) { if (bp instanceof SmartInstantiationAwareBeanPostProcessor) { SmartInstantiationAwareBeanPostProcessor ibp = (SmartInstantiationAwareBeanPostProcessor) bp; Constructor<?>[] ctors = ibp.determineCandidateConstructors(beanClass, beanName); if (ctors != null) { return ctors; } } } } return null; }调试发现：1.ConfigurationClassPostProcessor$ImportAwareBeanPostProcessor的后处理方法直接返回null。 2.AutowiredAnnotationBeanPostProcessor的determineCandidateConstructors()方法不为空，处理逻辑如下：
@Override @Nullable public Constructor<?>[] determineCandidateConstructors(Class<?> beanClass, final String beanName) throws BeanCreationException { // Let's check for lookup methods here... if (!this.lookupMethodsChecked.contains(beanName)) { if (AnnotationUtils.isCandidateClass(beanClass, Lookup.class)) { try { Class<?> targetClass = beanClass; do { ReflectionUtils.doWithLocalMethods(targetClass, method -> { Lookup lookup = method.getAnnotation(Lookup.class); if (lookup != null) { Assert.state(this.beanFactory != null, "No BeanFactory available"); LookupOverride override = new LookupOverride(method, lookup.value()); try { RootBeanDefinition mbd = (RootBeanDefinition) this.beanFactory.getMergedBeanDefinition(beanName); mbd.getMethodOverrides().addOverride(override); } catch (NoSuchBeanDefinitionException ex) { throw new BeanCreationException(beanName, "Cannot apply @Lookup to beans without corresponding bean definition"); } } }); targetClass = targetClass.getSuperclass(); } while (targetClass != null && targetClass != Object.class); } catch (IllegalStateException ex) { throw new BeanCreationException(beanName, "Lookup method resolution failed", ex); } } 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<>(rawCandidates.length); Constructor<?> requiredConstructor = null; Constructor<?> defaultConstructor = null; Constructor<?> primaryConstructor = BeanUtils.findPrimaryConstructor(beanClass); int nonSyntheticConstructors = 0; for (Constructor<?> candidate : rawCandidates) { if (!candidate.isSynthetic()) { nonSyntheticConstructors++; } else if (primaryConstructor != null) { continue; } MergedAnnotation<?> 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.getParameterCount() == 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.isInfoEnabled()) { logger.info("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<?>[0]); } else if (rawCandidates.length == 1 && rawCandidates[0].getParameterCount() > 0) { candidateConstructors = new Constructor<?>[] {rawCandidates[0]}; } else if (nonSyntheticConstructors == 2 && primaryConstructor != null && defaultConstructor != null && !primaryConstructor.equals(defaultConstructor)) { candidateConstructors = new Constructor<?>[] {primaryConstructor, defaultConstructor}; } else if (nonSyntheticConstructors == 1 && primaryConstructor != null) { candidateConstructors = new Constructor<?>[] {primaryConstructor}; } else { candidateConstructors = new Constructor<?>[0]; } this.candidateConstructorsCache.put(beanClass, candidateConstructors); } } } return (candidateConstructors.length > 0 ? candidateConstructors : null); }rawCandidates = beanClass.getDeclaredConstructors();执行后获得了构造函数： 上面的方法能够解析到我们定义的那个构造函数。于是代码回到createBeanInstance:1213, AbstractAutowireCapableBeanFactory 。调用栈如下图： createBeanInstance:1213, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support) doCreateBean:558, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support) createBean:517, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support) lambda$doGetBean 0 : 332 , A b s t r a c t B e a n F a c t o r y ( o r g . s p r i n g f r a m e w o r k . b e a n s . f a c t o r y . s u p p o r t ) g e t O b j e c t : − 1 , 1991294891 ( o r g . s p r i n g f r a m e w o r k . b e a n s . f a c t o r y . s u p p o r t . A b s t r a c t B e a n F a c t o r y 0:332, AbstractBeanFactory (org.springframework.beans.factory.support) getObject:-1, 1991294891 (org.springframework.beans.factory.support.AbstractBeanFactory 0:332,AbstractBeanFactory(org.springframework.beans.factory.support)getObject:−1,1991294891(org.springframework.beans.factory.support.AbstractBeanFactory$Lambda$32) getSingleton:238, DefaultSingletonBeanRegistry (org.springframework.beans.factory.support) doGetBean:330, AbstractBeanFactory (org.springframework.beans.factory.support) getBean:202, AbstractBeanFactory (org.springframework.beans.factory.support) preInstantiateSingletons:897, DefaultListableBeanFactory (org.springframework.beans.factory.support) finishBeanFactoryInitialization:879, AbstractApplicationContext (org.springframework.context.support) refresh:551, AbstractApplicationContext (org.springframework.context.support) :89, AnnotationConfigApplicationContext (org.springframework.context.annotation) main:9, Main (com.thinking) 进入代码块：
if (ctors != null || mbd.getResolvedAutowireMode() == AUTOWIRE_CONSTRUCTOR || mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {//如果解析到了构造函数，或者构造模式是自动注入，或者具有构造函数参数，或者构造函数参数不为空 return autowireConstructor(beanName, mbd, ctors, args);//构造函数自动注入 }于是需要解析autowireConstructor函数。由下面的代码块可知其将实现逻辑交给了ConstructorResolver类实现。
protected BeanWrapper autowireConstructor( String beanName, RootBeanDefinition mbd, @Nullable Constructor<?>[] ctors, @Nullable Object[] explicitArgs) { return new ConstructorResolver(this).autowireConstructor(beanName, mbd, ctors, explicitArgs); }主要函数autowireConstructor如下：
/** * "autowire constructor" (with constructor arguments by type) behavior. * Also applied if explicit constructor argument values are specified, * matching all remaining arguments with beans from the bean factory. * <p>This corresponds to constructor injection: In this mode, a Spring * bean factory is able to host components that expect constructor-based * dependency resolution. * @param beanName the name of the bean * @param mbd the merged bean definition for the bean * @param chosenCtors chosen candidate constructors (or {@code null} if none) * @param explicitArgs argument values passed in programmatically via the getBean method, * or {@code null} if none (-> use constructor argument values from bean definition) * @return a BeanWrapper for the new instance */ public BeanWrapper autowireConstructor(String beanName, RootBeanDefinition mbd, @Nullable Constructor<?>[] chosenCtors, @Nullable Object[] explicitArgs) { BeanWrapperImpl bw = new BeanWrapperImpl(); this.beanFactory.initBeanWrapper(bw); Constructor<?> constructorToUse = null; ArgumentsHolder argsHolderToUse = null; Object[] argsToUse = null; //explicitArgs通过getBean方法传入 //如果getBean方法调用的时候指定方法参数那么直接使用 if (explicitArgs != null) { argsToUse = explicitArgs; } else { //如果getBean方法时候没有指定则尝试从配置文件中解析 Object[] argsToResolve = null; //尝试从缓存中获取 synchronized (mbd.constructorArgumentLock) { constructorToUse = (Constructor<?>) mbd.resolvedConstructorOrFactoryMethod; if (constructorToUse != null && mbd.constructorArgumentsResolved) { // Found a cached constructor... //从缓存中取 argsToUse = mbd.resolvedConstructorArguments; if (argsToUse == null) { //配置的构造函数参数 argsToResolve = mbd.preparedConstructorArguments; } } } //如果缓存中存在 if (argsToResolve != null) { //解析参数类型，如给定方法的构造函数A(int,int)则通过此方法后就会把配置中的 //("1","1")转换为(1,1) //缓存中的值可能是原始值也可能是最终值 argsToUse = resolvePreparedArguments(beanName, mbd, bw, constructorToUse, argsToResolve, true); } } //没有被缓存 if (constructorToUse == null || argsToUse == null) { // Take specified constructors, if any. Constructor<?>[] candidates = chosenCtors; if (candidates == null) { Class<?> beanClass = mbd.getBeanClass(); try { candidates = (mbd.isNonPublicAccessAllowed() ? beanClass.getDeclaredConstructors() : beanClass.getConstructors()); } catch (Throwable ex) { throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Resolution of declared constructors on bean Class [" + beanClass.getName() + "] from ClassLoader [" + beanClass.getClassLoader() + "] failed", ex); } } if (candidates.length == 1 && explicitArgs == null && !mbd.hasConstructorArgumentValues()) { Constructor<?> uniqueCandidate = candidates[0]; if (uniqueCandidate.getParameterCount() == 0) { synchronized (mbd.constructorArgumentLock) { mbd.resolvedConstructorOrFactoryMethod = uniqueCandidate; mbd.constructorArgumentsResolved = true; mbd.resolvedConstructorArguments = EMPTY_ARGS; } bw.setBeanInstance(instantiate(beanName, mbd, uniqueCandidate, EMPTY_ARGS)); return bw; } } // Need to resolve the constructor. boolean autowiring = (chosenCtors != null || mbd.getResolvedAutowireMode() == AutowireCapableBeanFactory.AUTOWIRE_CONSTRUCTOR); ConstructorArgumentValues resolvedValues = null; int minNrOfArgs; if (explicitArgs != null) { minNrOfArgs = explicitArgs.length; } else { //提取配置文件中的配置的构造函数参数 ConstructorArgumentValues cargs = mbd.getConstructorArgumentValues(); //用于承载解析后的构造函数参数的值 resolvedValues = new ConstructorArgumentValues(); //能解析到的参数个数 minNrOfArgs = resolveConstructorArguments(beanName, mbd, bw, cargs, resolvedValues); } //排序给定的构造函数，public构造函数优先参数数量降序、非public构造函数参数数量降序 AutowireUtils.sortConstructors(candidates); int minTypeDiffWeight = Integer.MAX_VALUE; Set<Constructor<?>> ambiguousConstructors = null; LinkedList<UnsatisfiedDependencyException> causes = null; for (Constructor<?> candidate : candidates) { int parameterCount = candidate.getParameterCount(); if (constructorToUse != null && argsToUse != null && argsToUse.length > parameterCount) { // Already found greedy constructor that can be satisfied -> // do not look any further, there are only less greedy constructors left. //如果已经找到选用的构造函数或者需要的参数个数小于当前的构造函数参数个数则终止, //因为已经按照参数个数降序排列， break; } if (parameterCount < minNrOfArgs) { //参数个数不相等 continue; } ArgumentsHolder argsHolder; Class<?>[] paramTypes = candidate.getParameterTypes(); if (resolvedValues != null) { //有参数则根据值构造对应参数类型的参数 try { //注释上获取参数名称 String[] paramNames = ConstructorPropertiesChecker.evaluate(candidate, parameterCount); if (paramNames == null) {//注释上获取不到参数名称 //获取参数名称探索器 ParameterNameDiscoverer pnd = this.beanFactory.getParameterNameDiscoverer(); if (pnd != null) { //获取指定构造函数的参数名称 paramNames = pnd.getParameterNames(candidate); } } //根据名称和数据类型创建参数持有者 argsHolder = createArgumentArray(beanName, mbd, resolvedValues, bw, paramTypes, paramNames, getUserDeclaredConstructor(candidate), autowiring, candidates.length == 1); } catch (UnsatisfiedDependencyException ex) { if (logger.isTraceEnabled()) { logger.trace("Ignoring constructor [" + candidate + "] of bean '" + beanName + "': " + ex); } // Swallow and try next constructor. if (causes == null) { causes = new LinkedList<>(); } causes.add(ex); continue; } } else { // Explicit arguments given -> arguments length must match exactly. if (parameterCount != explicitArgs.length) { continue; } //构造函数没有参数的情况 argsHolder = new ArgumentsHolder(explicitArgs); } //探测是否有不确定性的构造函数存在，例如不同构造函数的参数为父子关系 int typeDiffWeight = (mbd.isLenientConstructorResolution() ? argsHolder.getTypeDifferenceWeight(paramTypes) : argsHolder.getAssignabilityWeight(paramTypes)); // Choose this constructor if it represents the closest match. //如果它代表着当前最接近的匹配则选择作为构造函数 if (typeDiffWeight < minTypeDiffWeight) { constructorToUse = candidate; argsHolderToUse = argsHolder; argsToUse = argsHolder.arguments; minTypeDiffWeight = typeDiffWeight; ambiguousConstructors = null; } else if (constructorToUse != null && typeDiffWeight == minTypeDiffWeight) { if (ambiguousConstructors == null) { ambiguousConstructors = new LinkedHashSet<>(); ambiguousConstructors.add(constructorToUse); } ambiguousConstructors.add(candidate); } } if (constructorToUse == null) { if (causes != null) { UnsatisfiedDependencyException ex = causes.removeLast(); for (Exception cause : causes) { this.beanFactory.onSuppressedException(cause); } throw ex; } throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Could not resolve matching constructor " + "(hint: specify index/type/name arguments for simple parameters to avoid type ambiguities)"); } else if (ambiguousConstructors != null && !mbd.isLenientConstructorResolution()) { throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Ambiguous constructor matches found in bean '" + beanName + "' " + "(hint: specify index/type/name arguments for simple parameters to avoid type ambiguities): " + ambiguousConstructors); } if (explicitArgs == null && argsHolderToUse != null) { //将解析的构造函数加入缓存 argsHolderToUse.storeCache(mbd, constructorToUse); } } Assert.state(argsToUse != null, "Unresolved constructor arguments"); bw.setBeanInstance(instantiate(beanName, mbd, constructorToUse, argsToUse));//构造实例对象 return bw; }执行到下面的那行代码时情况如下： 由于现在构造函数参数数量不为0，所以不会进入183行的代码。 上面进行配置的构造函数参数的解析。它调用BeanDefinition的方法判断配置中是否有构造函数的参数： 从上图可知没有配置构造函数参数。 具体解析构造函数参数的方法如下：
/** * Resolve the constructor arguments for this bean into the resolvedValues object. * This may involve looking up other beans. * <p>This method is also used for handling invocations of static factory methods. */ private int resolveConstructorArguments(String beanName, RootBeanDefinition mbd, BeanWrapper bw, ConstructorArgumentValues cargs, ConstructorArgumentValues resolvedValues) { TypeConverter customConverter = this.beanFactory.getCustomTypeConverter(); TypeConverter converter = (customConverter != null ? customConverter : bw); BeanDefinitionValueResolver valueResolver = new BeanDefinitionValueResolver(this.beanFactory, beanName, mbd, converter); int minNrOfArgs = cargs.getArgumentCount(); for (Map.Entry<Integer, ConstructorArgumentValues.ValueHolder> entry : cargs.getIndexedArgumentValues().entrySet()) { int index = entry.getKey(); if (index < 0) { throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Invalid constructor argument index: " + index); } if (index + 1 > minNrOfArgs) { minNrOfArgs = index + 1; } ConstructorArgumentValues.ValueHolder valueHolder = entry.getValue(); if (valueHolder.isConverted()) { resolvedValues.addIndexedArgumentValue(index, valueHolder); } else { Object resolvedValue = valueResolver.resolveValueIfNecessary("constructor argument", valueHolder.getValue()); ConstructorArgumentValues.ValueHolder resolvedValueHolder = new ConstructorArgumentValues.ValueHolder(resolvedValue, valueHolder.getType(), valueHolder.getName()); resolvedValueHolder.setSource(valueHolder); resolvedValues.addIndexedArgumentValue(index, resolvedValueHolder); } } for (ConstructorArgumentValues.ValueHolder valueHolder : cargs.getGenericArgumentValues()) { if (valueHolder.isConverted()) { resolvedValues.addGenericArgumentValue(valueHolder); } else { Object resolvedValue = valueResolver.resolveValueIfNecessary("constructor argument", valueHolder.getValue()); ConstructorArgumentValues.ValueHolder resolvedValueHolder = new ConstructorArgumentValues.ValueHolder( resolvedValue, valueHolder.getType(), valueHolder.getName()); resolvedValueHolder.setSource(valueHolder); resolvedValues.addGenericArgumentValue(resolvedValueHolder); } } return minNrOfArgs; }在下面的图片红色框内会由于解析失败而抛出异常： 由于异常抛出，跳转回来： 再次抛出异常： 在上图中销毁单例并抛出异常， 跳转到下面的getSingleton函数 快要跳出bean的创建代码了，如下： 结束如下： 应该是要给它配置好构造函数的输入参数才行。这样就不会抛出异常。由此可知如果没有提供默认构造函数，而且配置没有传递实现的构造函数需要的参数就会异常。 但是现在找到的只有通过xml文件注入基本属性，还没有自动注入基本数据类型的方法，只能使用下面的方式：
import org.springframework.beans.factory.annotation.Value; import org.springframework.stereotype.Component; import java.util.List; import java.util.Map; import java.util.Properties; import java.util.Set; /** * 注解方式不需要get ，set * @author wyy * @date 2020/6/28 15:39 */ @Component public class Hero { @Value("张三") private String name; @Value("18") private int age; @Value("#{l}") private List<String> list; @Value("#{s}") private Set<String> set; @Value("#{m}") private Map<String,String> map; @Value("#{p}") private Properties prop; @Override public String toString() { return "Hero{" + "name='" + name + '\'' + ", age=" + age + ", list=" + list + ", set=" + set + ", map=" + map + ", prop=" + prop + '}'; } }而不能通过构造函数？？
如果在原始类上加一个无参构造函数，就可以解析成功，而且不报错。
package com.thinking.bean.test; import org.springframework.stereotype.Component; @Component public class ConstructParam { int year; public ConstructParam() { } public ConstructParam(Integer year) { this.year = year; } }