Spring推断构造方法
贴个测试代码直接开干，这只是个样例，其他情况自行分析
@Componentpublic class OrderService { public OrderService() {System.out.println("无参构造方法");} @Autowired(required = false)public OrderService(UserService userService) {System.out.println("一个参数的构造方法");} @Autowired(required = false)public OrderService(String userName, String passWord) {System.out.println("两个参数的构造方法");}}
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#createBeanInstance
protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) { // 加载类// Make sure bean class is actually resolved at this point.Class<?> beanClass = resolveBeanClass(mbd, beanName); // 确保class不为空，并且访问权限为publicif (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());} // 配置的一种特殊的callback回调方法，通过这个callback创建bean// 检查BeanDefinition是否包含了一个SupplierSupplier<?> instanceSupplier = mbd.getInstanceSupplier();if (instanceSupplier != null) {// 如果有就直接调用Supplier的get方法得到一个对象直接返回return obtainFromSupplier(instanceSupplier, beanName);} // 通过工厂方法创建if (mbd.getFactoryMethodName() != null) {// 如果BeanDefinition中存在FactoryMethodName，那么调用工厂方法得到一个bean对象并返回return instantiateUsingFactoryMethod(beanName, mbd, args);} // 一个类可能有多个构造器，所以Spring得根据参数个数、类型确定需要调用的构造器// 在使用构造器创建实例后，Spring会将解析过后确定下来的构造器或工厂方法保存在缓存中，避免再次创建相同bean时再次解析// Shortcut when re-creating the same bean...boolean resolved = false;boolean autowireNecessary = false;if (args == null) {synchronized (mbd.constructorArgumentLock) {if (mbd.resolvedConstructorOrFactoryMethod != null) {// 已经解析过class的构造器resolved = true;autowireNecessary = mbd.constructorArgumentsResolved;}}}if (resolved) {// 已经解析过class的构造器，使用已经解析好的构造器if (autowireNecessary) {// 如果BeanDefinition中已经构造过// 构造函数自动注入// 自动装配构造函数，俗称推断构造方法return autowireConstructor(beanName, mbd, null, null);}else {// 使用默认构造器return instantiateBean(beanName, mbd);}} // TODO 推断构造方法// 需要根据参数解析、确定构造函数// 寻找当前实例化的bean中构造器是否有@Autowire注解// Candidate constructors for autowiring?Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName); // 解析的构造器不为空 || 注入类型为构造函数自动注入 || beanDefinition指定了构造方法参数值 || getBean时指定了构造方法参数if (ctors != null || mbd.getResolvedAutowireMode() == AUTOWIRE_CONSTRUCTOR ||mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) { // 到这里可能找到了多个构造方法，还要决定到底用哪个进行反射初始化return autowireConstructor(beanName, mbd, ctors, args);} // 默认构造的首选构造函数？// Preferred constructors for default construction?ctors = mbd.getPreferredConstructors();if (ctors != null) {return autowireConstructor(beanName, mbd, ctors, null);} // 无需特殊处理：只需使用默认的无参构造函数// No special handling: simply use no-arg constructor.return instantiateBean(beanName, mbd);}
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#determineConstructorsFromBeanPostProcessors
protected Constructor<?>[] determineConstructorsFromBeanPostProcessors(@Nullable Class<?> beanClass, String beanName)throws BeansException { // 装配beanPostProcessor的时候会判断其类型并设置 hasInstantiationAwareBeanPostProcessors 属性, 符合条件才去找构造函数if (beanClass != null && hasInstantiationAwareBeanPostProcessors()) { // getBeanPostProcessors拿到beanFactory中的所有BeanPostProcessor接口，找到一个合格的构造函数for (BeanPostProcessor bp : getBeanPostProcessors()) {if (bp instanceof SmartInstantiationAwareBeanPostProcessor) {SmartInstantiationAwareBeanPostProcessor ibp = (SmartInstantiationAwareBeanPostProcessor) bp; // 获取有autowire注解的构造函数 找到合格的构造函数// AutowiredAnnotationBeanPostProcessor.determineCandidateConstructorsConstructor<?>[] ctors = ibp.determineCandidateConstructors(beanClass, beanName);if (ctors != null) {return ctors;}}}}return null;}
org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor#determineCandidateConstructors
public Constructor<?>[] determineCandidateConstructors(Class<?> beanClass, final String beanName)throws BeanCreationException { // @Lookup标识的属性每次调用都会被重新初始化，// 有些场景下原型类型的Bean就需要这样做，否则每个Bean只会在spring容器初始化的时候创建一次，// 但是如果在一个单例的Bean中注入了一个原型的Bean，这样的话原本原型的Bean就相当于变成了一个单例的Bean失去了原有的意义，// 这时就需要@Lookup来解决，或者是每次都从新从spring容器中通过getBean来获取Bean// 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);} // 一般只有原型的bean才会创建多次// 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 {// 获取所有构造方法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);}// 定义要选举的构造方法集合List<Constructor<?>> candidates = new ArrayList<>(rawCandidates.length); // 加了@AutoWire()并且是require=true的构造方法Constructor<?> requiredConstructor = null; // 默认构造发给方法Constructor<?> defaultConstructor = null; // 返回与 Kotlin 主构造函数相对应的 Java 构造函数, 否则，特别是对于非 Kotlin 类，这只会返回 {@code null}。Constructor<?> primaryConstructor = BeanUtils.findPrimaryConstructor(beanClass); // 记录合成的构造方法数量，理解为可用的构造方法个数吧int nonSyntheticConstructors = 0; // 遍历所有的构造方法for (Constructor<?> candidate : rawCandidates) {if (!candidate.isSynthetic()) {nonSyntheticConstructors++;}else if (primaryConstructor != null) {continue;} // 加了@Autowired的构造方法MergedAnnotation<?> ann = findAutowiredAnnotation(candidate);if (ann == null) {Class<?> userClass = ClassUtils.getUserClass(beanClass);if (userClass != beanClass) {try {Constructor<?> superCtor = userClass.getDeclaredConstructor(candidate.getParameterTypes()); // 在父类中找@Autowired的构造方法ann = findAutowiredAnnotation(superCtor);}catch (NoSuchMethodException ex) {// Simply proceed, no equivalent superclass constructor found...}}}if (ann != null) {// 如果找到加了@Autowired注解的构造方法，再判断required属性 // 加了@AutoWire()并且是require=true的构造方法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) {// 否则如果构造函数参数个数为0，把它赋值给变量defaultConstructordefaultConstructor = candidate;}} // 处理上面遍历后的结果if (!candidates.isEmpty()) {// Add default constructor to list of optional constructors, as fallback.if (requiredConstructor == null) {// 如果加了@Autowired、并且没有指定required为true、并且存在默认的构造方法if (defaultConstructor != null) {// 把默认构造方法加到待筛选的集合中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]);}// 如果只有一个构造方法，并且构造数的参数大于0else if (rawCandidates.length == 1 && rawCandidates[0].getParameterCount() > 0) {candidateConstructors = new Constructor<?>[] {rawCandidates[0]};}// primaryConstructor 做java开发一般都是nullelse if (nonSyntheticConstructors == 2 && primaryConstructor != null &&defaultConstructor != null && !primaryConstructor.equals(defaultConstructor)) {candidateConstructors = new Constructor<?>[] {primaryConstructor, defaultConstructor};}// primaryConstructor 做java开发一般都是nullelse if (nonSyntheticConstructors == 1 && primaryConstructor != null) {candidateConstructors = new Constructor<?>[] {primaryConstructor};}else {candidateConstructors = new Constructor<?>[0];}// 把推断的构造方法数组放到缓存map中this.candidateConstructorsCache.put(beanClass, candidateConstructors);}}}return (candidateConstructors.length > 0 ? candidateConstructors : null);
推断构造方法第一步，先找出可用的构造方法，步骤如下：
1、先找出所有的构造方法。
2、遍历所有构造方法，找出加了@Autowire的构造方法，如果没找到就在父类中找，父类中还找不到，但是存在一个构造方法的参数的个数为0，就作为默认的构造方法；如果找到了加了@Autowire的构造方法，并且require都为true则直接报错。
3、再次过滤上面筛选过的构造方法，如果有默认构造方法就加入候选者的集合；如果上面筛选过后没有合适的构造方法，但是又只有参数个数大于0的构造方法，就把他加入到候选者的列表中。
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#autowireConstructor
protected BeanWrapper autowireConstructor(String beanName, RootBeanDefinition mbd, @Nullable Constructor<?>[] ctors, @Nullable Object[] explicitArgs) {// 带有参数情况的实例化return new ConstructorResolver(this).autowireConstructor(beanName, mbd, ctors, explicitArgs);}
org.springframework.beans.factory.support.ConstructorResolver#autowireConstructor
public BeanWrapper autowireConstructor(String beanName, RootBeanDefinition mbd,@Nullable Constructor<?>[] chosenCtors, @Nullable Object[] explicitArgs) { //实例化BeanWrapper，是包装bean的容器BeanWrapperImpl bw = new BeanWrapperImpl();this.beanFactory.initBeanWrapper(bw); Constructor<?> constructorToUse = null;ArgumentsHolder argsHolderToUse = null;Object[] argsToUse = null; // 1、首先判断是否通过getBean方法指定了构造方法参数值// 如果getBean中传入的参数不为空，那么就使用传入的参数if (explicitArgs != null) {argsToUse = explicitArgs;}// 否则就需要解析配置文件中的参数else {Object[] argsToResolve = null;// 先尝试从缓存中获取synchronized (mbd.constructorArgumentLock) {// 缓存中的构造器constructorToUse = (Constructor<?>) mbd.resolvedConstructorOrFactoryMethod; // 2、针对当前BeanDefinition是否缓存了构造方法和构造方法参数值if (constructorToUse != null && mbd.constructorArgumentsResolved) {// 在缓存中找到了构造器，就继续从缓存中寻找缓存的构造器参数// Found a cached constructor...argsToUse = mbd.resolvedConstructorArguments;if (argsToUse == null) {// 没有缓存的参数，就需要获取配置文件中配置的参数argsToResolve = mbd.preparedConstructorArguments;}}}// 如果缓存中没有缓存的参数的话，即argsToResolve不为空，就需要解析配置的参数if (argsToResolve != null) {// 解析参数类型，比如将配置的String类型转换成int、boolean等类型argsToUse = resolvePreparedArguments(beanName, mbd, bw, constructorToUse, argsToResolve, true);}} // 3、如果两者任意一个为空，则继续进行下面的步骤// 如果没有缓存，就需要从构造函数开始解析if (constructorToUse == null || argsToUse == null) { // 如果传入的构造器数组不为空，就使用传入的构造器参数，否则通过反射获取class中定义的构造器// Take specified constructors, if any.Constructor<?>[] candidates = chosenCtors; // 3.1 如果没有传入构造方法，那么则获取当前BeanDefinition对应的BeanClass中所有的构造方法作为候选者if (candidates == null) {Class<?> beanClass = mbd.getBeanClass();try {// 使用public的构造器或者所有构造器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);}} // 3.2 判断候选者构造方法是不是只有一个，并且没有指定构造方法参数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;}// 初始化并设置构造器参数bw.setBeanInstance(instantiate(beanName, mbd, uniqueCandidate, EMPTY_ARGS));return bw;}} // 是否需要解析构造器，在配置文件中指定注入方式为构造器注入// Need to resolve the constructor.boolean autowiring = (chosenCtors != null ||mbd.getResolvedAutowireMode() == AutowireCapableBeanFactory.AUTOWIRE_CONSTRUCTOR); // 存放解析后的构造方法参数值ConstructorArgumentValues resolvedValues = null; int minNrOfArgs;if (explicitArgs != null) {// getBean方法传入的参数minNrOfArgs = explicitArgs.length;}else {// 配置文件中的配置的参数ConstructorArgumentValues cargs = mbd.getConstructorArgumentValues();// 用于承载解析后的构造函数参数的值resolvedValues = new ConstructorArgumentValues();// 解析配置文件中的参数，并且返回参数个数minNrOfArgs = resolveConstructorArguments(beanName, mbd, bw, cargs, resolvedValues);} // 3.3 对候选者构造函数排序，public构造函数优先、参数数量降序排序AutowireUtils.sortConstructors(candidates); // 计算构造方法参数个数最少个数// 意思是如果指定了构造方法参数个数，所以当前BeanDefinition对应的BeanClass中所有构造方法参数个数至少满足手动指定的参数值个数int minTypeDiffWeight = Integer.MAX_VALUE; Set<Constructor<?>> ambiguousConstructors = null;LinkedList<UnsatisfiedDependencyException> causes = null; // 3.4 遍历所有的构造方法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.break;} // 如果候选者参数个数 < minNrOfArgs，则不匹配，继续下一个if (parameterCount < minNrOfArgs) {continue;} // 封装解析到的参数信息ArgumentsHolder argsHolder; Class<?>[] paramTypes = candidate.getParameterTypes(); // 解析配置文件得到的构造方法参数值if (resolvedValues != null) {try {// 3.5 判断通过getBean方法指定构造方法参数String[] paramNames = ConstructorPropertiesChecker.evaluate(candidate, parameterCount);if (paramNames == null) {ParameterNameDiscoverer pnd = this.beanFactory.getParameterNameDiscoverer();if (pnd != null) {paramNames = pnd.getParameterNames(candidate);}}// 参数个数匹配的情况下把所有参数封装为一个ArgumentsHolder对象，不匹配就直接报错了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 {// 处理参数由getBean方法传入的情况// Explicit arguments given -> arguments length must match exactly.if (parameterCount != explicitArgs.length) {continue;}argsHolder = new ArgumentsHolder(explicitArgs);} // 3.7 计算得到的构造方法参数值和参数的匹配程度// 因为不同构造函数的参数个数相同，而且参数类型为父子关系，所以需要找出类型最符合的一个构造函数// Spring用一种权重的形式来表示类型差异程度，差异权重越小越优先// 如果是以宽松的方式解析，默认为true，所以执行getTypeDifferenceWeightint typeDiffWeight = (mbd.isLenientConstructorResolution() ?argsHolder.getTypeDifferenceWeight(paramTypes) : argsHolder.getAssignabilityWeight(paramTypes)); // 当前构造函数最为匹配的话，清空先前ambiguousConstructors列表// Choose this constructor if it represents the closest match.if (typeDiffWeight < minTypeDiffWeight) {constructorToUse = candidate;argsHolderToUse = argsHolder;argsToUse = argsHolder.arguments;minTypeDiffWeight = typeDiffWeight;ambiguousConstructors = null;}// 存在相同权重的构造器，将构造器添加到一个ambiguousConstructors列表变量中// 注意,这时候constructorToUse 指向的仍是第一个匹配的构造函数else if (constructorToUse != null && typeDiffWeight == minTypeDiffWeight) {if (ambiguousConstructors == null) {ambiguousConstructors = new LinkedHashSet<>();ambiguousConstructors.add(constructorToUse);}ambiguousConstructors.add(candidate);}} /*******************************************************************************************************/ if (constructorToUse == null) {// 如果没有匹配的构造函数，抛出异常。略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()) {// 如果存在多个构造函数匹配程度相同，并且BeanDefinition中设置isLenientConstructorResolution为false(默认值为true)，// 表示构造器创建为严格模式的话，会抛出异常。异常代码略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) {argsHolderToUse.storeCache(mbd, constructorToUse);}} Assert.state(argsToUse != null, "Unresolved constructor arguments"); // 初始化bw.setBeanInstance(instantiate(beanName, mbd, constructorToUse, argsToUse));return bw;}
1、只有一个无参的构造方法，那么直接使用无参的构造方法进行实例化 candidates.length == 1
2、有多个构造方法或者bean需要通过构造方法自动进行注入 ResolvedAutowireMode() == 3
3、根据所指定的构造方法参数值，确定所需要的最少的构造方法参数值的个数 minNrOfArgs
4、对所有的构造方法进行排序，参数个数多的在前面 AutowireUtils.sortConstructors
5、遍历所有的构造方法
6、如果当前构造方法参数个数小于minNrOfArgs则不匹配，继续判断下一个构造方法
7、如果是调用getBean方法指定的参数就直接利用这些值，如果不是就根据构造方法参数类型找值（先byType再byName），匹配的话则封装成一个ArgumentsHolder对象
8、这里可能会匹配到多个构造方法，然后就需要那值和构造方法匹配程度计算一个权重，值越小优先级越高（因为如果是父子类的话子类匹配成功更高）
9、计算权重分为宽松型（默认）和严格型，严格型的情况下如果有多个匹配就报错
到此这篇关于Spring源码解析之推断构造方法的文章就介绍到这了,更多相关Spring推断构造方法内容请搜索以前的文章或继续浏览下面的相关文章希望大家以后多多支持！
别为荒漠的艰难而哭泣，只为奔流入海功成名就那一天，
