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本篇內容介紹了“Spring createBeanInstance怎么實例化Bean”的有關知識，在實際案例的操作過程中，不少人都會遇到這樣的困境，接下來就讓小編帶領大家學習一下如何處理這些情況吧！希望大家仔細閱讀，能夠學有所成！
Spring實例Bean的方法，在AbstractAutowireCapableBeanFactory中的
protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {
// Make sure bean class is actually resolved at this point.
//解析Bean的類型，確認需要創建的bean實例的類可以實例化。
//如果沒有設置通過Class.forName獲取Bean類型
Class<?> beanClass = resolveBeanClass(mbd, beanName);
// 確保class不為空，并且訪問權限是public
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());
}
//①Supplier方式創建Bean: 需要先有回調Bean
// 判斷當前beanDefinition中是否包含實例供應器，此處相當于一個回調方法，利用回調方法來創建bean
Supplier<?> instanceSupplier = mbd.getInstanceSupplier();
if (instanceSupplier != null) {
return obtainFromSupplier(instanceSupplier, beanName);
}
//②FactoryMethod方式創建Bean: 需要在XML中配置factory-method
// 判斷是否有工廠方法，如果存在，會嘗試調用該Bean定義信息中的工廠方法來獲取實例
if (mbd.getFactoryMethodName() != null) {
return instantiateUsingFactoryMethod(beanName, mbd, args);
}
// Shortcut when re-creating the same bean...
//一個類可能有多個構造器，所以Spring得根據參數個數、類型確定需要調用的構造器，當多次構建同一個 bean 時就不需要重新判斷應該使用那種方式構造Bean
boolean resolved = false;
//是否需要自動裝配
boolean autowireNecessary = false;
if (args == null) {
synchronized (mbd.constructorArgumentLock) {
// 因為判斷過程會比較，所以spring會將解析、確定好的構造函數緩存到BeanDefinition中的resolvedConstructorOrFactoryMethod字段中。
// 在下次創建相同時直接從RootBeanDefinition中的屬性resolvedConstructorOrFactoryMethod緩存的值獲取，避免再次解析，導致循環依賴
if (mbd.resolvedConstructorOrFactoryMethod != null) {
//標識以及解析過class的構造器
resolved = true;
autowireNecessary = mbd.constructorArgumentsResolved;
}
}
}
// 有構造參數的或者工廠
if (resolved) {
//已經解析過class的構造器，使用已經解析好的構造器
if (autowireNecessary) {
//構造函數自動注入
return autowireConstructor(beanName, mbd, null, null);
}
else {
//使用默認構造器
return instantiateBean(beanName, mbd);
}
}
// Candidate constructors for autowiring?
// 從bean后置處理器中為自動裝配尋找構造方法
// 以下情況符合其一即可進入
// 1、存在可選構造方法
// 2、自動裝配模型為構造函數自動裝配
// 3、給BeanDefinition中設置了構造參數值
// 4、有參與構造函數參數列表的參數
//一、確定構造參數
Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
if (ctors != null || mbd.getResolvedAutowireMode() == AUTOWIRE_CONSTRUCTOR ||
mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {
return autowireConstructor(beanName, mbd, ctors, args);
}
// Preferred constructors for default construction?
// 從bean后置處理器中為自動裝配尋找構造方法, 有且僅有一個有參構造或者有且僅有@Autowired注解構造
ctors = mbd.getPreferredConstructors();
if (ctors != null) {
// 構造函數自動注入
// 二、有參構造創建Bean
return autowireConstructor(beanName, mbd, ctors, null);
}
// No special handling: simply use no-arg constructor.
// 使用默認無參構造函數創建對象，如果沒有無參構造且存在多個有參構造且沒有@AutoWired注解構造，會報錯
//三、無參構造創建Bean
return instantiateBean(beanName, mbd);
}①：Supplier方式創建Bean：5、Spring源碼之Supplier
②：FactoryMethod方式創建Bean: 【Spring源碼】8.IOC之創建bean對象之FactoryMethod
③：自動裝配類型
int AUTOWIRE_NO = 0;//表示沒有外部定義的自動裝配
int AUTOWIRE_BY_NAME = 1;//通過名稱指示自動裝配bean屬性(適用于Bean所有屬性的setter)
int AUTOWIRE_BY_TYPE = 2;//通過類型指示自動裝配bean屬性(適用于Bean所有屬性的setter)
int AUTOWIRE_CONSTRUCTOR = 3;//構造函數
int AUTOWIRE_AUTODETECT = 4;//通過bean類的內省確定適當的自動裝配策略,在Spring3.0之后已經不再支持。
String ORIGINAL_INSTANCE_SUFFIX = ".ORIGINAL";//用于沒有代理的時候，也能強制返回實例
實現父類SmartInstantiationAwareBeanPostProcessor后置處理器的determineCandidateConstructors方法
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;
//執行后置處理器，確定構造函數
Constructor<?>[] ctors = ibp.determineCandidateConstructors(beanClass, beanName);
if (ctors != null) {
return ctors;
}
}
}
}
return null;
}這里會通過AutowiredAnnotationBeanPostProcessor后置處理器確定構造函數
詳情：http://www.mlszssj.com/article/277330.htm
創建構造器解析器自動寫入構造函數
protected BeanWrapper autowireConstructor(
String beanName, RootBeanDefinition mbd, @Nullable Constructor<?>[] ctors, @Nullable Object[] explicitArgs) {
return new ConstructorResolver(this).autowireConstructor(beanName, mbd, ctors, explicitArgs);
}public BeanWrapper autowireConstructor(String beanName, RootBeanDefinition mbd,
@Nullable Constructor<?>[] chosenCtors, @Nullable Object[] explicitArgs) {
//實例化BeanWrapper，是包裝bean的容器
BeanWrapperImpl bw = new BeanWrapperImpl();
this.beanFactory.initBeanWrapper(bw);
Constructor<?> constructorToUse = null;
ArgumentsHolder argsHolderToUse = null;
Object[] argsToUse = null;
//如果getBean中傳入的參數不為空，那么就使用傳入的參數
if (explicitArgs != null) {
argsToUse = explicitArgs;
}//解析構造參數
else {
Object[] argsToResolve = null;
//嘗試從緩存中獲取
synchronized (mbd.constructorArgumentLock) {
constructorToUse = (Constructor<?>) mbd.resolvedConstructorOrFactoryMethod;
//獲取緩存中的構造器
if (constructorToUse != null && mbd.constructorArgumentsResolved) {
// Found a cached constructor...
//在緩存中找到了構造器，就繼續從緩存中尋找緩存的構造器參數
argsToUse = mbd.resolvedConstructorArguments;
if (argsToUse == null) {
//構造器中沒有緩存的參數，就需要獲取配置文件中配置的參數
argsToResolve = mbd.preparedConstructorArguments;
}
}
}
//如果有構造器但是構造器中沒有參數，就需要解析構造參數
if (argsToResolve != null) {
//解析參數類型，比如將配置的String類型轉換成int、boolean等類型
argsToUse = resolvePreparedArguments(beanName, mbd, bw, constructorToUse, argsToResolve, true);
}
}
//如果沒有緩存，就需要先解析構造函數
if (constructorToUse == null || argsToUse == null) {
// Take specified constructors, if any.
// 如果傳入的構造器數組不為空，就使用傳入的構造器參數，否則通過反射獲取class中定義的構造器
Constructor<?>[] candidates = chosenCtors;
if (candidates == null) {
Class<?> beanClass = mbd.getBeanClass();
try {
//通過反射獲取class中定義的構造器
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);
}
}
//如果只有一個構造函數并且參數值為null，則直接使用無參構造器實例化
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.
//如果構造器不會空或者需要構造器注入則需要自動裝配
boolean autowiring = (chosenCtors != null ||
mbd.getResolvedAutowireMode() == AutowireCapableBeanFactory.AUTOWIRE_CONSTRUCTOR);
ConstructorArgumentValues resolvedValues = null;
int minNrOfArgs;
if (explicitArgs != null) {
minNrOfArgs = explicitArgs.length;
}
else {
//獲取構造參數值
ConstructorArgumentValues cargs = mbd.getConstructorArgumentValues();
resolvedValues = new ConstructorArgumentValues();
//2.1 解析參數并返回最小參數個數
minNrOfArgs = resolveConstructorArguments(beanName, mbd, bw, cargs, resolvedValues);
}
//給構造函數排序，public構造函數優先、參數數量降序排序
AutowireUtils.sortConstructors(candidates);
int minTypeDiffWeight = Integer.MAX_VALUE;
Set<Constructor<?>> ambiguousConstructors = null;
LinkedList<UnsatisfiedDependencyException> causes = null;
for (Constructor<?> candidate : candidates) {
int parameterCount = candidate.getParameterCount();
//如果找到已經滿足的構造器就直接返回
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;
}
//如果構造器參數值小于最小參數個數直接返回
if (parameterCount < minNrOfArgs) {
continue;
}
ArgumentsHolder argsHolder;
//獲取構造器參數類型
Class<?>[] paramTypes = candidate.getParameterTypes();
//需要解析的參數值不為空
if (resolvedValues != null) {
try {
//通過構造器上@ConstructorProperties注解獲取參數名稱
String[] paramNames = ConstructorPropertiesChecker.evaluate(candidate, parameterCount);
//如果參數名稱為空
if (paramNames == null) {
//獲取參數名稱解析器
ParameterNameDiscoverer pnd = this.beanFactory.getParameterNameDiscoverer();
if (pnd != null) {
//獲取參數名稱
paramNames = pnd.getParameterNames(candidate);
}
}
//根據獲取到的參數名和已經查到的構造參數和構造參數類型來創建用戶創建構造器用的構造參數數組
//這個數組中包含了原始的參數列表和構造后的參數列表，用來對比用
//2.2 創建構造參數數組
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;
}
argsHolder = new ArgumentsHolder(explicitArgs);
}
//如果是寬松的構造策略，則對比spring構造的參數數組的類型和獲取到的構造器參數的參數類型進行對比，返回不同的個數
//如果是嚴格的構造策略，則檢查能否將構造的參數數組賦值到構造器參數的參數列表中
int typeDiffWeight = (mbd.isLenientConstructorResolution() ?
argsHolder.getTypeDifferenceWeight(paramTypes) : argsHolder.getAssignabilityWeight(paramTypes));
// Choose this constructor if it represents the closest match.
// 當前構造函數最為匹配的話，清空先前ambiguousConstructors列表
if (typeDiffWeight < minTypeDiffWeight) {
constructorToUse = candidate;
argsHolderToUse = argsHolder;
argsToUse = argsHolder.arguments;
minTypeDiffWeight = typeDiffWeight;
ambiguousConstructors = null;
}
//存在相同權重的構造器，將構造器添加到一個ambiguousConstructors列表變量中
//注意,這時候constructorToUse 指向的仍是第一個匹配的構造函數
else if (constructorToUse != null && typeDiffWeight == minTypeDiffWeight) {
if (ambiguousConstructors == null) {
ambiguousConstructors = new LinkedHashSet<>();
ambiguousConstructors.add(constructorToUse);
}
ambiguousConstructors.add(candidate);
}
}
//如果沒有匹配的構造函數，拋出異常
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);
}
//緩存參數構造器，下次創建直接使用
//并設置constructorArgumentsResolved為true，表示已經解析過構造函數
if (explicitArgs == null && argsHolderToUse != null) {
argsHolderToUse.storeCache(mbd, constructorToUse);
}
}
Assert.state(argsToUse != null, "Unresolved constructor arguments");
//2.3 實例化Bean
bw.setBeanInstance(instantiate(beanName, mbd, constructorToUse, argsToUse));
return bw;
}private int resolveConstructorArguments(String beanName, RootBeanDefinition mbd, BeanWrapper bw,
ConstructorArgumentValues cargs, ConstructorArgumentValues resolvedValues) {
// 是否有定制的類型轉換器，沒有的話直接使用BeanWrapper進行類型轉換
TypeConverter customConverter = this.beanFactory.getCustomTypeConverter();
TypeConverter converter = (customConverter != null ? customConverter : bw);
// 構造一個BeanDefinitionValueResolver，專門用于解析constructor-arg中的value屬性，實際上還包括ref屬性，內嵌bean標簽等等
BeanDefinitionValueResolver valueResolver =
new BeanDefinitionValueResolver(this.beanFactory, beanName, mbd, converter);
// minNrOfArgs 記錄執行方法要求的最小參數個數，一般情況下就是等于constructor-arg標簽指定的參數數量
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);
}
// 假設A方法直接在配置文件中指定了index=3上要使用的參數，那么這個時候A方法至少需要4個參數
// 但是其余的3個參數可能不是通過constructor-arg標簽指定的，而是直接自動注入進來的，那么在配置文件中我們就只配置了index=3上的參數，也就是說 int minNrOfArgs = cargs.getArgumentCount()=1，這個時候 index=3,minNrOfArgs=1, 所以 minNrOfArgs = 3+1
if (index + 1 > minNrOfArgs) {
minNrOfArgs = index + 1;
}
ConstructorArgumentValues.ValueHolder valueHolder = entry.getValue();
// 如果已經轉換過了，直接添加到resolvedValues集合中
if (valueHolder.isConverted()) {
resolvedValues.addIndexedArgumentValue(index, valueHolder);
}
else {
// 解析value/ref/內嵌bean標簽等
Object resolvedValue =
valueResolver.resolveValueIfNecessary("constructor argument", valueHolder.getValue());
// 將解析后的resolvedValue封裝成一個新的ValueHolder，
// 并將其source設置為解析constructor-arg得到的那個ValueHolder，
// 后期會用到這個屬性進行判斷
ConstructorArgumentValues.ValueHolder resolvedValueHolder =
new ConstructorArgumentValues.ValueHolder(resolvedValue, valueHolder.getType(), valueHolder.getName());
resolvedValueHolder.setSource(valueHolder);
resolvedValues.addIndexedArgumentValue(index, resolvedValueHolder);
}
}
// 對getGenericArgumentValues進行解析
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;
}private ArgumentsHolder createArgumentArray(
String beanName, RootBeanDefinition mbd, @Nullable ConstructorArgumentValues resolvedValues,
BeanWrapper bw, Class<?>[] paramTypes, @Nullable String[] paramNames, Executable executable,
boolean autowiring, boolean fallback) throws UnsatisfiedDependencyException {
TypeConverter customConverter = this.beanFactory.getCustomTypeConverter();
TypeConverter converter = (customConverter != null ? customConverter : bw);
ArgumentsHolder args = new ArgumentsHolder(paramTypes.length);
Set<ConstructorArgumentValues.ValueHolder> usedValueHolders = new HashSet<>(paramTypes.length);
Set<String> autowiredBeanNames = new LinkedHashSet<>(4);
for (int paramIndex = 0; paramIndex < paramTypes.length; paramIndex++) {
Class<?> paramType = paramTypes[paramIndex];
String paramName = (paramNames != null ? paramNames[paramIndex] : "");
// Try to find matching constructor argument value, either indexed or generic.
// 嘗試找到匹配的構造函數參數值，無論是索引的還是泛型的。
ConstructorArgumentValues.ValueHolder valueHolder = null;
if (resolvedValues != null) {
valueHolder = resolvedValues.getArgumentValue(paramIndex, paramType, paramName, usedValueHolders);
// If we couldn't find a direct match and are not supposed to autowire,
// let's try the next generic, untyped argument value as fallback:
// it could match after type conversion (for example, String -> int).
// 如果我們找不到直接匹配并且不應該自動裝配，讓我們嘗試下一個通用的、無類型的參數值作為后備：它可以在類型轉換后匹配（例如，String -> int）。
if (valueHolder == null && (!autowiring || paramTypes.length == resolvedValues.getArgumentCount())) {
valueHolder = resolvedValues.getGenericArgumentValue(null, null, usedValueHolders);
}
}
if (valueHolder != null) {
// We found a potential match - let's give it a try.
// Do not consider the same value definition multiple times!
// 我們找到了一個潛在的匹配 - 讓我們試一試。不要多次考慮相同的值定義！
usedValueHolders.add(valueHolder);
Object originalValue = valueHolder.getValue();
Object convertedValue;
if (valueHolder.isConverted()) {
convertedValue = valueHolder.getConvertedValue();
args.preparedArguments[paramIndex] = convertedValue;
}
else {
MethodParameter methodParam = MethodParameter.forExecutable(executable, paramIndex);
try {
convertedValue = converter.convertIfNecessary(originalValue, paramType, methodParam);
}
catch (TypeMismatchException ex) {
throw new UnsatisfiedDependencyException(
mbd.getResourceDescription(), beanName, new InjectionPoint(methodParam),
"Could not convert argument value of type [" +
ObjectUtils.nullSafeClassName(valueHolder.getValue()) +
"] to required type [" + paramType.getName() + "]: " + ex.getMessage());
}
Object sourceHolder = valueHolder.getSource();
if (sourceHolder instanceof ConstructorArgumentValues.ValueHolder) {
Object sourceValue = ((ConstructorArgumentValues.ValueHolder) sourceHolder).getValue();
args.resolveNecessary = true;
args.preparedArguments[paramIndex] = sourceValue;
}
}
args.arguments[paramIndex] = convertedValue;
args.rawArguments[paramIndex] = originalValue;
}
else {
// 這部分就是超出了參數定義，需要自動注入參數的處理
MethodParameter methodParam = MethodParameter.forExecutable(executable, paramIndex);
// No explicit match found: we're either supposed to autowire or
// have to fail creating an argument array for the given constructor.
if (!autowiring) {
throw new UnsatisfiedDependencyException(
mbd.getResourceDescription(), beanName, new InjectionPoint(methodParam),
"Ambiguous argument values for parameter of type [" + paramType.getName() +
"] - did you specify the correct bean references as arguments?");
}
try {
Object autowiredArgument = resolveAutowiredArgument(
methodParam, beanName, autowiredBeanNames, converter, fallback);
args.rawArguments[paramIndex] = autowiredArgument;
args.arguments[paramIndex] = autowiredArgument;
args.preparedArguments[paramIndex] = autowiredArgumentMarker;
args.resolveNecessary = true;
}
catch (BeansException ex) {
throw new UnsatisfiedDependencyException(
mbd.getResourceDescription(), beanName, new InjectionPoint(methodParam), ex);
}
}
}
for (String autowiredBeanName : autowiredBeanNames) {
this.beanFactory.registerDependentBean(autowiredBeanName, beanName);
if (logger.isDebugEnabled()) {
logger.debug("Autowiring by type from bean name '" + beanName +
"' via " + (executable instanceof Constructor ? "constructor" : "factory method") +
" to bean named '" + autowiredBeanName + "'");
}
}
return args;
}private Object instantiate(String beanName, RootBeanDefinition mbd,
@Nullable Object factoryBean, Method factoryMethod, Object[] args) {
try {
if (System.getSecurityManager() != null) {
return AccessController.doPrivileged((PrivilegedAction<Object>) () ->
this.beanFactory.getInstantiationStrategy().instantiate(
mbd, beanName, this.beanFactory, factoryBean, factoryMethod, args),
this.beanFactory.getAccessControlContext());
}
else {
//四、使用實例化策略創建Bean
return this.beanFactory.getInstantiationStrategy().instantiate(
mbd, beanName, this.beanFactory, factoryBean, factoryMethod, args);
}
}
catch (Throwable ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Bean instantiation via factory method failed", ex);
}
}protected BeanWrapper instantiateBean(final String beanName, final RootBeanDefinition mbd) {
try {
Object beanInstance;
final BeanFactory parent = this;
if (System.getSecurityManager() != null) {
beanInstance = AccessController.doPrivileged((PrivilegedAction<Object>) () ->
getInstantiationStrategy().instantiate(mbd, beanName, parent),
getAccessControlContext());
}
else {
// 使用默認的實例化策略來實例化對象，默認為 CglibSubclassingInstantiationStrategy 實現，但是instantiate()方法只在SimpleInstantiationStrategy里有實現邏輯
//四、使用實例化策略創建Bean
beanInstance = getInstantiationStrategy().instantiate(mbd, beanName, parent);
}
BeanWrapper bw = new BeanWrapperImpl(beanInstance);
initBeanWrapper(bw);
return bw;
}
catch (Throwable ex) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Instantiation of bean failed", ex);
}
}這里會進入SimpleInstantiationStrategy的instantiate方法
@Override
public Object instantiate(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner,
final Constructor<?> ctor, Object... args) {
//在將 XML 配置解析成 BeanDefinition 的時候，bean標簽的lookup-method和replaced-method會被分別解析成 LookupOverride 和 ReplaceOverride 對象
//添加到 BeanDefinition 的methodOverrides成員變量中
//如果沒有配置就會走當前這個流程
if (!bd.hasMethodOverrides()) {
if (System.getSecurityManager() != null) {
// use own privileged to change accessibility (when security is on)
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
ReflectionUtils.makeAccessible(ctor);
return null;
});
}
//4.1、反射創建Bean
return BeanUtils.instantiateClass(ctor, args);
}
else {
//如果方法被覆蓋，通過Cglib實現代理類
//4.2、Cglib創建代理類
return instantiateWithMethodInjection(bd, beanName, owner, ctor, args);
}
}public static <T> T instantiateClass(Constructor<T> ctor, Object... args) throws BeanInstantiationException {
Assert.notNull(ctor, "Constructor must not be null");
try {
//設置訪問權限
ReflectionUtils.makeAccessible(ctor);
if (KotlinDetector.isKotlinReflectPresent() && KotlinDetector.isKotlinType(ctor.getDeclaringClass())) {
return KotlinDelegate.instantiateClass(ctor, args);
}
else {
Class<?>[] parameterTypes = ctor.getParameterTypes();
Assert.isTrue(args.length <= parameterTypes.length, "Can't specify more arguments than constructor parameters");
Object[] argsWithDefaultValues = new Object[args.length];
//初始化參數
for (int i = 0 ; i < args.length; i++) {
if (args[i] == null) {
Class<?> parameterType = parameterTypes[i];
argsWithDefaultValues[i] = (parameterType.isPrimitive() ? DEFAULT_TYPE_VALUES.get(parameterType) : null);
}
else {
argsWithDefaultValues[i] = args[i];
}
}
return ctor.newInstance(argsWithDefaultValues);
}
}
catch (InstantiationException ex) {
throw new BeanInstantiationException(ctor, "Is it an abstract class?", ex);
}
catch (IllegalAccessException ex) {
throw new BeanInstantiationException(ctor, "Is the constructor accessible?", ex);
}
catch (IllegalArgumentException ex) {
throw new BeanInstantiationException(ctor, "Illegal arguments for constructor", ex);
}
catch (InvocationTargetException ex) {
throw new BeanInstantiationException(ctor, "Constructor threw exception", ex.getTargetException());
}
}@Override
protected Object instantiateWithMethodInjection(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner,
@Nullable Constructor<?> ctor, Object... args) {
// Must generate CGLIB subclass...
return new CglibSubclassCreator(bd, owner).instantiate(ctor, args);
}創建Cglib代理類
public Object instantiate(@Nullable Constructor<?> ctor, Object... args) {
//創建Cglib增強子類
Class<?> subclass = createEnhancedSubclass(this.beanDefinition);
Object instance;
if (ctor == null) {
//4.1 反射創建Bean
instance = BeanUtils.instantiateClass(subclass);
}
else {
try {
//反射創建Bean
Constructor<?> enhancedSubclassConstructor = subclass.getConstructor(ctor.getParameterTypes());
instance = enhancedSubclassConstructor.newInstance(args);
}
catch (Exception ex) {
throw new BeanInstantiationException(this.beanDefinition.getBeanClass(),
"Failed to invoke constructor for CGLIB enhanced subclass [" + subclass.getName() + "]", ex);
}
}
// SPR-10785: set callbacks directly on the instance instead of in the
// enhanced class (via the Enhancer) in order to avoid memory leaks.
Factory factory = (Factory) instance;
factory.setCallbacks(new Callback[] {NoOp.INSTANCE,
new LookupOverrideMethodInterceptor(this.beanDefinition, this.owner),
new ReplaceOverrideMethodInterceptor(this.beanDefinition, this.owner)});
return instance;
}“Spring createBeanInstance怎么實例化Bean”的內容就介紹到這里了，感謝大家的閱讀。如果想了解更多行業相關的知識可以關注億速云網站，小編將為大家輸出更多高質量的實用文章！
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