spring-ioc Spring IOC
那么。什么是IOC呢？IOC是Inversion of Control的缩写，是一个很重要的面向对象法则。主要目的是用来消减计算机程序的耦合问题。相同也是Spring框架的核心。
IOC一般分为两种类型，依赖注入（Dependency Injection）和依赖查找（Dependency Lookup），在Spring Framework框架中主要是依赖注入
。作为spring的核心，那IOC究竟是什么呢？public class User{
private String id;
private String name;
private String password;
private Date birthday;
//ignore other properties...
//ignore setter getter method
}
public interface IUserDao{
public void add(User user);
public void delete(User user);
public List<User> findAll();
}
public class UserDaoImpl{
public void add(User user){
//ignore the implementation
}
public void delete(User user){
//ignore the implementation
}
public List<User> findAll(){
//ignore the implementation
}
}
public class UserController{
private IUserDao userDao = new UserDaoImpl();
@RequestMapping("/user/add")
public void add(User user){
userDao.add(user);
}
@RequestMapping("/user/delete")
public void delete(User user){
userDao.add(user);
}
@RequestMapping("/user/findAll")
public void findAll(User user){
List<User> allUser = userDao.findAll();
}
} 在这里面，UserController调用private IUserDao userDao = new UserDaoImpl()来初始化userDao。因为java是一门编译语言，也就是将.java变成.class的过程。在这个过程中捆绑了IUserDao的实现，也就是UserDaoImpl。尽管开发人员使用了面向接口编程的风格来书写代码，可是还是和UserDaoImpl捆绑在了一起。假设后期开发中，为IUserDao提供第二种实现，比方：将orm框架由mybatis换成了hibernate。那么就须要改动源代码UserController的实现。传统模式中，一个类依赖的其它类都由自己维护。须要什么类，就new一个。
这样的开发方式的耦合性比較高，不利于后期的维护。那么既然这样的方式不好。那么有没有一种其它办法来解决问题呢？没错，IOC能够很好的解决问题。
IOC组成
public class User{
private String id;
private String name;
private String password;
private Date birthday;
//ignore other properties...
//ignore setter getter method<span style="white-space:pre"> </span>
}
public interface IUserDao{
public void add(User user);
public void delete(User user);
public List<User> findAll();
}
@Repository
public class UserDaoImpl{
public void add(User user){
//ignore the implementation
}
public void delete(User user){
//ignore the implementation
}
public List<User> findAll(){
//ignore the implementation
}
}
@Controller
public class UserController{
//主动注入这个类
@Autowired
private IUserDao userDao userDao;
@RequestMapping("/user/add")
public void add(User user){
userDao.add(user);
}
@RequestMapping("/user/delete")
public void delete(User user){
userDao.add(user);
}
@RequestMapping("/user/findAll")
public void findAll(User user){
List<User> allUser = userDao.findAll();
}
} 从代码中我们能够看到，这两份代码差点儿是一样的，就仅仅是去掉了userDao的实现类，在userDao变量中增加了@Autowired注解而已。没错。这就是spring的厉害之处，由于spring是一种无侵入式的轻量级框架。那么spring是怎样实现控制反转的呢？以下先给出一个spring
ioc图
IOC的实现
当然，这个图不过一个思维导图，详细代码的细节。肯定得复杂的多。以下给出一个spring默认的实现类，不必要的信息做了删除
/**
*
* 一个BeanFactory的实现类，不必要的信息作了删除，有兴趣的读者能够查看源代码
* */
@SuppressWarnings("serial")
public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFactory
implements ConfigurableListableBeanFactory, BeanDefinitionRegistry, Serializable {
private static Class<?> javaxInjectProviderClass = null;
static {
ClassLoader cl = DefaultListableBeanFactory.class.getClassLoader();
try {
javaxInjectProviderClass = cl.loadClass("javax.inject.Provider");
}
catch (ClassNotFoundException ex) {
// JSR-330 API not available - Provider interface simply not supported then.
}
}
/** Map from serialized id to factory instance */
private static final Map<String, Reference<DefaultListableBeanFactory>> serializableFactories =
new ConcurrentHashMap<String, Reference<DefaultListableBeanFactory>>(8);
/** Optional id for this factory, for serialization purposes */
private String serializationId;
/** Whether to allow re-registration of a different definition with the same name */
private boolean allowBeanDefinitionOverriding = true;
/** Whether to allow eager class loading even for lazy-init beans */
private boolean allowEagerClassLoading = true;
/** Resolver to use for checking if a bean definition is an autowire candidate */
private AutowireCandidateResolver autowireCandidateResolver = new SimpleAutowireCandidateResolver();
/** 用于缓存解决好依赖关系的bean */
private final Map<Class<?>, Object> resolvableDependencies = new HashMap<Class<?>, Object>(16);
/** 保存源信息 */
private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<String, BeanDefinition>(64);
/** Map of singleton and non-singleton bean names keyed by dependency type */
private final Map<Class<?>, String[]> allBeanNamesByType = new ConcurrentHashMap<Class<?>, String[]>(64);
/** Map of singleton-only bean names keyed by dependency type */
private final Map<Class<?>, String[]> singletonBeanNamesByType = new ConcurrentHashMap<Class<?
>, String[]>(64);
/***/
private final List<String> beanDefinitionNames = new ArrayList<String>();
/** Whether bean definition metadata may be cached for all beans */
private boolean configurationFrozen = false;
/** Cached array of bean definition names in case of frozen configuration */
private String[] frozenBeanDefinitionNames;
/**
* Create a new DefaultListableBeanFactory.
*/
public DefaultListableBeanFactory() {
super();
}
/**
* Create a new DefaultListableBeanFactory with the given parent.
* @param parentBeanFactory the parent BeanFactory
*/
public DefaultListableBeanFactory(BeanFactory parentBeanFactory) {
super(parentBeanFactory);
}
/**
* Specify an id for serialization purposes, allowing this BeanFactory to be
* deserialized from this id back into the BeanFactory object, if needed.
*/
public void setSerializationId(String serializationId) {
if (serializationId != null) {
serializableFactories.put(serializationId, new WeakReference<DefaultListableBeanFactory>(this));
}
else if (this.serializationId != null) {
serializableFactories.remove(this.serializationId);
}
this.serializationId = serializationId;
}
/**
* Set whether it should be allowed to override bean definitions by registering
* a different definition with the same name, automatically replacing the former.
* If not, an exception will be thrown. This also applies to overriding aliases.
* <p>Default is "true".
* @see #registerBeanDefinition
*/
public void setAllowBeanDefinitionOverriding(boolean allowBeanDefinitionOverriding) {
this.allowBeanDefinitionOverriding = allowBeanDefinitionOverriding;
}
/**
* Set whether the factory is allowed to eagerly load bean classes
* even for bean definitions that are marked as "lazy-init".
* <p>Default is "true". Turn this flag off to suppress class loading
* for lazy-init beans unless such a bean is explicitly requested.
* In particular, by-type lookups will then simply ignore bean definitions
* without resolved class name, instead of loading the bean classes on
* demand just to perform a type check.
* @see AbstractBeanDefinition#setLazyInit
*/
public void setAllowEagerClassLoading(boolean allowEagerClassLoading) {
this.allowEagerClassLoading = allowEagerClassLoading;
}
/**
* Set a custom autowire candidate resolver for this BeanFactory to use
* when deciding whether a bean definition should be considered as a
* candidate for autowiring.
*/
public void setAutowireCandidateResolver(final AutowireCandidateResolver autowireCandidateResolver) {
Assert.notNull(autowireCandidateResolver, "AutowireCandidateResolver must not be null");
if (autowireCandidateResolver instanceof BeanFactoryAware) {
if (System.getSecurityManager() != null) {
final BeanFactory target = this;
AccessController.doPrivileged(new PrivilegedAction<Object>() {
public Object run() {
((BeanFactoryAware) autowireCandidateResolver).setBeanFactory(target);
return null;
}
}, getAccessControlContext());
}
else {
((BeanFactoryAware) autowireCandidateResolver).setBeanFactory(this);
}
}
this.autowireCandidateResolver = autowireCandidateResolver;
}
/**
* Return the autowire candidate resolver for this BeanFactory (never {@code null}).
*/
public AutowireCandidateResolver getAutowireCandidateResolver() {
return this.autowireCandidateResolver;
}
@Override
public void copyConfigurationFrom(ConfigurableBeanFactory otherFactory) {
super.copyConfigurationFrom(otherFactory);
if (otherFactory instanceof DefaultListableBeanFactory) {
DefaultListableBeanFactory otherListableFactory = (DefaultListableBeanFactory) otherFactory;
this.allowBeanDefinitionOverriding = otherListableFactory.allowBeanDefinitionOverriding;
this.allowEagerClassLoading = otherListableFactory.allowEagerClassLoading;
this.autowireCandidateResolver = otherListableFactory.autowireCandidateResolver;
this.resolvableDependencies.putAll(otherListableFactory.resolvableDependencies);
}
}
//---------------------------------------------------------------------
// Implementation of ListableBeanFactory interface
//---------------------------------------------------------------------
public <T> T getBean(Class<T> requiredType) throws BeansException {
Assert.notNull(requiredType, "Required type must not be null");
String[] beanNames = getBeanNamesForType(requiredType);
if (beanNames.length > 1) {
ArrayList<String> autowireCandidates = new ArrayList<String>();
for (String beanName : beanNames) {
if (getBeanDefinition(beanName).isAutowireCandidate()) {
autowireCandidates.add(beanName);
}
}
if (autowireCandidates.size() > 0) {
beanNames = autowireCandidates.toArray(new String[autowireCandidates.size()]);
}
}
if (beanNames.length == 1) {
return getBean(beanNames[0], requiredType);
}
else if (beanNames.length > 1) {
T primaryBean = null;
for (String beanName : beanNames) {
T beanInstance = getBean(beanName, requiredType);
if (isPrimary(beanName, beanInstance)) {
if (primaryBean != null) {
throw new NoUniqueBeanDefinitionException(requiredType, beanNames.length,
"more than one 'primary' bean found of required type: " + Arrays.asList(beanNames));
}
primaryBean = beanInstance;
}
}
if (primaryBean != null) {
return primaryBean;
}
throw new NoUniqueBeanDefinitionException(requiredType, beanNames);
}
else if (getParentBeanFactory() != null) {
return getParentBeanFactory().getBean(requiredType);
}
else {
throw new NoSuchBeanDefinitionException(requiredType);
}
}
@Override
public boolean containsBeanDefinition(String beanName) {
Assert.notNull(beanName, "Bean name must not be null");
return this.beanDefinitionMap.containsKey(beanName);
}
public int getBeanDefinitionCount() {
return this.beanDefinitionMap.size();
}
public String[] getBeanDefinitionNames() {
synchronized (this.beanDefinitionMap) {
if (this.frozenBeanDefinitionNames != null) {
return this.frozenBeanDefinitionNames;
}
else {
return StringUtils.toStringArray(this.beanDefinitionNames);
}
}
}
public String[] getBeanNamesForType(Class<?
> type) {
return getBeanNamesForType(type, true, true);
}
public String[] getBeanNamesForType(Class<?> type, boolean includeNonSingletons, boolean allowEagerInit) {
if (!isConfigurationFrozen() || type == null || !allowEagerInit) {
return doGetBeanNamesForType(type, includeNonSingletons, allowEagerInit);
}
Map<Class<?>, String[]> cache =
(includeNonSingletons ? this.allBeanNamesByType : this.singletonBeanNamesByType);
String[] resolvedBeanNames = cache.get(type);
if (resolvedBeanNames != null) {
return resolvedBeanNames;
}
resolvedBeanNames = doGetBeanNamesForType(type, includeNonSingletons, allowEagerInit);
cache.put(type, resolvedBeanNames);
return resolvedBeanNames;
}
private String[] doGetBeanNamesForType(Class<?> type, boolean includeNonSingletons, boolean allowEagerInit) {
List<String> result = new ArrayList<String>();
// Check all bean definitions.
String[] beanDefinitionNames = getBeanDefinitionNames();
for (String beanName : 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() || this.allowEagerClassLoading)) &&
!requiresEagerInitForType(mbd.getFactoryBeanName()))) {
// In case of FactoryBean, match object created by FactoryBean.
boolean isFactoryBean = isFactoryBean(beanName, mbd);
boolean matchFound = (allowEagerInit || !isFactoryBean || containsSingleton(beanName)) &&
(includeNonSingletons || 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 contains a placeholder: let's ignore it for type matching purposes.
if (this.logger.isDebugEnabled()) {
this.logger.debug("Ignoring bean class loading failure for bean '" + beanName + "'", ex);
}
onSuppressedException(ex);
}
catch (BeanDefinitionStoreException ex) {
if (allowEagerInit) {
throw ex;
}
// Probably contains a placeholder: let's ignore it for type matching purposes.
if (this.logger.isDebugEnabled()) {
this.logger.debug("Ignoring unresolvable metadata in bean definition '" + beanName + "'", ex);
}
onSuppressedException(ex);
}
}
}
// Check singletons too, to catch manually registered singletons.
String[] singletonNames = getSingletonNames();
for (String beanName : singletonNames) {
// Only check if manually registered.
if (!containsBeanDefinition(beanName)) {
// 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);
}
}
}
return StringUtils.toStringArray(result);
}
/**
* Check whether the specified bean would need to be eagerly initialized
* in order to determine its type.
* @param factoryBeanName a factory-bean reference that the bean definition
* defines a factory method for
* @return whether eager initialization is necessary
*/
private boolean requiresEagerInitForType(String factoryBeanName) {
return (factoryBeanName != null && isFactoryBean(factoryBeanName) && !containsSingleton(factoryBeanName));
}
public <T> Map<String, T> getBeansOfType(Class<T> type) throws BeansException {
return getBeansOfType(type, true, true);
}
public <T> Map<String, T> getBeansOfType(Class<T> type, boolean includeNonSingletons, boolean allowEagerInit)
throws BeansException {
String[] beanNames = getBeanNamesForType(type, includeNonSingletons, allowEagerInit);
Map<String, T> result = new LinkedHashMap<String, T>(beanNames.length);
for (String beanName : beanNames) {
try {
result.put(beanName, getBean(beanName, type));
}
catch (BeanCreationException ex) {
Throwable rootCause = ex.getMostSpecificCause();
if (rootCause instanceof BeanCurrentlyInCreationException) {
BeanCreationException bce = (BeanCreationException) rootCause;
if (isCurrentlyInCreation(bce.getBeanName())) {
if (this.logger.isDebugEnabled()) {
this.logger.debug("Ignoring match to currently created bean '" + beanName + "': " +
ex.getMessage());
}
onSuppressedException(ex);
// Ignore: indicates a circular reference when autowiring constructors.
// We want to find matches other than the currently created bean itself.
continue;
}
}
throw ex;
}
}
return result;
}
public Map<String, Object> getBeansWithAnnotation(Class<? extends Annotation> annotationType) {
Set<String> beanNames = new LinkedHashSet<String>(getBeanDefinitionCount());
beanNames.addAll(Arrays.asList(getBeanDefinitionNames()));
beanNames.addAll(Arrays.asList(getSingletonNames()));
Map<String, Object> results = new LinkedHashMap<String, Object>();
for (String beanName : beanNames) {
if (findAnnotationOnBean(beanName, annotationType) != null) {
results.put(beanName, getBean(beanName));
}
}
return results;
}
/**
* Find a {@link Annotation} of {@code annotationType} on the specified
* bean, traversing its interfaces and super classes if no annotation can be
* found on the given class itself, as well as checking its raw bean class
* if not found on the exposed bean reference (e.g. in case of a proxy).
*/
public <A extends Annotation> A findAnnotationOnBean(String beanName, Class<A> annotationType) {
A ann = null;
Class<?
> beanType = getType(beanName);
if (beanType != null) {
ann = AnnotationUtils.findAnnotation(beanType, annotationType);
}
if (ann == null && containsBeanDefinition(beanName)) {
BeanDefinition bd = getMergedBeanDefinition(beanName);
if (bd instanceof AbstractBeanDefinition) {
AbstractBeanDefinition abd = (AbstractBeanDefinition) bd;
if (abd.hasBeanClass()) {
ann = AnnotationUtils.findAnnotation(abd.getBeanClass(), annotationType);
}
}
}
return ann;
}
//---------------------------------------------------------------------
// Implementation of ConfigurableListableBeanFactory interface
//---------------------------------------------------------------------
public void registerResolvableDependency(Class<?> dependencyType, Object autowiredValue) {
Assert.notNull(dependencyType, "Type must not be null");
if (autowiredValue != null) {
Assert.isTrue((autowiredValue instanceof ObjectFactory || dependencyType.isInstance(autowiredValue)),
"Value [" + autowiredValue + "] does not implement specified type [" + dependencyType.getName() + "]");
this.resolvableDependencies.put(dependencyType, autowiredValue);
}
}
public boolean isAutowireCandidate(String beanName, DependencyDescriptor descriptor)
throws NoSuchBeanDefinitionException {
// Consider FactoryBeans as autowiring candidates.
boolean isFactoryBean = (descriptor != null && descriptor.getDependencyType() != null &&
FactoryBean.class.isAssignableFrom(descriptor.getDependencyType()));
if (isFactoryBean) {
beanName = BeanFactoryUtils.transformedBeanName(beanName);
}
if (containsBeanDefinition(beanName)) {
return isAutowireCandidate(beanName, getMergedLocalBeanDefinition(beanName), descriptor);
}
else if (containsSingleton(beanName)) {
return isAutowireCandidate(beanName, new RootBeanDefinition(getType(beanName)), descriptor);
}
else if (getParentBeanFactory() instanceof ConfigurableListableBeanFactory) {
// No bean definition found in this factory -> delegate to parent.
return ((ConfigurableListableBeanFactory) getParentBeanFactory()).isAutowireCandidate(beanName, descriptor);
}
else {
return true;
}
}
/**
* Determine whether the specified bean definition qualifies as an autowire candidate,
* to be injected into other beans which declare a dependency of matching type.
* @param beanName the name of the bean definition to check
* @param mbd the merged bean definition to check
* @param descriptor the descriptor of the dependency to resolve
* @return whether the bean should be considered as autowire candidate
*/
protected boolean isAutowireCandidate(String beanName, RootBeanDefinition mbd, DependencyDescriptor descriptor) {
resolveBeanClass(mbd, beanName);
if (mbd.isFactoryMethodUnique) {
boolean resolve;
synchronized (mbd.constructorArgumentLock) {
resolve = (mbd.resolvedConstructorOrFactoryMethod == null);
}
if (resolve) {
new ConstructorResolver(this).resolveFactoryMethodIfPossible(mbd);
}
}
return getAutowireCandidateResolver().isAutowireCandidate(
new BeanDefinitionHolder(mbd, beanName, getAliases(beanName)), descriptor);
}
@Override
public BeanDefinition getBeanDefinition(String beanName) throws NoSuchBeanDefinitionException {
BeanDefinition bd = this.beanDefinitionMap.get(beanName);
if (bd == null) {
if (this.logger.isTraceEnabled()) {
this.logger.trace("No bean named '" + beanName + "' found in " + this);
}
throw new NoSuchBeanDefinitionException(beanName);
}
return bd;
}
public void freezeConfiguration() {
this.configurationFrozen = true;
synchronized (this.beanDefinitionMap) {
this.frozenBeanDefinitionNames = StringUtils.toStringArray(this.beanDefinitionNames);
}
}
public boolean isConfigurationFrozen() {
return this.configurationFrozen;
}
/**
* Considers all beans as eligible for metadata caching
* if the factory's configuration has been marked as frozen.
* @see #freezeConfiguration()
*/
@Override
protected boolean isBeanEligibleForMetadataCaching(String beanName) {
return (this.configurationFrozen || super.isBeanEligibleForMetadataCaching(beanName));
}
public void preInstantiateSingletons() throws BeansException {
if (this.logger.isInfoEnabled()) {
this.logger.info("Pre-instantiating singletons in " + this);
}
List<String> beanNames;
synchronized (this.beanDefinitionMap) {
// Iterate over a copy to allow for init methods which in turn register new bean definitions.
// While this may not be part of the regular factory bootstrap, it does otherwise work fine.
beanNames = new ArrayList<String>(this.beanDefinitionNames);
}
for (String beanName : beanNames) {
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
if (isFactoryBean(beanName)) {
final FactoryBean<?
> factory = (FactoryBean<?
>) getBean(FACTORY_BEAN_PREFIX + beanName);
boolean isEagerInit;
if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
isEagerInit = AccessController.doPrivileged(new PrivilegedAction<Boolean>() {
public Boolean run() {
return ((SmartFactoryBean<?>) factory).isEagerInit();
}
}, getAccessControlContext());
}
else {
isEagerInit = (factory instanceof SmartFactoryBean &&
((SmartFactoryBean<?
>) factory).isEagerInit());
}
if (isEagerInit) {
getBean(beanName);
}
}
else {
getBean(beanName);
}
}
}
}
//---------------------------------------------------------------------
// Implementation of BeanDefinitionRegistry interface
//---------------------------------------------------------------------
public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
throws BeanDefinitionStoreException {
Assert.hasText(beanName, "Bean name must not be empty");
Assert.notNull(beanDefinition, "BeanDefinition must not be null");
if (beanDefinition instanceof AbstractBeanDefinition) {
try {
((AbstractBeanDefinition) beanDefinition).validate();
}
catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Validation of bean definition failed", ex);
}
}
synchronized (this.beanDefinitionMap) {
Object oldBeanDefinition = this.beanDefinitionMap.get(beanName);
if (oldBeanDefinition != null) {
if (!this.allowBeanDefinitionOverriding) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName +
"': There is already [" + oldBeanDefinition + "] bound.");
}
else {
if (this.logger.isInfoEnabled()) {
this.logger.info("Overriding bean definition for bean '" + beanName +
"': replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]");
}
}
}
else {
this.beanDefinitionNames.add(beanName);
this.frozenBeanDefinitionNames = null;
}
this.beanDefinitionMap.put(beanName, beanDefinition);
}
resetBeanDefinition(beanName);
}
public void removeBeanDefinition(String beanName) throws NoSuchBeanDefinitionException {
Assert.hasText(beanName, "'beanName' must not be empty");
synchronized (this.beanDefinitionMap) {
BeanDefinition bd = this.beanDefinitionMap.remove(beanName);
if (bd == null) {
if (this.logger.isTraceEnabled()) {
this.logger.trace("No bean named '" + beanName + "' found in " + this);
}
throw new NoSuchBeanDefinitionException(beanName);
}
this.beanDefinitionNames.remove(beanName);
this.frozenBeanDefinitionNames = null;
}
resetBeanDefinition(beanName);
}
/**
* Reset all bean definition caches for the given bean,
* including the caches of beans that are derived from it.
* @param beanName the name of the bean to reset
*/
protected void resetBeanDefinition(String beanName) {
// Remove the merged bean definition for the given bean, if already created.
clearMergedBeanDefinition(beanName);
// Remove corresponding bean from singleton cache, if any. Shouldn't usually
// be necessary, rather just meant for overriding a context's default beans
// (e.g. the default StaticMessageSource in a StaticApplicationContext).
destroySingleton(beanName);
// Remove any assumptions about by-type mappings.
clearByTypeCache();
// Reset all bean definitions that have the given bean as parent (recursively).
for (String bdName : this.beanDefinitionNames) {
if (!beanName.equals(bdName)) {
BeanDefinition bd = this.beanDefinitionMap.get(bdName);
if (beanName.equals(bd.getParentName())) {
resetBeanDefinition(bdName);
}
}
}
}
/**
* Only allows alias overriding if bean definition overriding is allowed.
*/
@Override
protected boolean allowAliasOverriding() {
return this.allowBeanDefinitionOverriding;
}
@Override
public void registerSingleton(String beanName, Object singletonObject) throws IllegalStateException {
super.registerSingleton(beanName, singletonObject);
clearByTypeCache();
}
@Override
public void destroySingleton(String beanName) {
super.destroySingleton(beanName);
clearByTypeCache();
}
/**
* Remove any assumptions about by-type mappings.
*/
private void clearByTypeCache() {
this.allBeanNamesByType.clear();
this.singletonBeanNamesByType.clear();
}
//---------------------------------------------------------------------
// Dependency resolution functionality
//---------------------------------------------------------------------
public Object resolveDependency(DependencyDescriptor descriptor, String beanName,
Set<String> autowiredBeanNames, TypeConverter typeConverter) throws BeansException {
descriptor.initParameterNameDiscovery(getParameterNameDiscoverer());
if (descriptor.getDependencyType().equals(ObjectFactory.class)) {
return new DependencyObjectFactory(descriptor, beanName);
}
else if (descriptor.getDependencyType().equals(javaxInjectProviderClass)) {
return new DependencyProviderFactory().createDependencyProvider(descriptor, beanName);
}
else {
return doResolveDependency(descriptor, descriptor.getDependencyType(), beanName, autowiredBeanNames, typeConverter);
}
}
protected Object doResolveDependency(DependencyDescriptor descriptor, Class<?> type, String beanName,
Set<String> autowiredBeanNames, TypeConverter typeConverter) throws BeansException {
Object value = getAutowireCandidateResolver().getSuggestedValue(descriptor);
if (value != null) {
if (value instanceof String) {
String strVal = resolveEmbeddedValue((String) value);
BeanDefinition bd = (beanName != null && containsBean(beanName) ? getMergedBeanDefinition(beanName) : null);
value = evaluateBeanDefinitionString(strVal, bd);
}
TypeConverter converter = (typeConverter != null ? typeConverter : getTypeConverter());
return (descriptor.getField() != null ?
converter.convertIfNecessary(value, type, descriptor.getField()) :
converter.convertIfNecessary(value, type, descriptor.getMethodParameter()));
}
if (type.isArray()) {
Class<?
> componentType = type.getComponentType();
Map<String, Object> matchingBeans = findAutowireCandidates(beanName, componentType, descriptor);
if (matchingBeans.isEmpty()) {
if (descriptor.isRequired()) {
raiseNoSuchBeanDefinitionException(componentType, "array of " + componentType.getName(), descriptor);
}
return null;
}
if (autowiredBeanNames != null) {
autowiredBeanNames.addAll(matchingBeans.keySet());
}
TypeConverter converter = (typeConverter != null ? typeConverter : getTypeConverter());
return converter.convertIfNecessary(matchingBeans.values(), type);
}
else if (Collection.class.isAssignableFrom(type) && type.isInterface()) {
Class<?> elementType = descriptor.getCollectionType();
if (elementType == null) {
if (descriptor.isRequired()) {
throw new FatalBeanException("No element type declared for collection [" + type.getName() + "]");
}
return null;
}
Map<String, Object> matchingBeans = findAutowireCandidates(beanName, elementType, descriptor);
if (matchingBeans.isEmpty()) {
if (descriptor.isRequired()) {
raiseNoSuchBeanDefinitionException(elementType, "collection of " + elementType.getName(), descriptor);
}
return null;
}
if (autowiredBeanNames != null) {
autowiredBeanNames.addAll(matchingBeans.keySet());
}
TypeConverter converter = (typeConverter != null ? typeConverter : getTypeConverter());
return converter.convertIfNecessary(matchingBeans.values(), type);
}
else if (Map.class.isAssignableFrom(type) && type.isInterface()) {
Class<?
> keyType = descriptor.getMapKeyType();
if (keyType == null || !String.class.isAssignableFrom(keyType)) {
if (descriptor.isRequired()) {
throw new FatalBeanException("Key type [" + keyType + "] of map [" + type.getName() +
"] must be assignable to [java.lang.String]");
}
return null;
}
Class<?> valueType = descriptor.getMapValueType();
if (valueType == null) {
if (descriptor.isRequired()) {
throw new FatalBeanException("No value type declared for map [" + type.getName() + "]");
}
return null;
}
Map<String, Object> matchingBeans = findAutowireCandidates(beanName, valueType, descriptor);
if (matchingBeans.isEmpty()) {
if (descriptor.isRequired()) {
raiseNoSuchBeanDefinitionException(valueType, "map with value type " + valueType.getName(), descriptor);
}
return null;
}
if (autowiredBeanNames != null) {
autowiredBeanNames.addAll(matchingBeans.keySet());
}
return matchingBeans;
}
else {
Map<String, Object> matchingBeans = findAutowireCandidates(beanName, type, descriptor);
if (matchingBeans.isEmpty()) {
if (descriptor.isRequired()) {
raiseNoSuchBeanDefinitionException(type, "", descriptor);
}
return null;
}
if (matchingBeans.size() > 1) {
String primaryBeanName = determinePrimaryCandidate(matchingBeans, descriptor);
if (primaryBeanName == null) {
throw new NoUniqueBeanDefinitionException(type, matchingBeans.keySet());
}
if (autowiredBeanNames != null) {
autowiredBeanNames.add(primaryBeanName);
}
return matchingBeans.get(primaryBeanName);
}
// We have exactly one match.
Map.Entry<String, Object> entry = matchingBeans.entrySet().iterator().next();
if (autowiredBeanNames != null) {
autowiredBeanNames.add(entry.getKey());
}
return entry.getValue();
}
}
/**
* Find bean instances that match the required type.
* Called during autowiring for the specified bean.
* @param beanName the name of the bean that is about to be wired
* @param requiredType the actual type of bean to look for
* (may be an array component type or collection element type)
* @param descriptor the descriptor of the dependency to resolve
* @return a Map of candidate names and candidate instances that match
* the required type (never {@code null})
* @throws BeansException in case of errors
* @see #autowireByType
* @see #autowireConstructor
*/
protected Map<String, Object> findAutowireCandidates(
String beanName, Class<?
> requiredType, DependencyDescriptor descriptor) {
String[] candidateNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(
this, requiredType, true, descriptor.isEager());
Map<String, Object> result = new LinkedHashMap<String, Object>(candidateNames.length);
for (Class<?> autowiringType : this.resolvableDependencies.keySet()) {
if (autowiringType.isAssignableFrom(requiredType)) {
Object autowiringValue = this.resolvableDependencies.get(autowiringType);
autowiringValue = AutowireUtils.resolveAutowiringValue(autowiringValue, requiredType);
if (requiredType.isInstance(autowiringValue)) {
result.put(ObjectUtils.identityToString(autowiringValue), autowiringValue);
break;
}
}
}
for (String candidateName : candidateNames) {
if (!candidateName.equals(beanName) && isAutowireCandidate(candidateName, descriptor)) {
result.put(candidateName, getBean(candidateName));
}
}
return result;
}
/**
* Determine the primary autowire candidate in the given set of beans.
* @param candidateBeans a Map of candidate names and candidate instances
* that match the required type, as returned by {@link #findAutowireCandidates}
* @param descriptor the target dependency to match against
* @return the name of the primary candidate, or {@code null} if none found
*/
protected String determinePrimaryCandidate(Map<String, Object> candidateBeans, DependencyDescriptor descriptor) {
String primaryBeanName = null;
String fallbackBeanName = null;
for (Map.Entry<String, Object> entry : candidateBeans.entrySet()) {
String candidateBeanName = entry.getKey();
Object beanInstance = entry.getValue();
if (isPrimary(candidateBeanName, beanInstance)) {
if (primaryBeanName != null) {
boolean candidateLocal = containsBeanDefinition(candidateBeanName);
boolean primaryLocal = containsBeanDefinition(primaryBeanName);
if (candidateLocal == primaryLocal) {
throw new NoUniqueBeanDefinitionException(descriptor.getDependencyType(), candidateBeans.size(),
"more than one 'primary' bean found among candidates: " + candidateBeans.keySet());
}
else if (candidateLocal && !primaryLocal) {
primaryBeanName = candidateBeanName;
}
}
else {
primaryBeanName = candidateBeanName;
}
}
if (primaryBeanName == null &&
(this.resolvableDependencies.values().contains(beanInstance) ||
matchesBeanName(candidateBeanName, descriptor.getDependencyName()))) {
fallbackBeanName = candidateBeanName;
}
}
return (primaryBeanName != null ?
primaryBeanName : fallbackBeanName);
}
/**
* Return whether the bean definition for the given bean name has been
* marked as a primary bean.
* @param beanName the name of the bean
* @param beanInstance the corresponding bean instance
* @return whether the given bean qualifies as primary
*/
protected boolean isPrimary(String beanName, Object beanInstance) {
if (containsBeanDefinition(beanName)) {
return getMergedLocalBeanDefinition(beanName).isPrimary();
}
BeanFactory parentFactory = getParentBeanFactory();
return (parentFactory instanceof DefaultListableBeanFactory &&
((DefaultListableBeanFactory) parentFactory).isPrimary(beanName, beanInstance));
}
/**
* Determine whether the given candidate name matches the bean name or the aliases
* stored in this bean definition.
*/
protected boolean matchesBeanName(String beanName, String candidateName) {
return (candidateName != null &&
(candidateName.equals(beanName) || ObjectUtils.containsElement(getAliases(beanName), candidateName)));
}
/**
* Raise a NoSuchBeanDefinitionException for an unresolvable dependency.
*/
private void raiseNoSuchBeanDefinitionException(
Class<?> type, String dependencyDescription, DependencyDescriptor descriptor)
throws NoSuchBeanDefinitionException {
throw new NoSuchBeanDefinitionException(type, dependencyDescription,
"expected at least 1 bean which qualifies as autowire candidate for this dependency. " +
"Dependency annotations: " + ObjectUtils.nullSafeToString(descriptor.getAnnotations()));
}
@Override
public String toString() {
StringBuilder sb = new StringBuilder(ObjectUtils.identityToString(this));
sb.append(": defining beans [");
sb.append(StringUtils.arrayToCommaDelimitedString(getBeanDefinitionNames()));
sb.append("]; ");
BeanFactory parent = getParentBeanFactory();
if (parent == null) {
sb.append("root of factory hierarchy");
}
else {
sb.append("parent: ").append(ObjectUtils.identityToString(parent));
}
return sb.toString();
}
//---------------------------------------------------------------------
// Serialization support
//---------------------------------------------------------------------
private void readObject(ObjectInputStream ois) throws IOException, ClassNotFoundException {
throw new NotSerializableException("DefaultListableBeanFactory itself is not deserializable - " +
"just a SerializedBeanFactoryReference is");
}
protected Object writeReplace() throws ObjectStreamException {
if (this.serializationId != null) {
return new SerializedBeanFactoryReference(this.serializationId);
}
else {
throw new NotSerializableException("DefaultListableBeanFactory has no serialization id");
}
}
/**
* Minimal id reference to the factory.
* Resolved to the actual factory instance on deserialization.
*/
private static class SerializedBeanFactoryReference implements Serializable {
private final String id;
public SerializedBeanFactoryReference(String id) {
this.id = id;
}
private Object readResolve() {
Reference<?
> ref = serializableFactories.get(this.id);
if (ref == null) {
throw new IllegalStateException(
"Cannot deserialize BeanFactory with id " + this.id + ": no factory registered for this id");
}
Object result = ref.get();
if (result == null) {
throw new IllegalStateException(
"Cannot deserialize BeanFactory with id " + this.id + ": factory has been garbage-collected");
}
return result;
}
}
/**
* Serializable ObjectFactory for lazy resolution of a dependency.
*/
private class DependencyObjectFactory implements ObjectFactory<Object>, Serializable {
private final DependencyDescriptor descriptor;
private final String beanName;
public DependencyObjectFactory(DependencyDescriptor descriptor, String beanName) {
this.descriptor = new DependencyDescriptor(descriptor);
this.descriptor.increaseNestingLevel();
this.beanName = beanName;
}
public Object getObject() throws BeansException {
return doResolveDependency(this.descriptor, this.descriptor.getDependencyType(), this.beanName, null, null);
}
}
/**
* Serializable ObjectFactory for lazy resolution of a dependency.
*/
private class DependencyProvider extends DependencyObjectFactory implements Provider<Object> {
public DependencyProvider(DependencyDescriptor descriptor, String beanName) {
super(descriptor, beanName);
}
public Object get() throws BeansException {
return getObject();
}
}
/**
* Separate inner class for avoiding a hard dependency on the {@code javax.inject} API.
*/
private class DependencyProviderFactory {
public Object createDependencyProvider(DependencyDescriptor descriptor, String beanName) {
return new DependencyProvider(descriptor, beanName);
}
}
}
BeanFactory
在IOC模块中，大量使用了工厂设计模式来完毕类的初始化。
整个IOC中，最大的工厂接口便是BeanFactory。里面定义了了一些主要的方法去获取java bean，例如以下代码所看到的
package org.springframework.beans.factory;
import org.springframework.beans.BeansException;
/**
* IOC中工厂类的基类，定义了一些列获取java bean对象的方法
*/
public interface BeanFactory {
String FACTORY_BEAN_PREFIX = "&";
/**依据名字获取java bean对象
* @param name the name of the bean to retrieve
* @return an instance of the bean
* @throws NoSuchBeanDefinitionException if there is no bean definition
* with the specified name
* @throws BeansException if the bean could not be obtained
*/
Object getBean(String name) throws BeansException;
/**
* 依据名字获取指定类型的java bean对象
* @return an instance of the bean
* @throws NoSuchBeanDefinitionException if there is no such bean definition
* @throws BeanNotOfRequiredTypeException if the bean is not of the required type
* @throws BeansException if the bean could not be created
*/
<T> T getBean(String name, Class<T> requiredType) throws BeansException;
/**
*依据类型获取指定类型的java bean对象，这里使用了泛型技术
* @return an instance of the single bean matching the required type
* @throws NoSuchBeanDefinitionException if no bean of the given type was found
* @throws NoUniqueBeanDefinitionException if more than one bean of the given type was found
* @since 3.0
* @see ListableBeanFactory
*/
<T> T getBean(Class<T> requiredType) throws BeansException;
/**
* Return an instance, which may be shared or independent, of the specified bean.
* <p>Allows for specifying explicit constructor arguments / factory method arguments,
* overriding the specified default arguments (if any) in the bean definition.
* @param name the name of the bean to retrieve
* @param args arguments to use if creating a prototype using explicit arguments to a
* static factory method. It is invalid to use a non-null args value in any other case.
* @return an instance of the bean
* @throws NoSuchBeanDefinitionException if there is no such bean definition
* @throws BeanDefinitionStoreException if arguments have been given but
* the affected bean isn't a prototype
* @throws BeansException if the bean could not be created
* @since 2.5
*/
Object getBean(String name, Object... args) throws BeansException;
/**
* 推断IOC容器中是否有指定名字的java bean对象
* @param name the name of the bean to query
* @return whether a bean with the given name is present
*/
boolean containsBean(String name);
/**
* 推断指定名字的java bean对象是否为单例模式
* @see #getBean
* @see #isPrototype
*/
boolean isSingleton(String name) throws NoSuchBeanDefinitionException;
/**
* 推断指定名字的java bean对象是否为原型设计模式
* @since 2.0.3
* @see #getBean
* @see #isSingleton
*/
boolean isPrototype(String name) throws NoSuchBeanDefinitionException;
/**
* 推断指定名字的java bean对象是否为targetType的类型
* @since 2.0.1
* @see #getBean
* @see #getType
*/
boolean isTypeMatch(String name, Class<?> targetType) throws NoSuchBeanDefinitionException;
/**
* 获取指定名字的java bean对象的类型
* @since 1.1.2
* @see #getBean
* @see #isTypeMatch
*/
Class<?> getType(String name) throws NoSuchBeanDefinitionException;
/**获取指定名字的java bean对象的别名，一个对象能够有多个名字
* @param name the bean name to check for aliases
* @return the aliases, or an empty array if none
* @see #getBean
*/
String[] getAliases(String name);
}
当然，只这几个普通的接口肯定是无法定义整个spring ioc须要的类的。可是BeanFactory作为基类，保持接口的精简是很必要的，其它的BeanFactory依据特性继承该接口就可以。以下贴出关于整个BeanFactory的继承体系。
只是从类的名字。我们大概能够猜到这些类或者接口的功能。
Bean
为写成JavaBean，类必须是详细的和公共的，而且具有无參数的构造器
。JavaBean 通过提供符合一致性设计模式的公共方法将内部域暴露成员属性。众所周知。属性名称符合这样的模式，其它Java 类能够通过自省机制发现和操作这些JavaBean 的属性。也就是我们经常使用的java bean对象都有例如以下几个模块组成，详细详情能够參考百度百科java bean- 构造方法
- 属性
- 方法
- 事件
作为一个框架，常常会更具反射去动态的载入一些类，spring IOC相同也是利用了反射的技术。在spring中，会依据源数据来实例化一个java bean，而且在实例化过程中注入依赖的类。或者是调用一些初始化、销毁方法。
对于spring 容器中的bean。主要由例如以下几个属性
|
class |
|
|
name |
类名 |
|
scope |
生存周期 |
|
constructor arguments |
构造參数 |
|
properties |
属性 |
|
autowiring mode |
注入模式（byName, byType, auto） |
|
lazy-initialization mode |
延迟载入模式 |
|
initialization method |
初始化时调用的方法 |
|
destruction method |
摧毁时调用的方法 |
开发人员掌握要点
- bean依赖对象的注入方式（以那种方式注入bean。比方通过setter。constructor。field等）
- bean依赖对象的查找方式，也就是依据哪一种方式来寻找依赖对象（no，byName， byType，autowired）
- 选择使用那种configuration
metadata（源数据）来管理bean（主要有两种。一种是xml方式，一种是注解方式）
- 懒载入模式
- bean对象实例化、或者摧毁时调用的方法
- bean对象的生命周期（singleton，prototype，request，session，global，application。当中request，session，global，application为web专用）。
在这里面。singleton代表的是单例。也就是一个class，spring container中仅仅用一个实例。
prototype为原型模式，也就是一个class有多个实例，差别例如以下图所看到的
源代码下载
总结
- 依赖倒置法则的应用
- java bean规范的使用
- 对象生命周期
- 工厂设计模式
- 面向接口编程