Spring source code read like this

xlecho 2021-04-16 19:08:32
spring source code read


Following the above question , Let's take a look at this chapter , Continue to analyze what our container is doing .

We talked about our ClassPathResource What did you do , But after we read the source code, we found that we just did some initialization . So we're guessing to get the configuration file , And then go to the configuration file to get the content of the speculation is still valid ? There's no need to rush , We can see the result step by step . Now that we've seen it ClassPathResource, Let's see new XmlBeanFactory(classPathResource); What did you do .

structure bean Factory

/**
* Create a new XmlBeanFactory with the given resource,
* which must be parsable using DOM.
* @param resource the XML resource to load bean definitions from
* @throws BeansException in case of loading or parsing errors
*/
public XmlBeanFactory(Resource resource) throws BeansException {
this(resource, null);
}
/**
* Create a new XmlBeanFactory with the given input stream,
* which must be parsable using DOM.
* @param resource the XML resource to load bean definitions from
* @param parentBeanFactory parent bean factory
* @throws BeansException in case of loading or parsing errors
*/
public XmlBeanFactory(Resource resource, BeanFactory parentBeanFactory) throws BeansException {
super(parentBeanFactory);
this.reader.loadBeanDefinitions(resource);
}

We use the first construct , But the first construct calls the second , The second construction has only two steps . Let's move on

Look again. XmlBeanFactory Initialization source

  • super(parentBeanFactory): Used to initialize the parent class
  • this.reader.loadBeanDefinitions(resource):spring Initialize the real implementation of resource loading

Let's take a look first “super(parentBeanFactory): Used to initialize the parent class ” What did you do in this step

/**
* First, call DefaultListableBeanFactory(@Nullable BeanFactory parentBeanFactory) Structural method with parameters
*/
public DefaultListableBeanFactory(@Nullable BeanFactory parentBeanFactory) {
super(parentBeanFactory);
}
/**
* Call the parent class AbstractAutowireCapableBeanFactory
*/
public AbstractAutowireCapableBeanFactory(@Nullable BeanFactory parentBeanFactory) {
this();
setParentBeanFactory(parentBeanFactory);
}
/**
* call AbstractAutowireCapableBeanFactory() Nonparametric construction method
*/
public AbstractAutowireCapableBeanFactory() {
super();
ignoreDependencyInterface(BeanNameAware.class);
ignoreDependencyInterface(BeanFactoryAware.class);
ignoreDependencyInterface(BeanClassLoaderAware.class);
}
/**
* Initializing XmlBeanFactory Containers
*/
public void setParentBeanFactory(@Nullable BeanFactory parentBeanFactory) {
if (this.parentBeanFactory != null && this.parentBeanFactory != parentBeanFactory) {
throw new IllegalStateException("Already associated with parent BeanFactory: " + this.parentBeanFactory);
}
this.parentBeanFactory = parentBeanFactory;
}

Is it clear that we know what we have done in this step ? Actually, it's over super(parentBeanFactory) There are two things we did when we discovered the source code of : Get add need to ignore the specified interface to realize automatic assembly and initialization of class . What did we do in the second step ?

this.reader.loadBeanDefinitions(resource) analysis

We said before that we should find the corresponding class according to the configuration file , Is the source code like this ? Just look at the implementation of this code .

/**
* First, call loadBeanDefinitions(Resource resource)
*/
public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
return loadBeanDefinitions(new EncodedResource(resource));
}
/**
* This method is exactly what we speculated before
* from xml Load in configuration file bean
*/
public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
Assert.notNull(encodedResource, "EncodedResource must not be null");
if (logger.isTraceEnabled()) {
logger.trace("Loading XML bean definitions from " + encodedResource);
}
Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get();
if (currentResources == null) {
currentResources = new HashSet<>(4);
this.resourcesCurrentlyBeingLoaded.set(currentResources);
}
if (!currentResources.add(encodedResource)) {
throw new BeanDefinitionStoreException(
"Detected cyclic loading of " + encodedResource + " - check your import definitions!");
}
try {
InputStream inputStream = encodedResource.getResource().getInputStream();
try {
InputSource inputSource = new InputSource(inputStream);
if (encodedResource.getEncoding() != null) {
inputSource.setEncoding(encodedResource.getEncoding());
}
return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
}
finally {
inputStream.close();
}
}
catch (IOException ex) {
throw new BeanDefinitionStoreException(
"IOException parsing XML document from " + encodedResource.getResource(), ex);
}
finally {
currentResources.remove(encodedResource);
if (currentResources.isEmpty()) {
this.resourcesCurrentlyBeingLoaded.remove();
}
}
}

After we post the code , Can we clearly see the actual evidence we speculated before ?

ClassPathResource and InputStream

We can see from the source code above , The class we define is in xml in , The source code contains InputStream. But only one was introduced ClassPathResource. How did he get into ClassPathResource What about ?

In fact, the connection here is relatively simple . Let's take a look at the class structure diagram of these classes  Insert picture description here

It's very clear that our InputStream How to deliver content into ClassPathResource

Really get bean

obtain bean That's the key to our operation , that bean How did you get it ? Post the main code here

protected <T> T doGetBean(final String name, @Nullable final Class<T> requiredType,
@Nullable final Object[] args, boolean typeCheckOnly) throws BeansException {
final String beanName = transformedBeanName(name);
Object bean;
// Eagerly check singleton cache for manually registered singletons.
Object sharedInstance = getSingleton(beanName);
if (sharedInstance != null && args == null) {
if (logger.isTraceEnabled()) {
if (isSingletonCurrentlyInCreation(beanName)) {
logger.trace("Returning eagerly cached instance of singleton bean '" + beanName +
"' that is not fully initialized yet - a consequence of a circular reference");
}
else {
logger.trace("Returning cached instance of singleton bean '" + beanName + "'");
}
}
bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
}
else {
// Fail if we're already creating this bean instance:
// We're assumably within a circular reference.
if (isPrototypeCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(beanName);
}
// Check if bean definition exists in this factory.
BeanFactory parentBeanFactory = getParentBeanFactory();
if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
// Not found -> check parent.
String nameToLookup = originalBeanName(name);
if (parentBeanFactory instanceof AbstractBeanFactory) {
return ((AbstractBeanFactory) parentBeanFactory).doGetBean(
nameToLookup, requiredType, args, typeCheckOnly);
}
else if (args != null) {
// Delegation to parent with explicit args.
return (T) parentBeanFactory.getBean(nameToLookup, args);
}
else if (requiredType != null) {
// No args -> delegate to standard getBean method.
return parentBeanFactory.getBean(nameToLookup, requiredType);
}
else {
return (T) parentBeanFactory.getBean(nameToLookup);
}
}
if (!typeCheckOnly) {
markBeanAsCreated(beanName);
}
try {
final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
checkMergedBeanDefinition(mbd, beanName, args);
// Guarantee initialization of beans that the current bean depends on.
String[] dependsOn = mbd.getDependsOn();
if (dependsOn != null) {
for (String dep : dependsOn) {
if (isDependent(beanName, dep)) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
}
registerDependentBean(dep, beanName);
try {
getBean(dep);
}
catch (NoSuchBeanDefinitionException ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"'" + beanName + "' depends on missing bean '" + dep + "'", ex);
}
}
}
// Create bean instance.
if (mbd.isSingleton()) {
sharedInstance = getSingleton(beanName, () -> {
try {
return createBean(beanName, mbd, args);
}
catch (BeansException ex) {
// Explicitly remove instance from singleton cache: It might have been put there
// eagerly by the creation process, to allow for circular reference resolution.
// Also remove any beans that received a temporary reference to the bean.
destroySingleton(beanName);
throw ex;
}
});
bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
}
else if (mbd.isPrototype()) {
// It's a prototype -> create a new instance.
Object prototypeInstance = null;
try {
beforePrototypeCreation(beanName);
prototypeInstance = createBean(beanName, mbd, args);
}
finally {
afterPrototypeCreation(beanName);
}
bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
}
else {
String scopeName = mbd.getScope();
final Scope scope = this.scopes.get(scopeName);
if (scope == null) {
throw new IllegalStateException("No Scope registered for scope name '" + scopeName + "'");
}
try {
Object scopedInstance = scope.get(beanName, () -> {
beforePrototypeCreation(beanName);
try {
return createBean(beanName, mbd, args);
}
finally {
afterPrototypeCreation(beanName);
}
});
bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
}
catch (IllegalStateException ex) {
throw new BeanCreationException(beanName,
"Scope '" + scopeName + "' is not active for the current thread; consider " +
"defining a scoped proxy for this bean if you intend to refer to it from a singleton",
ex);
}
}
}
catch (BeansException ex) {
cleanupAfterBeanCreationFailure(beanName);
throw ex;
}
}
// Check if required type matches the type of the actual bean instance.
if (requiredType != null && !requiredType.isInstance(bean)) {
try {
T convertedBean = getTypeConverter().convertIfNecessary(bean, requiredType);
if (convertedBean == null) {
throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
}
return convertedBean;
}
catch (TypeMismatchException ex) {
if (logger.isTraceEnabled()) {
logger.trace("Failed to convert bean '" + name + "' to required type '" +
ClassUtils.getQualifiedName(requiredType) + "'", ex);
}
throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
}
}
return (T) bean;
}

Just from the amount of code bean The loading of is a rather complicated process , It involves all kinds of considerations .

Let's summarize the above :

  • Conversion correspondence beanName.
  • Trying to load singleton from cache .
  • bean Instantiation .
  • Dependency checking of prototype patterns .
  • testing parentBeanFactory.
  • Will store XML Profile's GernericBeanDefinition Convert to RootBeanDefinition.
  • Looking for dependency .
  • For different scope Conduct bean The creation of .
  • Type conversion .( Strong go )

Actually, reading this , It's not hard for us to see , It's not very different from our previous conjecture , It's just that the developers of the source code are more strict with the logic of the code , And did a lot of necessary checks .

版权声明
本文为[xlecho]所创,转载请带上原文链接,感谢
https://javamana.com/2021/04/20210416172347883x.html

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