第4講:XmlBeanDefinitionReader與Resource
觀察defaultlistablebeanfactory的屬性
分析ClasspathResource的建立
分析DefaultListableBeanFactory的建立
1、classPathResource的構造方法
2、分析DefaultListableBeanFactory的建立
3、XmlBeanDefinitinRead的建立
1、classPathResource內部結構很簡單,有兩個重要屬性:
String path:儲存資源路徑的地址
ClassLoader classLoader:類載入器(負責將配置檔案(磁碟)載入到jvm中(記憶體),當然也負責類檔案載入到jvm中)
所以Resource類並沒有做什麼實際性的操作,只是定位資源資訊而已
2、DefaultListableBeanFactory(IOC容器)
就是平時我們所說的Ioc容器,它裡面定義了很多屬性:
我最關心的一個屬性:
Map<String, BeanDefinition> beanDefinitionMap:儲存bean定義資訊
其他幾個次要關心的屬性:
Map<Class<?>, String[]> allBeanNamesByType: 儲存bean名稱和bean型別的關聯關係
Map<Class<?>, String[]> singletonBeanNamesByType: 儲存單例bean名稱和單例bean型別的關聯關係
List<String> beanDefinitionNames: 儲存所有bean定義資訊的名稱
說實話,上述這幾個屬性不用可以去記,後面章節用到了你就知道了,這麼多屬性記住主要的就行了
所以說這個類本身就代表了一個容器,裡面有對這些屬性的一系列操作(crud),可以大膽猜測平時我們獲取bean應該就是直接跟這個類打交道,它就是IOC
3、XmlBeanDefinitinRead
這個類好像也是什麼都沒幹,只是定義了一些屬性而已,當然建立它的時候有會把BeanFactory當作BeanDefinitionRegistry屬性。因為BeanFactory實現了BeanDefinitionRegistry介面。
4、reader.loadBeanDefinitions(resource)
這個方法才在真正解析bean定義,上面的3個步驟都是在做一些準備工作。
/**
* Load bean definitions from the specified XML file.
* @param encodedResource the resource descriptor for the XML file,
* allowing to specify an encoding to use for parsing the file
* @return the number of bean definitions found
* @throws BeanDefinitionStoreException in case of loading or parsing errors
*/
public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
Assert.notNull(encodedResource, "EncodedResource must not be null");
if (logger.isInfoEnabled()) {
logger.info("Loading XML bean definitions from " + encodedResource.getResource());
}
//從ThreadLocal中獲取當前執行緒的Set<EncodedResource> 如需詳細瞭解ThreadLocal,連結:https://www.jianshu.com/p/3c5d7f09dfbd
Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get();
if (currentResources == null) {
currentResources = new HashSet<EncodedResource>(4);
this.resourcesCurrentlyBeingLoaded.set(currentResources);
}
if (!currentResources.add(encodedResource)) {
throw new BeanDefinitionStoreException(
"Detected cyclic loading of " + encodedResource + " - check your import definitions!");
}
try {
//獲取resource的輸入流 詳解見程式碼塊1
InputStream inputStream = encodedResource.getResource().getInputStream();
try {
//把inputstream包裝成一個InputSource
InputSource inputSource = new InputSource(inputStream);
if (encodedResource.getEncoding() != null) {
inputSource.setEncoding(encodedResource.getEncoding());
}
//真正載入beanDefinitions開始了 詳解見程式碼塊2
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();
}
}
}
程式碼塊1:encodedResource.getResource().getInputStream()
/**
* This implementation opens an InputStream for the given class path resource.
* @see java.lang.ClassLoader#getResourceAsStream(String)
* @see java.lang.Class#getResourceAsStream(String)
*/
@Override
public InputStream getInputStream() throws IOException {
InputStream is;
if (this.clazz != null) {
//clazz是要給Class物件,通過Class物件將一個路徑資源直接轉換成要給輸入流(詳解見:內部程式碼塊1)
is = this.clazz.getResourceAsStream(this.path);
}
else if (this.classLoader != null) {
is = this.classLoader.getResourceAsStream(this.path);
}
else {
is = ClassLoader.getSystemResourceAsStream(this.path);
}
if (is == null) {
throw new FileNotFoundException(getDescription() + " cannot be opened because it does not exist");
}
return is;
}
內部程式碼塊1:
public InputStream getResourceAsStream(String name) {
//通過下面的程式碼可以看到,其實還是通過呼叫類載入器的方法,實現把一個資源轉換成一個輸入流的
name = resolveName(name);
ClassLoader cl = getClassLoader0();
if (cl==null) {
// A system class.
return ClassLoader.getSystemResourceAsStream(name);
}
return cl.getResourceAsStream(name); //(詳解見:內部程式碼塊2)
}
內部程式碼塊2:
public InputStream getResourceAsStream(String name) {
//可以看到ClassLoader又是通過URL物件來實現對資源的解析的
URL url = getResource(name);
try {
return url != null ? url.openStream() : null;(詳解見:內部程式碼塊3)
} catch (IOException e) {
return null;
}
}
內部程式碼塊3:
public final InputStream openStream() throws java.io.IOException {
//更新的程式碼就不看了,我這裡猜想內部實現細節應該是會通過建立InputStream來獲取到資源輸入流
return openConnection().getInputStream();
}
程式碼塊2:doLoadBeanDefinitions(inputSource, encodedResource.getResource())
/**
* Actually load bean definitions from the specified XML file.
* @param inputSource the SAX InputSource to read from
* @param resource the resource descriptor for the XML file
* @return the number of bean definitions found
* @throws BeanDefinitionStoreException in case of loading or parsing errors
* @see #doLoadDocument
* @see #registerBeanDefinitions
*/
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
throws BeanDefinitionStoreException {
try {
//獲取到Document物件(詳解見:程式碼塊3)
Document doc = doLoadDocument(inputSource, resource);
//獲取到Document物件(詳解見:程式碼塊4)
return registerBeanDefinitions(doc, resource);
}
catch (BeanDefinitionStoreException ex) {
throw ex;
}
catch (SAXParseException ex) {
throw new XmlBeanDefinitionStoreException(resource.getDescription(),
"Line " + ex.getLineNumber() + " in XML document from " + resource + " is invalid", ex);
}
catch (SAXException ex) {
throw new XmlBeanDefinitionStoreException(resource.getDescription(),
"XML document from " + resource + " is invalid", ex);
}
catch (ParserConfigurationException ex) {
throw new BeanDefinitionStoreException(resource.getDescription(),
"Parser configuration exception parsing XML from " + resource, ex);
}
catch (IOException ex) {
throw new BeanDefinitionStoreException(resource.getDescription(),
"IOException parsing XML document from " + resource, ex);
}
catch (Throwable ex) {
throw new BeanDefinitionStoreException(resource.getDescription(),
"Unexpected exception parsing XML document from " + resource, ex);
}
}
程式碼塊3:doLoadDocument(inputSource, resource)
/**
* Actually load the specified document using the configured DocumentLoader.
* @param inputSource the SAX InputSource to read from
* @param resource the resource descriptor for the XML file
* @return the DOM Document
* @throws Exception when thrown from the DocumentLoader
* @see #setDocumentLoader
* @see DocumentLoader#loadDocument
*/
//通過DocumentLoader載入Document物件,具體細節不深入研究
protected Document doLoadDocument(InputSource inputSource, Resource resource) throws Exception {
return this.documentLoader.loadDocument(inputSource, getEntityResolver(), this.errorHandler,
getValidationModeForResource(resource), isNamespaceAware());
}
程式碼塊4:registerBeanDefinitions(doc, resource)
/**
* Register the bean definitions contained in the given DOM document.
* Called by {@code loadBeanDefinitions}.
* <p>Creates a new instance of the parser class and invokes
* {@code registerBeanDefinitions} on it.
* @param doc the DOM document
* @param resource the resource descriptor (for context information)
* @return the number of bean definitions found
* @throws BeanDefinitionStoreException in case of parsing errors
* @see #loadBeanDefinitions
* @see #setDocumentReaderClass
* @see BeanDefinitionDocumentReader#registerBeanDefinitions
*/
//該方法的返回值是beanDefinitin的個數(感覺沒卵用)
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
//獲取BeanDefinitionDocumentReader物件,用於真正解析Document物件 (詳解見:內部程式碼塊1)
BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
//獲取Document中BeanDefinition的個數
int countBefore = getRegistry().getBeanDefinitionCount();
//真正解析BeanDefinition (詳解見:第六講)
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
//註冊BeanDefinition的數量
return getRegistry().getBeanDefinitionCount() - countBefore;
}
內部程式碼塊1:
/**
* Create the {@link BeanDefinitionDocumentReader} to use for actually
* reading bean definitions from an XML document.
* <p>The default implementation instantiates the specified "documentReaderClass".
* @see #setDocumentReaderClass
*/
//該方法會返回要給BeanDefinitionDocumentReader 的實現類 DefaultBeanDefinitionDocumentReader (該類的介紹詳解見:內部程式碼塊2)
protected BeanDefinitionDocumentReader createBeanDefinitionDocumentReader() {
return BeanDefinitionDocumentReader.class.cast(BeanUtils.instantiateClass(this.documentReaderClass));
}
內部程式碼塊2:
//BeanDefinitionDocumentReader 該類是DefaultBeanDefinitionDocumentReader 的預設實現類,該類中定義了XML文件的結構、元素和屬性名,
//也就是說xml中出現的元素名稱、元素的屬性名都定義在了這個類的屬性中,如:
//String NESTED_BEANS_ELEMENT = "beans"; String ALIAS_ELEMENT = "alias"; String NAME_ATTRIBUTE = "name";String ALIAS_ATTRIBUTE = "alias";IMPORT_ELEMENT = "import";RESOURCE_ATTRIBUTE = "resource";PROFILE_ATTRIBUTE = "profile";
//更多的名稱可在 BeanDefinitionParserDelegate類中檢視,為什麼我會突然提到這個類呢?因為DefaultBeanDefinitionDocumentReader類中確實有引用到這個類
//BeanDefinitionDocumentReader 類中有一個重要的屬性:BeanDefinitionParserDelegate,它就是真正用於解析BeanDefinition的,是解析BeanDefinition的一個代理 (詳解見:第六講)