Spring容器概述
容器是spring的核心,Spring容器使用DI管理構成應用的組件,它會創建相互協作的組件之間的關聯,負責創建對象,裝配它們,配置它們並管理它們的生命週期,從生存到死亡(在這裏,可能就是new 到 finalize())。
Spring容器不只有一個。Spring自帶了多個容器實現,可以歸納爲兩種不同的類型:
1、bean工廠(由beanFactory接口定義)是最簡單的容器,提供基本的DI支持。
2、應用上下文(由ApplicationContext接口定義),基於BeanFactory構建,並且提供應用框架級別的服務。
ApplicationContext容器
相比bean工廠,ApplicationContext在實際的應用中顯得更受歡迎,下面着重介紹後者。
先來看下ApplicationContext的源碼。
package org.springframework.context;
import org.springframework.beans.factory.HierarchicalBeanFactory;
import org.springframework.beans.factory.ListableBeanFactory;
import org.springframework.beans.factory.config.AutowireCapableBeanFactory;
import org.springframework.core.env.EnvironmentCapable;
import org.springframework.core.io.support.ResourcePatternResolver;
/**
* Central interface to provide configuration for an application.
* This is read-only while the application is running, but may be
* reloaded if the implementation supports this.
*
* <p>An ApplicationContext provides:
* <ul>
* <li>Bean factory methods for accessing application components.
* Inherited from {@link org.springframework.beans.factory.ListableBeanFactory}.
* <li>The ability to load file resources in a generic fashion.
* Inherited from the {@link org.springframework.core.io.ResourceLoader} interface.
* <li>The ability to publish events to registered listeners.
* Inherited from the {@link ApplicationEventPublisher} interface.
* <li>The ability to resolve messages, supporting internationalization.
* Inherited from the {@link MessageSource} interface.
* <li>Inheritance from a parent context. Definitions in a descendant context
* will always take priority. This means, for example, that a single parent
* context can be used by an entire web application, while each servlet has
* its own child context that is independent of that of any other servlet.
* </ul>
*
* <p>In addition to standard {@link org.springframework.beans.factory.BeanFactory}
* lifecycle capabilities, ApplicationContext implementations detect and invoke
* {@link ApplicationContextAware} beans as well as {@link ResourceLoaderAware},
* {@link ApplicationEventPublisherAware} and {@link MessageSourceAware} beans.
*
* @author Rod Johnson
* @author Juergen Hoeller
* @see ConfigurableApplicationContext
* @see org.springframework.beans.factory.BeanFactory
* @see org.springframework.core.io.ResourceLoader
*/
public interface ApplicationContext extends EnvironmentCapable, ListableBeanFactory, HierarchicalBeanFactory,
MessageSource, ApplicationEventPublisher, ResourcePatternResolver {
/**
* Return the unique id of this application context.
* @return the unique id of the context, or {@code null} if none
*/
String getId();
/**
* Return a name for the deployed application that this context belongs to.
* @return a name for the deployed application, or the empty String by default
*/
String getApplicationName();
/**
* Return a friendly name for this context.
* @return a display name for this context (never {@code null})
*/
String getDisplayName();
/**
* Return the timestamp when this context was first loaded.
* @return the timestamp (ms) when this context was first loaded
*/
long getStartupDate();
/**
* Return the parent context, or {@code null} if there is no parent
* and this is the root of the context hierarchy.
* @return the parent context, or {@code null} if there is no parent
*/
ApplicationContext getParent();
/**
* Expose AutowireCapableBeanFactory functionality for this context.
* <p>This is not typically used by application code, except for the purpose of
* initializing bean instances that live outside of the application context,
* applying the Spring bean lifecycle (fully or partly) to them.
* <p>Alternatively, the internal BeanFactory exposed by the
* {@link ConfigurableApplicationContext} interface offers access to the
* {@link AutowireCapableBeanFactory} interface too. The present method mainly
* serves as a convenient, specific facility on the ApplicationContext interface.
* <p><b>NOTE: As of 4.2, this method will consistently throw IllegalStateException
* after the application context has been closed.</b> In current Spring Framework
* versions, only refreshable application contexts behave that way; as of 4.2,
* all application context implementations will be required to comply.
* @return the AutowireCapableBeanFactory for this context
* @throws IllegalStateException if the context does not support the
* {@link AutowireCapableBeanFactory} interface, or does not hold an
* autowire-capable bean factory yet (e.g. if {@code refresh()} has
* never been called), or if the context has been closed already
* @see ConfigurableApplicationContext#refresh()
* @see ConfigurableApplicationContext#getBeanFactory()
*/
AutowireCapableBeanFactory getAutowireCapableBeanFactory() throws IllegalStateException;
}
ApplicationContext是spring中較高級的容器。和BeanFactory類似,它可以加載配置文件中定義的bean,將所有的bean集中在一起,當有請求的時候分配bean。 另外,它增加了企業所需要的功能,比如,從屬性文件從解析文本信息和將事件傳遞給所指定的監聽器。這個容器在org.springframework.context.ApplicationContext接口中定義。ApplicationContext包含BeanFactory所有的功能,一般情況下,相對於BeanFactory,ApplicationContext會被推薦使用。但BeanFactory仍然可以在輕量級應用中使用,比如移動設備或者基於applet的應用程序。
ApplicationContext接口關係
1、訪問應用程序組件的Bean工廠方法。繼承自ListableBeanFactory。
2、訪問資源。這一特性主要體現在ResourcePatternResolver接口上,對Resource和ResourceLoader的支持,這樣我們可以從不同地方得到Bean定義資源。這種抽象使用戶程序可以靈活地定義Bean定義信息,尤其是從不同的IO途徑得到Bean定義信息。這在接口上看不出來,不過一般來說,具體ApplicationContext都是繼承了DefaultResourceLoader的子類。因爲DefaultResourceLoader是AbstractApplicationContext的基類。
3、支持應用事件。繼承了接口ApplicationEventPublisher,爲應用環境引入了事件機制,這些事件和Bean的生命週期的結合爲Bean的管理提供了便利。
4、解析消息的能力,支持國際化。繼承MessageSource。
5、從父上下文繼承。在後代的定義將始終優先。這意味着,例如,一個上下文可以被整個Web應用程序使用,而每個servlet都可以使用獨立於任何其他servlet的子環境。
ApplicationContext繼承體系
ApplicationContext容器實現類
常用的如下:
AnnotationConfigApplicationContext
從一個或者多個基於java的配置類中加載Spring應用上下文。例如:
ApplicationContext annotationConfigApplicationContext = new AnnotationConfigApplicationContext(test.class);
AnnotationConfigWebApplicationContext
加載spring web應用上下文。
ClassPathXmlApplicationContext
從類的路徑下的一個或多個XML配置文件中加載上下文,把應用上下文的定義文件作爲類資源
FileSystemXmlApplicationContext
和ClassPathXmlApplicationContext的區別在於後者是從指定的文件系統路徑下查找配置文件,而前者是在所有的類路徑下查找配置文件。
例如:
ApplicationContext fileSystemXmlApplicationContext = new FileSystemXmlApplicationContext("c:/user/pro.xml");
ApplicationContext classPathXmlApplicationContext = new ClassPathXmlApplicationContext("pro.xml");
容器的運作原理
下面就上述提到的FileSystemXmlApplicationContext的容器實現類說明容器運作原理。
FileSystemXmlApplicationContext源碼
package org.springframework.context.support;
import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.core.io.FileSystemResource;
import org.springframework.core.io.Resource;
/**
* Standalone XML application context, taking the context definition files
* from the file system or from URLs, interpreting plain paths as relative
* file system locations (e.g. "mydir/myfile.txt"). Useful for test harnesses
* as well as for standalone environments.
*
* <p><b>NOTE:</b> Plain paths will always be interpreted as relative
* to the current VM working directory, even if they start with a slash.
* (This is consistent with the semantics in a Servlet container.)
* <b>Use an explicit "file:" prefix to enforce an absolute file path.</b>
*
* <p>The config location defaults can be overridden via {@link #getConfigLocations},
* Config locations can either denote concrete files like "/myfiles/context.xml"
* or Ant-style patterns like "/myfiles/*-context.xml" (see the
* {@link org.springframework.util.AntPathMatcher} javadoc for pattern details).
*
* <p>Note: In case of multiple config locations, later bean definitions will
* override ones defined in earlier loaded files. This can be leveraged to
* deliberately override certain bean definitions via an extra XML file.
*
* <p><b>This is a simple, one-stop shop convenience ApplicationContext.
* Consider using the {@link GenericApplicationContext} class in combination
* with an {@link org.springframework.beans.factory.xml.XmlBeanDefinitionReader}
* for more flexible context setup.</b>
*
* @author Rod Johnson
* @author Juergen Hoeller
* @see #getResource
* @see #getResourceByPath
* @see GenericApplicationContext
*/
public class FileSystemXmlApplicationContext extends AbstractXmlApplicationContext {
/**
* Create a new FileSystemXmlApplicationContext for bean-style configuration.
* @see #setConfigLocation
* @see #setConfigLocations
* @see #afterPropertiesSet()
*/
public FileSystemXmlApplicationContext() {
}
/**
* Create a new FileSystemXmlApplicationContext for bean-style configuration.
* @param parent the parent context
* @see #setConfigLocation
* @see #setConfigLocations
* @see #afterPropertiesSet()
*/
public FileSystemXmlApplicationContext(ApplicationContext parent) {
super(parent);
}
/**
* Create a new FileSystemXmlApplicationContext, loading the definitions
* from the given XML file and automatically refreshing the context.
* @param configLocation file path
* @throws BeansException if context creation failed
*/
public FileSystemXmlApplicationContext(String configLocation) throws BeansException {
this(new String[] {configLocation}, true, null);
}
/**
* Create a new FileSystemXmlApplicationContext, loading the definitions
* from the given XML files and automatically refreshing the context.
* @param configLocations array of file paths
* @throws BeansException if context creation failed
*/
public FileSystemXmlApplicationContext(String... configLocations) throws BeansException {
this(configLocations, true, null);
}
/**
* Create a new FileSystemXmlApplicationContext with the given parent,
* loading the definitions from the given XML files and automatically
* refreshing the context.
* @param configLocations array of file paths
* @param parent the parent context
* @throws BeansException if context creation failed
*/
public FileSystemXmlApplicationContext(String[] configLocations, ApplicationContext parent) throws BeansException {
this(configLocations, true, parent);
}
/**
* Create a new FileSystemXmlApplicationContext, loading the definitions
* from the given XML files.
* @param configLocations array of file paths
* @param refresh whether to automatically refresh the context,
* loading all bean definitions and creating all singletons.
* Alternatively, call refresh manually after further configuring the context.
* @throws BeansException if context creation failed
* @see #refresh()
*/
public FileSystemXmlApplicationContext(String[] configLocations, boolean refresh) throws BeansException {
this(configLocations, refresh, null);
}
/**
* Create a new FileSystemXmlApplicationContext with the given parent,
* loading the definitions from the given XML files.
* @param configLocations array of file paths
* @param refresh whether to automatically refresh the context,
* loading all bean definitions and creating all singletons.
* Alternatively, call refresh manually after further configuring the context.
* @param parent the parent context
* @throws BeansException if context creation failed
* @see #refresh()
*/
public FileSystemXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)
throws BeansException {
super(parent);
setConfigLocations(configLocations);
if (refresh) {
refresh();
}
}
/**
* Resolve resource paths as file system paths.
* <p>Note: Even if a given path starts with a slash, it will get
* interpreted as relative to the current VM working directory.
* This is consistent with the semantics in a Servlet container.
* @param path path to the resource
* @return Resource handle
* @see org.springframework.web.context.support.XmlWebApplicationContext#getResourceByPath
*/
@Override
protected Resource getResourceByPath(String path) {
if (path != null && path.startsWith("/")) {
path = path.substring(1);
}
return new FileSystemResource(path);
}
}
編寫測試類
public class FileSystemXmlApplicationContextTest{
public static void main(String[] args) {
ApplicationContext fileSystemXmlApplicationContext = new FileSystemXmlApplicationContext("c:/user/pro.xml");
fileSystemXmlApplicationContext.getBean("test", Test.class);
}
}
源碼追蹤分析
/**
* Create a new FileSystemXmlApplicationContext with the given parent,
* loading the definitions from the given XML files.
* @param configLocations array of file paths
* @param refresh whether to automatically refresh the context,
* loading all bean definitions and creating all singletons.
* Alternatively, call refresh manually after further configuring the context.
* @param parent the parent context
* @throws BeansException if context creation failed
* @see #refresh()
*/
public FileSystemXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)
throws BeansException {
super(parent);
setConfigLocations(configLocations);
if (refresh) {
refresh();
}
}
通過分析FileSystemXmlApplicationContext的源代碼可以知道,在創建FileSystemXmlApplicationContext容器時,構造方法做以下兩項重要工作:
首先,調用父類容器的構造方法(super(parent)方法)爲容器設置好Bean資源加載器。
/**
* Create a new AbstractApplicationContext with the given parent context.
* @param parent the parent context
*/
public AbstractApplicationContext(ApplicationContext parent) {
this();
setParent(parent);
}
然後,setConfigLocations(configLocations);主要是加載配置文件的路徑。
/**
* Set the config locations for this application context.
* <p>If not set, the implementation may use a default as appropriate.
*/
public void setConfigLocations(String... locations) {
if (locations != null) {
Assert.noNullElements(locations, "Config locations must not be null");
this.configLocations = new String[locations.length];
for (int i = 0; i < locations.length; i++) {
this.configLocations[i] = resolvePath(locations[i]).trim();
}
}
else {
this.configLocations = null;
}
}
最主要的是refresh();方法的實現。Ioc容器的refresh()過程,是個非常複雜的過程,但不同的容器實現這裏都是相似的,因此基類中就將他們封裝好了。
我們繼續跟進refresh()方法
@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
initMessageSource();
// Initialize event multicaster for this context.
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
onRefresh();
// Check for listener beans and register them.
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
finishRefresh();
}
catch (BeansException ex) {
logger.warn("Exception encountered during context initialization - cancelling refresh attempt", ex);
// Destroy already created singletons to avoid dangling resources.
destroyBeans();
// Reset 'active' flag.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
}
}
refresh定義在AbstractApplicationContext類中,它詳細描述了整個ApplicationContext的初始化過程,比如BeanFactory的更新、MessageSource和PostProcessor的註冊等。這裏看起來像是對ApplicationContext進行初始化的模版或執行提綱,這個執行過程爲Bean的生命週期管理提供了條件。
/**
* Prepare this context for refreshing, setting its startup date and
* active flag as well as performing any initialization of property sources.
*/
protected void prepareRefresh() {
this.startupDate = System.currentTimeMillis();
this.active.set(true);
if (logger.isInfoEnabled()) {
logger.info("Refreshing " + this);
}
// Initialize any placeholder property sources in the context environment
initPropertySources();
// Validate that all properties marked as required are resolvable
// see ConfigurablePropertyResolver#setRequiredProperties
getEnvironment().validateRequiredProperties();
}
走到這裏prepareRefresh()方法主要是爲準備刷新容器, 獲取容器的當時時間, 同時給容器設置同步標識 。
繼續往下走obtainFreshBeanFactory();
/**
* Tell the subclass to refresh the internal bean factory.
* @return the fresh BeanFactory instance
* @see #refreshBeanFactory()
* @see #getBeanFactory()
*/
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
refreshBeanFactory();
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
if (logger.isDebugEnabled()) {
logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
}
return beanFactory;
}
看看refreshBeanFactory();幹了些什麼
/**
* This implementation performs an actual refresh of this context's underlying
* bean factory, shutting down the previous bean factory (if any) and
* initializing a fresh bean factory for the next phase of the context's lifecycle.
*/
@Override
protected final void refreshBeanFactory() throws BeansException {
if (hasBeanFactory()) { //如果已經有容器,銷燬容器中的bean,關閉容器
destroyBeans();
closeBeanFactory();
}
try {
//創建IoC容器
DefaultListableBeanFactory beanFactory = createBeanFactory();
beanFactory.setSerializationId(getId());
//對IoC容器進行定製化,如設置啓動參數,開啓註解的自動裝配等
customizeBeanFactory(beanFactory);
//調用載入Bean定義的方法,在當前類中只定義了抽象的loadBeanDefinitions方法,具體的實現調用子類容器
loadBeanDefinitions(beanFactory);
synchronized (this.beanFactoryMonitor) {
this.beanFactory = beanFactory;
}
}
catch (IOException ex) {
throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
}
}
在這個方法中,先判斷BeanFactory是否存在,如果存在則先銷燬beans並關閉beanFactory,接着創建DefaultListableBeanFactory,並調用loadBeanDefinitions(beanFactory)裝載bean。
接着跟進loadBeanDefinitions()方法:
AbstractRefreshableApplicationContext中只定義了抽象的loadBeanDefinitions方法,容器真正調用的是其子類AbstractXmlApplicationContext對該方法的實現,AbstractXmlApplicationContext的主要源碼如下:
/**
* Loads the bean definitions via an XmlBeanDefinitionReader.
* @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader
* @see #initBeanDefinitionReader
* @see #loadBeanDefinitions
*/
@Override
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
//創建XmlBeanDefinitionReader,即創建Bean讀取器,並通過回調設置到容器中去,容 器使用該讀取器讀取Bean定義資源
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
//爲Bean讀取器設置Spring資源加載器,AbstractXmlApplicationContext的
//祖先父類AbstractApplicationContext繼承DefaultResourceLoader,因此,容器本身也是一個資源加載器
beanDefinitionReader.setEnvironment(this.getEnvironment());
beanDefinitionReader.setResourceLoader(this);
//爲Bean讀取器設置SAX xml解析器
beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
//當Bean讀取器讀取Bean定義的Xml資源文件時,啓用Xml的校驗機制
initBeanDefinitionReader(beanDefinitionReader);
//Bean讀取器真正實現加載的方法
loadBeanDefinitions(beanDefinitionReader);
}
看下執行:
Xml Bean讀取器(XmlBeanDefinitionReader)調用其父類AbstractBeanDefinitionReader的 reader.loadBeanDefinitions方法讀取Bean定義資源。
下面將繼續研究讀取Bean定義資源的部分:
BeanDefinitionReader在其抽象父類AbstractBeanDefinitionReader中定義了載入過程
//重載方法,調用下面的loadBeanDefinitions(String, Set<Resource>);方法
public int loadBeanDefinitions(String location) throws BeanDefinitionStoreException {
return loadBeanDefinitions(location, null);
}
public int loadBeanDefinitions(String location, Set<Resource> actualResources) throws BeanDefinitionStoreException {
//獲取在IoC容器初始化過程中設置的資源加載器
ResourceLoader resourceLoader = getResourceLoader();
if (resourceLoader == null) {
throw new BeanDefinitionStoreException(
"Cannot import bean definitions from location [" + location + "]: no ResourceLoader available");
}
if (resourceLoader instanceof ResourcePatternResolver) {
try {
//將指定位置的Bean定義資源文件解析爲Spring IoC容器封裝的資源
//加載多個指定位置的Bean定義資源文件
Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
//委派調用其子類XmlBeanDefinitionReader的方法,實現加載功能
int loadCount = loadBeanDefinitions(resources);
if (actualResources != null) {
for (Resource resource : resources) {
actualResources.add(resource);
}
}
if (logger.isDebugEnabled()) {
logger.debug("Loaded " + loadCount + " bean definitions from location pattern [" + location + "]");
}
return loadCount;
}
catch (IOException ex) {
throw new BeanDefinitionStoreException(
"Could not resolve bean definition resource pattern [" + location + "]", ex);
}
}
else {
//將指定位置的Bean定義資源文件解析爲Spring IoC容器封裝的資源
//加載單個指定位置的Bean定義資源文件
Resource resource = resourceLoader.getResource(location);
//委派調用其子類XmlBeanDefinitionReader的方法,實現加載功能
int loadCount = loadBeanDefinitions(resource);
if (actualResources != null) {
actualResources.add(resource);
}
if (logger.isDebugEnabled()) {
logger.debug("Loaded " + loadCount + " bean definitions from location [" + location + "]");
}
return loadCount;
}
}
//重載方法,調用loadBeanDefinitions(String);
public int loadBeanDefinitions(String... locations) throws BeanDefinitionStoreException {
Assert.notNull(locations, "Location array must not be null");
int counter = 0;
for (String location : locations) {
counter += loadBeanDefinitions(location);
}
return counter;
}
loadBeanDefinitions(Resource…resources)方法和上面分析的3個方法類似,同樣也是調用XmlBeanDefinitionReader的loadBeanDefinitions方法。
從對AbstractBeanDefinitionReader的loadBeanDefinitions方法源碼分析可以看出該方法做了以下兩件事:
首先,調用資源加載器的獲取資源方法resourceLoader.getResource(location),獲取到要加載的資源。
其次,真正執行加載功能是其子類XmlBeanDefinitionReader的loadBeanDefinitions方法。
XmlBeanDefinitionReader通過調用其父類DefaultResourceLoader的getResource方法獲取要加載的資源,其源碼如下
//獲取Resource的具體實現方法
public Resource getResource(String location) {
Assert.notNull(location, "Location must not be null");
//如果是類路徑的方式,那需要使用ClassPathResource 來得到bean 文件的資源對象
if (location.startsWith(CLASSPATH_URL_PREFIX)) {
return new ClassPathResource(location.substring(CLASSPATH_URL_PREFIX.length()), getClassLoader());
}
try {
// 如果是URL 方式,使用UrlResource 作爲bean 文件的資源對象
URL url = new URL(location);
return new UrlResource(url);
}
catch (MalformedURLException ex) {
}
//如果既不是classpath標識,又不是URL標識的Resource定位,則調用
//容器本身的getResourceByPath方法獲取Resource
return getResourceByPath(location);
}
FileSystemXmlApplicationContext容器提供了getResourceByPath方法的實現,就是爲了處理既不是classpath標識,又不是URL標識的Resource定位這種情況。
protected Resource getResourceByPath(String path) {
if (path != null && path.startsWith("/")) {
path = path.substring(1);
}
//這裏使用文件系統資源對象來定義bean 文件
return new FileSystemResource(path);
}
這樣代碼就回到了 FileSystemXmlApplicationContext 中來,他提供了FileSystemResource 來完成從文件系統得到配置文件的資源定義。
這樣,就可以從文件系統路徑上對IOC 配置文件進行加載 - 當然我們可以按照這個邏輯從任何地方加載,在Spring 中我們看到它提供 的各種資源抽象,比如ClassPathResource, URLResource,FileSystemResource 等來供我們使用。上面我們看到的是定位Resource 的一個過程,而這只是加載過程的一部分.
XmlBeanDefinitionReader加載Bean定義資源:
Bean定義的Resource得到了
繼續回到XmlBeanDefinitionReader的loadBeanDefinitions(Resource …)方法看到代表bean文件的資源定義以後的載入過程。
//XmlBeanDefinitionReader加載資源的入口方法
public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
//將讀入的XML資源進行特殊編碼處理
return loadBeanDefinitions(new EncodedResource(resource));
}
//這裏是載入XML形式Bean定義資源文件方法
public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
.......
try {
//將資源文件轉爲InputStream的IO流
InputStream inputStream = encodedResource.getResource().getInputStream();
try {
//從InputStream中得到XML的解析源
InputSource inputSource = new InputSource(inputStream);
if (encodedResource.getEncoding() != null) {
inputSource.setEncoding(encodedResource.getEncoding());
}
//這裏是具體的讀取過程
return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
}
finally {
//關閉從Resource中得到的IO流
inputStream.close();
}
}
.........
26}
//從特定XML文件中實際載入Bean定義資源的方法
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
throws BeanDefinitionStoreException {
try {
int validationMode = getValidationModeForResource(resource);
//將XML文件轉換爲DOM對象,解析過程由documentLoader實現
Document doc = this.documentLoader.loadDocument(
inputSource, this.entityResolver, this.errorHandler, validationMode, this.namespaceAware);
//這裏是啓動對Bean定義解析的詳細過程,該解析過程會用到Spring的Bean配置規則
return registerBeanDefinitions(doc, resource);
}
.......
}
通過源碼分析,載入Bean定義資源文件的最後一步是將Bean定義資源轉換爲Document對象,該過程由documentLoader實現
DocumentLoader將Bean定義資源轉換成Document對象的源碼如下:
//使用標準的JAXP將載入的Bean定義資源轉換成document對象
public Document loadDocument(InputSource inputSource, EntityResolver entityResolver,
ErrorHandler errorHandler, int validationMode, boolean namespaceAware) throws Exception {
//創建文件解析器工廠
DocumentBuilderFactory factory = createDocumentBuilderFactory(validationMode, namespaceAware);
if (logger.isDebugEnabled()) {
logger.debug("Using JAXP provider [" + factory.getClass().getName() + "]");
}
//創建文檔解析器
DocumentBuilder builder = createDocumentBuilder(factory, entityResolver, errorHandler);
//解析Spring的Bean定義資源
return builder.parse(inputSource);
}
protected DocumentBuilderFactory createDocumentBuilderFactory(int validationMode, boolean namespaceAware)
throws ParserConfigurationException {
//創建文檔解析工廠
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setNamespaceAware(namespaceAware);
//設置解析XML的校驗
if (validationMode != XmlValidationModeDetector.VALIDATION_NONE) {
factory.setValidating(true);
if (validationMode == XmlValidationModeDetector.VALIDATION_XSD) {
factory.setNamespaceAware(true);
try {
factory.setAttribute(SCHEMA_LANGUAGE_ATTRIBUTE, XSD_SCHEMA_LANGUAGE);
}
catch (IllegalArgumentException ex) {
ParserConfigurationException pcex = new ParserConfigurationException(
"Unable to validate using XSD: Your JAXP provider [" + factory +
"] does not support XML Schema. Are you running on Java 1.4 with Apache Crimson? " +
"Upgrade to Apache Xerces (or Java 1.5) for full XSD support.");
pcex.initCause(ex);
throw pcex;
}
}
}
return factory;
}
該解析過程調用JavaEE標準的JAXP標準進行處理。
至此Spring IoC容器根據定位的Bean定義資源文件,將其加載讀入並轉換成爲Document對象過程完成。
接下來我們要繼續分析Spring IoC容器將載入的Bean定義資源文件轉換爲Document對象之後,是如何將其解析爲Spring IoC管理的Bean對象並將其註冊到容器中的。
XmlBeanDefinitionReader類中的doLoadBeanDefinitions方法是從特定XML文件中實際載入Bean定義資源的方法,該方法在載入Bean定義資源之後將其轉換爲Document對象,接下來調用registerBeanDefinitions啓動Spring IoC容器對Bean定義的解析過程,registerBeanDefinitions方法源碼如下:
//按照Spring的Bean語義要求將Bean定義資源解析並轉換爲容器內部數據結構
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
//得到BeanDefinitionDocumentReader來對xml格式的BeanDefinition解析
BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
//獲得容器中註冊的Bean數量
int countBefore = getRegistry().getBeanDefinitionCount();
//解析過程入口,這裏使用了委派模式,BeanDefinitionDocumentReader只是個接口,//具體的解析實現過程有實現類DefaultBeanDefinitionDocumentReader完成
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
//統計解析的Bean數量
return getRegistry().getBeanDefinitionCount() - countBefore;
}
//創建BeanDefinitionDocumentReader對象,解析Document對象
protected BeanDefinitionDocumentReader createBeanDefinitionDocumentReader() {
return BeanDefinitionDocumentReader.class.cast(BeanUtils.instantiateClass(this.documentReaderClass));
}
Bean定義資源的載入解析分爲以下兩個過程:
首先,通過調用XML解析器將Bean定義資源文件轉換得到Document對象,但是這些Document對象並沒有按照Spring的Bean規則進行解析。這一步是載入的過程
其次,在完成通用的XML解析之後,按照Spring的Bean規則對Document對象進行解析。
按照Spring的Bean規則對Document對象解析的過程是在接口BeanDefinitionDocumentReader的實現類DefaultBeanDefinitionDocumentReader中實現的。
BeanDefinitionDocumentReader接口通過registerBeanDefinitions方法調用其實現類DefaultBeanDefinitionDocumentReader對Document對象進行解析,解析的代碼如下:
//根據Spring DTD對Bean的定義規則解析Bean定義Document對象
public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
//獲得XML描述符
this.readerContext = readerContext;
logger.debug("Loading bean definitions");
//獲得Document的根元素
Element root = doc.getDocumentElement();
//具體的解析過程由BeanDefinitionParserDelegate實現,
//BeanDefinitionParserDelegate中定義了Spring Bean定義XML文件的各種元素
BeanDefinitionParserDelegate delegate = createHelper(readerContext, root);
//在解析Bean定義之前,進行自定義的解析,增強解析過程的可擴展性
preProcessXml(root);
//從Document的根元素開始進行Bean定義的Document對象
parseBeanDefinitions(root, delegate);
//在解析Bean定義之後,進行自定義的解析,增加解析過程的可擴展性
postProcessXml(root);
}
//創建BeanDefinitionParserDelegate,用於完成真正的解析過程
protected BeanDefinitionParserDelegate createHelper(XmlReaderContext readerContext, Element root) {
BeanDefinitionParserDelegate delegate = new BeanDefinitionParserDelegate(readerContext);
//BeanDefinitionParserDelegate初始化Document根元素
delegate.initDefaults(root);
return delegate;
}
//使用Spring的Bean規則從Document的根元素開始進行Bean定義的Document對象
protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
//Bean定義的Document對象使用了Spring默認的XML命名空間
if (delegate.isDefaultNamespace(root)) {
//獲取Bean定義的Document對象根元素的所有子節點
NodeList nl = root.getChildNodes();
for (int i = 0; i < nl.getLength(); i++) {
Node node = nl.item(i);
//獲得Document節點是XML元素節點
if (node instanceof Element) {
Element ele = (Element) node;
//Bean定義的Document的元素節點使用的是Spring默認的XML命名空間
if (delegate.isDefaultNamespace(ele)) {
//使用Spring的Bean規則解析元素節點
parseDefaultElement(ele, delegate);
}
else {
//沒有使用Spring默認的XML命名空間,則使用用戶自定義的解//析規則解析元素節點
delegate.parseCustomElement(ele);
}
}
}
}
else {
//Document的根節點沒有使用Spring默認的命名空間,則使用用戶自定義的
//解析規則解析Document根節點
delegate.parseCustomElement(root);
}
}
//使用Spring的Bean規則解析Document元素節點
private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
//如果元素節點是<Import>導入元素,進行導入解析
if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
importBeanDefinitionResource(ele);
}
//如果元素節點是<Alias>別名元素,進行別名解析
else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
processAliasRegistration(ele);
}
//元素節點既不是導入元素,也不是別名元素,即普通的<Bean>元素,
//按照Spring的Bean規則解析元素
else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
processBeanDefinition(ele, delegate);
}
}
//解析<Import>導入元素,從給定的導入路徑加載Bean定義資源到Spring IoC容器中
protected void importBeanDefinitionResource(Element ele) {
//獲取給定的導入元素的location屬性
String location = ele.getAttribute(RESOURCE_ATTRIBUTE);
//如果導入元素的location屬性值爲空,則沒有導入任何資源,直接返回
if (!StringUtils.hasText(location)) {
getReaderContext().error("Resource location must not be empty", ele);
return;
}
//使用系統變量值解析location屬性值
location = SystemPropertyUtils.resolvePlaceholders(location);
Set<Resource> actualResources = new LinkedHashSet<Resource>(4);
//標識給定的導入元素的location是否是絕對路徑
boolean absoluteLocation = false;
try {
absoluteLocation = ResourcePatternUtils.isUrl(location) || ResourceUtils.toURI(location).isAbsolute();
}
catch (URISyntaxException ex) {
//給定的導入元素的location不是絕對路徑
}
//給定的導入元素的location是絕對路徑
if (absoluteLocation) {
try {
//使用資源讀入器加載給定路徑的Bean定義資源
int importCount = getReaderContext().getReader().loadBeanDefinitions(location, actualResources);
if (logger.isDebugEnabled()) {
logger.debug("Imported " + importCount + " bean definitions from URL location [" + location + "]");
}
}
catch (BeanDefinitionStoreException ex) {
getReaderContext().error(
"Failed to import bean definitions from URL location [" + location + "]", ele, ex);
}
}
else {
//給定的導入元素的location是相對路徑
try {
int importCount;
//將給定導入元素的location封裝爲相對路徑資源
Resource relativeResource = getReaderContext().getResource().createRelative(location);
//封裝的相對路徑資源存在
if (relativeResource.exists()) {
//使用資源讀入器加載Bean定義資源
importCount = getReaderContext().getReader().loadBeanDefinitions(relativeResource);
actualResources.add(relativeResource);
}
//封裝的相對路徑資源不存在
else {
//獲取Spring IoC容器資源讀入器的基本路徑
String baseLocation = getReaderContext().getResource().getURL().toString();
//根據Spring IoC容器資源讀入器的基本路徑加載給定導入
//路徑的資源
importCount = getReaderContext().getReader().loadBeanDefinitions(
StringUtils.applyRelativePath(baseLocation, location), actualResources);
}
if (logger.isDebugEnabled()) {
logger.debug("Imported " + importCount + " bean definitions from relative location [" + location + "]");
}
}
catch (IOException ex) {
getReaderContext().error("Failed to resolve current resource location", ele, ex);
}
catch (BeanDefinitionStoreException ex) {
getReaderContext().error("Failed to import bean definitions from relative location [" + location + "]",
ele, ex);
}
}
Resource[] actResArray = actualResources.toArray(new Resource[actualResources.size()]);
//在解析完<Import>元素之後,發送容器導入其他資源處理完成事件
getReaderContext().fireImportProcessed(location, actResArray, extractSource(ele));
}
//解析<Alias>別名元素,爲Bean向Spring IoC容器註冊別名
protected void processAliasRegistration(Element ele) {
//獲取<Alias>別名元素中name的屬性值
String name = ele.getAttribute(NAME_ATTRIBUTE);
//獲取<Alias>別名元素中alias的屬性值
String alias = ele.getAttribute(ALIAS_ATTRIBUTE);
boolean valid = true;
//<alias>別名元素的name屬性值爲空
if (!StringUtils.hasText(name)) {
getReaderContext().error("Name must not be empty", ele);
valid = false;
}
//<alias>別名元素的alias屬性值爲空
if (!StringUtils.hasText(alias)) {
getReaderContext().error("Alias must not be empty", ele);
valid = false;
}
if (valid) {
try {
//向容器的資源讀入器註冊別名
getReaderContext().getRegistry().registerAlias(name, alias);
}
catch (Exception ex) {
getReaderContext().error("Failed to register alias '" + alias +
"' for bean with name '" + name + "'", ele, ex);
}
//在解析完<Alias>元素之後,發送容器別名處理完成事件
getReaderContext().fireAliasRegistered(name, alias, extractSource(ele));
}
}
//解析Bean定義資源Document對象的普通元素
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
// BeanDefinitionHolder是對BeanDefinition的封裝,即Bean定義的封裝類
//對Document對象中<Bean>元素的解析由BeanDefinitionParserDelegate實現 BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
if (bdHolder != null) {
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
try {
//向Spring IoC容器註冊解析得到的Bean定義,這是Bean定義向IoC容器註冊的入口
BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
}
catch (BeanDefinitionStoreException ex) {
getReaderContext().error("Failed to register bean definition with name '" +
bdHolder.getBeanName() + "'", ele, ex);
}
//在完成向Spring IoC容器註冊解析得到的Bean定義之後,發送註冊事件
getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
}
}
通過上述Spring IoC容器對載入的Bean定義Document解析可以看出,我們使用Spring時,在Spring配置文件中可以使用元素來導入IoC容器所需要的其他資源,Spring IoC容器在解析時會首先將指定導入的資源加載進容器中。使用別名時,Spring IoC容器首先將別名元素所定義的別名註冊到容器中。
對於既不是元素,又不是元素的元素,即Spring配置文件中普通的元素的解析由BeanDefinitionParserDelegate類的parseBeanDefinitionElement方法來實現。
Bean定義資源文件中的和元素解析在DefaultBeanDefinitionDocumentReader中已經完成,對Bean定義資源文件中使用最多的元素交由BeanDefinitionParserDelegate來解析,其解析實現的源碼如下:
//解析<Bean>元素的入口
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele) {
return parseBeanDefinitionElement(ele, null);
}
//解析Bean定義資源文件中的<Bean>元素,這個方法中主要處理<Bean>元素的id,name
//和別名屬性
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, BeanDefinition containingBean) {
//獲取<Bean>元素中的id屬性值
String id = ele.getAttribute(ID_ATTRIBUTE);
//獲取<Bean>元素中的name屬性值
String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);
////獲取<Bean>元素中的alias屬性值
List<String> aliases = new ArrayList<String>();
//將<Bean>元素中的所有name屬性值存放到別名中
if (StringUtils.hasLength(nameAttr)) {
String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, BEAN_NAME_DELIMITERS);
aliases.addAll(Arrays.asList(nameArr));
}
String beanName = id;
//如果<Bean>元素中沒有配置id屬性時,將別名中的第一個值賦值給beanName
if (!StringUtils.hasText(beanName) && !aliases.isEmpty()) {
beanName = aliases.remove(0);
if (logger.isDebugEnabled()) {
logger.debug("No XML 'id' specified - using '" + beanName +
"' as bean name and " + aliases + " as aliases");
}
}
//檢查<Bean>元素所配置的id或者name的唯一性,containingBean標識<Bean>
//元素中是否包含子<Bean>元素
if (containingBean == null) {
//檢查<Bean>元素所配置的id、name或者別名是否重複
checkNameUniqueness(beanName, aliases, ele);
}
//詳細對<Bean>元素中配置的Bean定義進行解析的地方
AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
if (beanDefinition != null) {
if (!StringUtils.hasText(beanName)) {
try {
if (containingBean != null) {
//如果<Bean>元素中沒有配置id、別名或者name,且沒有包含子//<Bean>元素,爲解析的Bean生成一個唯一beanName並註冊
beanName = BeanDefinitionReaderUtils.generateBeanName(
beanDefinition, this.readerContext.getRegistry(), true);
}
else {
//如果<Bean>元素中沒有配置id、別名或者name,且包含了子//<Bean>元素,爲解析的Bean使用別名向IoC容器註冊
beanName = this.readerContext.generateBeanName(beanDefinition);
//爲解析的Bean使用別名註冊時,爲了向後兼容 //Spring1.2/2.0,給別名添加類名後綴
String beanClassName = beanDefinition.getBeanClassName();
if (beanClassName != null &&
beanName.startsWith(beanClassName) && beanName.length() > beanClassName.length() &&
!this.readerContext.getRegistry().isBeanNameInUse(beanClassName)) {
aliases.add(beanClassName);
}
}
if (logger.isDebugEnabled()) {
logger.debug("Neither XML 'id' nor 'name' specified - " +
"using generated bean name [" + beanName + "]");
}
}
catch (Exception ex) {
error(ex.getMessage(), ele);
return null;
}
}
String[] aliasesArray = StringUtils.toStringArray(aliases);
return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
}
//當解析出錯時,返回null
return null;
}
//詳細對<Bean>元素中配置的Bean定義其他屬性進行解析,由於上面的方法中已經對//Bean的id、name和別名等屬性進行了處理,該方法中主要處理除這三個以外的其他屬性數據
public AbstractBeanDefinition parseBeanDefinitionElement(
Element ele, String beanName, BeanDefinition containingBean) {
//記錄解析的<Bean>
this.parseState.push(new BeanEntry(beanName));
//這裏只讀取<Bean>元素中配置的class名字,然後載入到BeanDefinition中去
//只是記錄配置的class名字,不做實例化,對象的實例化在依賴注入時完成
String className = null;
if (ele.hasAttribute(CLASS_ATTRIBUTE)) {
className = ele.getAttribute(CLASS_ATTRIBUTE).trim();
}
try {
String parent = null;
//如果<Bean>元素中配置了parent屬性,則獲取parent屬性的值
if (ele.hasAttribute(PARENT_ATTRIBUTE)) {
parent = ele.getAttribute(PARENT_ATTRIBUTE);
}
//根據<Bean>元素配置的class名稱和parent屬性值創建BeanDefinition
//爲載入Bean定義信息做準備
AbstractBeanDefinition bd = createBeanDefinition(className, parent);
//對當前的<Bean>元素中配置的一些屬性進行解析和設置,如配置的單態(singleton)屬性等
parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
//爲<Bean>元素解析的Bean設置description信息 bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));
//對<Bean>元素的meta(元信息)屬性解析
parseMetaElements(ele, bd);
//對<Bean>元素的lookup-method屬性解析
parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
//對<Bean>元素的replaced-method屬性解析
parseReplacedMethodSubElements(ele, bd.getMethodOverrides());
//解析<Bean>元素的構造方法設置
parseConstructorArgElements(ele, bd);
//解析<Bean>元素的<property>設置
parsePropertyElements(ele, bd);
//解析<Bean>元素的qualifier屬性
parseQualifierElements(ele, bd);
//爲當前解析的Bean設置所需的資源和依賴對象
bd.setResource(this.readerContext.getResource());
bd.setSource(extractSource(ele));
return bd;
}
catch (ClassNotFoundException ex) {
error("Bean class [" + className + "] not found", ele, ex);
}
catch (NoClassDefFoundError err) {
error("Class that bean class [" + className + "] depends on not found", ele, err);
}
catch (Throwable ex) {
error("Unexpected failure during bean definition parsing", ele, ex);
}
finally {
this.parseState.pop();
}
//解析<Bean>元素出錯時,返回null
return null;
}
只要使用過Spring,對Spring配置文件比較熟悉的人,通過對上述源碼的分析,就會明白我們在Spring配置文件中元素的中配置的屬性就是通過該方法解析和設置到Bean中去的。
注意:在解析元素過程中沒有創建和實例化Bean對象,只是創建了Bean對象的定義類BeanDefinition,將元素中的配置信息設置到BeanDefinition中作爲記錄,當依賴注入時才使用這些記錄信息創建和實例化具體的Bean對象。
上面方法中一些對一些配置如元信息(meta)、qualifier等的解析,我們在Spring中配置時使用的也不多,我們在使用Spring的元素時,配置最多的是屬性,因此我們下面繼續分析源碼,瞭解Bean的屬性在解析時是如何設置的。
BeanDefinitionParserDelegate在解析調用parsePropertyElements方法解析元素中的屬性子元素,解析源碼如下:
//解析<Bean>元素中的<property>子元素
public void parsePropertyElements(Element beanEle, BeanDefinition bd) {
//獲取<Bean>元素中所有的子元素
NodeList nl = beanEle.getChildNodes();
for (int i = 0; i < nl.getLength(); i++) {
Node node = nl.item(i);
//如果子元素是<property>子元素,則調用解析<property>子元素方法解析
if (isCandidateElement(node) && nodeNameEquals(node, PROPERTY_ELEMENT)) {
parsePropertyElement((Element) node, bd);
}
}
}
//解析<property>元素
public void parsePropertyElement(Element ele, BeanDefinition bd) {
//獲取<property>元素的名字
String propertyName = ele.getAttribute(NAME_ATTRIBUTE);
if (!StringUtils.hasLength(propertyName)) {
error("Tag 'property' must have a 'name' attribute", ele);
return;
}
this.parseState.push(new PropertyEntry(propertyName));
try {
//如果一個Bean中已經有同名的property存在,則不進行解析,直接返回。
//即如果在同一個Bean中配置同名的property,則只有第一個起作用
if (bd.getPropertyValues().contains(propertyName)) {
error("Multiple 'property' definitions for property '" + propertyName + "'", ele);
return;
}
//解析獲取property的值
Object val = parsePropertyValue(ele, bd, propertyName);
//根據property的名字和值創建property實例
PropertyValue pv = new PropertyValue(propertyName, val);
//解析<property>元素中的屬性
parseMetaElements(ele, pv);
pv.setSource(extractSource(ele));
bd.getPropertyValues().addPropertyValue(pv);
}
finally {
this.parseState.pop();
}
}
//解析獲取property值
public Object parsePropertyValue(Element ele, BeanDefinition bd, String propertyName) {
String elementName = (propertyName != null) ?
"<property> element for property '" + propertyName + "'" :
"<constructor-arg> element";
//獲取<property>的所有子元素,只能是其中一種類型:ref,value,list等
NodeList nl = ele.getChildNodes();
Element subElement = null;
for (int i = 0; i < nl.getLength(); i++) {
Node node = nl.item(i);
//子元素不是description和meta屬性
if (node instanceof Element && !nodeNameEquals(node, DESCRIPTION_ELEMENT) &&
!nodeNameEquals(node, META_ELEMENT)) {
if (subElement != null) {
error(elementName + " must not contain more than one sub-element", ele);
}
else {//當前<property>元素包含有子元素
subElement = (Element) node;
}
}
}
//判斷property的屬性值是ref還是value,不允許既是ref又是value
boolean hasRefAttribute = ele.hasAttribute(REF_ATTRIBUTE);
boolean hasValueAttribute = ele.hasAttribute(VALUE_ATTRIBUTE);
if ((hasRefAttribute && hasValueAttribute) ||
((hasRefAttribute || hasValueAttribute) && subElement != null)) {
error(elementName +
" is only allowed to contain either 'ref' attribute OR 'value' attribute OR sub-element", ele);
}
//如果屬性是ref,創建一個ref的數據對象RuntimeBeanReference,這個對象
//封裝了ref信息
if (hasRefAttribute) {
String refName = ele.getAttribute(REF_ATTRIBUTE);
if (!StringUtils.hasText(refName)) {
error(elementName + " contains empty 'ref' attribute", ele);
}
//一個指向運行時所依賴對象的引用
RuntimeBeanReference ref = new RuntimeBeanReference(refName);
//設置這個ref的數據對象是被當前的property對象所引用
ref.setSource(extractSource(ele));
return ref;
}
//如果屬性是value,創建一個value的數據對象TypedStringValue,這個對象
//封裝了value信息
else if (hasValueAttribute) {
//一個持有String類型值的對象
TypedStringValue valueHolder = new TypedStringValue(ele.getAttribute(VALUE_ATTRIBUTE));
//設置這個value數據對象是被當前的property對象所引用
valueHolder.setSource(extractSource(ele));
return valueHolder;
}
//如果當前<property>元素還有子元素
else if (subElement != null) {
//解析<property>的子元素
return parsePropertySubElement(subElement, bd);
}
else {
//propery屬性中既不是ref,也不是value屬性,解析出錯返回null error(elementName + " must specify a ref or value", ele);
return null;
}
}
通過對上述源碼的分析,我們可以瞭解在Spring配置文件中,元素中元素的相關配置是如何處理的:
a. ref被封裝爲指向依賴對象一個引用。
b.value配置都會封裝成一個字符串類型的對象。
c.ref和value都通過“解析的數據類型屬性值.setSource(extractSource(ele));”方法將屬性值/引用與所引用的屬性關聯起來。
在方法的最後對於元素的子元素通過parsePropertySubElement 方法解析,我們繼續分析該方法的源碼,瞭解其解析過程。
解析元素的子元素:在BeanDefinitionParserDelegate類中的parsePropertySubElement方法對中的子元素解析,源碼如下:
//解析<property>元素中ref,value或者集合等子元素
public Object parsePropertySubElement(Element ele, BeanDefinition bd, String defaultValueType) {
//如果<property>沒有使用Spring默認的命名空間,則使用用戶自定義的規則解析//內嵌元素
if (!isDefaultNamespace(ele)) {
return parseNestedCustomElement(ele, bd);
}
//如果子元素是bean,則使用解析<Bean>元素的方法解析
else if (nodeNameEquals(ele, BEAN_ELEMENT)) {
BeanDefinitionHolder nestedBd = parseBeanDefinitionElement(ele, bd);
if (nestedBd != null) {
nestedBd = decorateBeanDefinitionIfRequired(ele, nestedBd, bd);
}
return nestedBd;
}
//如果子元素是ref,ref中只能有以下3個屬性:bean、local、parent
else if (nodeNameEquals(ele, REF_ELEMENT)) {
//獲取<property>元素中的bean屬性值,引用其他解析的Bean的名稱
//可以不再同一個Spring配置文件中,具體請參考Spring對ref的配置規則
String refName = ele.getAttribute(BEAN_REF_ATTRIBUTE);
boolean toParent = false;
if (!StringUtils.hasLength(refName)) {
//獲取<property>元素中的local屬性值,引用同一個Xml文件中配置
//的Bean的id,local和ref不同,local只能引用同一個配置文件中的Bean
refName = ele.getAttribute(LOCAL_REF_ATTRIBUTE);
if (!StringUtils.hasLength(refName)) {
//獲取<property>元素中parent屬性值,引用父級容器中的Bean
refName = ele.getAttribute(PARENT_REF_ATTRIBUTE);
toParent = true;
if (!StringUtils.hasLength(refName)) {
error("'bean', 'local' or 'parent' is required for <ref> element", ele);
return null;
}
}
}
//沒有配置ref的目標屬性值
if (!StringUtils.hasText(refName)) {
error("<ref> element contains empty target attribute", ele);
return null;
}
//創建ref類型數據,指向被引用的對象
RuntimeBeanReference ref = new RuntimeBeanReference(refName, toParent);
//設置引用類型值是被當前子元素所引用
ref.setSource(extractSource(ele));
return ref;
}
//如果子元素是<idref>,使用解析ref元素的方法解析
else if (nodeNameEquals(ele, IDREF_ELEMENT)) {
return parseIdRefElement(ele);
}
//如果子元素是<value>,使用解析value元素的方法解析
else if (nodeNameEquals(ele, VALUE_ELEMENT)) {
return parseValueElement(ele, defaultValueType);
}
//如果子元素是null,爲<property>設置一個封裝null值的字符串數據
else if (nodeNameEquals(ele, NULL_ELEMENT)) {
TypedStringValue nullHolder = new TypedStringValue(null);
nullHolder.setSource(extractSource(ele));
return nullHolder;
}
//如果子元素是<array>,使用解析array集合子元素的方法解析
else if (nodeNameEquals(ele, ARRAY_ELEMENT)) {
return parseArrayElement(ele, bd);
}
//如果子元素是<list>,使用解析list集合子元素的方法解析
else if (nodeNameEquals(ele, LIST_ELEMENT)) {
return parseListElement(ele, bd);
}
//如果子元素是<set>,使用解析set集合子元素的方法解析
else if (nodeNameEquals(ele, SET_ELEMENT)) {
return parseSetElement(ele, bd);
}
//如果子元素是<map>,使用解析map集合子元素的方法解析
else if (nodeNameEquals(ele, MAP_ELEMENT)) {
return parseMapElement(ele, bd);
}
//如果子元素是<props>,使用解析props集合子元素的方法解析
else if (nodeNameEquals(ele, PROPS_ELEMENT)) {
return parsePropsElement(ele);
}
//既不是ref,又不是value,也不是集合,則子元素配置錯誤,返回null
else {
error("Unknown property sub-element: [" + ele.getNodeName() + "]", ele);
return null;
}
}
通過上述源碼分析,我們明白了在Spring配置文件中,對元素中配置的Array、List、Set、Map、Prop等各種集合子元素的都通過上述方法解析,生成對應的數據對象,比如ManagedList、ManagedArray、ManagedSet等,這些Managed類是Spring對象BeanDefiniton的數據封裝,對集合數據類型的具體解析有各自的解析方法實現,解析方法的命名非常規範,一目瞭然,我們對集合元素的解析方法進行源碼分析,瞭解其實現過程。
解析子元素:在BeanDefinitionParserDelegate類中的parseListElement方法就是具體實現解析元素中的集合子元素,源碼如下:
//解析<list>集合子元素
public List parseListElement(Element collectionEle, BeanDefinition bd) {
//獲取<list>元素中的value-type屬性,即獲取集合元素的數據類型
String defaultElementType = collectionEle.getAttribute(VALUE_TYPE_ATTRIBUTE);
//獲取<list>集合元素中的所有子節點
NodeList nl = collectionEle.getChildNodes();
//Spring中將List封裝爲ManagedList
ManagedList<Object> target = new ManagedList<Object>(nl.getLength());
target.setSource(extractSource(collectionEle));
//設置集合目標數據類型
target.setElementTypeName(defaultElementType);
target.setMergeEnabled(parseMergeAttribute(collectionEle));
//具體的<list>元素解析
parseCollectionElements(nl, target, bd, defaultElementType);
return target;
}
//具體解析<list>集合元素,<array>、<list>和<set>都使用該方法解析
protected void parseCollectionElements(
NodeList elementNodes, Collection<Object> target, BeanDefinition bd, String defaultElementType) {
//遍歷集合所有節點
for (int i = 0; i < elementNodes.getLength(); i++) {
Node node = elementNodes.item(i);
//節點不是description節點
if (node instanceof Element && !nodeNameEquals(node, DESCRIPTION_ELEMENT)) {
//將解析的元素加入集合中,遞歸調用下一個子元素
target.add(parsePropertySubElement((Element) node, bd, defaultElementType));
}
}
}
經過對Spring Bean定義資源文件轉換的Document對象中的元素層層解析,Spring IoC現在已經將XML形式定義的Bean定義資源文件轉換爲Spring IoC所識別的數據結構——BeanDefinition,它是Bean定義資源文件中配置的POJO對象在Spring IoC容器中的映射,我們可以通過AbstractBeanDefinition爲入口,榮IoC容器進行索引、查詢和操作。
通過Spring IoC容器對Bean定義資源的解析後,IoC容器大致完成了管理Bean對象的準備工作,即初始化過程,但是最爲重要的依賴注入還沒有發生,現在在IoC容器中BeanDefinition存儲的只是一些靜態信息,接下來需要向容器註冊Bean定義信息才能全部完成IoC容器的初始化過程
解析過後的BeanDefinition在IoC容器中的註冊:
讓我們繼續跟蹤程序的執行順序,接下來會到我們第3步中分析DefaultBeanDefinitionDocumentReader對Bean定義轉換的Document對象解析的流程中,在其parseDefaultElement方法中完成對Document對象的解析後得到封裝BeanDefinition的BeanDefinitionHold對象,然後調用BeanDefinitionReaderUtils的registerBeanDefinition方法向IoC容器註冊解析的Bean,BeanDefinitionReaderUtils的註冊的源碼如下:
//將解析的BeanDefinitionHold註冊到容器中
public static void registerBeanDefinition(BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
throws BeanDefinitionStoreException {
//獲取解析的BeanDefinition的名稱
String beanName = definitionHolder.getBeanName();
//向IoC容器註冊BeanDefinition
registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());
//如果解析的BeanDefinition有別名,向容器爲其註冊別名
String[] aliases = definitionHolder.getAliases();
if (aliases != null) {
for (String aliase : aliases) {
registry.registerAlias(beanName, aliase);
}
}
}
當調用BeanDefinitionReaderUtils向IoC容器註冊解析的BeanDefinition時,真正完成註冊功能的是DefaultListableBeanFactory。
DefaultListableBeanFactory向IoC容器註冊解析後的BeanDefinition:
DefaultListableBeanFactory中使用一個HashMap的集合對象存放IoC容器中註冊解析的BeanDefinition,向IoC容器註冊的主要源碼如下:
//存儲註冊的俄BeanDefinition
private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<String, BeanDefinition>();
//向IoC容器註冊解析的BeanDefiniton
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");
//校驗解析的BeanDefiniton
if (beanDefinition instanceof AbstractBeanDefinition) {
try {
((AbstractBeanDefinition) beanDefinition).validate();
}
catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Validation of bean definition failed", ex);
}
}
//註冊的過程中需要線程同步,以保證數據的一致性
synchronized (this.beanDefinitionMap) {
Object oldBeanDefinition = this.beanDefinitionMap.get(beanName);
//檢查是否有同名的BeanDefinition已經在IoC容器中註冊,如果已經註冊,
//並且不允許覆蓋已註冊的Bean,則拋出註冊失敗異常
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 {//如果允許覆蓋,則同名的Bean,後註冊的覆蓋先註冊的
if (this.logger.isInfoEnabled()) {
this.logger.info("Overriding bean definition for bean '" + beanName +
"': replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]");
}
}
}
//IoC容器中沒有已經註冊同名的Bean,按正常註冊流程註冊
else {
this.beanDefinitionNames.add(beanName);
this.frozenBeanDefinitionNames = null;
}
this.beanDefinitionMap.put(beanName, beanDefinition);
//重置所有已經註冊過的BeanDefinition的緩存
resetBeanDefinition(beanName);
}
}
至此,Bean定義資源文件中配置的Bean被解析過後,已經註冊到IoC容器中,被容器管理起來,真正完成了IoC容器初始化所做的全部工作。現 在IoC容器中已經建立了整個Bean的配置信息,這些BeanDefinition信息已經可以使用,並且可以被檢索,IoC容器的作用就是對這些註冊的Bean定義信息進行處理和維護。這些的註冊的Bean定義信息是IoC容器控制反轉的基礎,正是有了這些註冊的數據,容器纔可以進行依賴注入。
總結
Spring 的核心容器包括 Spring-Core、Spring-Context、Spring-beans、Spring-expression四個模塊,本文就Spring-Context中的ApplicationContext 中 FileSystemXmlApplicationContext的初始化實現進行了源碼探索,Spring-Core模塊主要就是定義了訪問資源的方式,以及對於各種資源進行用統一的接口來抽象。而Context模塊的主要作用則是爲Bean對象提供、標識一個運行時環境,初始化BeanFactory並利用BeanFactory來將解析已經註冊的Bean進而進行依賴注入,保存Bean對象之間的依賴關係。以此看來,Context的主要職責是將Core和Bean兩個模塊融合在一起。