有道無術,術可求;
有術無道,止于術;
讀原始碼是一個很枯燥的程序，但是Spring原始碼里面有很多值得學習的地方
加油~！！！！！
前言
使用SpringMVC的時候，通常使用下面這行代碼來加載Spring的組態檔
ApplicationContext application = new ClassPathXmlApplicationContext("webmvc.xml")，那么這行代碼到底進行了怎么的操作,接下來就一探究境，看看是如何加載組態檔的
Spring的組態檔
這個組態檔對于已經學會使用SpringMVC的你來說已經再熟悉不過了
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.0.xsd">
<bean id="study" >
</bean>
</beans>
那么Spring是如何進行Bean的注冊的呢？經過這幾天的原始碼查看我寫下了這篇文章來作為筆記，
因為我剛開始看Spring的原始碼，里面有些內容可能理解的不是很到位，有錯誤請指出
原始碼查看
再此之前我先bb幾句，為了方便查看原始碼，可以去GitHub上下載Spring的原始碼匯入到Idea或者是eclipse中這樣查看起來更方便些，同時還可以在上面寫一些注釋
既然使用的是ClassPathXmlApplicationContext("webmvc.xml")那就找到這個類的單參構造器查看跟蹤下原始碼
/**
* Create a new ClassPathXmlApplicationContext, loading the definitions
* from the given XML file and automatically refreshing the context.
* @param configLocation resource location
* @throws BeansException if context creation failed
* 這個是創建 了 一個 ClassPathXmlApplicationContext，用來從給的XMl檔案中加載規定
*/
public ClassPathXmlApplicationContext(String configLocation) throws BeansException {
this(new String[] {configLocation}, true, null);
}
這里呼叫的是本類中的另外一個三個引數的構造方法,便進入到了下面這些代碼中
/**
* Create a new ClassPathXmlApplicationContext with the given parent,
* loading the definitions from the given XML files.
* @param configLocations array of resource locations
* @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 ClassPathXmlApplicationContext(
String[] configLocations, boolean refresh, @Nullable ApplicationContext parent)
throws BeansException {
super(parent);
//設定組態檔的路徑
setConfigLocations(configLocations);
if (refresh) {
//重要的方法，需要進入查看
refresh();
}
}
這里來說下這個方法的引數的意思：
- configLocations：這個里面保存的是組態檔的路徑
- Refresh：是否自動重繪背景關系
- parent：父背景關系
設定資源加載器
要跟蹤下super(parent)這行代碼，在它的父類中(AbstractApplicationContext類里面)，有下面的代碼，這段代碼的作 用是獲取一個SpringResource的加載器用來加載資源檔案(這里你可以理解為是為了加載webmvc.xml組態檔做前期的準備)
protected ResourcePatternResolver getResourcePatternResolver() {
return new PathMatchingResourcePatternResolver(this);
}
//下面的方法在PathMatchingResourcePatternResolver類中，為了查看方便我將這兩個方法寫在了一起
public PathMatchingResourcePatternResolver(ResourceLoader resourceLoader) {
Assert.notNull(resourceLoader, "ResourceLoader must not be null");
this.resourceLoader = resourceLoader;
}
在PathMatchingResourcePatternResolver構造方法中就設定了一個資源加載器
設定Bean資訊位置
這個里面有一個setConfigLocations方法，這個里面會設定Bean配置資訊的位置，這個方法的所在的類是AbstractRefreshableConfigApplicationContext,它和CLassPathXmlApplicationContext之間是繼承的關系
@Nullable
private String[] configLocations;
public void setConfigLocations(@Nullable 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;
}
}
這里面的configLocations的是一個陣列，setConfigLocations方法的引數是一個可變引數，這個方法的作用是將多個路徑放到configLocations陣列中
閱讀refresh
這個方法可以說是一個非常重要的一個方法,這在個方法里面規定了容器的啟動流程，具體的邏輯通過ConfigurableApplicationContext介面的子類實作
@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.
//進入到此方法查看
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);
try {
//這里面的代碼我洗掉掉了，因為我們本文是看的決議XML創建 Bean的文章，這里的代碼暫時用不到，我就洗掉了，要不然代碼太多了
}
catch (BeansException ex) {
if (logger.isWarnEnabled()) {
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;
}
finally {
// Reset common introspection caches in Spring's core, since we
// might not ever need metadata for singleton beans anymore...
resetCommonCaches();
}
}
}
Bean的組態檔是在這個方法里面的refreshBeanFactory方法來處理的,這個方法是在AbstractRefreshableApplicationContext類中實作的
@Override
protected final void refreshBeanFactory() throws BeansException {
if (hasBeanFactory()) {
destroyBeans();
closeBeanFactory();
}
try {
DefaultListableBeanFactory beanFactory = createBeanFactory();
beanFactory.setSerializationId(getId());
customizeBeanFactory(beanFactory);
//開始決議組態檔
loadBeanDefinitions(beanFactory);
synchronized (this.beanFactoryMonitor) {
this.beanFactory = beanFactory;
}
}
catch (IOException ex) {
throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
}
}
這里有一個方法是loadBeanDefinitions(beanFactory)在這個方法里面就開始決議組態檔了，進入這個方法
@Override
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
// Create a new XmlBeanDefinitionReader for the given BeanFactory.
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
// Configure the bean definition reader with this context's
// resource loading environment.
beanDefinitionReader.setEnvironment(this.getEnvironment());
beanDefinitionReader.setResourceLoader(this);
beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
// Allow a subclass to provide custom initialization of the reader,
// then proceed with actually loading the bean definitions.
initBeanDefinitionReader(beanDefinitionReader);
//Bean讀取器實作加載的方法
loadBeanDefinitions(beanDefinitionReader);
}
進入到loadBeanDefinitions(XmlBeanDefinitionReader reader)方法
XML Bean讀取器加載Bean配置資源
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
//獲娶Bean配置資源的位置
Resource[] configResources = getConfigResources();
if (configResources != null) {
reader.loadBeanDefinitions(configResources);
}
String[] configLocations = getConfigLocations();
if (configLocations != null) {
reader.loadBeanDefinitions(configLocations);
}
}
但是本文的教程是通過ClassPathXmlApplicationContext來舉的例子,getConfigResources()方法回傳的是空的，就執行下面的分支
說點和本文有關也有可能沒有關系的話
當代碼看到這里，學習過設計模式的同鞋可能會發現我們看過的這些代碼里也涉及到了委派模式和策略模式因為Spring框架中使用到了很多的設計模式，所以說在看一些框架原始碼的時候，我們盡可能的先學習下設計模式，不管是對于看原始碼來說或者是對于在公司中作業都是啟到了很重要的作用，在作業中使用了設計模式對于以后系統的擴展或者是維護來說都是比較方便的，當然學習設計模式也是沒有那么的簡單，或許你看了關于設計模式的視頻或者是一些書籍，但是在作業中如果是想很好的運用出來，還是要寫很多的代碼和常用設計模式的，
學習設計模式也是投入精力的，Scott Mayer在《Effective C++》也說過：C++新手和老手的區別就是前者手背上有很多的傷疤，
回到正文
這個方法是在AbstractBeanDefinitionReader類中的方法，里面的代碼我會做適當的刪減
public int loadBeanDefinitions(String location, @Nullable Set<Resource> actualResources) throws BeanDefinitionStoreException {
ResourceLoader resourceLoader = getResourceLoader();
//resourceLoader的判空 處理....
if (resourceLoader instanceof ResourcePatternResolver) {
// Resource pattern matching available.
try {
//將對應位置的配置資訊決議成Resource資源
Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
//委派呼叫子類的XmlBeanDefinitionReader的方法
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 {
//......代碼被我洗掉了，因為這里的代碼不會說到
}
}
上面int loadCount = loadBeanDefinitions(resources);代碼是通過委派模式來呼叫的XmlBeanDefinitionReader方法，那就來看下這個類中的代碼
public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
//....
try {
InputStream inputStream = encodedResource.getResource().getInputStream();
try {
InputSource inputSource = new InputSource(inputStream);
if (encodedResource.getEncoding() != null) {
inputSource.setEncoding(encodedResource.getEncoding());
}
//這個方法開始讀取組態檔
return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
}
finally {
inputStream.close();
}
}
//...
}
再來查看下doLoadBeanDefinitions方法，這個里面有具體的讀取流程
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
throws BeanDefinitionStoreException {
try {
//將XML檔案轉換成了DOm物件
Document doc = doLoadDocument(inputSource, resource);
//此方法中有對Bean定義決議的詳細程序
return registerBeanDefinitions(doc, resource);
}
//...
}
doLoadDocument方法最后呼叫的是DefaultDocumentLoader類中的loadDocument方法
@Override
public Document loadDocument(InputSource inputSource, EntityResolver entityResolver,
ErrorHandler errorHandler, int validationMode, boolean namespaceAware) throws Exception {
//創建檔案的決議工廠
DocumentBuilderFactory factory = createDocumentBuilderFactory(validationMode, namespaceAware);
if (logger.isDebugEnabled()) {
logger.debug("Using JAXP provider [" + factory.getClass().getName() + "]");
}
//創建檔案的決議器
DocumentBuilder builder = createDocumentBuilder(factory, entityResolver, errorHandler);
//決議Bean配置的資訊
return builder.parse(inputSource);
}
loadDocument方法先看到這里，如果想要深入的看，自已可以跟蹤下代碼，接下來再看registerBeanDefinitions代碼
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
//拿到BeanDefinitionDocumentReader來對XML格式的組態檔進行決議
BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
int countBefore = getRegistry().getBeanDefinitionCount();
//具體的決議程序是實作類DefaultBeanDefinititonDocumentReader完成的
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
return getRegistry().getBeanDefinitionCount() - countBefore;
}
到這里先來總結下Bean配置載入的程序：
- 調手XML決議器將配置資訊轉成檔案的物件
- 在完成XML決議后，將按SPring IOC 的定義規則對檔案物件決議
在DefaultBeanDefinititonDocumentReader類中看下registerBeanDefinitions
@Override
public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
this.readerContext = readerContext;
logger.debug("Loading bean definitions");
//獲取到Root元素
Element root = doc.getDocumentElement();、
//注冊Bean的定義
doRegisterBeanDefinitions(root); //進入方法
}
protected void doRegisterBeanDefinitions(Element root) {
BeanDefinitionParserDelegate parent = this.delegate;
this.delegate = createDelegate(getReaderContext(), root, parent);
if (this.delegate.isDefaultNamespace(root)) {
String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);
if (StringUtils.hasText(profileSpec)) {
String[] specifiedProfiles = StringUtils.tokenizeToStringArray(
profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);
if (!getReaderContext().getEnvironment().acceptsProfiles(specifiedProfiles)) {
if (logger.isInfoEnabled()) {
logger.info("Skipped XML bean definition file due to specified profiles [" + profileSpec +
"] not matching: " + getReaderContext().getResource());
}
return;
}
}
}
preProcessXml(root);
//在檔案的Root元素開始對檔案決議
parseBeanDefinitions(root, this.delegate); //進入這個方法
postProcessXml(root);
this.delegate = parent;
}
到了下面的這一步就是通過Bean規則決議檔案元素了
private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
//import
if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
importBeanDefinitionResource(ele);
}
//alias
else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
processAliasRegistration(ele);
}
//bean
else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
processBeanDefinition(ele, delegate);
}
else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
// recurse
doRegisterBeanDefinitions(ele);
}
}
這里面是一堆的分支陳述句，對應的是決議到那一個節點，『import』『alias』，如果那個都不是將按普通的Bean來處理
這里我們重要看下processBeanDefinition方法
/**
* Process the given bean element, parsing the bean definition
* and registering it with the registry.
*/
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
if (bdHolder != null) {
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
try {
//向IOC中注冊決議獲得Bean的定義，Bean定義向IOC注冊的入口
// Register the final decorated instance.
BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
}
catch (BeanDefinitionStoreException ex) {
getReaderContext().error("Failed to register bean definition with name '" +
bdHolder.getBeanName() + "'", ele, ex);
}
// Send registration event.
//完成IOC注冊決議獲到Bean定義后，發送注冊
getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
}
}
查看parseBeanDefinitionElement代碼
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, @Nullable BeanDefinition containingBean) {
//獲取bean元素中的id值
String id = ele.getAttribute(ID_ATTRIBUTE);
//獲取bean元素中的name值
String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);
//獲取bean元素中aliases值
List<String> aliases = new ArrayList<>();
//將Bean元素中的name屬值存放到別名中
if (StringUtils.hasLength(nameAttr)) {
String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, MULTI_VALUE_ATTRIBUTE_DELIMITERS);
aliases.addAll(Arrays.asList(nameArr));
}
String beanName = id;
//如果bean元素中沒有配置id屬性，將別名中的第一個值給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");
}
}
if (containingBean == null) {
checkNameUniqueness(beanName, aliases, ele);
}
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 name 沒有子元素 則為決議的bean生成一個唯一的beanName注冊到容器
beanName = BeanDefinitionReaderUtils.generateBeanName(
beanDefinition, this.readerContext.getRegistry(), true);
}
else {
//如果bean元素中沒有配置id 別名 name 有子元素 則為決議的bean生成一個唯一的beanName注冊到容器
beanName = this.readerContext.generateBeanName(beanDefinition);
// Register an alias for the plain bean class name, if still possible,
// if the generator returned the class name plus a suffix.
// This is expected for Spring 1.2/2.0 backwards compatibility.
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);
}
return null;
}
上面的流程完成后，我們再回到了DefaultBeanDefinitionDocumnetReader類中的processBeanDefinition方法
在這個方法里面我們在查看registerBeanDefinition方法
public static void registerBeanDefinition(
BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
throws BeanDefinitionStoreException {
// Register bean definition under primary name.
String beanName = definitionHolder.getBeanName();
//向IOC容器中注冊definitionHolder 在注冊的時候，真正的完成注冊功能是DefaultListableBeanFactory
registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition()); //進入這個方法
// Register aliases for bean name, if any.
// 如果在決議的程序中拿到了別名，則向IOC注冊別名
String[] aliases = definitionHolder.getAliases();
if (aliases != null) {
for (String alias : aliases) {
registry.registerAlias(beanName, alias);
}
}
}
查看registerBeanDefinition方法，這個方法在DefaultListableBeanFactory類中，
//在這個Map里面保存了Bean定義物件的映射
private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<>(256);
@Override
public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
throws BeanDefinitionStoreException {
//....
if (beanDefinition instanceof AbstractBeanDefinition) {
try {
((AbstractBeanDefinition) beanDefinition).validate();
}
catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Validation of bean definition failed", ex);
}
}
BeanDefinition oldBeanDefinition;
oldBeanDefinition = this.beanDefinitionMap.get(beanName);
if (oldBeanDefinition != null) {
if (!isAllowBeanDefinitionOverriding()) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName +
"': There is already [" + oldBeanDefinition + "] bound.");
}
else if (oldBeanDefinition.getRole() < beanDefinition.getRole()) {
// e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
if (this.logger.isWarnEnabled()) {
this.logger.warn("Overriding user-defined bean definition for bean '" + beanName +
"' with a framework-generated bean definition: replacing [" +
oldBeanDefinition + "] with [" + beanDefinition + "]");
}
}
else if (!beanDefinition.equals(oldBeanDefinition)) {
if (this.logger.isInfoEnabled()) {
this.logger.info("Overriding bean definition for bean '" + beanName +
"' with a different definition: replacing [" + oldBeanDefinition +
"] with [" + beanDefinition + "]");
}
}
else {
if (this.logger.isDebugEnabled()) {
this.logger.debug("Overriding bean definition for bean '" + beanName +
"' with an equivalent definition: replacing [" + oldBeanDefinition +
"] with [" + beanDefinition + "]");
}
}
this.beanDefinitionMap.put(beanName, beanDefinition);
}
else {
if (hasBeanCreationStarted()) {
// 在這里對啟動的資訊進行鎖定，不可以在修改，保證資料一致
//這里是注冊的程序
synchronized (this.beanDefinitionMap) {
this.beanDefinitionMap.put(beanName, beanDefinition);
List<String> updatedDefinitions = new ArrayList<>(this.beanDefinitionNames.size() + 1);
updatedDefinitions.addAll(this.beanDefinitionNames);
updatedDefinitions.add(beanName);
this.beanDefinitionNames = updatedDefinitions;
if (this.manualSingletonNames.contains(beanName)) {
Set<String> updatedSingletons = new LinkedHashSet<>(this.manualSingletonNames);
updatedSingletons.remove(beanName);
this.manualSingletonNames = updatedSingletons;
}
}
}
else {
// Still in startup registration phase
this.beanDefinitionMap.put(beanName, beanDefinition);
this.beanDefinitionNames.add(beanName);
this.manualSingletonNames.remove(beanName);
}
this.frozenBeanDefinitionNames = null;
}
//檢查是否已經注冊過相同的BeanDefinition
if (oldBeanDefinition != null || containsSingleton(beanName)) {
resetBeanDefinition(beanName);
}
}
到這里就完成了IOC容器初始化的作業，
在注冊的流程里面關于子元素(property list)加載沒有寫到，會在另一篇文章中寫到
轉載請註明出處，本文鏈接：https://www.uj5u.com/houduan/151711.html
標籤：Java
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