spring 加載bean過程源碼簡易解剖

時間 2019-12-24

原文原文鏈接

這一篇主要是講用載入bean的過程。其實就是IOC.低調低調。。

我把重要的都挑出來了。一步步往下看就明白spring載入bean.xml裏面bean的原理。
感受像候傑的 MFC深刻淺出，哈哈。

觀看規則

接下表示下一層代碼。
接上表示最近上面要調用的代碼的詳細部分。

node

Java代碼 spring

public class XmlBeanFactory extends DefaultListableBeanFactory { dom
//新建一個bean分析器，把this註冊到裏面是由於，在分析器解析好一個bean時，能夠當即用這個this裏的註冊方法去保存bean，往下看就明白。任何bean到最後都是保存在XmlBeanFactory裏的（實際上是DefaultListableBeanFactory）。 ui
private final XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(this); this
public XmlBeanFactory(Resource resource, BeanFactory parentBeanFactory) throws BeansException { spa
super(parentBeanFactory); xml
//載入xml文件索引
this.reader.loadBeanDefinitions(resource); //往下-> get
} it
}
public class XmlBeanDefinitionReader extends AbstractBeanDefinitionReader {
//接上
public int loadBeanDefinitions(Resource resource) throws BeansException {
InputStream is = null;
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setValidating(this.validating);
DocumentBuilder docBuilder = factory.newDocumentBuilder();
docBuilder.setErrorHandler(this.errorHandler);
if (this.entityResolver != null) {
docBuilder.setEntityResolver(this.entityResolver);
}
is = resource.getInputStream();
//用Xerces解析xml,生成dom
Document doc = docBuilder.parse(is);
//registerBeanDefinitions分析dom
return registerBeanDefinitions(doc, resource); //往下
}
//接上
public int registerBeanDefinitions(Document doc, Resource resource) throws BeansException {
XmlBeanDefinitionParser parser = (XmlBeanDefinitionParser) BeanUtils.instantiateClass(this.parserClass);
//這個parserClass 是 DefaultXmlBeanDefinitionParser.class
return parser.registerBeanDefinitions(this, doc, resource); //往下->
}
}
public class DefaultXmlBeanDefinitionParser implements XmlBeanDefinitionParser {
//明顯就是bean.xml裏面出現的很熟悉的標籤，說明已經快到底層類了
public static final String AUTOWIRE_BY_NAME_VALUE = "byName";
public static final String AUTOWIRE_BY_TYPE_VALUE = "byType";
public static final String DEFAULT_LAZY_INIT_ATTRIBUTE = "default-lazy-init";
public static final String DEFAULT_DEPENDENCY_CHECK_ATTRIBUTE = "default-dependency-check";
public static final String DEFAULT_AUTOWIRE_ATTRIBUTE = "default-autowire";
public static final String NAME_ATTRIBUTE = "name";
public static final String ALIAS_ATTRIBUTE = "alias";
public static final String BEAN_ELEMENT = "bean";
public static final String ID_ATTRIBUTE = "id";
public static final String PARENT_ATTRIBUTE = "parent";
public static final String CLASS_ATTRIBUTE = "class";
public static final String SINGLETON_ATTRIBUTE = "singleton";
public static final String LAZY_INIT_ATTRIBUTE = "lazy-init";
public static final String AUTOWIRE_ATTRIBUTE = "autowire";
//...
//接上
public int registerBeanDefinitions(BeanDefinitionReader reader, Document doc, Resource resource) throws BeanDefinitionStoreException {
this.beanDefinitionReader = reader;
this.resource = resource;;
Element root = doc.getDocumentElement();
//...
//這裏準備開始正式解析bean
int beanDefinitionCount = parseBeanDefinitions(root);//往下->
//這個beanDefinitionCount 就是解析出了多少個<bean></bean>
//...
return beanDefinitionCount;
}
protected int parseBeanDefinitions(Element root) throws BeanDefinitionStoreException {
//Xerces開始循環找<bean>標籤
NodeList nl = root.getChildNodes();
int beanDefinitionCounter = 0;
for (int i = 0; i < nl.getLength(); i++) {
Node node = nl.item(i);
if (node instanceof Element) {
Element ele = (Element) node;
if // ...
//..
else if (BEAN_ELEMENT.equals(node.getNodeName())) {//這裏是重點，開始解析bean
beanDefinitionCounter++;
//分兩步走，看下面詳解。1.先把bean放到BeanDefinitionHolder
BeanDefinitionHolder bdHolder = parseBeanDefinitionElement(ele);//往下 1.->
//2.而後XmlBeanFactory去註冊
BeanDefinitionReaderUtils.registerBeanDefinition(
bdHolder, this.beanDefinitionReader.getBeanFactory()); //往下 2. ->
}
}
}
return beanDefinitionCounter;
}
//接上1. 哈哈，下面是第一步，是正常解析bean，在同一個類中
protected BeanDefinitionHolder parseBeanDefinitionElement(Element ele) throws BeanDefinitionStoreException {
//...
//下面能夠看到其實最底層的解析bean在同一個類的parseBeanDefinitionElement方法裏。由於spring把bean封裝成BeanDefinition 再把BeanDefinition 封裝成BeanDefinitionHolder
BeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName);//往下
//...
return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
}
//接上，這個方法很長，畢竟<bean>裏attribute不少。
protected BeanDefinition parseBeanDefinitionElement(Element ele, String beanName) throws BeanDefinitionStoreException {
try {
//下面解析<bean>裏的<property>，這個我不分析了。
MutablePropertyValues pvs = parsePropertyElements(ele, beanName);
//將BeanDefinition封裝成AbstractBeanDefinition
AbstractBeanDefinition bd = BeanDefinitionReaderUtils.createBeanDefinition(
className, parent, cargs, pvs, this.beanDefinitionReader.getBeanClassLoader());
//...
return bd;
}
catch (/*...*/)
//...
}
}
}
//bean解析部分到此結束。。。。
//接上2. 這裏是第二部，註冊部分，回到上面註釋裏的分兩部走這裏。
public class BeanDefinitionReaderUtils {
public static void registerBeanDefinition(
BeanDefinitionHolder bdHolder, BeanDefinitionRegistry beanFactory) throws BeansException {
//beanFactory就是XmlBeanFactory，實際上是它的父類 DefaultListableBeanFactory在執行registerBeanDefinition
beanFactory.registerBeanDefinition(bdHolder.getBeanName(), bdHolder.getBeanDefinition()); //往下
//...
}
}
public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFactory
implements ConfigurableListableBeanFactory, BeanDefinitionRegistry {
/** Whether to allow re-registration of a different definition with the same name */
private boolean allowBeanDefinitionOverriding = true;
/** Map of bean definition objects, keyed by bean name */
//下面是真正藏bean的地方，實際上是個Map，跟我預想的同樣。
private final Map beanDefinitionMap = new HashMap();
//下面List多是給bean的名字作個索引，這是個人初步猜測。
/** List of bean definition names, in registration order */
private final List beanDefinitionNames = new ArrayList();
//接上
public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition) throws BeanDefinitionStoreException {
//...
Object oldBeanDefinition = this.beanDefinitionMap.get(beanName);
if (oldBeanDefinition != null) {
//根據allowBeanDefinitionOverriding這個變量來決定在bean.xml裏的bean萬一有同名的狀況下否覆蓋，由於allowBeanDefinitionOverriding默認是true，因此覆蓋。
if (!this.allowBeanDefinitionOverriding) {
throw new BeanDefinitionStoreException(...);
}
else {
//...只用註釋提醒相同bean將要被覆蓋了
}
}
else {
//索引List里加上這個bean名字
this.beanDefinitionNames.add(beanName);
}
//將bean藏在map裏。用名字來索引。
this.beanDefinitionMap.put(beanName, beanDefinition);
}
//...
}
//結束