Spring版本
5.2.5.RELEASE
参考
学习Spring源码（二）自定义标签属性
源码解读
在Spring源码中，bean标签的解析交由processBeanDefinition处理：
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
// 解析bean，如果解析成功，获得持有name和alias的BeanDefinitionHolder，即BeanDefinitionHolder对象，解析失败返回null
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
if (bdHolder != null) {
// bean支持定义属性和内部嵌套自定义标签，进行这一部分的处理
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
try {
// 注册bean
// 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);
}
// 通知监听器注册事件
// Send registration event.
getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
}
}
该方法主要做了以下三点：
- 解析bean标签
- 解析bean标签的自定义属性和bean标签下嵌套的自定义标签
- 注册bean，并且在注册成功之后通知监听器注册事件
1. parseBeanDefinitionElement
@Nullable
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele) {
return parseBeanDefinitionElement(ele, null);
}
继续交由重载方法：
@Nullable
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, @Nullable BeanDefinition containingBean) {
String id = ele.getAttribute(ID_ATTRIBUTE);
String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);
// 将name属性值进行切割，塞进别名集合
List aliases = new ArrayList<>();
if (StringUtils.hasLength(nameAttr)) {
String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, MULTI_VALUE_ATTRIBUTE_DELIMITERS);
aliases.addAll(Arrays.asList(nameArr));
}
// 如果没有声明id属性，将上面解析出来的第一个别名当成beanName
String beanName = id;
if (!StringUtils.hasText(beanName) && !aliases.isEmpty()) {
beanName = aliases.remove(0);
if (logger.isTraceEnabled()) {
logger.trace("No XML 'id' specified - using '" + beanName +
"' as bean name and " + aliases + " as aliases");
}
}
if (containingBean == null) {
// 检查beanName和aliases中的元素是否唯一
checkNameUniqueness(beanName, aliases, ele);
}
AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
if (beanDefinition != null) {
if (!StringUtils.hasText(beanName)) {
try {
if (containingBean != null) {
// 生成唯一beanName
beanName = BeanDefinitionReaderUtils.generateBeanName(
beanDefinition, this.readerContext.getRegistry(), true);
}
else {
// 生成唯一beanName
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.isTraceEnabled()) {
logger.trace("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);
// 构建BeanDefinitionHolder对象，返回
return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
}
return null;
}
逻辑在于构建一个包含beanDefinition、beanName和aliasesArray的BeanDefinitionHolder对象，因此，整个过程也就可以拆分成三个部分来查看：
- 生成aliasesArray
- 解析获取beanDefinition对象
- 生成beanName
1.1 生成aliasesArray
// 将name属性值进行切割，塞进别名集合
List aliases = new ArrayList<>();
if (StringUtils.hasLength(nameAttr)) {
String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, MULTI_VALUE_ATTRIBUTE_DELIMITERS);
aliases.addAll(Arrays.asList(nameArr));
}
获取到name属性的值，之后切割并组装成List类型的aliases，在构建BeanDefinitionHolder的时候，将List类型的aliases转化为数组类型并作为构造参数：
String[] aliasesArray = StringUtils.toStringArray(aliases);
1.2 解析获取beanDefinition对象
核心方法在于：
AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
查看parseBeanDefinitionElement方法：
@Nullable
public AbstractBeanDefinition parseBeanDefinitionElement(
Element ele, String beanName, @Nullable BeanDefinition containingBean) {
// ParseState的定义生命信息如下：
// Simple {@link LinkedList}-based structure for tracking the logical position during a parsing process.
// 看起来，parseState是用于追踪bean解析过程中的逻辑位置
// 追踪parseState的使用方式，应该是解析过程报错的情况下可以轻易找到当前正在被解析的bean吧
this.parseState.push(new BeanEntry(beanName));
String className = null;
if (ele.hasAttribute(CLASS_ATTRIBUTE)) {
className = ele.getAttribute(CLASS_ATTRIBUTE).trim();
}
String parent = null;
if (ele.hasAttribute(PARENT_ATTRIBUTE)) {
parent = ele.getAttribute(PARENT_ATTRIBUTE);
}
try {
// createBeanDefinition用于创建一个AbstractBeanDefinition对象，且将className进行加载，设置进该对象的beanClass属性，同时将parent设置进去parentName属性
AbstractBeanDefinition bd = createBeanDefinition(className, parent);
// 解析bean的各种属性，比如autowire，lazyinit，设置到bd中
parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
// 解析description子元素内容，getChildElementValueByTagName可以从ele中找到符合DESCRIPTION_ELEMENT的第一个子元素的内容文本值
bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));
// 解析meta子元素
parseMetaElements(ele, bd);
// 解析lookup-method子元素
parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
// 解析replace-method子元素
parseReplacedMethodSubElements(ele, bd.getMethodOverrides());
// 解析construct-arg子元素
parseConstructorArgElements(ele, bd);
// 解析property子元素
parsePropertyElements(ele, bd);
// 解析qualifier子元素
parseQualifierElements(ele, bd);
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();
}
return null;
}
逻辑可以归纳为以下几个步骤：
- 将当前解析的beanName压入parseState栈中，方便解析过程报错的时候定位到当前被解析元素
- 获取class属性和parent属性，调用createBeanDefinition方法构建AbstractBeanDefinition对象，在调用createBeanDefinition方法的时候，对className进行了加载
- 解析bean标签的属性
- 解析bean标签下的子标签
- 解析完毕，从parseState中退栈
1.2.1 createBeanDefinition
public static AbstractBeanDefinition createBeanDefinition(
@Nullable String parentName, @Nullable String className, @Nullable ClassLoader classLoader) throws ClassNotFoundException {
GenericBeanDefinition bd = new GenericBeanDefinition();
bd.setParentName(parentName);
if (className != null) {
if (classLoader != null) {
bd.setBeanClass(ClassUtils.forName(className, classLoader));
}
else {
bd.setBeanClassName(className);
}
}
return bd;
}
可以看到，该方法构建一个GenericBeanDefinition对象，之后如果className和classLoader不为空，则加载类，并设置为beanClass属性，否则将className设置进beanClassName属性
1.2.2 parseBeanDefinitionAttributes
解析bean标签的众多属性，包含：
- scope
- abstract
- lazy-init
- autowire
- depends-on
- autowire-candidate
- primary
- init-method
- destroy-method
- factory-method
- factory-bean
代码逻辑较为简单，不赘述
1.2.3 生成beanName
首先获取id属性作为beanName：
String beanName = id;
如果没有生命id属性，则使用别名的第一个元素作为beanName：
if (!StringUtils.hasText(beanName) && !aliases.isEmpty()) {
beanName = aliases.remove(0);
if (logger.isTraceEnabled()) {
logger.trace("No XML 'id' specified - using '" + beanName +
"' as bean name and " + aliases + " as aliases");
}
}
在上述beanName的基础上生成一个唯一的beanName：
if (containingBean != null) {
// 生成唯一beanName
beanName = BeanDefinitionReaderUtils.generateBeanName(
beanDefinition, this.readerContext.getRegistry(), true);
}
else {
// 生成唯一beanName
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);
}
}
2. decorateBeanDefinitionIfRequired
bean标签支持自定义属性，我们简单使用一个demo演示该部分内容：
2.1 demo
2.1.1 Student
public class Student {
private String id;
private String name;
private String desc;
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getDesc() {
return desc;
}
public void setDesc(String desc) {
this.desc = desc;
}
}
2.1.2 student.xsd
2.1.3 StudentNamespaceHandler
public class StudentNamespaceHandler extends NamespaceHandlerSupport {
@Override
public void init() {
registerBeanDefinitionDecoratorForAttribute("student-desc", new StudentBeanDefinitionDecorator());
}
}
2.1.4 StudentBeanDefinitionDecorator
public class StudentBeanDefinitionDecorator implements BeanDefinitionDecorator {
@Override
public BeanDefinitionHolder decorate(Node node, BeanDefinitionHolder definition, ParserContext parserContext) {
definition.getBeanDefinition().getPropertyValues().add("desc", ((Attr)node).getValue());
return definition;
}
}
2.1.5 spring.handlers
http\://www.customAttribute.com/schema/student-desc=com.kungyu.custom.element.StudentNamespaceHandler
2.1.6 spring.schemas
http\://www.customAttribute.com/schema/student.xsd=META-INF/student.xsd
2.1.7 spring.xml
2.1.8 测试
public class Test {
public static void main(String[] args) {
ApplicationContext context = new ClassPathXmlApplicationContext("spring.xml");
Student student = (Student) context.getBean("student");
System.out.println(student.getId() + "----" + student.getName() + "---" + student.getDesc());
}
}
2.1.9 结果
bean自定义属性结果
在
spring.xml中，我们并没有为id为student的bean指定desc属性的值，而是通过自定义属性student-desc，之后交由在StudentNamespaceHandler中注册的StudentBeanDefinitionDecorator进行处理，在StudentBeanDefinitionDecorator的decorate中给BeanDefinition定义student的desc属性的值。
2.2 源码解读
public BeanDefinitionHolder decorateBeanDefinitionIfRequired(
Element ele, BeanDefinitionHolder originalDef, @Nullable BeanDefinition containingBd) {
BeanDefinitionHolder finalDefinition = originalDef;
// 解析bean标签里面的自定义属性
// Decorate based on custom attributes first.
NamedNodeMap attributes = ele.getAttributes();
for (int i = 0; i < attributes.getLength(); i++) {
Node node = attributes.item(i);
finalDefinition = decorateIfRequired(node, finalDefinition, containingBd);
}
// 解析嵌套在bean标签里面的自定义标签
// Decorate based on custom nested elements.
NodeList children = ele.getChildNodes();
for (int i = 0; i < children.getLength(); i++) {
Node node = children.item(i);
if (node.getNodeType() == Node.ELEMENT_NODE) {
finalDefinition = decorateIfRequired(node, finalDefinition, containingBd);
}
}
return finalDefinition;
}
俩个步骤：
- 解析bean标签的自定义属性
- 解析bean标签内部嵌套的自定义标签
以上俩个步骤都通过decorateIfRequired方法实现：
public BeanDefinitionHolder decorateIfRequired(
Node node, BeanDefinitionHolder originalDef, @Nullable BeanDefinition containingBd) {
String namespaceUri = getNamespaceURI(node);
if (namespaceUri != null && !isDefaultNamespace(namespaceUri)) {
// 同解析自定义标签一样，获取自定义的handler
NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
if (handler != null) {
// 调用自定义handler的decorate方法
BeanDefinitionHolder decorated =
handler.decorate(node, originalDef, new ParserContext(this.readerContext, this, containingBd));
if (decorated != null) {
return decorated;
}
}
else if (namespaceUri.startsWith("http://www.springframework.org/schema/")) {
error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", node);
}
else {
// A custom namespace, not to be handled by Spring - maybe "xml:...".
if (logger.isDebugEnabled()) {
logger.debug("No Spring NamespaceHandler found for XML schema namespace [" + namespaceUri + "]");
}
}
}
return originalDef;
}
该方法很明显逻辑在于：
- 查找到自定义的handler
- 通过handler，调用自定义的decorate方法
3. registerBeanDefinition
public static void registerBeanDefinition(
BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
throws BeanDefinitionStoreException {
// Register bean definition under primary name.
String beanName = definitionHolder.getBeanName();
// 注册，将beanName和beanDefinition写入缓存map中
registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());
// 别名注册
// Register aliases for bean name, if any.
String[] aliases = definitionHolder.getAliases();
if (aliases != null) {
for (String alias : aliases) {
registry.registerAlias(beanName, alias);
}
}
}
逻辑都比较简单，就直接贴代码了
3.1 registerBeanDefinition
@Override
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");
if (beanDefinition instanceof AbstractBeanDefinition) {
try {
// 对methodOverrides进行校验
((AbstractBeanDefinition) beanDefinition).validate();
}
catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Validation of bean definition failed", ex);
}
}
// 获取缓存
BeanDefinition existingDefinition = this.beanDefinitionMap.get(beanName);
// 如果缓存存在
if (existingDefinition != null) {
// 如果不允许BeanDefinition覆盖，抛出异常
if (!isAllowBeanDefinitionOverriding()) {
throw new BeanDefinitionOverrideException(beanName, beanDefinition, existingDefinition);
}
else if (existingDefinition.getRole() < beanDefinition.getRole()) {
// 如果缓存的BeanDefinition角色比注册的BeanDefinition的角色d低
// e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
if (logger.isInfoEnabled()) {
logger.info("Overriding user-defined bean definition for bean '" + beanName +
"' with a framework-generated bean definition: replacing [" +
existingDefinition + "] with [" + beanDefinition + "]");
}
}
else if (!beanDefinition.equals(existingDefinition)) {
// 如果俩个BeanDefinition不同
if (logger.isDebugEnabled()) {
logger.debug("Overriding bean definition for bean '" + beanName +
"' with a different definition: replacing [" + existingDefinition +
"] with [" + beanDefinition + "]");
}
}
else {
if (logger.isTraceEnabled()) {
logger.trace("Overriding bean definition for bean '" + beanName +
"' with an equivalent definition: replacing [" + existingDefinition +
"] with [" + beanDefinition + "]");
}
}
// 进行覆盖
this.beanDefinitionMap.put(beanName, beanDefinition);
}
else {
// 如果不存在缓存
// 判断是否已经开始Bean创建的进程
if (hasBeanCreationStarted()) {
// 如果已开始，进行同步控制
// Cannot modify startup-time collection elements anymore (for stable iteration)
synchronized (this.beanDefinitionMap) {
// 写入缓存
this.beanDefinitionMap.put(beanName, beanDefinition);
// 将beanName加入beanDefinitionNames
List updatedDefinitions = new ArrayList<>(this.beanDefinitionNames.size() + 1);
updatedDefinitions.addAll(this.beanDefinitionNames);
updatedDefinitions.add(beanName);
this.beanDefinitionNames = updatedDefinitions;
removeManualSingletonName(beanName);
}
}
else {
// Still in startup registration phase
this.beanDefinitionMap.put(beanName, beanDefinition);
this.beanDefinitionNames.add(beanName);
removeManualSingletonName(beanName);
}
this.frozenBeanDefinitionNames = null;
}
if (existingDefinition != null || containsSingleton(beanName)) {
resetBeanDefinition(beanName);
}
}
核心其实就是将BeanDefinition写入缓存中：
this.beanDefinitionMap.put(beanName, beanDefinition);
3.2 registerAlias
该方法在《Spring源码解析（五）-解析alias标签》已经讲述过了，感兴趣可以戳