# Spring 自定义标签解析
- Author: [HuiFer](https://github.com/huifer)
- 源码阅读仓库: [SourceHot-Spring](https://github.com/SourceHot/spring-framework-read)
- 与自定义标签解析相关的类
1. `org.springframework.beans.factory.xml.AbstractSingleBeanDefinitionParser`
2. `org.springframework.beans.factory.xml.NamespaceHandlerSupport`
- 开始源码之前先搭建一个环境
## 环境搭建
- 创建对象
```java
public class UserXtd {
private String userName;
private String emailAddress;
public String getUserName() {
return userName;
}
public void setUserName(String userName) {
this.userName = userName;
}
public String getEmailAddress() {
return emailAddress;
}
public void setEmailAddress(String emailAddress) {
this.emailAddress = emailAddress;
}
}
```
- 创建 xsd 文件
```xml
```
- 创建 namespaceHandler
```java
public class UserNamespaceHandler extends NamespaceHandlerSupport {
@Override
public void init() {
registerBeanDefinitionParser("myUser", new UserBeanDefinitionParser());
}
}
```
- 创建 beanDefinitionParser
```java
public class UserBeanDefinitionParser extends AbstractSingleBeanDefinitionParser {
/**
* 标签对应class
* @param element the {@code Element} that is being parsed
* @return
*/
@Override
protected Class getBeanClass(Element element) {
return UserXtd.class;
}
@Override
protected void doParse(Element element, ParserContext parserContext, BeanDefinitionBuilder builder) {
// 获取 userName 标签属性值
String name = element.getAttribute("userName");
// 获取 emailAddress 标签属性值
String address = element.getAttribute("emailAddress");
if (StringUtils.hasText(name)) {
builder.addPropertyValue("userName", name);
}
if (StringUtils.hasText(address)) {
builder.addPropertyValue("emailAddress", address);
}
}
}
```
- 创建 resource/META-INF/spring.handlers
```text
http\://www.huifer.com/schema/user=com.huifer.source.spring.parser.UserNamespaceHandler
```
- 创建 resource/META-INF/spring.schemas
```text
http\://www.huifer.com/schema/user.xsd=META-INF/spring-test.xsd
```
- 创建测试用例xml
```xml
```
- 创建 Java 运行方法
```java
/**
* 自定义标签测试用例
*/
public class XSDDemo {
public static void main(String[] args) {
ApplicationContext applicationContext = new ClassPathXmlApplicationContext("XTD-xml.xml");
UserXtd user = (UserXtd) applicationContext.getBean("testUserBean");
System.out.println(user.getEmailAddress());
}
}
```
- 这里我们希望输出结果是`huifer97@163.com`,运行后结果也确实是`huifer97@163.com`
## 解析 DefaultNamespaceHandlerResolver
- 入口方法`org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader.parseBeanDefinitions`
```java
protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
if (delegate.isDefaultNamespace(root)) {
NodeList nl = root.getChildNodes();
for (int i = 0; i < nl.getLength(); i++) {
Node node = nl.item(i);
if (node instanceof Element) {
Element ele = (Element) node;
if (delegate.isDefaultNamespace(ele)) {
// 不同标签的解析
parseDefaultElement(ele, delegate);
}
else {
// 非spring 默认标签解析
delegate.parseCustomElement(ele);
}
}
}
}
else {
delegate.parseCustomElement(root);
}
}
```
- 调用链路
- `org.springframework.beans.factory.xml.BeanDefinitionParserDelegate.parseCustomElement(org.w3c.dom.Element)`
- `org.springframework.beans.factory.xml.BeanDefinitionParserDelegate.parseCustomElement(org.w3c.dom.Element, org.springframework.beans.factory.config.BeanDefinition)`
```java
/**
* Parse a custom element (outside of the default namespace).
*
* 自定义标签解析
*
* @param ele the element to parse
* @param containingBd the containing bean definition (if any)
* @return the resulting bean definition
*/
@Nullable
public BeanDefinition parseCustomElement(Element ele, @Nullable BeanDefinition containingBd) {
// 自定义标签解析
String namespaceUri = getNamespaceURI(ele);
if (namespaceUri == null) {
return null;
}
// 根据命名空间获取处理类
NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
if (handler == null) {
error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", ele);
return null;
}
// 自定义处理器
return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));
}
```
- `http://www.huifer.com/schema/user`和我们定义的xsd文件中的url相同，如何找到对应的NamespaceHandler,在`META-INF/spring.handlers`中有定义,
`http\://www.huifer.com/schema/user=com.huifer.source.spring.parser.UserNamespaceHandler`
`NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);`这行代码就是获取`spring.handlers`中的定义
- 处理方法`org.springframework.beans.factory.xml.DefaultNamespaceHandlerResolver.resolve`
```java
/**
* Locate the {@link NamespaceHandler} for the supplied namespace URI
* from the configured mappings.
*
* 根据 namespaceUri 获取对应的 {@link NamespaceHandler}
* @param namespaceUri the relevant namespace URI
* @return the located {@link NamespaceHandler}, or {@code null} if none found
*/
@Override
@Nullable
public NamespaceHandler resolve(String namespaceUri) {
// 获取handlerMapping
Map handlerMappings = getHandlerMappings();
// 从 handlerMapping 中获取类名
Object handlerOrClassName = handlerMappings.get(namespaceUri);
if (handlerOrClassName == null) {
return null;
}
// 判断是否处理过,处理过直接返回
else if (handlerOrClassName instanceof NamespaceHandler) {
return (NamespaceHandler) handlerOrClassName;
}
else {
// 没有处理,进行反射还原类
String className = (String) handlerOrClassName;
try {
// 通过反射还原类
Class handlerClass = ClassUtils.forName(className, this.classLoader);
if (!NamespaceHandler.class.isAssignableFrom(handlerClass)) {
throw new FatalBeanException("Class [" + className + "] for namespace [" + namespaceUri +
"] does not implement the [" + NamespaceHandler.class.getName() + "] interface");
}
// 初始化类
NamespaceHandler namespaceHandler = (NamespaceHandler) BeanUtils.instantiateClass(handlerClass);
// 调用init()方法,自定义类中实现
namespaceHandler.init();
// 放入缓存
handlerMappings.put(namespaceUri, namespaceHandler);
// 返回自定义的 namespaceHandler
return namespaceHandler;
}
catch (ClassNotFoundException ex) {
throw new FatalBeanException("Could not find NamespaceHandler class [" + className +
"] for namespace [" + namespaceUri + "]", ex);
}
catch (LinkageError err) {
throw new FatalBeanException("Unresolvable class definition for NamespaceHandler class [" +
className + "] for namespace [" + namespaceUri + "]", err);
}
}
}
```
- `org.springframework.beans.factory.xml.DefaultNamespaceHandlerResolver#getHandlerMappings`跟踪这个方法
```JAVA
/**
* Load the specified NamespaceHandler mappings lazily.
*
* 获取handlerMappings
*/
private Map getHandlerMappings() {
Map handlerMappings = this.handlerMappings;
}
```
- 这里直接存在数据了,他是从什么时候加载的?
- `org.springframework.beans.factory.xml.XmlBeanDefinitionReader#registerBeanDefinitions`
这个方法在注册bean定义的时候调用
```java
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
int countBefore = getRegistry().getBeanDefinitionCount();
// 注册方法
// createReaderContext 初始化HandlerMapping
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
return getRegistry().getBeanDefinitionCount() - countBefore;
}
```
- 继续跟踪`createReaderContext`
```java
org.springframework.beans.factory.xml.XmlBeanDefinitionReader#createReaderContext
```
```java
public XmlReaderContext createReaderContext(Resource resource) {
return new XmlReaderContext(resource, this.problemReporter, this.eventListener,
this.sourceExtractor, this, getNamespaceHandlerResolver());
}
```
- 继续跟踪`getNamespaceHandlerResolver`
`org.springframework.beans.factory.xml.XmlBeanDefinitionReader#getNamespaceHandlerResolver`
```java
public NamespaceHandlerResolver getNamespaceHandlerResolver() {
if (this.namespaceHandlerResolver == null) {
this.namespaceHandlerResolver = createDefaultNamespaceHandlerResolver();
}
return this.namespaceHandlerResolver;
}
```
- 继续跟踪`createDefaultNamespaceHandlerResolver`
`org.springframework.beans.factory.xml.XmlBeanDefinitionReader#createDefaultNamespaceHandlerResolver`
```java
protected NamespaceHandlerResolver createDefaultNamespaceHandlerResolver() {
ClassLoader cl = (getResourceLoader() != null ? getResourceLoader().getClassLoader() : getBeanClassLoader());
return new DefaultNamespaceHandlerResolver(cl);
}
```
- 继续跟踪`DefaultNamespaceHandlerResolver`
`org.springframework.beans.factory.xml.DefaultNamespaceHandlerResolver`
```java
public DefaultNamespaceHandlerResolver(@Nullable ClassLoader classLoader) {
this(classLoader, DEFAULT_HANDLER_MAPPINGS_LOCATION);
}
```
他回到了我们之前疑问的地方 `handlerMappings` 如何出现的
断点
```JAVA
public DefaultNamespaceHandlerResolver(@Nullable ClassLoader classLoader) {
this(classLoader, DEFAULT_HANDLER_MAPPINGS_LOCATION);
}
```
`public static final String DEFAULT_HANDLER_MAPPINGS_LOCATION = "META-INF/spring.handlers";`
此时还是空
走完
```java
@Override
public String toString() {
return "NamespaceHandlerResolver using mappings " + getHandlerMappings();
}
```
```JAVA
/**
* Load the specified NamespaceHandler mappings lazily.
*
* 获取handlerMappings
*/
private Map getHandlerMappings() {
Map handlerMappings = this.handlerMappings;
// 缓存不存在
if (handlerMappings == null) {
synchronized (this) {
handlerMappings = this.handlerMappings;
if (handlerMappings == null) {
if (logger.isTraceEnabled()) {
logger.trace("Loading NamespaceHandler mappings from [" + this.handlerMappingsLocation + "]");
}
try {
// 将本地文件读出
Properties mappings =
PropertiesLoaderUtils.loadAllProperties(this.handlerMappingsLocation, this.classLoader);
if (logger.isTraceEnabled()) {
logger.trace("Loaded NamespaceHandler mappings: " + mappings);
}
handlerMappings = new ConcurrentHashMap<>(mappings.size());
// 转换成map结构
CollectionUtils.mergePropertiesIntoMap(mappings, handlerMappings);
this.handlerMappings = handlerMappings;
}
catch (IOException ex) {
throw new IllegalStateException(
"Unable to load NamespaceHandler mappings from location [" + this.handlerMappingsLocation + "]", ex);
}
}
}
}
return handlerMappings;
}
```
## org.springframework.beans.factory.xml.DefaultNamespaceHandlerResolver#resolve
```java
@Override
@Nullable
public NamespaceHandler resolve(String namespaceUri) {
// 获取handlerMapping
Map handlerMappings = getHandlerMappings();
// 从 handlerMapping 中获取类名
Object handlerOrClassName = handlerMappings.get(namespaceUri);
if (handlerOrClassName == null) {
return null;
}
// 判断是否处理过,处理过直接返回
else if (handlerOrClassName instanceof NamespaceHandler) {
return (NamespaceHandler) handlerOrClassName;
}
else {
// 没有处理,进行反射还原类
String className = (String) handlerOrClassName;
try {
// 通过反射还原类
Class handlerClass = ClassUtils.forName(className, this.classLoader);
if (!NamespaceHandler.class.isAssignableFrom(handlerClass)) {
throw new FatalBeanException("Class [" + className + "] for namespace [" + namespaceUri +
"] does not implement the [" + NamespaceHandler.class.getName() + "] interface");
}
// 初始化类
NamespaceHandler namespaceHandler = (NamespaceHandler) BeanUtils.instantiateClass(handlerClass);
// 调用init()方法,自定义类中实现
namespaceHandler.init();
// 放入缓存
handlerMappings.put(namespaceUri, namespaceHandler);
// 返回自定义的 namespaceHandler
return namespaceHandler;
}
catch (ClassNotFoundException ex) {
throw new FatalBeanException("Could not find NamespaceHandler class [" + className +
"] for namespace [" + namespaceUri + "]", ex);
}
catch (LinkageError err) {
throw new FatalBeanException("Unresolvable class definition for NamespaceHandler class [" +
className + "] for namespace [" + namespaceUri + "]", err);
}
}
}
```
执行`init`方法
```java
public class UserNamespaceHandler extends NamespaceHandlerSupport {
@Override
public void init() {
registerBeanDefinitionParser("myUser", new UserBeanDefinitionParser());
}
}
```
```java
/**
* Subclasses can call this to register the supplied {@link BeanDefinitionParser} to
* handle the specified element. The element name is the local (non-namespace qualified)
* name.
*
* 将标签名称,标签解析类放入
*/
protected final void registerBeanDefinitionParser(String elementName, BeanDefinitionParser parser) {
this.parsers.put(elementName, parser);
}
```
- 方法走完，回到开始的方法
```java
/**
* Parse a custom element (outside of the default namespace).
*
* 自定义标签解析
*
* @param ele the element to parse
* @param containingBd the containing bean definition (if any)
* @return the resulting bean definition
*/
@Nullable
public BeanDefinition parseCustomElement(Element ele, @Nullable BeanDefinition containingBd) {
// 自定义标签解析
String namespaceUri = getNamespaceURI(ele);
if (namespaceUri == null) {
return null;
}
// 根据命名空间获取处理类
// org.springframework.beans.factory.xml.DefaultNamespaceHandlerResolver.resolve
NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
if (handler == null) {
error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", ele);
return null;
}
// 自定义处理器
return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));
}
```
## org.springframework.beans.factory.xml.NamespaceHandler#parse
- `org.springframework.beans.factory.xml.NamespaceHandlerSupport.parse`
```java
@Override
@Nullable
public BeanDefinition parse(Element element, ParserContext parserContext) {
BeanDefinitionParser parser = findParserForElement(element, parserContext);
return (parser != null ? parser.parse(element, parserContext) : null);
}
```
### org.springframework.beans.factory.xml.NamespaceHandlerSupport#findParserForElement
```java
@Nullable
private BeanDefinitionParser findParserForElement(Element element, ParserContext parserContext) {
// 获取标签名称
String localName = parserContext.getDelegate().getLocalName(element);
// 在map中获取对应的标签解析类
BeanDefinitionParser parser = this.parsers.get(localName);
// 空报错
if (parser == null) {
parserContext.getReaderContext().fatal(
"Cannot locate BeanDefinitionParser for element [" + localName + "]", element);
}
// 不为空返回
return parser;
}
```
### org.springframework.beans.factory.xml.BeanDefinitionParser#parse
- `org.springframework.beans.factory.xml.AbstractBeanDefinitionParser#parse`
```java
public final BeanDefinition parse(Element element, ParserContext parserContext) {
/**
* {@link AbstractSingleBeanDefinitionParser#parseInternal(org.w3c.dom.Element, org.springframework.beans.factory.xml.ParserContext)}
*/
AbstractBeanDefinition definition = parseInternal(element, parserContext);
}
```
### org.springframework.beans.factory.xml.AbstractSingleBeanDefinitionParser#parseInternal
```java
@Override
protected final AbstractBeanDefinition parseInternal(Element element, ParserContext parserContext) {
BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition();
String parentName = getParentName(element);
if (parentName != null) {
builder.getRawBeanDefinition().setParentName(parentName);
}
// 调用自己实现的方法 com.huifer.source.spring.parser.UserBeanDefinitionParser.getBeanClass
Class beanClass = getBeanClass(element);
if (beanClass != null) {
builder.getRawBeanDefinition().setBeanClass(beanClass);
}
else {
// getBeanClassName 同样也是可以在自定义的解析类中实现
String beanClassName = getBeanClassName(element);
if (beanClassName != null) {
builder.getRawBeanDefinition().setBeanClassName(beanClassName);
}
}
builder.getRawBeanDefinition().setSource(parserContext.extractSource(element));
BeanDefinition containingBd = parserContext.getContainingBeanDefinition();
if (containingBd != null) {
// Inner bean definition must receive same scope as containing bean.
// 设置scope
builder.setScope(containingBd.getScope());
}
if (parserContext.isDefaultLazyInit()) {
// Default-lazy-init applies to custom bean definitions as well.
// 设置 lazy-init
builder.setLazyInit(true);
}
// 执行解析方法,在自定义解析类中存在com.huifer.source.spring.parser.UserBeanDefinitionParser.doParse
doParse(element, parserContext, builder);
return builder.getBeanDefinition();
}
```
执行`com.huifer.source.spring.parser.UserBeanDefinitionParser#doParse`
```JAVA
@Override
protected void doParse(Element element, ParserContext parserContext, BeanDefinitionBuilder builder) {
// 获取 userName 标签属性值
String name = element.getAttribute("userName");
// 获取 emailAddress 标签属性值
String address = element.getAttribute("emailAddress");
if (StringUtils.hasText(name)) {
builder.addPropertyValue("userName", name);
}
if (StringUtils.hasText(address)) {
builder.addPropertyValue("emailAddress", address);
}
}
```