今天我们继续Spring源码的学习，上一篇文章分析了 BeanDefinitionReader 的创建过程，本篇文章分析 BeanDefinitionReader 加载BeanDefinition过程。
/**
* Load bean definitions from the specified XML file.
* @param resource the resource descriptor for the XML file
* @return the number of bean definitions found
* @throws BeanDefinitionStoreException in case of loading or parsing errors
*/
@Override
public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
return loadBeanDefinitions(new EncodedResource(resource));
}
考虑到Resource的读取可能存在编码要求，首先将Resource封装成EncodedResource，同样的EncodedResource 也实现了InputStreamSource接口。
EncodedResource 封装指定编码的Resource，EncodedResource 内部维护了 Resource 的引用，将 Resource 和编码封装在一起。
public class EncodedResource implements InputStreamSource {
private final Resource resource;
@Nullable
private final String encoding;
@Nullable
private final Charset charset;
/**
* Create a new {@code EncodedResource} for the given {@code Resource},
* not specifying an explicit encoding or {@code Charset}.
* @param resource the {@code Resource} to hold (never {@code null})
*/
public EncodedResource(Resource resource) {
this(resource, null, null);
}
private EncodedResource(Resource resource, @Nullable String encoding, @Nullable Charset charset) {
super();
Assert.notNull(resource, "Resource must not be null");
this.resource = resource;
this.encoding = encoding;
this.charset = charset;
}
/**
* Open a {@code java.io.Reader} for the specified resource, using the specified
* {@link #getCharset() Charset} or {@linkplain #getEncoding() encoding}
* (if any).
* @throws IOException if opening the Reader failed
* @see #requiresReader()
* @see #getInputStream()
*/
public Reader getReader() throws IOException {
if (this.charset != null) {
return new InputStreamReader(this.resource.getInputStream(), this.charset);
}
else if (this.encoding != null) {
return new InputStreamReader(this.resource.getInputStream(), this.encoding);
}
else {
return new InputStreamReader(this.resource.getInputStream());
}
}
/**
* Open an {@code InputStream} for the specified resource, ignoring any specified
* {@link #getCharset() Charset} or {@linkplain #getEncoding() encoding}.
* @throws IOException if opening the InputStream failed
* @see #requiresReader()
* @see #getReader()
*/
@Override
public InputStream getInputStream() throws IOException {
return this.resource.getInputStream();
}
/**
* Return the encoding to use for reading from the {@linkplain #getResource() resource},
* or {@code null} if none specified.
*/
@Nullable
public final String getEncoding() {
return this.encoding;
}
// 其他方法，此处省略
}
loadBeanDefinitions 内部调用了重载方法 loadBeanDefinitions(EncodedResource encodedResource)
/**
* Load bean definitions from the specified XML file.
* @param encodedResource the resource descriptor for the XML file,
* allowing to specify an encoding to use for parsing the file
* @return the number of bean definitions found
* @throws BeanDefinitionStoreException in case of loading or parsing errors
*/
public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
Assert.notNull(encodedResource, "EncodedResource must not be null");
if (logger.isTraceEnabled()) {
logger.trace("Loading XML bean definitions from " + encodedResource);
}
// 判断资源文件是否循环加载.
Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get();
if (currentResources == null) {
currentResources = new HashSet<>(4);
this.resourcesCurrentlyBeingLoaded.set(currentResources);
}
if (!currentResources.add(encodedResource)) {
throw new BeanDefinitionStoreException(
"Detected cyclic loading of " + encodedResource + " - check your import definitions!");
}
try {
// 从Resource 中获取输入流InputStream.
InputStream inputStream = encodedResource.getResource().getInputStream();
try {
// 将Resource中的InputStream封装成InputSource，并指定编码.
InputSource inputSource = new InputSource(inputStream);
if (encodedResource.getEncoding() != null) {
inputSource.setEncoding(encodedResource.getEncoding());
}
// 调动内部方法
return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
}
finally {
// 关闭输入流
inputStream.close();
}
}
catch (IOException ex) {
throw new BeanDefinitionStoreException(
"IOException parsing XML document from " + encodedResource.getResource(), ex);
}
finally {
currentResources.remove(encodedResource);
if (currentResources.isEmpty()) {
this.resourcesCurrentlyBeingLoaded.remove();
}
}
}
InputStream 类是JDK提供的位于org.xml.sax包下，Spring采用SAX解析XML配置文件。
loadBeanDefinitions 方法内部有个值得关注的地方，Spring是如何判断资源文件循环加载的（通过import标签导入自身）呢？
Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get();
resourcesCurrentlyBeingLoaded 成员变量是ThreadLocal的子类NamedThreadLocal，内部通过 HashSet 判断资源文件的循环加载。（考点，HashSet 底层是 HashMap实现的，EncodedResource 内部重写了equals 和 hashCode 方法）。使用ThreadLocal最后一定要remove，避免内存泄漏（zhuanlan.zhihu.com/p/354153342…
InputStream inputStream = encodedResource.getResource().getInputStream();
这行代码解释了【Spring源码】ClassPathResource 资源文件源码分析 最后留下的问题，ClassPathResource 类的 getInputStream() 方法在什么地方被执行的呢？
继续跟踪代码，实际执行从指定的XML文件加载BeanDefinition的方法。
/**
* Actually load bean definitions from the specified XML file.
* @param inputSource the SAX InputSource to read from
* @param resource the resource descriptor for the XML file
* @return the number of bean definitions found
* @throws BeanDefinitionStoreException in case of loading or parsing errors
* @see #doLoadDocument
* @see #registerBeanDefinitions
*/
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
throws BeanDefinitionStoreException {
try {
// 将XML文件解析成Document对象
Document doc = doLoadDocument(inputSource, resource);
// 注册BeanDefinition
int count = registerBeanDefinitions(doc, resource);
if (logger.isDebugEnabled()) {
logger.debug("Loaded " + count + " bean definitions from " + resource);
}
return count;
}
// 省略异常捕获部分代码
}
通过BeanDefinitionDocumentReader 注册BeanDefinition。
/**
* Register the bean definitions contained in the given DOM document.
* Called by {@code loadBeanDefinitions}.
* <p>Creates a new instance of the parser class and invokes
* {@code registerBeanDefinitions} on it.
* @param doc the DOM document
* @param resource the resource descriptor (for context information)
* @return the number of bean definitions found
* @throws BeanDefinitionStoreException in case of parsing errors
* @see #loadBeanDefinitions
* @see #setDocumentReaderClass
* @see BeanDefinitionDocumentReader#registerBeanDefinitions
*/
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
// 通过反射的方式创建DefaultBeanDefinitionDocumentReader的实例
BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
// 获取之前容器中的BeanDefinition数量
int countBefore = getRegistry().getBeanDefinitionCount();
// BeanDefinitionDocumentReader 负责实际的Bean注册
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
// 返回新增的BeanDefinition数量
return getRegistry().getBeanDefinitionCount() - countBefore;
}
/**
* Create the {@link BeanDefinitionDocumentReader} to use for actually
* reading bean definitions from an XML document.
* <p>The default implementation instantiates the specified "documentReaderClass".
* @see #setDocumentReaderClass
*/
protected BeanDefinitionDocumentReader createBeanDefinitionDocumentReader() {
return BeanUtils.instantiateClass(this.documentReaderClass);
}
getRegistry().getBeanDefinitionCount();
BeanDefinitionRegistry 的实现类 DefaultListableBeanFactory 中的成员变量 Map<String, BeanDefinition> beanDefinitionMap 中获取BeanDefinition的个数。
九转十八弯，流程最后转入BeanDefinitionDocumentReader 接口的实现类DefaultBeanDefinitionDocumentReader 中。
/**
* This implementation parses bean definitions according to the "spring-beans" XSD
* (or DTD, historically).
* <p>Opens a DOM Document; then initializes the default settings
* specified at the {@code <beans/>} level; then parses the contained bean definitions.
*/
@Override
public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
this.readerContext = readerContext;
doRegisterBeanDefinitions(doc.getDocumentElement());
}
BeanDefinitionDocumentReader 内部实现我们下篇再分析，敬请期待。
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