Apache Tika源码研究（二）

shenhp

　　上文分析了Apache Tika的编码识别相关接口和实现类
　　本文接着分析Apache Tika用到的一个关键类ParseContext，这里要明白Tika解析文档的方式，Tika将文件都解析为XHTML格式的文档，然后采用SAX基于事件的方式来解析这个XHTML格式，先来看看ParseContext类的源码：



public class ParseContext implements Serializable {
/** Serial version UID. */
private static final long serialVersionUID = -5921436862145826534L;
/** Map of objects in this context */
private final Map context = new HashMap();
/**
* Adds the given value to the context as an implementation of the given
* interface.
*
* @param key the interface implemented by the given value
* @param value the value to be added, or null to remove
*/
public  void set(Class key, T value) {
if (value != null) {
context.put(key.getName(), value);
} else {
context.remove(key.getName());
}
}
/**
* Returns the object in this context that implements the given interface.
*
* @param key the interface implemented by the requested object
* @return the object that implements the given interface,
*         or null if not found
*/
@SuppressWarnings("unchecked")
public  T get(Class key) {
return (T) context.get(key.getName());
}
/**
* Returns the object in this context that implements the given interface,
* or the given default value if such an object is not found.
*
* @param key the interface implemented by the requested object
* @param defaultValue value to return if the requested object is not found
* @return the object that implements the given interface,
*         or the given default value if not found
*/
public  T get(Class key, T defaultValue) {
T value = get(key);
if (value != null) {
return value;
} else {
return defaultValue;
}
}
/**
* Returns the SAX parser specified in this parsing context. If a parser
* is not explicitly specified, then one is created using the specified
* or the default SAX parser factory.
*
* @see #getSAXParserFactory()
* @since Apache Tika 0.8
* @return SAX parser
* @throws TikaException if a SAX parser could not be created
*/
public SAXParser getSAXParser() throws TikaException {
SAXParser parser = get(SAXParser.class);
if (parser != null) {
return parser;
} else {
try {
return getSAXParserFactory().newSAXParser();
} catch (ParserConfigurationException e) {
throw new TikaException("Unable to configure a SAX parser", e);
} catch (SAXException e) {
throw new TikaException("Unable to create a SAX parser", e);
}
}
}
/**
* Returns the SAX parser factory specified in this parsing context.
* If a factory is not explicitly specified, then a default factory
* instance is created and returned. The default factory instance is
* configured to be namespace-aware and to use
* {@link XMLConstants#FEATURE_SECURE_PROCESSING secure XML processing}.
*
* @since Apache Tika 0.8
* @return SAX parser factory
*/
public SAXParserFactory getSAXParserFactory() {
SAXParserFactory factory = get(SAXParserFactory.class);
if (factory == null) {
factory = SAXParserFactory.newInstance();
factory.setNamespaceAware(true);
try {
factory.setFeature(
XMLConstants.FEATURE_SECURE_PROCESSING, true);
} catch (ParserConfigurationException e) {
} catch (SAXNotSupportedException e) {
} catch (SAXNotRecognizedException e) {
// TIKA-271: Some XML parsers do not support the
// secure-processing feature, even though it's required by
// JAXP in Java 5. Ignoring the exception is fine here, as
// deployments without this feature are inherently vulnerable
// to XML denial-of-service attacks.
            }
}
return factory;
}
}
　　从该类的源码可以看出，ParseContext类的主要作用是获取XML的SAX解析类SAXParser
　　如果了解JAXP，上面的源码是很容易看懂的，Tika是采用SAX方式解析XML格式文档的，SAXParserFactory为抽象类，具体采用的哪个实现类呢，待分析