Java Enterprise Best Practices

Use the InputSource Class Correctly

When using the SAX API, all input begins with the org.xml.sax.InputSource class. This is a class that allows the specification of an input (e.g., a file or I/O stream), as well as a public and system ID. SAX then extracts this information from the InputSource at parse time and is able to resolve external entities and other document source-specific resources.

In fact, SAX uses the InputSource class even when you do not. Consider the code fragment in Example 5-6, which uses JAXP to initiate a SAX parse.

Example 5-6. Using JAXP to initiate a SAX parse

import java.io.*;
import java.xml.parsers.*;
   
File myFile = ...
DefaultHandler myHandler = ...
   
SAXParserFactory spf = SAXParserFactory.newInstance(  );
SAXParser parser = spf.newSAXParser(  );
   
parser.parse(myFile, myHandler);

Even though a java.io.File is passed in to the SAXParser parse( ) method, this is converted to a SAX InputSource before being handed off to the underlying SAX implementation. That’s because this JAXP code will eventually hand off its unparsed data to the org.xml.sax.XMLReader class, which offers only the following two signatures for its parse( ) method:

public void parse(InputSource inputSource);
public void parse(String systemID);

You might think the second method is easier, but most SAX implementations actually turn around and convert the string-based system ID into an InputSource and recall the first parse( ) method. Put succinctly, all roads lead to the parse( ) method ...