Recipe 21.6 Generating Your Own XML with DOM

Problem

You want to generate your own XML files or modify existing documents.

Solution

Use DOM or JDOM; parse or create the document and call its write method.

Discussion

Sun's XmlDocument class has a write( ) method that can be called with either an OutputStream or a Writer. To use it, create an XML document object using the XmlDocument constructor. Create nodes, append them into the tree, and then call the document's write( ) method. For example, suppose you want to generate a poem in XML. Running the program and letting the XML appear on the standard output might look something like this:

$ java DocWrite <?xml version="1.0" encoding="UTF-8"?> <Poem>   <Stanza>     <Line>Once, upon a midnight dreary</Line>     <Line>While I pondered, weak and weary</Line>   </Stanza> </Poem> $

The code for this is fairly short; see Example 21-9 for the code using DOM. Code for using JDOM is similar; see DocWriteJDOM.java in the online source code.

Example 21-9. DocWriteDOM.java

import java.io.IOException; import javax.xml.parsers.DocumentBuilder; import javax.xml.parsers.DocumentBuilderFactory; import org.w3c.dom.Document; import org.w3c.dom.Node; /** Make up and write an XML document, using DOM  * UPDATED FOR JAXP.  * @author Ian Darwin, http://www.darwinsys.com/  * @version $Id: ch21.xml,v 1.5 2004/05/04 20:13:38 ian Exp $  */ public class DocWriteDOM {     public static void main(String[] av) throws IOException {         DocWriteDOM dw = new DocWriteDOM( );         Document doc = dw.makeDoc( );         // Sadly, the write( ) method is not in the DOM spec, so we         // have to cast the Document to its implementing class         // in order to call the Write method.         //         // WARNING         //         // This code therefore depends upon the particular         // parser implementation.         //         ((org.apache.crimson.tree.XmlDocument)doc).write(System.out);     }     /** Generate the XML document */     protected Document makeDoc( ) {         try {             DocumentBuilderFactory fact = DocumentBuilderFactory.newInstance( );             DocumentBuilder parser = fact.newDocumentBuilder( );             Document doc = parser.newDocument( );             Node root = doc.createElement("Poem");             doc.appendChild(root);             Node stanza = doc.createElement("Stanza");             root.appendChild(stanza);                          Node line = doc.createElement("Line");             stanza.appendChild(line);             line.appendChild(doc.createTextNode("Once, upon a midnight dreary"));             line = doc.createElement("Line");             stanza.appendChild(line);             line.appendChild(doc.createTextNode("While I pondered, weak and weary"));             return doc;         } catch (Exception ex) {             System.err.println("+============================+");             System.err.println("|        XML Error           |");             System.err.println("+============================+");             System.err.println(ex.getClass( ));             System.err.println(ex.getMessage( ));             System.err.println("+============================+");             return null;         }     } }

A more complete program would create an output file and have better error reporting. It would also have more lines of the poem than I can remember.

Sun's XmlDocument class is not a committed part of the standard, which is why the code casts the object to org.apache.crimson.tree.XmlDocument before calling its write method. However, other vendors' APIs have similar functionality.