Add nodes to an xml at runtime?

Question

I am writing an application that must update parts of an already existing xml file based on a set of files in a directory. An example of this xml file can be seen below:

http://izpack.org/documentation/sample-install-definition.html

In the below scope a list of files is added and its specified if they should be "parsable" (used for parameter substitution):

  <packs>
    <pack name="Main Application" required="yes" installGroups="New Application" >
          <file src="post-install-tasks.bat" targetdir="$INSTALL_PATH"/>
          <file src="build.xml" targetdir="$INSTALL_PATH"/>
          <parsable targetfile="$INSTALL_PATH/post-install-tasks.bat"/>
          <parsable targetfile="$INSTALL_PATH/build.xml"/>
    </pack>
  </packs>

Now the number of files that must be added to this scope can change each time the application is run. To make this possible I have considered the following approach:

1) Read the whole xml into a org.w3c.dom.*; Document and add nodes based on result from reading the directory.

2) Somehow add the content from a .properties file to the scope. This way its possible to update the filelist without recompiling the code.

3) ??

Any suggestions on a good approach to this kind of task?

Answer 1

3) Overwrite the old file with your new, modified version. The DOM parsers keep comments intact, but you could end up with formatting differences. In order to write to a file, do:

Source source = new DOMSource(doc);
File file = new File(filename);
Result result = new StreamResult(file); 
Transformer xformer = TransformerFactory.newInstance().newTransformer();
xformer.transform(source, result); 

Answer 2

if there's a chance that your XML configuration might be of significant size, then it is really not good to go ahead with a DOM based approach [due to the associated memory footprint of loading a large XML document]

you should take a look at StaX. it has a highly optimised approach for both parsing and writing XML documents.