As described earlier, XOM does not retain insignificant whitespace when representing XML documents. This is in keeping with one of XOM’s design goals—to disregard anything that has no syntactic significance in XML. (Another example of this is how text is treated identically whether created using character entities, CDATA sections, or regular characters.)
Today’s next project is the DomainWriter application, which adds a comment to the beginning of the XML document feeds2.rss and serializes it with indented lines, producing the version shown in Listing 19.5.
The Serializer class in nu.xom offers control over how an XML document is formatted when it is displayed or stored serially. Indentation, character encoding, line breaks, and other formatting are established by objects of this class.
A Serializer object can be created by specifying an output stream and character encoding as arguments to the constructor:
File inFile = new File(arguments[0]);
FileOutputStream fos = new FileOutputStream(“new_” +
inFile.getName());
Serializer output = new Serializer(fos, “ISO-8859-1”);
These statements serialize a file using the ISO-8859-1 character encoding. The file is given a name based on a command-line argument. Serializer supports 20 encodings, including ISO-10646-UCS-2, ISO-8859-1 through
ISO-8859-10, ISO-8859-13 through ISO-8859-16, UTF-8, and UTF-16. There’s also a Serializer() constructor that takes only an output stream as an argument; this uses the UTF-8 encoding by default.
Indentation is set by calling the serializer’s setIndentation() method with an integer argument specifying the number of spaces:
output.setIndentation(2);
An entire XML document is written to the serializer destination by calling the serializer’s write() method with the document as an argument:
output.write(doc);
The DomainWriter application inserts a comment atop the XML document instead of appending it at the end of a parent node’s children. This requires another method of the parent node, insertChild(), which is called with two arguments—the element to add and the integer position of the insertion:
Builder builder = new Builder();
Document doc = builder.build(arguments[0]);
Comment timestamp = new Comment(“File created “ +
new java.util.Date());
doc.insertChild(timestamp, 0);
The comment is placed at position 0 atop the document, moving the domains tag down one line but remaining below the XML declaration.
Listing 19.6 contains the source code of the application.
The DomainWriter application takes an XML filename as a command-line argument when run:
java DomainWriter feeds2.rss
This command produces a file called new_feeds2.rss that contains an indented copy of the XML document with a time stamp inserted as a comment.
