Parsing and serializing XML

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Revision as of 23:25, 10 March 2005 by Grimholtz (talk | contribs) (made less cryptic for newbies per asqueella request)
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Mozilla doesn't support the W3C's Document Object Model Load and Save at this moment, so the easiest way to serialize and deserialize DOM trees is to use the following Mozilla-specific interfaces:


Serializing DOM trees to strings

First, create a DOM tree using code like this.

Now, let's serialize doc — the DOM tree — to a string:

var serializer = new XMLSerializer();
var xml = serializer.serializeToString(doc);

Serializing DOM trees to files

First, create a DOM tree using code like this.

Now, let's serialize doc — the DOM tree — to a file (you can read more about using files in Mozilla here):

var serializer = new XMLSerializer();
var foStream = Components.classes["@mozilla.org/network/file-output-stream;1"]
               .createInstance(Components.interfaces.nsIFileOutputStream);
var file = Components.classes["@mozilla.org/file/directory_service;1"]
           .getService(Components.interfaces.nsIProperties)
           .get("ProfD", Components.interfaces.nsIFile); // get profile folder
file.append("extensions");   // extensions sub-directory
file.append("{5872365E-67D1-4AFD-9480-FD293BEBD20D}");   // GUID of your extension
file.append("myXMLFile.xml");   // filename
foStream.init(file, 0x02 | 0x08 | 0x20, 0664, 0);   // write, create, truncate
serializer.serializeToFile(doc, foStream, "IS0-8859-1");   // rememeber, doc is the DOM tree
foStream.close();

Parsing strings into DOM trees

var theString='<a id="a"><b id="b">hey!</b></a>';
var parser = new DOMParser();
var dom = parser.parseFromString(theString, "text/xml");
// print the name of the root element
dump(dom.documentElement.nodeName);

Parsing files into DOM trees

XMLHttpRequest

As was previously mentioned, even though DOMParser does have a method named parseFromStream(), it's easier to use XMLHttpRequest. That's what we'll demonstrate here.

First, read the local or remote XML file into a string:

var req = new XMLHttpRequest();
req.open("foo-bar!", "chrome://passwdmaker/content/people.xml", false); 
req.send(null);

The foo-bar argument of XMLHttpRequest.open() specifies the HTTP method to use if the URL (the second argument) is an HTTP(S) URL. Since we're using a chrome:// URL, the first argument to XMLHttpRequest.open() is ignored. You should change this to an HTTP(S) method (e.g., GET/POST) if using an HTTP(S) URL.

Now that we have the XML as a string (in req.responseText), we can use the code similar to that in Parsing strings into DOM trees to get the XML into a DOM tree:

var parser = new DOMParser();
var dom = parser.parseFromString(req.responseText, "text/xml");
// print the name of the root element
dump(dom.documentElement.nodeName);

io.js

If you prefer io.js, this code will also parse a file into a DOM tree. Unlike XMLHttpRequest, it will not work with remote files:

var file = DirIO.get("ProfD"); // %Profile% dir
file.append("extensions");
file.append("{5872365E-67D1-4AFD-9480-FD293BEBD20D}");
file.append("people.xml");
var fileContents = FileIO.read(file);
var domParser = new DOMParser();
var doc = domParser.parseFromString(fileContents);
// print the name of the root element
dump(doc.documentElement.nodeName);