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Parsing and serializing XML

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*[http://xulplanet.com/references/objref/XMLSerializer.html XMLSerializer] to serialize '''DOM trees to strings or to files''' *[http://xulplanet.com/references/objref/XMLSerializer.html XMLSerializer] to serialize '''DOM trees to strings or to files'''
*[http://xulplanet.com/references/objref/DOMParser.html DOMParser] to parse XML from '''strings into DOM trees''' *[http://xulplanet.com/references/objref/DOMParser.html DOMParser] to parse XML from '''strings into DOM trees'''
-*[http://xulplanet.com/references/objref/XMLHttpRequest.html XMLHttpRequest] to parse XML from '''files into DOM trees'''. Although <code>[http://xulplanet.com/references/objref/DOMParser.html DOMParser]</code> does have a method named <code>[http://xulplanet.com/references/objref/DOMParser.html#method_parseFromStream parseFromStream()]</code>, it's actually easier to [[XMLHttpRequest|use XMLHttpRequest]] which works for remote '''and''' local files.+*[http://xulplanet.com/references/objref/XMLHttpRequest.html XMLHttpRequest] to parse XML from '''files into DOM trees'''. Although <code>DOMParser</code> does have a method named <code>parseFromStream()</code>, it's actually easier to [[XMLHttpRequest|use XMLHttpRequest]] which works for remote '''and''' local files.
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First, create a DOM tree using code [[How to Create a DOM tree| like this]]. If you have already have a DOM tree from using [[XMLHttpRequest]], skip to the end of this section. First, create a DOM tree using code [[How to Create a DOM tree| like this]]. If you have already have a DOM tree from using [[XMLHttpRequest]], skip to the end of this section.
-Now, let's serialize <code>doc</code> &mdash; the DOM tree &mdash; to a file (you can read more about using files in Mozilla [[Dev : Extensions : Example Code : File IO | here]]):+Now, let's serialize <code>doc</code> &mdash; the DOM tree &mdash; to a file (you can read more [[File IO|about using files in Mozilla]]):
<pre> <pre>
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==Serializing XMLHttpRequest objects to files== ==Serializing XMLHttpRequest objects to files==
-If you have already have a DOM tree from using [[XMLHttpRequest]], use the same code as above but replace <code>serializer.serializeToStream(doc, foStream, "")</code> with <code>serializer.serializeToStream(xmlHttpRequest.responseText, foStream, "")</code> where <code>xmlHttpRequest</code> is an instance of [[XMLHttpRequest]].+If you have already have a DOM tree from using [[XMLHttpRequest]], use the same code as above but replace <code>serializer.serializeToStream(doc, foStream, "")</code> with <code>serializer.serializeToStream(xmlHttpRequest.responseText, foStream, "")</code> where <code>xmlHttpRequest</code> is an instance of XMLHttpRequest.
==Parsing strings into DOM trees== ==Parsing strings into DOM trees==
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==Parsing files into DOM trees== ==Parsing files into DOM trees==
===XMLHttpRequest=== ===XMLHttpRequest===
-As was previously mentioned, even though <code>[http://xulplanet.com/references/objref/DOMParser.html DOMParser]</code> does have a method named <code>[http://xulplanet.com/references/objref/DOMParser.html#method_parseFromStream parseFromStream()]</code>, it's easier to use [[XMLHttpRequest]] to parse XML files into DOM trees ([[XMLHttpRequest]] works for both local and remote files). Here is sample code which reads and parses a local XML file into a DOM tree:+As was previously mentioned, even though <code>DOMParser</code> does have a method named <code>parseFromStream()</code>, it's easier to use [[XMLHttpRequest]] to parse XML files into DOM trees (XMLHttpRequest works for both local and remote files). Here is sample code which reads and parses a local XML file into a DOM tree:
<pre> <pre>
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===io.js=== ===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:+If you prefer [[io.js]], this code will also parse a file into a DOM tree. Unlike <code>XMLHttpRequest</code>, it will not work with remote files:
<pre> <pre>
var file = DirIO.get("ProfD"); // %Profile% dir var file = DirIO.get("ProfD"); // %Profile% dir

Revision as of 09:17, 31 March 2005

This page is part of the extension development documentation project.

Ask your questions in MozillaZine Forums. Also try browsing example code.

Note: development documentation is in process of being moved to Mozilla Development Center (MDC).

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:

  • XMLSerializer to serialize DOM trees to strings or to files
  • DOMParser to parse XML from strings into DOM trees
  • XMLHttpRequest to parse XML from files into DOM trees. Although DOMParser does have a method named parseFromStream(), it's actually easier to use XMLHttpRequest which works for remote and local files.


Contents

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. If you have already have a DOM tree from using XMLHttpRequest, skip to the end of this section.

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

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.serializeToStream(doc, foStream, "");   // rememeber, doc is the DOM tree
foStream.close();

Serializing XMLHttpRequest objects to files

If you have already have a DOM tree from using XMLHttpRequest, use the same code as above but replace serializer.serializeToStream(doc, foStream, "") with serializer.serializeToStream(xmlHttpRequest.responseText, foStream, "") where xmlHttpRequest is an instance of XMLHttpRequest.

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 or error message
dump(dom.documentElement.nodeName == "parsererror" ? "error while parsing" : 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 to parse XML files into DOM trees (XMLHttpRequest works for both local and remote files). Here is sample code which reads and parses a local XML file into a DOM tree:

var req = new XMLHttpRequest();
req.open("GET", "chrome://passwdmaker/content/people.xml", false); 
req.send(null);
// print the name of the root element or error message
var dom = req.responseXML;
dump(dom.documentElement.nodeName == "parsererror" ? "error while parsing" : dom.documentElement.nodeName);

req.responseXML is a Document instance.

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, "text/xml");
// print the name of the root element or error message
dump(dom.documentElement.nodeName == "parsererror" ? "error while parsing" : dom.documentElement.nodeName);

Resources

  • Sarissa - Sarissa is a cross-browser ECMAScript library for client side XML manipulation, including loading XML from URLs or strings, performing XSLT transformations, XPath queries and more. Supported: Gecko (Mozilla, Firefox etc), IE, KHTML (Konqueror, Safari). If you're writing JavaScript that is used in both XUL applications and HTML pages, and the HTML pages may be viewed in non-Gecko-based applications (such as Internet Explorer, Opera, Konqueror, Safari), you should consider using Sarissa to parse and/or serialize XML. Note: Do not create a DOM object using document.implementation.createDocument() and then use Sarissa classes and methods to manipulate that object. It will not work. You must use Sarissa to create the initial DOM object.
  • Parsing and Serializing XML at XulPlanet