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GWT Mini Pattern: Configuration Reader

I’ve written about configuration options to GWT widgets before. Basically, the idea is that you have some configuration that lets the widget change behavior without redeploying or compiling code. In fact, nontechnical users (like designers) can change configuration, if it’s documented. These are the ways I know to specify configuration:

Meta tags

In the page:

<meta content="bar" name="foo" id="foo" />

Updated 4/1/2008, to have id in the meta tag attbute.

In your code:

String var = DOM.getElementProperty(DOM.getElementById("foo"), "content");

You can also request only Boolean and Int:

String var = DOM.getElementPropertyInt(DOM.getElementById("foo"), "content");

This is simple, all browsers ignore these tags, and you can place them anywhere in a page and get them read. However, attributes can only contain strings.

Hidden spans

In the page:

<span id="foo" style="display: none">bar</span>

In your code:

String var = DOM.getInnerHTML(DOM.getElementById("foo"));

This is a good choice if you want configuration to be more structured than what a tag attribute can provide--you can parse the 'var' string further.

Javascript using jsni

<script type="text/javascript">
var ID = 'bar';

And in your code:

private native String getIDAsString()/*-{
if ($wnd.ID == undefined) {
return "";
} else {
return $wnd.ID;

private Integer getID() {
Integer id = new Integer(-1);
try {
id = Integer.valueOf(getIDAsString());
} catch (NumberFormatException ignore) {}
return id;

Integer foo = getID();

This method is great when you have variables that are used by other javascript components that you'd like to leverage for your GWT component, or if you have a really complex configuration that is multiple levels in structure.

Javascript using dictionary

(As outlined here and here.)
In the page:

<script type="text/javascript">
var dictionary = {
foo: "bar"

In your code:

Dictionary theme = Dictionary.getDictionary("dictionary");
String bar = theme.get("foo");

This is good for simple hash datastructures. I haven't tried it, but from the documentation, it doesn't look like it supports anything past String key value pairs, and your module must inherit from

Regardless of your configuration method, I've found myself using a ConfigReader to isolate this logic. It looks something like this:

public class ConfigReader{

private final boolean opt1;
private final String opt2;

public ConfigReader(){
// init opt1 and opt2 using one of the four methods above.

public boolean isOpt1() {
return opt1;

public String getOpt2() {
return opt2;

2 thoughts on “GWT Mini Pattern: Configuration Reader

  1. Bruce says:

    In your meta tags section you need to set the id of the tag, not the name, for your example to work. At least that is what is needed in Firefox.

  2. moore says:

    Bruce, you’re absolutely correct. Let me update the example.

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