I'm at the beginning/middle of a project that we chose to implement using GWT. Has anyone encountered any major pitfalls in using GWT (and GWT-EXT) that were unable to be overcome? How about from a performance perspective?
A couple things that we've seen/heard already include:
Looking for any additional feedback on these items as well. Thanks!
No major pitfalls that I haven't been able to overcome easily. Use hosted mode heavily. As you are using GWT-ext you will almost never need to touch CSS yourself unless you want to tweak the out of the box look.
My recommendation is to use a GWT "native" widget over a library one where they are close in features.
Re search engine indexing: yes the site will not have navigable URLs normally (unless you are only adding widgets to elements of a regular web site). You can do history back/forward functionality though.
I'll start by saying that I'm a massive GWT fan, but yes there are many pitfalls, but most if not all we were able to overcome:
Problem: Long compile times, as your project grows so does the amount of time it takes to compile it. I've heard of reports of 20 minute compiles, but mine are on average about 1 minute.
Solution: Split your code into seperate modules, and tell ant to only build it when it's changed. Also while developing, you can massively speed up compile times by only building for one browser. You can do this by putting this into your .gwt.xml file:
<set-property name="user.agent" value="gecko1_8" />
Where gecko1_8 is Firefox 2+, ie6 is IE, etc.
Problem: Hosted mode is very slow (on OS X at least) and does not come close to matching the 'live' changes you get when you edit things like JSPs or Rails pages and hit refresh in your browser.
Solution: You can give the hosted mode more memory (I generally got for 512M) but it's still slow, I've found once you get good enough with GWT you stop using this. You make a large chunk of changes, then compile for just one browser (generally 20s worth of compile) and then just hit refresh in your browser.
Update: With GWT 2.0+ this is no longer an issue, because you use the new 'Development Mode'. It basically means you can run code directly in your browser of choice, so no loss of speed, plus you can firebug/inspect it, etc.
http://code.google.com/p/google-web-toolkit/wiki/UsingOOPHM
Problem: GWT code is java, and has a different mentality to laying out a HTML page, which makes taking a HTML design and turning it into GWT harder
Solution: Again you get used to this, but unfortunately converting a HTML design to a GWT design is always going to be slower than doing something like converting a HTML design to a JSP page.
Problem: GWT takes a bit of getting your head around, and is not yet mainstream. Meaning that most developers that join your team or maintain your code will have to learn it from scratch
Solution: It remains to be seen if GWT will take off, but if you're a company in control of who you hire, then you can always choose people that either know GWT or want to learn it.
Problem: GWT is a sledgehammer compared to something like jquery or just plain javascript. It takes a lot more setup to get it happening than just including a JS file.
Solution: Use libraries like jquery for smaller, simple tasks that are suited to those. Use GWT when you want to build something truly complex in AJAX, or where you need to pass your data back and forth via the RPC mechanism.
Problem: Sometimes in order to populate your GWT page, you need to make a server call when the page first loads. It can be annoying for the user to sit there and watch a loading symbol while you fetch the data you need.
Solution: In the case of a JSP page, your page was already rendered by the server before becoming HTML, so you can actually make all your GWT calls then, and pre-load them onto the page, for an instant load. See here for details:
Speed up Page Loading by pre-serializing your GWT calls
I've never had any problems CSS styling my widgets, out of the box, custom or otherwise, so I don't know what you mean by that being a pitfall?
As for performance, I've always found that once compiled GWT code is fast, and AJAX calls are nearly always smaller than doing a whole page refresh, but that's not really unique to GWT, though the native RPC packets that you get if you use a JAVA back end are pretty compact.
One major pitfall is that sometimes you need to explicitly assign an id to what ultimately becomes an HTML element to be able to use certain CSS styles. For instance: a GWT TabPanel will only do :hover over tabBarItems when the tabBar of the tabPanel has been assigned an id and you specify a :hover on that elementId.
I wrote about some other disadvantages of GWT elsewhere, but they are already covered by rustyshelfs answer :).
I used GWT and GWT-ext together on a project a while ago. I found the experience quite smooth as web development goes, but my advice would be this:
Don't mix GWT native widgets with EXT widgets. It's confusing as hell, since usually the names are the same (GWT.Button or GWText.Button?)
One thing that happened to me that really made the code more complex than I'd like, was that I wanted a Panel that was a) dynamically updatable b) cascadable
GWT native panels are dynamic, Ext panels are cascadable. Solution? A GWT.VerticalPanel wrapping a GWTExt Panel... Chaos. :)
But hey, it works. ;)
I'm working on a project right now that uses EXT GWT (GXT) not to be confused with GWT EXT. There is a difference, EXT GWT is the one that is actually produced by the company that wrote ExtJS the javascript library. GWT EXT is a GWT wrapper around the ExtJS library. GXT is native GWT.
Anyways, GXT is still somewhat immature and lacks a solid community that I feel GWT EXT has. However, the future is with GXT, as it's native GWT and actually developed by the company that made ExtJS. GWT EXT is somewhat crippled as the license changed on the ExtJS library, thus slowing the development of GWT EXT.
Overall, I think GWT/GXT is a good solution for developing a web application. I actually quite like hosted mode for development, it makes things quick and easy. You also get the benefit of being able to debug your code as well. Unit testings with JUnit is pretty solid as well. I haven't yet seen a great JavaScript unit testing framework that I felt was mature enough for testing an enterprise application.
For more information on GWT EXT: http://gwt-ext.com/
For more information on EXT GWT (GXT): http://extjs.com/products/gxt/
Pitfalls that we've run into:
While you can get a lot of mileage from using something like GWT EXT, any time you use this sort of thin veneer on top of a JavaScript library, you lose the ability to debug. More than once I've bashed my head on the desk because I cannot inspect (inside my IntelliJ debugger) what's happening in the GWT EXT table class... All you can see is that it's a JavaScriptObject. This makes it quite difficult to figure out what's gone wrong...
Not having someone on your team who knows CSS. From my experience, it didn't matter that the person wasn't expert...it's enough that he has some good working knowledge, and knows the right terms to google when necessary.
Debugging across browsers. Keep an eye on Out of Process Hosted Mode[1][2][3], hopefully coming in GWT 1.6... For now, you just have to get things good with hosted mode, then use the "Compile/Browse" button, where you can play with other browsers. For me, working on Windows, this means I can view my work in FireFox, and use FireBug to help tweak and make things better.
IE6. It's amazing how different IE 6 will render things. I've taken the approach of applying a style to the outermost "viewport" according to the browser so that I can have CSS rules like:
.my-style { /* stuff that works most everywhere */ }
.msie6 .my-style { /* "override" so that styles work on IE 6 */
Finally, make sure you use an editor that helps you. I use IntelliJ -- it's got lots of GWT smarts. E.g., If I try to use a class that isn't handled by the JRE emulation, it lets me know; if I specify a style for a widget, and I haven't defined that style yet, the code gets the little red squiggly... Or, when looking at the CSS, it will tell me when I've specified conflicting attributes in a single rule. (I haven't tried it yet, but I understand that version 8 has even better GWT support, like keeping the "local" and "async" RPC interfaces and implementations in sync.)
[1]http://code.google.com/p/google-web-toolkit/wiki/DesignOOPHM
[3]http://groups.google.com/group/Google-Web-Toolkit/browse_thread/thread/1203bb0f1eb36ad5
We've had a very hard time marrying our GWT codebase with HTML web templates that we got from a web designer (static HTML pages with specific div ids that we wanted GWT to manage). At least back when we used it, we couldn't get GWT to integrate with parts of our website that were not coded in GWT. We had it working eventually, but it was a big hack.
I second the comment from ykagano, the biggest disadvantage is losing the V in MVC. Although you can separate the true ui class from the rest of your client side code, you cannot easily use an HTML page generated by a graphic/web designer. This means you need a developer to translate HTML into java.
Get a wysiwyg ui editor, it will save you lots of time. I use GWTDesigner.
The biggest upside of GWT is being able to forget about cross browser issues. Its not 100% but takes almost all that pain away. Combined with the benefit of hosted mode debugging (as opposed to Firebug which is excellent but not the same as a java debugger) it gives the developer a huge advantage in generating complex ajax apps.
Oh and its fast at runtime, especially if you use a gzip filter.
Slightly off-topic, but the #gwt channel on irc is very helpful, in-case you have a persistent problem.
I'll add some points to the ones already mentioned:
TextField fname, faddress; ... fname.setText(person.getName()); faddress.setText(person.getAddress()); ...
IMHO, GWT is missing a framework that has out of the box support for all of the issues mentioned on this 'thread'.
We have been working with gwt for almost 2 years. We have learned a lot of lessons. Here is what we think:
1) Dont use third party widget libraries especially gwt-ext. It will kill your debugging, development and runtime performance. If you have questions about how this happens, contact me directly.
2) Use gwt to only fill in the dynamic parts of your apps. So if you have some complex user interactions with lots of fields. However, don't use the panels that come with it. Take your existing stock designer supplied pages. Carve out the areas that will contain the controls for your app. Attach these controls to the page within onModuleLoad(). This way you can use the standard pages from your designer and also do all the styling outside the gwt.
3) Don't build the entire app as one standard page that then dynamically builds all the pieces. If you do what I suggest in item 2, this won't happen anyway. If you build everything dynamically you will kill performance and consume huge amounts of memory for medium to large apps. Also, if you do what I am suggesting, the back button will work great, so will search engine indexing etc.
The other commenters also had some good suggestions. The rule of thumb i use is to create pages like you were doing a standard web page. Then carve out the pieces that need to be dynamic. Replace them with elements that have id's and then use RootPanel.get( id ).add( widget ) to fill those areas in.
I have done a lot of work on GWT recently, and this is wht i have to say:
I do not know much about GWT-EXT, But i too am of the belief that there is no need to include Third party libraries.
Best of luck on your decision :)
GWT 2.0, which is supposed to come out sometime in the next few months, solves a lot of the issues discussed.
Re-using RPC service objects.
It causes race conditions with symptoms that look like the app hanging.
GWT is pretty straight-forward and intuitive.
Especially with the release of UIBinder to allow GWT widgets to be laid out in XML and then coded-behind in Java.
So if you have used other Ajax or Flash design tools, or Silverlight, etc, GWT is very easy to learn.
The major hurdle, if not pitfall, is GWT RPC. The very reason you wish to use GWT is because of GWT async RPC. Otherwise, why not just rely on css to format your page?
GWT RPC is that element that allows your server to refresh data on your server without having to refresh the page. This is an absolute requirement for pages such as stock performance monitoring (or the current national and public debt of the US or the number of unborn babies aborted worldwide by the second).
GWT RPC takes some effort to understand but given a few hours, it should come all clear.
Above that, after putting in some effort to learn GWT RPC, you finally discover that you cannot use JSPs as the service component for RPC, unless ... I have an 8 part (I think) series on my blog on how to use JSP as the GWT RPC servicer. However, since you had not asked for answers but just issues, I shall desist from advertising my blog.
So. I very much believe that the worst roadblocks/pitfalls to using GWT is finding out how to properly deploy GWT async RPC and how to enable it to use JSP servicers.
Not "unable to be overcome" but a bit of a pain for something basic.
Date handling:
GWT uses the deprecated java.util.Date which can lead to unexpected behaviour when dealing with dates on the client side. java.util.Calendar is not supported by GWT. More info here.
Related problem examples: