20 Sep 2012, 1:32pm
gwt java:

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  • Using GWT’s DateTimeFormat in Server-Side Code

    I was work­ing on some util­ity class to for­mat dates. As the for­mat­ting is the same on server and client the same class should be used on both, server and client. Within the GWT frame­work there is the DateTimeFormat class which seems to be sup­posed to do exactly that.

    But despite being in the shared pack­age (com.google.gwt.i18n.shared.DateTimeFormat) using it in the server-side code causes

    java.lang.UnsupportedOperationException: ERROR: GWT.create() is only usable in client code!  It cannot be called, for example, from server code. If you are running a unit test, check that your test case extends GWTTestCase and that GWT.create() is not called from within an initializer or constructor.

    Hav­ing a look into the code of the DateTimeFormat class (which is part of the shared pack­age of the GWT frame­work, thus can be used on server and client) reveals there is an import of com.google.gwt.i18n.client.LocaleInfo. But this class is part of the client pack­age — thus, it can not be used in the server-side code. It’s unclear to me why this was done like that because it sim­ply can not work by definition…

    Going down a bit fur­ther in the code of the DateTimeFormat class shows that the client pack­age class LocaleInfo is used only once like this:

    private static DateTimeFormatInfo getDefaultDateTimeFormatInfo() {
      // MUSTFIX(jat): implement
      return LocaleInfo.getCurrentLocale().getDateTimeFormatInfo();
    }

    The line is marked as “MUSTFIX” but for some rea­son it has not been fixed yet.
    There is a way to fix this issue that worked for me:

    • Copy the con­tent of DateTimeFormat to a new file in your own code
    • Remove the import of LocaleInfo
    • Chang­ing the fol­low­ing method (start­ing in line 656) like this:
    private static DateTimeFormatInfo getDefaultDateTimeFormatInfo() {
      return new DefaultDateTimeFormatInfo();
    }
    • And use this newly cre­ated class from now on in all your code.

    The fix does not seem to cause any major harm, but as John A. Tam­plin (cf. his com­ment below) clearly pointed out, apply­ing this fix will ren­der all dates using the default locale instead of using the user’s locale. Thus, this fix should be con­sid­ered a hack rather than a patch — but it does the trick until the bug has been fixed officially.

    The hack can be applied quickly — or sim­ply down­load the fixed class here.

    p.s. Unfor­tu­nately, it is not pos­si­ble to just over­write the method in a derived class because it’s a sta­tic method and pri­vate any­way.
    p.p.s. As sug­gested in the com­ments, you might also ini­tial­ize the DateTimeFormat with a new DefaultDateTimeFormatInfo() as the sec­ond para­menter. (Please note that I did not ver­ify this sug­ges­tion) In gen­eral, both ways of fix­ing this issue will cause that the date and time to be for­mated using the default locale rather than the user’s cur­rent locale, unfortunately.

    15 May 2012, 12:08pm
    gwt java:

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  • JUnit-Testing and GAE APIs

    Some issues I encoun­tered when test­ing a new Java library for load­ing mul­ti­ple URLs in par­al­lel on the Google Apps Engine (GAE) (more about that library in another post).

    Here are some of the typ­i­cal errors you might encounter:

    Miss­ing time­out class

    java.lang.NoSuchMethodError: org.mortbay.thread.Timeout

    Con­text menu on project: Prop­er­ties -> Build Path -> Order and Export: move GWT SDK *above* App Engine SDK (cf. here)

    Com­pi­la­tion unit was not seen

    com.google.gwt.junit.JUnitFatalLaunchException: The test class 'com.test.client.MyTest' was not found in module 'com.text.Module'; no compilation unit for that type was seen

    • The test class needs to be within a pack­age that is con­fig­ured in the mod­ule file (*.gwt.xml). You should cre­ate a new source folder (Con­text menu on project -> New -> Source Folder) and cre­ate the whole pack­age struc­ture you use within your project up to client, e.g. com.company.client, and put your GWT tests in it. This way you make sure that the tests are not going to be deployed to GAE later on.
    • If you are test­ing client-side code, your test class needs imple­ment GWTU­nit *and* be run as GWTU­nitTest *not* as JUnitTest ;)

    API pack­age not found

    java.util.concurrent.ExecutionException: com.google.apphosting.api.ApiProxy$CallNotFoundException: The API package 'urlfetch' or call 'Fetch()' was not found.

    The GAE envi­ron­ment has not been initialized.

    • Set up the required libraries for testing:
      • Con­text menu on project -> Prop­er­ties -> Build Path -> Libraries -> Add Vari­able -> Con­fig­ure Vari­ables -> New…: Set “SDK_ROOT” as name and search you disk for “appengine-api-stubs.jar” and copy the part before “/lib/impl” into the text box named “Path”
      • Select “SDK_ROOT” from the pre­vi­ous dia­log, click “Extend…”, unfold lib and impl and select “…labs.jar”, “…stubs.jar”, and “…api.jar”; unfold “lib/testing” and select “…testing.jar” — done, whew.
    • Add fol­low­ing lines to your test class:
      private final LocalServiceTestHelper helper = new LocalServiceTestHelper(new LocalURLFetchServiceTestConfig());
      @Before public void setUp() { helper.setUp(); }
      @After public void tearDown() { helper.tearDown(); }
    • Have a look in com.google.appengine.tools.development.testing to see all the services/APIs avail­able for test­ing and replace LocalURLFetchServiceTestConfig with the one you need.

    I tried to keep it as brief as pos­si­ble, for more details have a look at this page.

    18 Jan 2012, 10:50am
    gwt java:

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  • Sorting Lists in GWT

    Quick one:
    Lists.sort(list, comparator) is not imple­mented in the GAE JVM.
    But, as a replacement/alternative, Collections.sort(list, comparator) is.

    17 Jan 2011, 6:38pm
    gwt jobs:

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  • Testing GWT Application in Virtual Machine

    I am devel­op­ing on a Mac, but to test my GWT appli­ca­tions for cross-browser com­pat­i­bil­ity in Inter­net Explorer I need to use Win­dows, thus I got Win­dows 7 installed using Par­al­lels. Just by the way, to be able to test in dif­fer­ent Inter­net Explorer ver­sion, I am using a pretty handy appli­ca­tion called IETester.
    But try­ing to access local­host with IE in the vir­tual machine did not work. I got a “404 page not found” error instead of see­ing my app run­ning on the local App Engine instance. Obvi­ously, Par­al­lels does not auto­mat­i­cally for­ward local­host requests to OSX and maybe that is actu­ally a good idea security-wise.
    To fix the issue, you need to run Google App Engine on a pub­lic net­work inter­face, or in other words, bind the App Engine server to all avail­able IP addresses. The down side: every­body know­ing your IP address can see the GWT app now, but oth­er­wise you are not allowed to access it in the viru­tal machine as from your OSX’s point of view, that Win­dows machine is “some other guy access­ing from the out­side”, too. To make GAE acces­si­ble from the out­side, add the para­me­ter “-bindAd­dress 0.0.0.0″ when launch­ing you local GAE. Using Eclipse you can achieve that by right click­ing your project -> Run As -> Run Con­fig­u­ra­tions -> Choose “(x)= Argu­ments” tab; add the option to the top most box titled “Pro­gram argu­ments” in the options area (e.g. before “-port 8888″).

    The first part of the list of argu­ments should look some­thing like that:

    -remoteUI "${gwt_remote_ui_server_port}:${unique_id}" -startupUrl GlocalUiPg2.html -logLevel INFO -codeServerPort 9997 -bindAddress 0.0.0.0 -port 8888 ...

    Now, you can access you app using the OSX’s pub­lic IP address. (You can get to know your IP by hav­ing a look at the net­work pref­er­ences panel.) Launch­ing GAE from Eclipse, you will see a dif­fer­ent link (URL) in the “Devel­op­ment Mode” tab now, con­tain­ing the pub­lic IP already. Using that one in, say, your Fire­fox on Mac, it will ask you now whether you want to allow the debug­ger access. That is also due to the fact, that you are now using a pub­lic address, so it is not clear to your local debug server, whether that request came from the same com­puter or some­one else in the network.

    17 Sep 2010, 3:49pm
    gwt java:

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  • Uploading File to Server: Access Denied

    Sim­ple task: upload a file to the server. Achieved so far: upload form works and the file gets trans­ferred to the server.
    But as soon as the file is writ­ten, I get one of that:
    “java.security.AccessControlException: access denied (java.io.FilePermission /some/folder/upload__71c20601_12b1b66bc39__7ffa_00000000.tmp write)“
    I am amazed how much search­ing is required to find some infor­ma­tion about how to mod­ify the file per­mis­sions for the local app engine! And in the end, it turns out that there is an issue with the GAE on Mac but with­out a way to con­fig­ure the local Jetty server to allow write access. :(
    As soon as I deploy the app to a Tom­cat on Linux, it works like a charm!