25 Sep 2014, 7:10pm
linux:

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  • Setting up a linux server to forward all incoming mails

    Typ­i­cal thing when hav­ing a new site up: you want to get whatever@yourdomain.com to end up in you nor­mal inbox, say Gmail.

    Here are the steps!
    Note: If you are logged in as root, you do not need to use “sudo” in front of each command.

    Prepa­ra­tions

    It’s rec­om­mended to have a user account to receive the mail other than root.
    So either choose a user you have cre­ated already or cre­ate a new one:

    sudo adduser [username]

    Does your provider require you to use an SMTP relay? (check the doc­u­men­ta­tion, or ask). You need to know this to continue.

    Install post­fix

    Post­fix is a soft­ware pack­age, a MTA, it han­dles incom­ing mail and forwarding.

    sudo apt-get install postfix

    And answer all con­fig­u­ra­tion ques­tions as below:
    Server con­fig­u­ra­tion type: If you use an SMTP relay, choose “Inter­net with smarthost”, oth­er­wise “Inter­net“
    Sys­tem mail name: [yourdomain.com] (no sub­do­main)
    SMTP relay host: [smtp.yourprivider.com] (only show­ing if you chose “Inter­net with smarthost”)
    Root and post­mas­ter mail recip­i­ent: The created/chosen before (not root)
    Other des­ti­na­tions to accept mail for: keep the sug­gested defaults and add in front [yourdomain.com] and a space
    Force syn­chro­nous updates on mail queue: no
    Local net­works: keep sug­gested
    Use proc­mail for local deliv­ery?: yes
    Mail­box size limit: 0
    Local address exten­sion char­ac­ter: +
    Inter­net pro­to­cols to use: all

    Man­ual configuration

    All edits with sudo if you not logged in as root.
    Edit /etc/postfix/main.cf add fol­low­ing two lines to the end

    virtual_alias_domains = [yourdomain.com]
    virtual_alias_maps = hash:/etc/postfix/virtual

    Create/edit /etc/postfix/virtual and add

    @[yourdomain.com]    [your.email.address@somewhere.com]

    Finally, after edit­ing this file call

    sudo postmap /etc/postfix/virtual

    so that postmap actu­ally applies your changes.

    Notes

    If you for­ward to Gmail, do not use the same address to send test mails that the mails will be for­warded to — Gmail will silently ignore/delete mail where the sender and recip­i­ent are the same and you will think the for­ward­ing does not work.

    26 Dec 2013, 12:25pm
    linux:

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  • Scale images for the web — quickly

    Start­ing Gimp just to scale down some pho­tos to send them by mail? Meh.
    How about mark them, right-click, “Send To” -> “Scale for web”?
    No prob­lemo:
    First, get a tool to scale images:

    sudo apt-get install imagemagick

    Now, cre­ate a script that takes a list of images as input, scales them down, and stores them with a pre­fixed file name. Go!

    #!/bin/bash
    pwd > ~/f0.txt
    echo "$@" > ~/f1.txt
    for file in $@
    do
    	convert "$file" -quality 50 -resize 1024x768 "${file%/*}/web-${file##*/}"
    done

    Make sure we chmod +x the script file we just cre­ated.
    Next, let’s inte­grate it into “Send To”. (This is an exam­ple for Thu­nar)
    Cre­ate a .desktop file in the sendto folder, e.g. /usr/share/Thunar/sendto/scale-for-web.desktop with fol­low­ing content:

    # Scale images for the web
    [Desktop Entry]
    Type=Application
    Version=1.0
    Encoding=UTF-8
    TryExec=scale-for-web
    Exec=scale-for-web %F
    Icon=
    Name=Scale for the web
    MimeType=image/jpeg;image/jpg;image/png
    

    Replace both scale-for-web with the name you gave to your script file. Is the script’s folder in $PATH? No idea? Then just put the entire path+filename.
    Now, open Thu­nar, select some images (Jpeg or Png), right-click, “Send To” -> “Scale for the web”, wait a few sec­onds and you’ll see web-....jpg files appear­ing in the same folder. :)

    Ref­er­ences: how to scale images with imageMag­ick, extract path seg­ments, more details on string manipulation

    14 Dec 2013, 11:03pm
    javascript:

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  • Hash in JS

    Gen­er­at­ing hashes from strings is a very handy thing to have. Sur­pris­ingly, in JavaScript, an arithmetic-operation-based algo­rithm is about *three times* faster than one using bit-wise oper­a­tors–see for your­self. I sug­gested to add the most per­for­mant method as hash method to underscore.string.js.

    So much about state­ments on stack­over­flow like

    The hash << 5 - hash is the same as hash * 31 + char but a LOT faster.

    (cf. here)

    In times of inter­preted lan­guages and vir­tual machines one should recon­sider before apply­ing the same old rules again.

    p.s. If you know about alter­na­tive algorithms/implementations, please add them to the test and leave a com­ment here, I’m curi­ous to see what else there is. Btw. I was very sur­prised that the neat reduce-based ver­sion failed so miserably.

    7 Oct 2013, 10:07am
    javascript:

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  • Callback Method for Twitter’s Typeahead

    When you start using Twitter’s typea­head, e.g. because you switched from Boot­strap 2.3 to 3.0, you will notice that it is NOT a sim­ple drop-in replace­ment for Bootstrap’s orig­i­nal typea­head!
    Before, you gen­er­ated the sug­ges­tions shown to the user by imple­ment­ing a call­back method while cre­at­ing the typea­head like this:

    $(field).typeahead({
      source: function(query, process) { 
        ... return a list of suggestions (see doc for details) 
      }
    });

    Since ver­sion 3, Boot­strap does not pro­vide its own typea­head any more, instead it is using Twitter’s own imple­men­ta­tion which seems to be a good choice at least on the long run. But it does not pro­vide any mean for defin­ing a call­back method to pro­vide the sug­ges­tions — no clue why.
    Instead you can pro­vide a pre­de­fined array locally, a pre­de­fined array that will be loaded on start-up, or a remote ser­vice defined by a URL.
    You will find sev­eral good exam­ples of why you need a call­back method sometimes.

    • You want/have to use a Javascript library to access the service.
    • There is no data­base for the sug­ges­tions, they a gen­er­ated on the fly, e.g.if you want to sug­gest sen­tence com­ple­tion while the user types.
    • You are using Meteor’s col­lec­tions hold­ing your sug­ges­tions, thus, there is no URL you could point to.

    But tak­ing a look into the inter­nals revealed fol­low­ing solu­tion: com­pletely by-pass the inter­nal sug­ges­tion aggre­ga­tion of Twitter’s typea­head by replac­ing the getSuggestions(query, callback) method of the first dataset, which we defined by local: [];.

    (t = $("field")).typeahead({ local: [] });
    t.data("ttView").datasets[0].getSuggestions = function(query, callback) {
      var suggestions = ... gather your suggestions here ...
      var data = [];
      for (suggestion in suggestions) { data.push(this._transformDatum(suggestion)); }
      callback(data)
    }

    (Trans­lated from Cof­fee­script on-the-fly — con­sider as a draft than an out-of-the-box solution.)

    Happy hack­ing. :)

    p.s. for Meteor users: The call­back breaks each time the tem­plate gets re-rendered — despite that you use the pack­age preserve-inputs or <#constant> due to a bug. Some­how, con­stant areas and that par­tic­u­lar pack­age do not get along with each other. Solu­tion: removed the pack­age and use con­stant areas around typea­head input fields works. This should be fixed as soon as the new tem­plate engine gets rolled out.

    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.

    2 Jun 2012, 7:32pm
    gwt:

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  • How to Use JQuery in GWT

    After adding the JQuery script to your project HTML file’s header section

    <script src="http://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js" type="text/javascript"></script>

    You will be able to use JQuery in native (JSNI) meth­ods by prepend­ing $wnd., e.g.:

    private native void someMethod() /*-{
    	$wnd.$(function() {
    		$wnd.$('#somediv').doSomething();
    	});
    }-*/;

    With­out $wnd. you will end up with fol­low­ing error: com.google.gwt.core.client.JavaScriptException: (ReferenceError): $ is not defined

    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.

    26 Apr 2012, 9:58am
    gwt java:

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  • Multiple Projects and GWT

    When work­ing on sev­eral large scale projects (in Eclipse), it’s con­ve­nient and of course more effi­cient to share and reuse code via com­mon libraries. While those are in an early stage they need to be changed a lot and there­fore it’s handy to link projects in instead of cre­at­ing new jars each time the library has been updated.
    Unfor­tu­nately, this stan­dard approach for Java devel­op­ment in Eclipse does not work that straight for­ward as with plain old Java projects, it requires three steps in total:

    1. Link the library project to all rel­e­vant projects (“Project Pref­er­ences” -> “Java Build Path” -> “Projects” -> “Add…”)
    2. Then, add the client-side code of the library (by adding it as a mod­ule.) There­fore, edit the gwt.xml of your appli­ca­tion and add for exam­ple <inherits name="net.svenbuschbeck.gwt.lib.SuperLib "/> where Super­Lib is the file name of the gwt.xml file in you library project and before that is the pack­age it lies in.
    3. Add the code to the project by link­ing a source folder. Unfor­tu­nately, this is required if you do not want to write an Ant script to com­pile your appli­ca­tion. (If you pre­fer Ant check this out) I don’t like the idea of using such a script because if you for­get to run it each time you make changes, you will end up in confusion—let’s go for the con­ve­nient, auto­matic way then.
      1. Add a folder to your appli­ca­tion project; open the “advanced” sec­tion in the folder cre­ation dia­log, select “Link to alter­nate loca­tion” and pick the source folder (usu­ally “src”) of your library project. (Hint: if you work within a team using a ver­sion­ing sys­tem, you can cre­ate a vari­able for that folder and use this instead. This way, each of your col­leagues can put the library project in a dif­fer­ent folder and accom­mo­date for that by adjust­ing the vari­able :) )
      2. Right click the folder, “Build Path” -> “Use as Source Folder”. Done.

    Sur­pris­ingly, the GWT plu­gin for Eclipse does not honor the project link­ing, thus all the ref­er­ences need to be made explicit or you will end up with lots of the fol­low­ing: ClassNotFoundException.

    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.

    28 Feb 2011, 11:10pm
    gwt java:

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  • How to Execute Code When the GWT Application Is Going Down

    My goal was to store the UI state of my appli­ca­tion just before it gets ter­mi­nated to be able to restore it next time the way the user left it the other day.

    I tried to add an addAttachHandler to the RootPanel to get informed about the root panel get­ting detached from the DOM so that I can final­ize my appli­ca­tion. Sur­pris­ingly, that does not work in Chrome (tested Chrome and Fire­fox only).

    But besides that this sounds like a bug to me, I found the “proper” way of doing things before the appli­ca­tion ends:

    Window.addWindowClosingHandler(new Window.ClosingHandler() {
    	@Override public void onWindowClosing(ClosingEvent event) { ... } 
    });

    In the end, I think some­thing like Document.addUnloadHandler would be more sug­ges­tive… clos­ing the win­dow or reload­ing a page is both exit­ing the appli­ca­tion by unload­ing the DOM — not clos­ing the window.

    18 Feb 2011, 1:27pm
    gwt:

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  • Disable an Anchor in GWT

    Unex­pect­edly, call­ing setEnabled(false) does not pre­vent a link/anchor from being clicked. That means, the click events still get trig­gered.
    The rea­son is more or less a bug in GWT as it updates the list of events that are going to be trig­gered only at the moment when it gets attached to the DOM (Btw, in GWT, this process is called to sink and to unsink events, where the for­mer enables a spe­cific event to be trig­gered and the lat­ter dis­ables it).
    I found a workaround by cre­at­ing my own Anchor class and forc­ing the under­ly­ing GWT Anchor to update the list of events to be sunk.

    ...
    import com.google.gwt.event.dom.client.ClickHandler;
    import com.google.gwt.user.client.Event;
    
    public class Anchor extends com.google.gwt.user.client.ui.Anchor {
    
    	@Override public void setEnabled(boolean enabled) {
    		super.setEnabled(enabled);
    		if (isAttached()) {
    			onDetach();
    			if (enabled) {
    				sinkEvents(Event.ONCLICK);
    			} else {
    				unsinkEvents(Event.ONCLICK);
    			}
    			onAttach();
    		}
    	}
    
    	@Override protected void onLoad() {
    		super.onLoad();
    		if (isEnabled()) {
    			sinkEvents(Event.ONCLICK);
    		} else {
    			unsinkEvents(Event.ONCLICK);
    		}
    	}
    }

    Note the onLoad method, it sets up the state when the wid­get gets attached to the DOM the first time. It is required because setEnabled() could have been called before the anchor got attached.

    If you encoun­tered the same issue, please vote for this bug report.

    7 Feb 2011, 2:58pm
    java:

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  • Java Cookies from the Future Past

    While work­ing with cook­ies in Java/GWT and thus—to set the expire date—with Date, I found a doubt­ful Java behavior.

    My goal was to set a cookie to expire in about one month from today like this:

    Date expires = new Date(new Date().getTime() + 1000 * 60 * 60 * 24 * 30);
    Cookies.setCookie("myCookie", "myData", expires);

    And kept won­der­ing why the cookie never got stored.

    And finally cre­ated a sim­ple test case like this:

    Date today = new Date();
    Date tomorrow = new Date(today.getTime() + 1000 * 60 * 60 * 24);
    Date nextMonth = new Date(today.getTime() + 1000 * 60 * 60 * 24 * 30);

    And got fol­low­ing dates:

    today=Mon Feb 07 14:27:50 CET 2011
    tomorrow=Tue Feb 08 14:27:50 CET 2011
    nextMonth=Tue Jan 18 21:25:02 CET 2011

    Accord­ing to Java’s cal­cu­la­tion, the cookie was expired already before even being set.

    Took me a bit to under­stand why:
    1000 * 60 * 60 * 24 * 30 = 2,592,000,000 = 0x9A7EC800
    Thus, the first bit got set to one… a clas­si­cal over­flow caus­ing the inte­ger value to become neg­a­tive — just try:

    System.out.println(1000 * 60 * 60 * 24 * 30);

    It will print out -1702967296.

    Fix: Add a lit­tle L will solve the issue by forc­ing the com­piler to cal­cu­late using the scope of long:

    Date nextMonthLong = new Date(today.getTime() + 1000L * 60 * 60 * 24 * 30);

    I guess I will fall for that one again some­time as the error is not obvi­ous in my opin­ion — espe­cially because getTime() returns a long and still, the com­piler sticks with an int for the mul­ti­pli­ca­tion part.

    4 Feb 2011, 10:10pm
    gwt:

    1 comment




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  • Disable Context Menu in GWT

    To make use of the right mouse but­ton, it is nec­es­sary to dis­able the native browser con­text menu (the popup menu appear­ing on right click). This can be achieved like this:

    RootLayoutPanel.get().addDomHandler(new ContextMenuHandler() {
    
    	@Override public void onContextMenu(ContextMenuEvent event) {
    		event.preventDefault();
    		event.stopPropagation();
    	}
    }, ContextMenuEvent.getType());

    Same should work for RootPanel.

    After that, it is pos­si­ble to make use of the right mouse but­ton for exam­ple like this:

    someWidget.addDomHandler(new MouseMoveHandler() {
    
    	@Override public void onMouseMove(MouseMoveEvent event) {
    		if (event.getNativeButton() == NativeEvent.BUTTON_RIGHT) {
    		...
    2 Feb 2011, 11:41pm
    java projects:

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  • Authentication with FlickrJ

    When you know about user­name and pass­word logins, the whole Flickr authen­ti­ca­tion process for web appli­ca­tions seems a lit­tle weird on first sight, nev­er­the­less it is log­i­cal and nec­es­sary after you have done some read­ing (for exam­ple the offi­cial Flickr WebApp Auth HowTo).
    To get started and into cod­ing quickly (using FlickrJ and Java) I rec­om­mend this page. Espe­cially the code exam­ple is excel­lent in my opin­ion! Thanks Andy Sacher!

    14 Dec 2010, 11:49am
    java:

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  • Casting collections in Java

    Assum­ing two classes A and B as

    class A {}
    class B extends A {}

    It is just log­i­cal that cast­ing B to A works fine:

    A anObjectOfClassA = new B();

    But when it comes to col­lec­tions of As and Bs, a strange phe­nom­e­non appears in Java:

    Collection<B> collectionOfBs = new LinkedList<B>();
    Collection<A> collectionOfAs = (Collection<A>)collectionOfBs; // this line does not compile!

    That is, though the col­lec­tion wrap­per (the java.util.Collection class) is the same and B extends A, cast­ing a col­lec­tion of objects of class B to a col­lec­tion of objects of class A throws an compile-time error.

    But it works using gener­ics (the whole class for the sake of com­plete­ness and reusability):

    import java.util.Collection;
    import java.util.LinkedList;
    
    public class CollectionCastingExample {
    
      class A {}
      class B extends A {}
    	
      Collection<B> collectionOfBs = new LinkedList<B>();
    //  Collection<A> collectionOfAs = (Collection<A>)collectionOfBs;
    	
      Collection<A> collectionOfAs = downCastCollection(collectionOfBs, A.class);
    	
      /**
       * Casts a collection of objects of class B where B extends A to a collection of objects of class A.
       * 
       * @param <T> Base class
       * @param collection Collection of objects of a class extending T 
       * @param aClass Representation of T
       * @return Collection of objects of T casted from given collection of objects of a class extending T.
       */
      @SuppressWarnings("unchecked")
      public static <T> Collection<T> downCastCollection(Collection<? extends T> collection,
          Class<T> aClass) {
        return (Collection<T>) collection;
      }
    }

    Despite the fact that a @SuppressWarnings("unchecked") is required, it avoids iter­at­ing over the whole col­lec­tion of Bs and cast­ing each of them from B to A plus adding them to a new col­lec­tion of As.

    3 Dec 2010, 4:02pm
    gwt:

    2 comments




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  • Adding a New Service (GWT)

    Adding a new servlet/service to you GWT appli­ca­tion is quite straight for­ward, e.g. by copy­ing the exam­ple “greet­ingSer­vice” or cre­at­ing a new servlet. But it’s easy to over­look a required change/adjustment of your project’s con­fig­u­ra­tion and you might end up with an error mes­sage like “Blocked attempt to access inter­face ‘some.package.SomeService’, which is not imple­mented by ‘some.other.package.SomeOtherServiceImpl’; this is either mis­con­fig­u­ra­tion or a hack attempt”.

    Check list (some should be replaced with what­ever you want to call your new service):

    • Copy or cre­ate files:
      SomeService.java and SomeServiceAsync.java in client pack­age
      SomeServiceImpl.java in server pack­age + change imple­men­ta­tion state­ment to SomeSer­vice
    • Adjust web.xml:
      <servlet>
      	<servlet-name>someServlet</servlet-name>
      	<servlet-class>some.package.SomeServiceImpl</servlet-class>
      </servlet>
      <servlet-mapping>
      	<servlet-name>someServlet</servlet-name>
      	<url-pattern>/[copy base directory name from other service declaration]/some</url-pattern>
      </servlet-mapping>
    • Anno­tate inter­face SomeService.java:
      @RemoteServiceRelativePath("some")
    • Con­nect to your new ser­vice in the client:
      private final SomeServiceAsync someService = GWT.create(SomeService.class);

    Def­i­nitely some pos­si­bil­i­ties to make a mis­takes or miss some­thing here.

    17 Sep 2010, 4:16pm
    jobs projects:

    1 comment




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  • Using the XML Parser in GWT

    I tried using the XML pars­ing fea­tures of the GWT like that:

    form.addSubmitCompleteHandler(new SubmitCompleteHandler() {
    	@Override
    	public void onSubmitComplete(SubmitCompleteEvent event) {
    		// One time upload only, to upload again, user needs to start the upload process from scatch – keeping it simple for now
    		panel.clear();
    		Window.alert(event.getResults());
    		Document result = XMLParser.parse(event.getResults());
    		...
    });

    But GWT kept telling me “No source code is avail­able for type com.google.gwt.xml.client.Document; did you for­get to inherit a required mod­ule?”. It turns out, you are required to explic­itly add the XML func­tion­al­i­ties to your project by adding fol­low­ing line to your .…gwt.xml file:

    <inherits name='com.google.gwt.xml.XML'/>

    Raises a ques­tion: What’s the point of AJAX (Asyn­chro­nous JavaScript and XML) with­out XML? Or in other words there is no AJAX with­out XML! So it’s up to you to add the AX part to GWT man­u­ally. What’s next?

    5 Aug 2009, 1:12pm
    php:

    leave a comment




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  • Simple redirection using PHP and HTML meta tag

    Some­thing every­one needs once in a while… maybe you moved a file on your server or you did not install word­press in the root folder of your web­server — like I did nei­ther ;) — a redi­rec­tion or for­ward­ing can be an easy answer.

    The script is rather sim­ple — it redi­rects in three ways to pro­vide a rea­son­able fall back if any of the auto­matic redi­rect­ing fails. To use it on your server, just enter the URL/address/file name/folder you would like the user to be redi­rected to in the sec­ond line of the page/script.

    Put the whole code and markup in a file with file exten­sion “.php”.
    In my case, every user end­ing up at “www.svenbuschbeck.net” should to be for­warded to “www.svenbuschbeck.net/wordpress/home”. So I adjusted the script below like “$url = ‘wordpress/home’”, named the file “index.php” and put it in the root folder. Done :) .
    <?php
    $url = 'put your URL between the parenthesis';
    header("Location: $url");
    ?>
    <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
    <html>
    <head>
    <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"/>
    <meta http-equiv="refresh" content="0;url=<?php echo $url; ?>"/>
    <title>You will be redirected... </title>
    </head>
    <body>
    If you are not redirected automatically, please click <a href="<?php echo $url; ?>">here</a>.
    </body>
    </html>
    29 Jul 2009, 10:30pm
    hci:

    leave a comment




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  • good & bad usablity
    the tap example

    Every­one inter­ested in HCI and Usabil­ity saw the cover pic­ture of The Design of Every­day Things by Don­ald Nor­man. But there are exam­ples about good and bad usabil­ity all around us, every day and I want to share one of mine.

    I real­ized how much more com­fort­able the shower tap at my par­ents place is, com­pared to the one in my shared flat.

    don't move! If you are lucky, the water gets only turned of... otherwise you get frozen or boiled...

    Don’t move! If you touch it and you are lucky, the water gets only turned off… oth­er­wise you get frozen or boiled.

    an good example of a water-tap for a shower

    A good exam­ple of a water-tap for a shower.

    .

    The exam­ple to the left  is a typ­i­cal one — most prob­a­bly fol­low­ing an assump­tion like “this tap is work­ing for the wash­bowl, so it will do for a shower as well”. As it is mounted waist-high, it is easy to reach, also by mis­take, which can be quite dan­ger­ous as it can eas­ily be turned towards hot water by a slight touch. The re-engineered exam­ple on the right shows a func­tional and easy-to-use solu­tion, in addi­tion, the water tem­per­a­ture can be set up very pre­cisely, but most impor­tant, there is no way to change the water tem­per­a­ture by acci­dent as it is selected with a knob. Addi­tion­ally, due to the knob, its almost impos­si­ble to reach the han­dle, which is used to set up the water amount, by accident.

    24 Jun 2009, 3:03pm
    jobs projects:

    4 comments




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  • fixing flex VideoDisplay CuePointManager

    I was cre­at­ing a Flex appli­ca­tion to show slides and a pre­sen­ta­tion video of pre­vi­ously recorded pre­sen­ta­tions. Accord­ingly, each slide should appear at a cer­tain point of time in the video — calls for cue points!

    As all slides and there appear­ance are stored in a text file in my case, I started adding cue points with Action­Script. But as soon as the video can be con­trolled with a slider, allow­ing to shift for– and back­wards, the event han­dler “cue­Point” was not trig­gered any more. Thus, the slides where not changed cor­rectly as the user jumps ahead, as the cue points between the pre­vi­ous and the new posi­tion did not cause and cue point event.

    Finally I wrote AdvCue­Point­Man­ager, inher­it­ing from Cue­Point­Man­ager, but which can deal with jump­ing back– and forward.

    Copy it to “<your source folder>/net/svenbuschbeck/flex/video” and use it as follows:

    <mx:VideoDisplay cuePointManagerClass="net.svenbuschbeck.flex.video.AdvCuePointManager" />
    16 Apr 2009, 5:46pm
    jobs:

    3 comments




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  • how to install memchached 1.2.2 from source

    I have installed an instance of mem­chached ver­sion 1.2.2 on one of our servers (Debian etch) today and to keep you from spend­ing a whole after­noon, see my everything-step-by-step instruc­tion below.

    Mem­chached is a dis­trib­uted hash map, which can be used for exam­ple to speed up any kind of web appli­ca­tion, see web­site for details. In our case, we want to use it as tem­po­rary data store. I will report about the expe­ri­ences in a lat­ter post.

    intro­duc­tion

    Always refer to this page for details, but I cre­ated a ver­sion with less text but includ­ing steps to really start from scratch.

    All lines start­ing with # are com­mand lines, i.e. you need to type into a linux shell.
    Out­put of any kind is always sur­rounded by ” even if it is mul­ti­line output.

    con­tent

    a. get libevent (needed to install mem­cached)
    b. get mem­cached and ver­ify instal­la­tion
    c. use and test mem­cached within Java with junit/ant

    a. installing libevent 1.3

    a.1. check for cur­rent ver­sion of libevent

    a.1a.

    Log in as root or get super user rights by call­ing su

    # updat­edb
    # locate libevent

    If there is out­put includ­ing “libevent1” and/or “libevent-1″ (ignore pack­age files like *.deb) -> a.1b, oth­er­wise a.2

    a.1b. remov­ing old libevent version

    # apt-get remove –purge libevent1
    # Y

    # updat­edb
    # locate libevent
    Should now return noth­ing or pack­age files only, i.e. you are ready for installation

    a.2. installing libevent 1.3

    a.2a down­load­ing and unpacking

    # cd /usr/local/src
    # wget http://monkey.org/~provos/libevent-1.3b.tar.gz
    # tar zxvf libevent-1.3b.tar.gz
    # cd libevent-1.3b

    a.2b. con­fig­ur­ing

    # ./configure
    check the out­put, if it con­tains some­thing like “con­fig­ure: error: no accept­able C com­piler found in $PATH” -> a.2c. oth­er­wise a.2d.

    a.2c. com­pil­ing

    # apt-get install gcc

    Redo a.2b.
    I got out­put like “C com­piler can­not cre­ate exe­cuta­bles”, read­ing file ‘config.log’ did not help me at all. Googling finally did, as I found a forum entry, point­ing out a miss­ing lib.
    So try this:

    # apt-get install libc-dev

    Redo a.2b.
    If that did  not solve it… sorry … google on, there is no sense in going on with­out solv­ing this issue. :-/

    a.2d. make it!

    # make && make install

    If you get some­thing like “-bash: make: com­mand not found” -> A.2e, oth­er­wise A.3.

    a.2e.

    # apt-get install make

    Redo a.2d.

    a.3. con­fig­u­ra­tion

    Press the Esc key as you read [esc] in the com­mands below.

    # vim /etc/ld.so.conf.d/libevent-i386.conf
    # i/usr/local/lib/[esc]:wq
    # ldconfig

    b. install mem­chached and ver­ify installation

    b.1. down­load, unpack and install memchached

    # cd /usr/local/src
    # wget http://danga.com/memcached/dist/memcached-1.2.2.tar.gz
    # tar zxvf memcached-1.2.2.tar.gz
    # cd memcached-1.2.2
    # ./configure
    # make && make install

    After installing gcc and libc-dev in sec­tion a, this one went eas­ily for me — if you skipped sec­tion a and run in prob­lems here, please install gcc and libc-dev (see a.2c).

    b.2. ver­ify instal­la­tion of memchached

    b.2a. start mem­chached server

    # mem­cached –u www-data –vv

    Out­put should end with line “<3 server lis­ten­ing”. Per­fect! :)

    b.2b test server

    I will refer to this shell in front of you as server shell below. Now, open another shell on the same machine, I will refer to it a client shell.

    # tel­net local­host 11211

    You should see some­thing like “<7 new client con­nec­tion” on the server shell, switch back to client shell.

    # set test1 1 10000 1
    # a

    You should see “STORED” on client shell and the two fol­low­ing lines on server shell
    ”<7 set test1 1 10000 1
    >7 STORED

    Per­fect!
    You did it, your mem­cached is up and run­ning :)

    c. mem­cached and Java

    I wrote a lit­tle test pack­age using a Java client library for mem­cached from here, together with junit and ant. You can down­load it to have a look how sim­ple using mem­cache is and to ver­ify your instal­la­tion with an included  junit test, auto­mated with an ant build file.