Bits By The Pound

Used to be that getting a GWT project together using Maven and Eclipse was a tedious and frustrating task. Times have changed so that the process is quite a bit easier.

Uses:
openjdk-6-jdk
Eclipse 3.5
Google plugin for Eclipse 1.32 http://code.google.com/intl/en/eclipse/
gwt-maven-plugin 1.2 http://mojo.codehaus.org/gwt-maven-plugin/
Maven plugin for Eclipse 0.10.0 http://m2eclipse.sonatype.org/

Install the Google plugin for Eclipse into eclipse specifying the update site url http://dl.google.com/eclipse/plugin/3.5 through Eclipse’s Help->Install New Software->Add… and specify the url

If you have a previous version of the m2 plugin you will need to uninstall it as the 0.10.0 version will not upgrade properly otherwise. Install the Maven plugin.

From Eclipse, create a new Maven project:
File->New->Other->Maven->Maven Project

Do not check Create a simple project as we want to do archetype selection, but fill the rest in as you see fit then click Next.

Select either Nexus Indexer or All Catalogs as the catalog, then scroll down the list looking for a Group Id of org.codehaus.mojo with an Artifact Id of gwt-maven-plugin and choose the highest version (1.2 at this time) then click Next.

Fill in your Group Id and your Artifact Id and the rest of the fields and click Finish.

The next set of the instructions are mostly from http://code.google.com/intl/en/eclipse/docs/faq.html#gwt_with_maven.

In Eclipse, select your project then choose Project->Properties->Google->Web Toolkit and click Use Google Web Toolkit.

Then click on Web Application (Project->Properties->Google->Web Application and change the War Directory to src/main/webapp and uncheck Launch and deploy from this directory then click OK.

Open the pom.xml file under your project and check some Properties values. You want gwt-version to be 2.0.3 and maven.compiler.source and maven.compiler.source to be 1.6.

Right click on your project and select Run As->Maven Clean, then Run As->Maven Package.

Right-click your project and select Run As->Web Application. The first time you do this, you’ll have to select the location of the exploded WAR directory (by default it should be /target/-).

If everything works out fine, you are now running in hosted mode. Click on the Development Mode view tab down where the Console tab is and copy and paste the URL shown there into a browser to see your app running.

GWT development/hosted mode is now running out of the WAR directory created by Maven. You can step through and debug your code as usual. If you make changes, it is sometimes possible to have your running application reflect those changes without restarting your debugging session:

• If you change client-side code, just click Refresh in your browser.
• To have server-side code changes reflected, your project’s build output path must be set to /target/-/WEB-INF/classes (Project properties > Java Build Path > Source > Default output folder). Then, when you change a server-side class click the Reload web server button in the Development Mode view.
• If you change resource or configuration files in your WAR directory (HTML, JSP, CSS, etc.), you’ll have to terminate the launch configuration, run mvn clean package, and then launch again.

While trying to figure out while my laptop, a Dell Inspiron 1720, has been freezing occasionally, I found out that you can use SysRq codes to communicate directly with the Linux kernel to get system operations done even while the machine is locked up. This is handy as it allows you to specify a sequence of actions to safely sync your disks prior to rebooting your computer. Then you don’t have to go through the trouble of running fsck on your filesystems.

The typical sequence that you are told to input is to hold down Alt+SysRq and then slowly type r e i s u b. This presents a slight problem on the Inspiron 1720 since the SysRq key is shared with F11. Accessing the SysRq key requires pressing the Fn key but you must not have the Fn key depressed while you type the subsequent letters or they are interpreted as something different. I have found the easiest way to perform this magical little finger dance is to use your right hand to press the right Alt key with your thumb and the SysRq with a finger. So the sequence is:

Left hand: Press and hold “Fn” key (between Ctrl and the Windows key)
Right hand: Press and hold “Alt” + “SysRq” keys (Alt+F11)
Left hand: Release “Fn” key
Left hand: Press and release “r” key. (Screenshot dialogs may start popping up. Ignore them)
Left hand: Press and release “e” key. (Your GUI should collapse to a tty, most processes terminated)
Left hand: Press and release “i” key. (Progress of key shown in the tty, most proceses killed)
Left hand: Press and release “s” key. (Progress of key shown in the tty, syncs filesystems)
Left hand: Press and release “u” key. (Progress of key shown in the tty, unmounts filesystems)
Left hand: Press and release “b” key. (Progress of key shown in the tty, starts reboot)
Right hand: Release all keys

Over the past couple of days, I have seen a situation where I boot my laptop (Ubuntu Karmic) and the Network Manager applet insists that the wireless is disabled. Rebooting does not help. Examining the syslog showed that the OS found 2 kill switches and one of them was disabling the wireless. Examining the state showed that each kill switch state was affected by the single physical kill switch, but their states were the opposite of each other. So regardless of which position the kill switch is in, one of the kill switch devices would disable the wireless.

I turned the kill switch off and reboot the computer. When it came up, the kill switch drivers were now synchronized and turning the kill switch on caused the Network Manager to start looking for Wireless connections. Listing the kill switch states shows they are again synchronized.

This post at LinuxTrap shows that others are experiencing a similar condition.

Once you have built your wave extension, you will need a way to install it into the user interface of the Google Wave client. A Wave Extension Installer is just that beast. You will need to create an Extension Manifest, which is an XML file describing where to find your extension, where you want it installed in the client UI and other information you want displayed.

We started out with the Wave Extension Installer Guide, but this document has some problems with the robot extension installer sample. Maybe its out of date, I don’t know.

The part that is in error is that there is no action element defined within the menuHook element. This is easily fixed by wrapping the participant element by the createNewWave element.

Once this was straightened out, we put together an extension manifest for our existing sample robot, Frakky.

Once you have your extension manifest set up for your extension, you need to make it Internet accessible. A reasonable place to put this is next to the index.html file for your robot, in the war directory. We named the file install.xml. Then whenever you upload your robot to Google App Engine, the extension manifest will be uploaded to http:/yourappname.appspot.com/install.xml. To be able to install this manifest in Google Wave Preview, you will need to install the Extension Installer. Yeah, its name is a little confusing but I am not sure that calling it Extension Installer Extension (which better describes its function) is any less confusing.

Once this is done, you can select the dropdown next to New Wave in the center panel and choose New Extension Installer. When you are asked for the Extension Manifest URL, be sure to specify the URL including the http:// portion or else you will end up receiving an error message that implies there is something wrong with the manifest instead of saying it just cannot find the manifest. This creates a wave with a puzzle piece from which you can install the manifest into the Google Wave client. Push the Install Extension button to hook it up.

Extension Almost Installed

You will notice that the attributes you specified in the extension element such as name, description and thumbnailURL are used to display the puzzle piece.

Now, if you check the muted wave, Extension Settings, your extension is listed at the bottom.

Installed Extension

Since our manifest added a new item to the New Wave button, clicking the dropdown next to this gives us an entry that says “Creates a new Frakky wave.” Clicking this creates a new wave with our robot set as a participant.

Note these instructions are for Ubuntu 9.10 (Karmic).

In prior versions of Ubuntu, I have had some problems getting the VGA and S-Video outputs on my Inspiron 1720 working, so today I tackled this problem. In Karmic, this process is quite straightforward. Once you connect your video cable to the laptop, whether it is S-Video to a television or VGA to a monitor, you can cycle through various video distribution modes using the Fn-F8 keys. This is marked as “CRT/LCD” on the F8 key. Here is the cycle that I found using S-Video output.

1. LCD on at full resolution ; TV off
2. LCD off ; TV on at 848×480
3. LCD on at full resolution ; TV on and to right of LCD, 848×480 ; desktop shared across both screens
4. LCD on, 1024×768 ; TV on, 1024×768 ; mirrored desktop

You can change the parameters of each of these cycles by running the Display Preferences applet (System->Preferences->Display). This applet has a spacial depiction of  both displays and you may drag a display to be in a specific location with respect to the other display. For example, if in 3 above, you wanted the TV to appear logically above the CRT, you would drag the TV rectangle (labeled “unknown” for me) above the rectangle labeled “Laptop 17″.

Mode 3 shares the desktop over the 2 screens so that you can move the mouse cursor from one screen to the other screen, effectively extending your desktop. If you use an image as your desktop background, you may get the background color showing around the edges of the image as the image is centered in the extended display resolution.

Mode 4 shows the same content on the laptop LCD panel as on the connected screen. Note that in this mode for a connected television, the video quality is less crisp than in mode 3 due to the scaling of the 1024×768 resolution to something the television can handle.

If you connect a VGA cable to a monitor, a similar cycle is used, but the VGA resolutions used will be different.

Out of curiosity, I connected both a VGA monitor and S-Video to the TV, but preference seems to be given to the VGA monitor such that the TV never gets a signal.

Extracted from a Slashdot article.

http://www.teamviewer.com/ [teamviewer.com]

https://secure.logmein.com/products/free/ [logmein.com]

http://www.copilot.com/ [copilot.com]

http://skype.com/ [skype.com]

http://www.uvnc.com/addons/singleclick.html [uvnc.com] (reverse VNC)

http://www.crossloop.com/ [crossloop.com]

http://www.mikogo.com/en/ [mikogo.com]

http://showmypc.com/ [showmypc.com]

https://www.ntrconnect.com/ [ntrconnect.com]

http://www.zolved.com/remote_control [zolved.com]

http://www.wippien.com/ [wippien.com] (VPN)

http://code.google.com/p/gitso/ [google.com] (reverse VNC)

Today I got fed up with the overall poor search performance and poor rendering of Evince on 64 bit Ubuntu and looked around for an alternative. I use Foxit on my Windows machine and am generally very happy with it, having only had problems with it with government security clearance documents. A quick search shows that there is indeed a Linux version of Foxit.

Note that Foxit is a 32 bit executable so if you are running a 64 bit version of Linux, you will need to install ia32-libs from your repository.

Since a new version is supposed to be available within a couple of months, we may as make the upgrade path easier. I chose to download it to a local directory and then after uncompressing, moving it to /usr/local/foxit1.1

We now have a link to the directory at /usr/local/foxit which we can change to the 1.2 version when it becomes available.

Now lets add it into the Gnome menu. Click on System->Preferences->Main Menu. Select Accessories then click new Item. Fill in the form, pointing to FoxitReader.

Click OK and now Foxit shows up in your Accessories list.

Now, lets change the file associations for PDF files so that if you click on a PDF from the File Browser that it opens Foxit. From the File Browser, find a PDF file and then right click and select Properties and click the Open With tab.

Click on Add, then dropdown Use a custom command and browse to where FoxitReader lives. Click Close.

This adds FoxitReader into the Open With list. Select FoxitReader and click Close.

Now you should be able to click on any PDF in the File Browser and Foxit will be launched with the contents of the document.

Wink is great tutorial building software for Linux and Windows. It used to be available in the Ubuntu repositories but is no longer included. Currently, the Linux variant of Wink is version 1.5 and the Windows variant is version 2.0. Even though they share the same build number, they are not the same.

Unfortunately, running the newer, Windows version under Wine is not an option that I can see because there isn’t a way to capture the input from native Linux windows.

Go to the download page and download the wink15.tar.gz tarball to a temporary directory. This makes cleanup easier, since it is actually a tarbomb, extracting to the current directory.

Unzip the tarball which creates an installer.sh script and an installdata tarball.

Now, run the installer script.

Oops. I am running a 64 bit version of Ubuntu and this is a 32 bit binary only. Lets check what is in the installdata.tar.gz tarbomb.

This creates an entire directory structure in place including the wink executable. Lets install some basic 32 bit libraries.

Now lets check whats missing.

The “libexpat.so.0 => not found” line tells us that libexpat.so.0 is missing. What is odd is that the executable also links against libexpat.so.1.

I could try and find a 32 bit version of libexpat.so.0, but it might be worth a try to fake it.

Ha, it runs! Initial tests shows that it captures fine and can save to HTML, PDF and Flash.

Copy the entire directory structure to a its final resting place.

Now you can either run it from the wink directory or set up some desktop links to it.

While building a Robot that inserts a Gadget into the wave I discovered something that made me shake my head. A lot of the Wave Robot API classes have methods that violate their documented contracts. The worst offender I think has to be the Event interface. Whenever an event is delivered to your Robot, you interrogate the event to gather the information the robot requires. But there are many different events that can occur and each is trying to tell the robot a different thing.

For example, one of the methods on the Event interface is getAddedParticipants(). This method makes sense only on an event where the participants have changed such as BLIP_CONTRIBUTORS_CHANGED. However the method is available for all events. The javadoc for this method is

getAddedParticipants

java.util.Collection<java.lang.String> getAddedParticipants()

Returns a list of participants added to the Wavelet (if applicable).

Returns:

a list of participants.

You will of course note its contract specifies that it returns a list of participants. So you write your code so that it wil handle a Collection of participants. And if there are no added participants, it will return an empty collection. Except that it does not return an empty Collection when there are no added participants. It returns null. Um, that behaviour is not in the contract.

Another case that is really nasty is the case of Wavelet.getRootBlip(). There are many reasons why you may want to access the root blip. Maybe the robot created a widget there and wants access to it. Sometimes you might want to compare the id of the root blip to see if it is the same as the id of the modified blip in the event you just received. The javadoc says that it returns “the root blip”. Just don’t do the following while handling the BLIP_SUBMITTED event or you will be sorely surprised.

Apparently when you receive an event, you do not receive the entire wavelet, but rather only information about the current blip for which the event occurred and that blip’s parent. If neither of those is the root blip then wavelet.getRootBlip() returns a non-null value, but this blip is not the actual root blip and contains no blip data in violation of its contract. This blip has been described as empty or hollow. So when you call getBlipId() on what you thought was the root blip, a null pointer exception occurs in getBlipId() because it attempts to dereference a null blip data object within the hollow root blip.

However, using Wavelet.getRootBlipId() gives you the ID of the root blip without the API experiencing a null pointer exception. Which is fine if you only want to compare blip IDs, but does not help you if you want to actually examine the contents of the root blip, since you don’t have access to it. The recommendation from Google is to save all needed blips in your AppEngine datastore and update them as they change and retrieve them as necessary.

Hopefully these annoying API contract violations (and bugs) will be fixed soon.

After upgrading to Ubuntu 9.10 from 9.04, the GWT plugin for Eclipse doesn’t work so well when trying to run an app in hosted mode.

** Unable to load Mozilla for hosted mode **
java.lang.UnsatisfiedLinkError: /home/igough/installs/eclipse-3.5/plugins/com.google.gwt.eclipse.sdkbundle.linux_1.7.1.v200909221731/gwt-linux-1.7.1/mozilla-1.7.12/libxpcom.so: libstdc++.so.5: cannot open shared object file: No such file or directory

Karmic does not have libstdc++.so.5 as part of the distribution but you can download the one from 9.04 from the Ubuntu repository. I am running 64 bit Ubuntu, and would normally download the 64 bit version of the library, but the GWT Eclipse plugin uses a 32 bit version of Mozilla for hosted mode. And its hosted mode that wants the Standard C++ library. So we must download and install the 32 bit version.

Download libstdc++5_3.3.6-17ubuntu1_i386.deb from the Ubuntu respository link above. Then install using:

Once you do this, hosted mode should work again.