Slf4j NoClassDefFoundError when compiling SparkJava sample project

Problem:

When trying out the SparkJava demo for websockets (spark-websockets, "Using WebSockets and Spark to create a real-time chat app"), I get the following compilation error:

Exception in thread "main" java.lang.NoClassDefFoundError: org/slf4j/LoggerFactory
 at spark.Service.<clinit>(Service.java:56)
 at spark.Spark$SingletonHolder.<clinit>(Spark.java:51)
 at spark.Spark.getInstance(Spark.java:55)
 at spark.Spark.<clinit>(Spark.java:61)
 at Chat.main(Chat.java:19)
Caused by: java.lang.ClassNotFoundException: org.slf4j.LoggerFactory
 at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
 at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
 at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:349)
 at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
 ... 5 more

Workaround:

The following workaround worked as a quick way to try out the demo code:

• Open the project's pom.xml file
• Add the following dependency:

  
  <dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-api</artifactId>
    <version>1.7.21</version>
    <scope>compile</scope>
  </dependency>
  
  

If this worked, the project should now compile properly.

Notes:

The above workaround is one of many solutions that can work towards a successful compile. Others include adding a JAR file for a logger, for example. This solution was chosen as it is the quickest for a beginner to do while learning how to use SparkJava or while learning programming in Java.

This how-to was verified to work in revision 8cc09e8cea9257a0df3449106a57ad0467faf39b (Sep 4, 2017) of the spark-websockets project. Your results may vary for other revisions.

References:

• https://github.com/tipsy/spark-websocket
• more about slf4j logging https://mvnrepository.com/artifact/org.slf4j

Meteor VSCode esversion 6 jslint error

Problem:

When using Visual Studio Code to edit my Meteor project, I keep seeing the error:

'import' is only available in ES6 (use 'esversion: 6'). (W119) jshint(W119)

For example:

Workaround:

• To hide the jshint errors: in the main folder of your Meteor project, if the file named ".jshintrc" does not exist then add it
• In this .jshintrc file, add the following text:

  {
      "esversion": 6
  }
  

You may need to close and reopen the project in VSCode. If the workaround is successful, you should no longer see the esversion 6 error.

Notes:

This workaround was verified to help remove the jslint errors while using Visual Studio Code version 1.43.1 with Meteor 1.10.1. Your results may vary given different versions. Please also note that this workaround hides the jshint error from being highlighted, but it won't fix compilation errors if your Meteor project isn't properly setup to compile esversion 6.

References:

https://jshint.com/docs/options/

Catalina Jekyll bad interpreter error

Problem:

When trying to run jekyll in Terminal, I get the following error:

zsh: /usr/local/bin/jekyll: bad interpreter: /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/bin/ruby: no such file or directory

I recently upgraded MacOS.

Before you start:

This how-to assumes you already have knowledge of Terminal and the 'sudo' command, given that you've already installed Jekyll in the past. If not, please proceed at your discretion as 'sudo' command can be harmful if used incorrectly.

Solution:

In Terminal, reinstall jekyll via homebrew:

sudo gem install jekyll

Why this works:

The upgrade to Catalina changed key dependencies of Jekyll. While it is possible to manually link them or add them to your PATH, reinstalling Jekyll should provide an easier and more robust solution. You'll likely also need to reinstall any other gems you need.

Disclaimer:

This solution was verified to work in MacOS 10.15.3 with Jekyll 4.0.0. Your mileage may vary with other versions.

References:

• https://talk.jekyllrb.com/t/cant-run-jekyll-in-mac-os-sierra/1263/2
• https://muffinman.io/macos-catalina-ruby-bad-interpreter-error/ (useful read if you prefer using the Homebrew version)

Reminder: SparkJava 2.7.2 pom.xml known to work for new projects

Problem

For SparkJava 2.7.2, I'd like a known set of POM.xml dependencies and properties that work so I can kick-start my project. The settings in the SparkJava "getting started" tutorial result in exceptions.

Example POM.xml snippet

In your POM.xml, try these to start off:

    <properties>
        <java.version>1.8</java.version>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
    </properties>
  
  
    <dependencies>
  
        <dependency>
            <groupId>org.eclipse.jetty</groupId>
            <artifactId>jetty-server</artifactId>
            <version>9.4.6.v20170531</version>
        </dependency>
  
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>1.7.21</version>
            <scope>compile</scope>
        </dependency>

        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-simple</artifactId>
            <version>1.7.21</version>
        </dependency>
 
        <dependency>
            <groupId>com.sparkjava</groupId>
            <artifactId>spark-core</artifactId>
            <version>2.7.2</version>
        </dependency>
    </dependencies>

Notes

The above dependency versions and properties were observed to work on 2018-10-03 with SparkJava version 2.7.2. Your mileage may vary.

Once you have your SparkJava project working, feel free to change versions to suit your own project needs.

References

• http://sparkjava.com/documentation.html#getting-started
• http://sparkjava.com/documentation.html#examples-and-faq
• https://www.slf4j.org/manual.html#projectDep

Fix 07_BoggieBot.playground errors "Cannot call value of non-function type 'NSGraphicsContext?" and "Cannot convert value of type 'NSApplication.ModalResponse' to expected argument type 'Int'"

Problem:

When trying to learn from 07_BoogieBot.playground alongside Apple's Everyone Can Code "Intro to App Development with Swift", I get errors similar to:

07_BoogieBot.playground/Sources/Recorder.swift:26:51: Cannot call value of non-function type 'NSGraphicsContext?'
07_BoogieBot.playground/Sources/Recorder.swift:33:99: Cannot call value of non-function type 'NSGraphicsContext?'
07_BoogieBot.playground/Sources/Recorder.swift:70:31: Cannot convert value of type 'NSApplication.ModalResponse' to expected argument type 'Int'

The console shows me the following:

Playground execution failed: error: /var/folders/1g/_b7g8rjd71j_mwjxdj29vllc5x9cxx/T/playground11-16e897..swift:3:8: error: no such module '_7_BoogieBot_Sources' import _7_BoogieBot_Sources

I am using XCode 9.4.1 and macOS 10.13.5

Before you start:

You'll want to make a backup of lesson 7's code first. Just make a copy of the folder in Finder. We'll be editing the code that runs the playground, so this way you can undo by restoring the backup if you've forgotten what you changed and introduced a bug.

Workaround:

You're learning coding for the first time, and you've been given a chance to debug the playground you're learning from. Cool!

Here's a few quick steps to get your BoogieBot lesson going!

Step: Have a look at the errors

In XCode you can view what errors have broken your code. In our case, click here:

You'll see a list of errors appear in the navigator in red. Try to click one:

Wow, that's more code that you've seen in the previous lessons. No worries. Just focus on the problem you're trying to solve and ignore the rest.

Step: Fix the 'context' bug

For the lines that have:

if let context = NSGraphicsContext.current()?.cgContext

Remove the (), so they look like:

if let context = NSGraphicsContext.current?.cgContext

If you save the file and the 2 errors go away, you've made progress. Congrats on debugging so far!

Why does this code change work?

Someone at Apple had changed NSGraphicsContext.current from a function to a property.

As you recall from an earlier lesson, programmers will often have to build on code made by others. In this case the code happens to be from those who worked on part of the graphics programming for macOS 10.13. These are changes you'd see if coding in XCode 9 (instead of XCode 8).

Step: Fix the Modal.Response bug

For the code that looks like:

if (savePanel.runModal() == NSFileHandlingPanelOKButton) {

Change it to look like:

if (savePanel.runModal() == .OK) {

Why does this code change work?

Without getting too technical, essentially someone at Apple had changed the way this test should work.

IF you're really curious and aren't learning to code for the first time, have a look at https://developer.apple.com/documentation/appkit/nsapplication/modalresponse

Step: Go back to the BoogieBot Playground

Now that you've debugged the code and saved it, check that no errors still exist. (The yellow warnings won't block you from lesson 7.)

Cool. Now you can return to learning about BoogieBot by clicking here and going back to your playground:

Happy boogie-ing!

Notes

This how-to was tested to work using XCode 9.4.1 and macOS 10.13.5. The bug was seen in the playground downloaded sometime June 2018. Your results may vary depending on versions, and if Apple fixed the playground by the time you read this post. Code can change pretty quickly in real life.

If you ran into this bug, hopefully you were able to fix it and learn how to make your boogie bot dance using Swift!

How to fix kernel_require.rb:55:in `require': cannot load such file -- xcodeproj (LoadError)

Problem:

When I try to build and deploy in XCode 9.3, I get the following error related to: "kernel_require.rb:55:in `require': cannot load such file -- xcodeproj (LoadError)"

/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in `require': cannot load such file -- xcodeproj (LoadError)
 from /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in `require'
 from /Development/ELD.iOS/ELD/Scripts/generate_resources.rb:4:in `
'
Command /bin/sh failed with exit code 1

Possible solutions to try:

There are several possible ways to address this issue. Two are listed here to try.

1. Install XCode command line tools from Apple
2. Install the gem "xcodeproj"

To install XCode command line tools...

1. Go to https://developer.apple.com/download/more/ and login
2. Search for the command line tools for your version of XCode, download it, then install it.
   

To instead install the gem "xcodeproj"...

1. Open a Terminal window
2. Use the command:
   sudo gem install xcodeproj

Notes:

This how-to was tested to work for a project on macOS High Sierra 10.13.4 and XCode 9.3. Your results may vary. It assumes a little working knowledge of XCode and Terminal.

Best of luck!

Cannot type into Spotlight in macOS

Problem:

I suddenly cannot type anything into Spotlight.

It opens and closes, and even does so with the Command-Space shortcut. I just can't type in it when it's open.

Workaround:

• Open Terminal
• Use the following command:

  killall Spotlight

• If all goes well, the magnifying glass for Spotlight will disappear and reappear, and you'll be able to type into Spotlight again

Notes:

This was tested to work in macOS 10.12.6.

Seamonkey XPCOMGlueLoad error

Problem:

I updated Seamonkey on Linux Mint and it now won't launch. I am running a 64-bit version of Linux Mint.

In terminal, I tried to run Seamonkey but got an error similar to:

$ /path/to/seamonkey/seamonkey

XPCOMGlueLoad error for file /path/to/seamonkey/libmozgtk.so:
libgtk-3.so.0: cannot open shared object file: No such file or directory
Couldn't load XPCOM.

When checking, I do have GTK 3:

$ locate libgtk-3.so.0

/usr/lib/x86_64-linux-gnu/libgtk-3.so.0
/usr/lib/x86_64-linux-gnu/libgtk-3.so.0.1800.9

Solution:

It may be that you're attempting to run a 32-bit version of Seamonkey on 64-bit Linux Mint. The default Seamonkey download from Mozilla as of Jan 2018 is the 32-bit version.

You can find the 64-bit version in their releases page: http://archive.mozilla.org/pub/seamonkey/releases/

For example, for 2.49.1:

Notes:

This solution worked for Seamonkey 2.49.1 running on 64-bit Linux Mint 18.1 Serena as of Jan 2018. Your mileage may vary with other versions and configurations.

Also for the system tested, the auto-update is not an issue because this browser will only be used on a local network. (You'll see the note from Mozilla when you launch the browser... at least for version 2.49.1). Keep this in mind if your situation is different and you need a browser that reliably auto-updates.

References:

http://archive.mozilla.org/pub/seamonkey/releases/ http://forums.mozillazine.org/viewtopic.php?f=40&t=3005417

XQuartz move offscreen windows back on-screen in macOS/OS X

Problem:

I have several XQuartz/X11 windows in macOS/OS X that are offscreen. I want to move them on-screen so I can save my work.

Example scenario:

You can create an example of off-screen X11 windows when using macOS/OS X with an external monitor and a screen geometry where one monitor is higher and further left to another (scroll down to see a screenshot example).

In the lower-right monitor, when opening certain windows in programs like Inkscape, those windows will be created at coordinate that you cannot access with your mouse cursor.

Workaround:

Pre:

• If not already installed, then install xdotool (easiest way is to use Homebrew)

To find out window ids and geometry:

• In Terminal, you can use:
  xwininfo -tree -root
• If you want to filter by an application, you can pipe to grep, for example:
  xwininfo -tree -root | grep "inkscape"

To move a window to a visible coordinate:

• If not already installed, then install xdotool (easiest way is to use Homebrew)
• Make note of a valid coordinate. Use the output of xwininfo from the above step to find a visible top-left coordinate for your window (e.g. it can be an existing window that you can already see and use with your mouse. In the screenshot below, a visible coordinate is 1070 1102)
• In Terminal, use the following command and replace [options] [window] [x] [y] with the appropriate values:
  xdotool windowmove [options] [window] [x] [y]

Example:

Consider the following window geometry:

Inkscape has spawned the "document properties" window to a coordinate that is out of desktop 1:

Use xwininfo to find out window IDs, geometry, as well as to to find a set of on-screen coordinates:

Use xdotool to move off-screen window to an on-screen coordinate on desktop 1:

If all goes well, the window should now be visible.

Now would be a good time to save your work.

Also note that there might be some unexpected behaviour for XQuartz windows moved this way (e.g. "show all windows" still shows incorrect placement, etc.)

Where to go from here?

Some ideas:

• write a script to automatically collect all windows of a certain app into visible coordinates if they're not visible
• if you're able to and have the time to volunteer, contribute to the XQuartz project a feature to collect or clamp all windows to a given desktop :) (thanks in advance!)

Notes:

This workaround was verified to work with macOS Sierra 10.12.6, XQuartz 2.7.11, xdotool 3.20160805.1. Other versions may have different results.

References:

• https://github.com/XQuartz
• https://www.semicomplete.com/projects/xdotool/xdotool.xhtml
• https://linux.die.net/man/1/xwininfo
• https://brew.sh/

Exit XQuartz Full Screen Mode macOS Sierra

Problem:

How do I exit XQuartz full-screen mode?

Solution:

When in XQuartz:

• Press the keyboard shortcut Command-, (command + comma)
• Uncheck full-screen mode in the preferences
  

References:

• https://discussions.apple.com/thread/1638358