Configure Java AWT and Java Swing in Matlab Docker Image

To make a custom style cheker that we want to run in Jenkins as one of a auto-test we use:

function indentedText = indentcode(text,language)

it is needed to get right indentation in the code.

This function utilizes something undocumented interacting with Java Swing :

function indentedText = indentcode(text,language)
%indentcode Indents code.
%   indentcode(T) indents text T according to user's preferences specified
%   for the MATLAB language. Indented text retains the same line separator
%   style as specified by the input text.
%
%   indentcode(T,L) specifies language L and must be one of the following:
%       'c', 'java', 'matlab', 'plain', 'simscape', 'tlc', 'verilog',
%       'vhdl', 'xml'.
%
%   This file is for internal use only and is subject to change without
%   notice.

%   Copyright 2012 The MathWorks, Inc.

error(javachk('swing'));
narginchk(1,2);
if ~ischar(text)
    error(message('MATLAB:INDENTCODE:NotString'));
end
if nargin < 2
    language = 'matlab';
end
if strcmp(text, '')
    indentedText = text;
    return
end
switch language
    case 'c'
        langInst = com.mathworks.widgets.text.cplusplus.CLanguage.INSTANCE;
    case 'java'
        langInst = com.mathworks.widgets.text.java.JavaLanguage.INSTANCE;
    case 'matlab'
        langInst = com.mathworks.widgets.text.mcode.MLanguage.INSTANCE;
    case 'simscape'
        langInst = com.mathworks.widgets.text.simscape.SimscapeLanguage.INSTANCE;
    case 'xml'
        langInst = com.mathworks.widgets.text.xml.XMLLanguage.INSTANCE;
    otherwise
        error(message('MATLAB:INDENTCODE:InvalidLanguage'));
end
indentedText = char(com.mathworks.widgets.text.EditorLanguageUtils.indentText(...
    langInst,text));
end

It works fine in a normal Matlab with GUI, but does not work inside the Matlab Docker Image.

We tried to install Java into the Matlab Docker Image, but it did not help.

Here is a question, is it possible to run this function inside the Matlab Docker Image?

Thank you!

[Daniel]

Hi Angelina, did you find a solution to your question? I'd be curious to know. Thanks, Daniel

Answer 1

[Swastik Sarkar]

Hello @Angelina Prokopeva,

It seems you're attempting to use the 'indentcode' function within a MATLAB Docker image but are encountering the ‘Swing is currently not available’ error.

This issue typically arises because MATLAB, when run without a display, does not load all Java Libraries. You can verify which Java libraries are loaded with the 'javachk' command.

To address this, I recommend a workaround that involves simulating an X display to ensure all Java Libraries are loaded. Here's how you can proceed:

1. Start by getting a shell to your Docker container. Use the -shell flag with your docker image command like so:

 docker run -it -- rm -p 8888:8888  --shm-size=512M mathworks/matlab:r2021b -shell

2. Once in the shell, update your package lists and install OpenJDK and Xvfb (X virtual framebuffer):

 sudo apt update 
 sudo apt install openjdk-17-jdk xvfb 

3. After installing the dependencies, initiate a dummy X Display server. In this example, we'll use port :99:

 sudo Xvfb :99 & 

4. With the X Display server running, you can now execute the ‘indentcode’ function in MATLAB, specifying the display to use:

 matlab -batch "indentcode('disp(a);')" -display :99 

Hope this helps you use ‘indentcode’ in your Docker container and smoothly integrate with Jenkins.