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Using VS Code for Compiling COMSOL^® API for Java Projects

Visual Studio Code (VS Code) can be used for editing and compiling Java files. Setting up the code editor to compile Java code that uses the COMSOL^® API is straightforward but requires a few steps to properly set up. Here, we will outline these steps. Follow along by first downloading and installing the VS Code editor.

Note: The JAR files included with the COMSOL API are compiled using Java 8, so some Java Development Kits (version 21 or higher) may not work with Java 8 without warnings or requiring modifications to the settings.

VS Code is platform independent, similar to Java. This step-by-step guide usesWindows^® operating systems but can be referenced as a general procedure to follow for other platforms, with a few modifications to the paths used. Please note that VS Code is updated frequently, and thus some steps in this guide may have changed since it was created.

Create Java File

To start, we create a small test Java file (available to download here) that uses the COMSOL API to connect to a COMSOL Multiphysics server, solve a model, and print the result on the screen.

A screenshot of the test Java file.

Install Java Extensions

Next, we install the Java extensions for VS Code. Open the Extension Marketplaceand search for Java. Select Extension Pack for Javaand click Install. The installation will take a few minutes and install a set of extensions.

VS Code may suggest that you restart your workstation.

Create a Java Project

Now we create a new Java project. This creates settings files and a directory structure that VS Code will use when compiling your project.

Open the Command Paletteby pressing Shift+Ctrl+P or by selecting Viewfrom the menu and choosing Command Palette. Select Java: Create Java Project… from the expanded drop-down list.

The Command Palette open in VS Code.

From there, select the No build tools option. Alternatively, you can choose one of the suggested build tools.

A screenshot of VS Code with the options for project type displayed with No build tools selected.

We are then prompted to select the project location. Create a few folders in the C drive and use C:\models\java for the project location. Click the Select the project location button to close the dialog box.

The Windows^® Explorer open with the project location selected.

Next, we are prompted at the top of the window to name the Java project. Enter the name javatest. Then, VS Code might ask if you trust the authors of the files in this location. Choose: Yes, I trust the authors.

In VS Code, the project name is entered for the new Java project created.

The dialog box that displays in VS Code upon entering the project name.

Now, open the default App.java file by selecting it under the src node in the Explorer pane.

A screenshot of VS Code with the App.java file open in the Java test project.

If you do not have any previously written code for your project,you can start coding by modifying this file. In this case, you can replace its current contents with those of the App.java file shown previously.

The contents of the test Java file in the VS Code editor, in which multiple syntax errors have been highlighted.

After replacing the file and opening it in the code editor, you will see multiple parts of code in which a syntax error has been detected (underlined with a red line). This is expected because VS Code does not know where the JAR files in COMSOL Multiphysics are installed. To define the paths to these JAR files, open the project settings. You can do this by selecting the settings.jsonnode under .vscodein the Explorerpane.

The project settings open in VS Code.

Change the settings of java.project.referencedLibraries to C:/Program Files/COMSOL/COMSOL63/Multiphysics/apiplugins/*.jar, which is the default location on Windows^®. Note that the backslashes between directories have been replaced by regular slashes. Alternatively, you can enter double backslashes. Remember to save the settings (Press Ctrl+S). You will notice that all the former syntax errors highlighted in the code have been cleared.

The contents of the test Java file in the VS Code editor.

Testing the Java Project

To start a COMSOL Multiphysics server, open a command window and execute the following command: '"c:\Program Files\COMSOL\COMSOL63\Multiphysics\bin\win64\comsolmphserver.exe"'. Remember to include the quotation marks. Check that the server writes that it is using the port number 2036, since the code expects this port number. You may update the Java code if you need to support other port numbers.

The command prompt window after executing the command to start a COMSOL Multiphysics server.

Start the application by clicking on the Run link right above the line that says public static void main(String[] args).

The contents of the test Java file open in VS Code, with the Run link available within the code.

Upon clicking the Run link, you obtain the following outputs in the server window and VS Code, respectively.

The output in the Command Prompt window after selecting the Run link in VS Code.

The output in VS Code after selecting the Run link.

Update Java JDK Settings

VS Code will look for any installed Java Development Kits (JDKs) at startup. You can specify additional Java Virtual Machines (JVMs) if preferred, but you need to edit the configuration files manually for this. To do so, first open the Settings window. Click the Managebutton (the gear icon in the bottom left of the window)and select Settings.

A screenshot of VS Code with the settings open.

Search the settings for java.configuration and click on the link Edit in settings.json.

The search results for the settings in VS Code.

From here you can make the necessary changes in the file. Examples of potential entries are available here. Remember to save the file.

You may need to force VS Code to recompile your project after changing the JDK settings. To do so, open the Command Palette, enter compilation, and select Java: Force Java compilation. If you do not already have a Java JDK installed when going through the procedure above, then VS Code may ask you to download and install a JDK.

A screenshot of VS Code with the option to install JDK highlighted.

The code editor is now enabled to compile Java code that uses the COMSOL® API.

Note that the JAR files that are part of the COMSOL API are compiled using Java 8, and some newer JDKs (version 21 or higher) may not work with Java 8 without warnings or requiring modifications to the settings.