Java files can be used with the COMSOL API to programmatically complete modeling tasks via code instructions instead of interacting directly with the user interface (UI). In this article, we will demonstrate how to use Visual Studio Code (VS Code) to create, edit, and compile Java files for use with COMSOL Multiphysics®. VS Code is platform independent, similar to Java; however, this step-by-step guide demonstrates how to set up the editor to compile Java code that uses the COMSOL API.
Note: The general procedure is shown using the Windows® operating system, but details of the procedure may differ depending on your operating system or future updates to VS Code.
Download Visual Studio Code for your operating system. Run the setup file; you may need to agree to the terms and choose your preferred settings. Complete the installation and open VS Code.
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A screenshot of VS Code being installed on Windows®.
Next, we install the Java extensions for VS Code. Open Extensions (Ctrl+Shift+X) and search for Java in the Marketplace. Select the Extension Pack for Java and click Install. The installation will take a few minutes and install a set of extensions. VS Code may suggest that you restart your workstation.
A screenshot of VS Code open to the Extension Pack for Java.
The Extension Pack for Java page in VS Code, after being installed through the Extension Marketplace.
After you install the Extension Pack for Java, follow the walkthrough to get started. You can access walkthroughs to help you get started by opening the Help menu and selecting Welcome.
A screenshot of the walkthrough for the Extension Pack for Java
The walkthrough page associated with the Extension Pack for Java prompts the user to install a new JDK.
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.
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. In our case, we will create a few folders in the C drive and save the file to C:\models\java. This Java file assumes our model file is in the same folder. The busbar.mph file is included with COMSOL Multiphysics®, but you can also download it from the Application Gallery and save it in the newly created directory.
A screenshot of a Java file containing several lines of text.
A screenshot of the test Java file.
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 Palette by pressing Ctrl+Shift+P or by selecting View from the menu and choosing Command Palette. Select Java: Create Java Project... from the expanded drop-down list.
A screenshot of the code editor window with a drop-down menu containing various options expanded with the option for compiling highlighted.
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 the code editor window open with a drop-down menu containing various project types expanded and with the option for having no build tools selected.
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. We will use the folder C:\models\java for the project location. Click the Select the project location button to close the dialog box.
A screenshot of the file explorer window with the project location folder shown and selected.
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.
A screenshot of the code editor window open with text entered in the field for the project name.
In VS Code, the project name is entered for the new Java project created.
A screenshot of the code editor window grayed out, with another window over it containing button options to trust or not trust the authors, with the button to trust the authors highlighted.
The dialog box that displays in VS Code, asking the user if they trust the authors of the files in the selected folder.
Now, open the default App.java file by selecting it under the src node in the Explorer pane.
A screenshot of the code editor window open with a few lines of text for code.
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.
A screenshot of the code editor window open and containing several lines of text of code, some of which exhibit a red, squiggly line underneath the text to indicate an error.
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.json node under .vscode in the Explorer pane.
A screenshot of the code editor window open with some lines of text of code for the project settings.
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 (Ctrl+S). You will notice that all the former syntax errors highlighted in the code have been cleared.
The file path will differ based on the installed version.
A screenshot of the code editor window open and containing several lines of text of code.
The contents of the test Java file in the VS Code editor.
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.
A screenshot of the command prompt window containing a couple lines of commands.
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).
A screenshot of the code editor window open and containing several lines of text of code.
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.
A screenshot of the command prompt window containing a couple lines of commands.
The output in the Command Prompt window after selecting the Run link in VS Code.
A screenshot of the code editor window containing several lines of code.
The output in VS Code after selecting the Run link.
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 Manage button (the gear icon in the bottom left of the window) and select Settings.
A screenshot of the code editor window with the settings open and the configuration settings displayed.
A screenshot of VS Code with the settings open.
Search the settings for java.configuration and click on the link Edit in settings.json.
A screenshot of the code editor window with the link to edit the settings highlighted.
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 the code editor window with the Welcome pane open and the button to install JDK highlighted.
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.
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