Deploy MATLAB Function That Accepts Struct Array as Input Argument to Java Application

This example shows how to package a MATLAB^® function that accepts a struct array as input and deploy it to a Java^® application. The workflow is supported on Windows^®, Linux^®, and macOS systems. This example uses a workflow based on Windows.

Prerequisites

• Create a new work folder that is visible to the MATLAB search path. This example uses a folder named work.

• Verify that you have set up a Java development environment. For details, see Set Up Java Development Environment.

• Verify that you have met all of the MATLAB Compiler SDK™ Java target requirements. For details, see MATLAB Compiler SDK Java Target Requirements.

• End users must have an installation of MATLAB Runtime to run the application. For details, see Download and Install MATLAB Runtime.

  For testing purposes, you can use an installation of MATLAB instead of MATLAB Runtime.

Data Management

To exchange data between the deployed MATLAB code and the Java application, use the MATLAB Data API for Java. This API is also used by MATLAB Engine. For details, see Java Data Type Conversions.

Create MATLAB Function

Create a MATLAB file named analyzeData.m with the following code:

function outputStruct = analyzeData(inputStruct)
% This function takes a MATLAB struct 'inputStruct' as input, performs
% statistical analysis on each numeric field, and returns a struct
% 'outputStruct' containing the results of these analyses. Non-numeric
% fields in the input struct are ignored.
%
% Inputs:
%   inputStruct - Struct with fields containing numeric data.
%
% Outputs:
%   outputStruct - Struct with the same fields as 'inputStruct'. Each
%                  field is a struct with 'mean', 'std', and 'max'
%                  of the corresponding field in 'inputStruct'.

% Initialize outputStruct
outputStruct = struct();

% Get field names from the input struct
fields = fieldnames(inputStruct);

% Loop over each field and perform analysis
for i = 1:length(fields)
    fieldName = fields{i};

    % Ensure the field contains numeric data
    if isnumeric(inputStruct.(fieldName))
        % Calculate mean
        outputStruct.(fieldName).mean = mean(inputStruct.(fieldName));

        % Calculate standard deviation
        outputStruct.(fieldName).std = std(inputStruct.(fieldName));

        % Calculate max value
        outputStruct.(fieldName).max = max(inputStruct.(fieldName));
    else
        warning('Field %s is not numeric and was skipped.', fieldName);
    end
end
end

Test the MATLAB function at the command prompt.

data = struct();
data.temperatures = [72, 75, 69, 68, 70];
data.pressures = [30, 29.5, 30.2, 29.9, 30.1];
output = analyzeData(data)
output.temperatures(:)
output.pressures(:)

output = 
  struct with fields:

    temperatures: [1×1 struct]
       pressures: [1×1 struct]
ans = 
  struct with fields:

    mean: 70.8000
     std: 2.7749
     max: 75
ans = 
  struct with fields:

    mean: 29.9400

Create Java Package Using compiler.build.javaPackage

Use the compiler.build.javaPackage function to generate a code archive (.ctf file) from the MATLAB function.

buildResults = compiler.build.javaPackage( ...
    "analyzeData.m",...
    Interface="matlab-data",...
    Verbose="on", OutputDir=".\output",....
    PackageName="com.example.matlabfunction")

Integrate MATLAB Code into Java Application

Use Java Command Line API to Build Application

1. Create a Java driver application named AnalyzeDataExample.java with the following code:

    AnalyzeDataExample.java

   import com.mathworks.runtime.*;
   import com.mathworks.matlab.types.*;
   import java.io.Writer;
   
   public class AnalyzeDataExample {
       public static void main(String[] args) {
           String ctfPath = "P:/MATLAB/work/output/matlabfunction.ctf";
   
           try (MatlabRuntime runtime = MatlabRuntime.startMatlab(ctfPath)) {
               // Create input struct using the constructor
               Struct inputStruct = new Struct(
                   "temperatures", new double[]{72, 75, 69, 68, 70},
                   "pressures", new double[]{30, 29.5, 30.2, 29.9, 30.1}
               );
   
               // Call MATLAB analyzeData function
               Writer output = null;  // Use system output
               Writer error = null;   // Use system error
               Struct outputStruct = runtime.<Struct>feval("analyzeData", output, error, inputStruct);
   
               // Print the results
               printMATLABStruct(outputStruct);
   
           } catch (Exception e) {
               System.err.println("An error occurred: " + e.getMessage());
               e.printStackTrace();
           } finally {
               MatlabRuntime.terminateMatlabClient(); 
           }
       }
   
       public static void printMATLABStruct(Struct matlabStruct) {
           for (String fieldName : matlabStruct.keySet()) {
               System.out.println("Field: " + fieldName);
               Struct nestedStruct = (Struct) matlabStruct.get(fieldName);
               printNestedFields(nestedStruct);
           }
       }
   
       private static void printNestedFields(Struct nestedStruct) {
           for (String fieldName : nestedStruct.keySet()) {
               double fieldValue = (Double) nestedStruct.get(fieldName);
               System.out.printf("  %s: %.4f%n", fieldName, fieldValue);
           }
       }
   }

   The resulting directory structure after creating this file is as follows:

   work/
   ├── AnalyzeDataExample.java
   └── output/
       ├── matlabfunction.ctf
       └── ...

2. Compile your Java code by setting the classpath to include matlabruntime.jar.

   REM End-users use MATLAB Runtime path since MATLAB is not be installed.
   set MATLABROOT=C:\Program Files\MATLAB\R2026a
   
   javac -classpath ".;%MATLABROOT%\toolbox\javabuilder\jar\matlabruntime.jar" AnalyzeDataExample.java

3. Run your Java application by setting the classpath to include matlabruntime.jar and by configuring access to the native runtime libraries. For details, see Set MATLAB Library Paths for Testing Deployed Applications.

   java -classpath ".;%MATLABROOT%\toolbox\javabuilder\jar\matlabruntime.jar" AnalyzeDataExample
   

   Field: temperatures
     std: 2.7749
     max: 75.0000
     mean: 70.8000
   Field: pressures
     std: 0.2702
     max: 30.2000
     mean: 29.9400

   Running a Java application without setting the environment variables to provide access to the native runtime libraries from MATLAB or MATLAB Runtime results in a java.lang.UnsatisfiedLinkError.

   Note

   When testing applications on a machine with a full MATLAB installation, you can set up native library access using the MATLAB installation.

   In a deployment scenario where MATLAB Runtime is used, you must explicitly specify the location of the native libraries within an installation of MATLAB Runtime. This distinction ensures that deployed applications run independently of a full MATLAB installation.

   For details, see:

   • Set MATLAB Library Paths for Testing Deployed Applications

   • Set MATLAB Runtime Library Paths for Deployment