Operating R in Java

First, install the "Rserve" package in R.

If you are using the RGui graphical interface, you can complete this step in the menu bar under Packages - Install Packages. If you are using the pure R Console, you can use the following command:

install.packages("Rserve", repos = "https://mirrors.ustc.edu.cn/CRAN/")

After Rserve is installed, there will be a library directory in the root directory of R, where you can find the Rserve/java directory. Inside this directory, you will find two files: REngine.jar and Rserve.jar.

These two files are the R interface libraries in Java.

Note: Java cannot use R functionalities independently without the R system!

Step 1: Start Rserve

Enter R and input the following code to start Rserve:

library("Rserve")
Rserve()

If the startup is successful, R will output the path of Rserve.

Step 2: Write a Java Program

First, import the two jar libraries mentioned earlier.

After importing, we recognize a key class: RConnection, which can be used to connect to Rserve.

Now, we will use R in Java to perform an inverse matrix operation:

Example

import org.rosuda.REngine.Rserve.*;

public class Main {

    public static void main(String[] args) {
        RConnection rcon = null;
        try {
            // Establish a connection to Rserve
            rcon = new RConnection("127.0.0.1");
            
            // The eval() function is used to make R execute R statements
            // Here, a matrix m1 is created
            rcon.eval("m1 = matrix(c(1, 2, 3, 4), 2, 2, byrow=TRUE)");
            
            // The solve() function calculates the inverse of matrix m1 in R
            // and returns the result. The asDoubleMatrix function converts the data
            // into a double two-dimensional array in Java to represent the matrix
            double[][] m1 = rcon.eval("solve(m1)").asDoubleMatrix();
            
            // Output the contents of the matrix
            for (int i = 0; i < m1.length; i++) {
                for (int j = 0; j < m1[0].length; j++)
                    System.out.print(m1[i][j] + "\t");
                System.out.println();
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (rcon != null) rcon.close();
        }
    }
}

Execution Result:

-1.9999999999999998    1.0    
1.4999999999999998    -0.49999999999999994

Clearly, the result is correct, but since it involves floating-point numbers, the printed output might not be visually appealing, though it does not affect the use of the data.