Load data using rJava

I use rJava to integrate Java and R in my project.

I need to load GWmodel R package in my application and calculate the distance matrix from Java.

This is my function to load GWmodel and calculating distance matrix :

Rengine engine = new Rengine(new String[] { "--no-save" }, false, null);
engine.eval("library(GWmodel)");
engine.eval("data(LondonHP)");
engine.eval("DM <- gw.dist(dp.locat=coordinates(londonhp))");
double[][] matrix = engine.eval("DM").asMatrix();

But the code result an error :

Exception in thread "main" java.lang.NullPointerException
    at rjavaexm.RJavaExm.main(RJavaExm.java:30)

So, I want to know, is it possible to load R package and data using rJava from Java like code above?

Or are there any appropriate ways to do that?

Solution

I'm using maven so i have the following (generated from a simple maven project)

mvn archetype:generate   -DgroupId=com.test.rserve  -DartifactId=com.test.rserve

Select default choice.

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.test.rserve</groupId>
  <artifactId>com.test.rserve</artifactId>
  <packaging>jar</packaging>
  <version>1.0-SNAPSHOT</version>
  <name>com.test.rserve</name>
  <url>http://maven.apache.org</url>
  <dependencies>
  <dependency>  
    <groupId>org.rosuda.REngine</groupId>
    <artifactId>Rserve</artifactId>
    <version>1.8.1</version>
    </dependency>    
  </dependencies>
</project>

App.java

package com.test.rserve;

import org.rosuda.REngine.REXP;
import org.rosuda.REngine.REXPMismatchException;
import org.rosuda.REngine.Rserve.RConnection;
import org.rosuda.REngine.Rserve.RserveException;


public class App {

    public static void main(String[] args) throws RserveException,
            REXPMismatchException {
        RConnection c = new RConnection();
        REXP x = c.eval("R.version.string");
        System.out.println(x.asString());   
    c.eval("library(GWmodel)");
    c.eval("data(LondonHP)");
    c.eval("DM <- gw.dist(dp.locat=coordinates(londonhp))");
    REXP y = c.eval("dim(DM)[1]");
    System.out.println(y.asString());
    c.close();
    }
}

Make sure package Rserve is installed in your R environment.

from R

library(Rserve)
Rserve()

with maven (command line, another shell)

mvn exec:java -Dexec.mainClass="com.test.rserve.App"

We get with my settings :

R version 3.2.4 (2016-03-16)
316

Don't forget to close the Rserve server/process afterwards ...