JRI REngine eval() method always returns null

Question

I have a Java servlet running on Tomcat6 which uses JRI (rJava) to communicate with R installed on an Amazon linux server. I installed R from source, installed rJava via cran and set R_HOME and my classpath for Tomcat. I had to setup a few symlinks in one of my java.library.path directories to the necessary native libraries (libjri.so, libR.so and libRblas.so) because I couldn't configure java.library.path to include the directories that they installed in, but I don't think that's a problem. When I run

    ./run rtest

from the command line in $R_HOME/library/rJava/jri/ I get the expected output and the REngine class seems to be making R statements via eval() fine. But when I call eval() from my class, I get a null instead of REXP object returned in almost all cases. There are no errors logged with or without DEBUG on. The only case where I've gotten a REXP returned is when I set an array, e.g.

    array1=c(7245.0, 6003.0, 5504.0)

In this case, I get a REXP whose toString() value is

    [REAL* (7245.0, 6003.0, 5504.0)]

But if I then make an eval() call with

    summary(array1)

I get back a null instead of the expected REXP. The code, which works on my Mac, is:

private REXP multipleRegression(Datalist list) {
    String fitStr = "fit <- lm(";
    for (int i = 0; i < list.size(); i++) {
        Datastream ds = list.get(i);
        String dsStr = ds.getId() + "=" + ds.toArrayString();
        System.out.println("VALUE: " + this.eval(dsStr));
        System.out.println("SUMMARY: " + this.eval("summary(" + ds.getId() + ")"));
        fitStr += ds.getId();
        if (i == 0)
            fitStr += " ~ ";
        else if (i == list.size() - 1)
            fitStr += ")";
        else
            fitStr += " + ";
    }
    if (list.size() == 1) {
        fitStr += "1)";
    }
    this.eval(fitStr);
    return this.eval("summary(fit)");
}

Again, this works on my Mac, so I'm pretty certain the problem is with the environment and not the code. I done several hours of searching and have yet to find a solution. Any help would be wonderful.

Answer 1

Alright, so it did have to do with the native libraries and their symlinks. I got exceptions in my application when I didn't get the symlinks for libjri.so, libR.so and libRblas.so into my java.library.path, but once I got those in, no more exceptions. It turned out I also needed libRlapack.so. Once I symlinked that, I started getting the expected REXP values back.