Re: Calling a C function from Java using the JNI

Hi Roedy,

OK, I also got the code to work using the ProcessBuilder class, which
is new in Java 5,
using your very helpful and extensive website (plus lots of other
interesting things
outside of programming).

I modified my bean so that it is now:

package com.corejsf;

import java.io.*;
import java.util.*;

public class UserBean {
   private String name;
   private String password;

   // PROPERTY: name
   public String getName() { return name; }
   public void setName(String newValue) {
       System.out.println("Now in UserBean.setName()");
       System.out.println(newValue);
       try {
           ProcessBuilder pb = new ProcessBuilder("/home/csharp/
shelltests/called-from-java",
                               "first_argument", "second_argument",
"third_argument");
           pb.directory(new File("/home/csharp"));
           pb.start();
       } catch (Exception e) {
           System.out.println("Error executing script");
       }
       name = newValue;
   }

   // PROPERTY: password
   public String getPassword() { return password; }
   public void setPassword(String newValue) { password = newValue; }
}

with the JNI removed. It calls up the script in the path given above,
and the contents of
"called-from-java" are:

#!/bin/sh
ls -lt > scriptout
echo $0 >> scriptout
echo $1 >> scriptout
echo $2 >> scriptout
echo $3 >> scriptout

which lists the files in the directory specified in the "directory()"
method. If I don't do
that, Glassfish writes to a file with root privileges in its own
directory, which is highly
undesirable. One thing is that the statement

pb.directory("/home/csharp");

does not compile and generates a syntax error, even though you have
something like that on
your website. The "new FILE(....)" has to be nested in the method
call for the code to
compile, at least on my computer, which has Java 6.

Anyway, although the JNI isn't required here, as was mentioned
earlier, at least I now know
how to use it.

Christopher