Test java closing mapped files and GC

gistfile1.java

package com.company;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;

/**
 * Opens a file, maps a chunk, closes. Expect to see many open filehandles until it GCs.
 * http://mail-archives.apache.org/mod_mbox/kafka-users/201503.mbox/%[email protected]%3E
 */
public class Main {

    public static void main(String[] args) throws Exception {
        File f = new File("mapfile.dat");
        if (!f.exists()) {
            System.out.println("Creating " + f.getCanonicalPath());
            FileOutputStream o = new FileOutputStream(f);
            o.write(new byte[16 << 10]);
            o.close();
        }

        int total = 0;
        while (true) {
            for (int ii = 0; ii < 100; ii++) {
                ++total;
                FileInputStream in = new FileInputStream(f);
                FileChannel ch = in.getChannel();
                MappedByteBuffer b = ch.map(FileChannel.MapMode.READ_ONLY, 0, f.length());
                in.close();
            }
            System.out.println("Created " + total + " mappings");
            Thread.sleep(1000);
            //System.gc();
            //System.runFinalization();
        }
    }
}