Anyone knows how to convert .pcap file to plain text file in Java ?

There are at least two libraries: pcap4j and jNetPcap.

It seems as though pcap4j is working on OS X, while the other is not. (And it is newer).

There is a sample for reading a file:

package org.pcap4j.sample;
import java.io.EOFException;
import java.util.concurrent.TimeoutException;
import org.pcap4j.core.NotOpenException;
import org.pcap4j.core.PcapHandle;
import org.pcap4j.core.PcapHandle.TimestampPrecision;
import org.pcap4j.core.PcapNativeException;
import org.pcap4j.core.Pcaps;
import org.pcap4j.packet.Packet;
@SuppressWarnings("javadoc")
public class ReadPacketFile {
private static final int COUNT = 5;
private static final String PCAP_FILE_KEY
= ReadPacketFile.class.getName() + ".pcapFile";
private static final String PCAP_FILE
= System.getProperty(PCAP_FILE_KEY, "src/main/resources/echoAndEchoReply.pcap");
public static void main(String[] args) throws PcapNativeException, NotOpenException {
PcapHandle handle;
try {
handle = Pcaps.openOffline(PCAP_FILE, TimestampPrecision.NANO);
} catch (PcapNativeException e) {
handle = Pcaps.openOffline(PCAP_FILE);
}
for (int i = 0; i < COUNT; i++) {
  try {
    Packet packet = handle.getNextPacketEx();
    System.out.println(handle.getTimestamp());
    System.out.println(packet);
  } catch (TimeoutException e) {
  } catch (EOFException e) {
    System.out.println("EOF");
    break;
  }
}

handle.close();

}
}