在Java中，可以使用RXTXcomm庫來實現串口通信，通過創建多個線程來實現多個串口之間的通信。

以下是一個簡單的示例代碼，演示如何使用多線程的方式實現串口通信：

import gnu.io.CommPortIdentifier;
import gnu.io.SerialPort;

import java.io.InputStream;
import java.io.OutputStream;

public class SerialCommExample {

    public static void main(String[] args) {
        try {
            CommPortIdentifier portIdentifier = CommPortIdentifier.getPortIdentifier("/dev/ttyUSB0");
            SerialPort serialPort = (SerialPort) portIdentifier.open("SerialCommExample", 1000);

            serialPort.setSerialPortParams(9600, SerialPort.DATABITS_8, SerialPort.STOPBITS_1, SerialPort.PARITY_NONE);

            InputStream in = serialPort.getInputStream();
            OutputStream out = serialPort.getOutputStream();

            Thread readerThread = new Thread(new SerialReader(in));
            Thread writerThread = new Thread(new SerialWriter(out));

            readerThread.start();
            writerThread.start();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static class SerialReader implements Runnable {
        private InputStream in;

        public SerialReader(InputStream in) {
            this.in = in;
        }

        @Override
        public void run() {
            try {
                int data;
                while ((data = in.read()) > -1) {
                    System.out.print((char) data);
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    public static class SerialWriter implements Runnable {
        private OutputStream out;

        public SerialWriter(OutputStream out) {
            this.out = out;
        }

        @Override
        public void run() {
            try {
                while (true) {
                    out.write("Hello, World!".getBytes());
                    Thread.sleep(1000);
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}

在這個示例中，我們創建了兩個線程分別用于讀取串口數據和向串口寫入數據。讀取線程通過調用SerialReader類來實現，寫入線程通過調用SerialWriter類來實現。這樣就實現了在Java中通過多線程的方式來進行串口通信。