Send String from Java to Arduino (simple example)

Question

It is solved. I put a Thread.sleep(4000); after opening the port in the java code and now it works. The problem was that the arduino is reset everytime the port is opened. When i was sending the data, the arduino wasn't ready to listen.

I'm new to arduino and Java, but i made a program so simple that I don't get why isn't working.

I send a String to the serial port that correspond to arduino (COM5):

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

public class SimpleWrite {

static Enumeration portList;
static CommPortIdentifier portId;
static String messageString = "color FF00FFEND";
static SerialPort serialPort;
static OutputStream outputStream;

public static void main(String[] args) {
    portList = CommPortIdentifier.getPortIdentifiers();


    while (portList.hasMoreElements()) {

        portId = (CommPortIdentifier) portList.nextElement();
        if (portId.getPortType() == CommPortIdentifier.PORT_SERIAL) {

             if (portId.getName().equals("COM5")) {

                try {
                    serialPort = (SerialPort)
                    portId.open("SimpleWriteApp", 2000);

                    outputStream = serialPort.getOutputStream();

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

                    outputStream.write(messageString.getBytes());
                    System.out.println(messageString);

                    outputStream.close();
                    serialPort.close();
                } 
                catch (IOException e) {System.out.println("err3");}
                catch (PortInUseException e) {System.out.println("err");}
                catch (IOException e) {System.out.println("err1");}
                catch (UnsupportedCommOperationException e) {System.out.println("err2");}
            }
        }
    }
}
}

and the code in arduino to get that string:

char inputBuffer[10];   

void setup() {                
  Serial.begin(9600);  
}

void loop() {
    while (true) 
    {
      if (Serial.available() > 0) {
          Serial.readBytes(inputBuffer, Serial.available());
          delay(5000);
          Serial.print("I got this ->");
          Serial.print(inputBuffer);
          Serial.println("<-");
      }
    }
}

the while(true) is for testing purposes. I dont get nothing printed, and I dont know where the problem is. I have seen all the post about arduino and java here and i dont find nothing that helps. Thanks for the help and sorry if it is a stupid question, im a newbie to this

Im using RXTXcomm.jar. Version: RXTX-2.2-20081207

Solution 1

It is solved. I put a Thread.sleep(4000) after opening the port in the java code and now it works. The problem was that the Arduino is reset everytime the port is opened, so I was sending the data when the Arduino wasn't ready to listen.

char inputBuffer[10];   

void setup()
{                
    Serial.begin(9600);  
}

void loop()
{
     while (true) 
     {
          if (Serial.available() > 0)
          {
              Serial.readBytes(inputBuffer, 10);
              delay(5000);
              Serial.print("I got this ->");
              Serial.print(inputBuffer);
              Serial.println("<-");
          }
     }
}

Solution 2

You could use the Java-Arduino Communication Library. It can be found here: https://sourceforge.net/projects/javaarduinolibrary/. (be sure to download both jars) Then your code would look something like this:

import arduino.*;
class JavaArduinoComm {
        public static void main(String[] args) {
        Arduino obj = new Arduino('PortDescription', BAUD_RATE);
        obj.openConnection();
    }
}

Then you can use any of the following methods:

1. String serialRead(int limit) - returns a string containing as many readings as the value of limit. recommended for reading
2. void serialWrite(String s) - writes the contents of the entire string to the serial at once. written as string to serial.
3. void serialWrite(String s, int noOfChars, int delay) - writes the contents of the strings to the serial gradually. It writes the string in incremental steps with 'noOfChars' charaacters each time, with a pause of 'delay' milliseconds between each write. written as string to serial. recommended to write String
4. void serialWrite(char c) - writes the individual char to the serial in datatype char.
5. void serialWrite(char c, int delay) - writes the individual char to the serial in datatype char and pauses the thread for delay milliseconds after. recommended to write char

Comments

[Georgi Peev]

For ~1500ms are enough. Another way is to send a message from the Arduino in the setup function and have a polling for the data from the Java side waiting for that message and when received to unblock your sending of the data from the Java side.