问题
I have no idea of what is happening to my code. i am getting no errors and no response as well. I am writing the data to the serialport and waiting for the response by activating port.notifyOnDataAvailable(true); but this event is not triggered and inputstream.available() returns 0 always. What might be wrong ? I am using RXTX in linux.
EDIT
package testConn;
import forms_helper.global_variables;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintStream;
import java.io.UnsupportedEncodingException;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.comm.*;
import java.util.*;
/** Check each port to see if it is open. **/
public class openPort implements SerialPortEventListener {
static Enumeration portList;
static CommPortIdentifier portId;
static String messageString;
public static SerialPort serialPort;
static OutputStream outputStream;
InputStream inputStream;
static boolean outputBufferEmptyFlag = false;
private BufferedReader is;
private PrintStream os;
public void open() {
Enumeration port_list = CommPortIdentifier.getPortIdentifiers();
while (port_list.hasMoreElements()) {
// Get the list of ports
CommPortIdentifier port_id = (CommPortIdentifier) port_list.nextElement();
if (port_id.getName().equals("/dev/ttyS1")) {
// Attempt to open it
try {
SerialPort port = (SerialPort) port_id.open("PortListOpen", 20000);
System.out.println("Opened successfully:"+port);
try {
int baudRate = 9600; //
port.setSerialPortParams(
baudRate,
SerialPort.DATABITS_7,
SerialPort.STOPBITS_1,
SerialPort.PARITY_EVEN);
port.setDTR(true);
port.setFlowControlMode(SerialPort.FLOWCONTROL_NONE);
System.out.println("properties are set");
} catch (UnsupportedCommOperationException e) {
System.out.println(e);
}
try {
//input = new SerialReader(in);
port.addEventListener(this);
System.out.println("listeners attached" + this);
} catch (TooManyListenersException e) {
System.out.println("too many listeners");
}
port.notifyOnDataAvailable(true);
//port.notifyOnOutputEmpty(true);
//sendMessage(port,"@PL");
//port.close ();
try {
is = new BufferedReader(new InputStreamReader(port.getInputStream()));
} catch (IOException e) {
System.err.println("Can't open input stream: write-only");
is = null;
}
try {
os = new PrintStream(port.getOutputStream(), true);
} catch (IOException ex) {
Logger.getLogger(openPort.class.getName()).log(Level.SEVERE, null, ex);
}
try {
inputStream = port.getInputStream();
System.out.println("inputstream" + inputStream.available());
outputStream = (OutputStream) port.getOutputStream();
os = new PrintStream(port.getOutputStream(), true, "US-ASCII");
} catch (IOException e) {
System.out.println(e);
}
//set the created variables to global variables
global_variables.port = port;
global_variables.inputStream = inputStream;
System.out.println(inputStream);
System.out.println(outputStream);
global_variables.outputStream = outputStream;
global_variables.os = os;
} catch (PortInUseException pe) {
System.out.println("Open failed");
String owner_name = port_id.getCurrentOwner();
if (owner_name == null) {
System.out.println("Port Owned by unidentified app");
} else // The owner name not returned correctly unless it is
// a Java program.
{
System.out.println(" " + owner_name);
}
}
}
}
}
public static void sendMessage(SerialPort port, String msg) {
if (port != null) {
System.out.println(msg);
try {
byte[] bytes = msg.getBytes("US-ASCII");
try {
global_variables.outputStream.write(bytes);
System.out.println(bytes.length);
global_variables.outputStream.flush();
} catch (IOException ex) {
Logger.getLogger(openPort.class.getName()).log(Level.SEVERE, null, ex);
}
} catch (UnsupportedEncodingException ex) {
Logger.getLogger(openPort.class.getName()).log(Level.SEVERE, null, ex);
}
System.out.println("Opened successfully:"+msg.getBytes());
//global_variables.outputStream.write(msg.getBytes());
//global_variables.outputStream.flush();
//global_variables.os.print(msg);
System.out.println(global_variables.outputStream);
try {
Thread.sleep(2000); // Be sure data is xferred before closing
System.out.println("read called");
//SimpleRead read = new SimpleRead();
//int read = global_variables.inputStream.read();
//System.out.println("read call ended"+read);
} catch (Exception e) {
}
}
}
public void serialEvent(SerialPortEvent event) {
System.out.println(event.getEventType());
String line;
try {
line = is.readLine();
if (line == null) {
System.out.println("EOF on serial port.");
System.exit(0);
}
os.println(line);
} catch (IOException ex) {
System.err.println("IO Error " + ex);
}
switch (event.getEventType()) {
/*
case SerialPortEvent.BI:
case SerialPortEvent.OE:
case SerialPortEvent.FE:
case SerialPortEvent.PE:
case SerialPortEvent.CD:
case SerialPortEvent.CTS:
case SerialPortEvent.DSR:
case SerialPortEvent.RI:
case SerialPortEvent.OUTPUT_BUFFER_EMPTY:
System.out.println("event.getEventType()");
break;
*
*/
case SerialPortEvent.DATA_AVAILABLE:
System.out.println("inside event handler data available");
byte[] readBuffer = new byte[20];
try {
while (inputStream.available() > 0) {
int numBytes = inputStream.read(readBuffer);
}
System.out.print(new String(readBuffer));
System.exit(1);
} catch (IOException e) {
System.out.println(e);
}
break;
}
}
} // PortListOpen
I am opening the port on main method and sending the message on a button click event inside the application.
回答1:
.available() can not be used in inter-process communication (serial included), since it only checks if there is data available (in input buffers) in current process.
In serial communication, when you send a messaga and then immediately call available() you will mostly get 0 as serial port did not yet reply with any data.
The solution is to use blocking read() in a separate thread (with interrupt() to end it):
Thread interrupt not ending blocking call on input stream read
回答2:
To partially answer your question.
From the javadocs
The available method for class InputStream always returns 0.
http://download.oracle.com/javase/6/docs/api/java/io/InputStream.html#available()
So that part at least is as expected
回答3:
By using a PrintStream you are suppressing exceptions that you need to know about in any request/response scenario.
Most probably you haven't even sent anything yet.
来源：https://stackoverflow.com/questions/5826198/inputstream-available-is-0-always