Question

我是Java的初学者。我正在通过串口从设备读取数据。我每隔一分钟就会获得一次数据，但是在数据正确显示之后，第一次读数将会减半。

我得到的输出是：

6050.003120815340006050.003120815350006050.0

正确的输出应该是这样的：

03120815340006050.003120815350006050.0

我的代码是：

import java.io.*;
import java.util.*; //import gnu.io.*;
import javax.comm.*;

public class SimpleRead implements Runnable, SerialPortEventListener {
    static CommPortIdentifier portId;
    static Enumeration portList;

InputStream inputStream;
SerialPort serialPort;
Thread readThread;
byte[] readBuffer;

public static void main(String[] args) {
    portList = CommPortIdentifier.getPortIdentifiers();
    System.out.println("portList... " + portList);
    while (portList.hasMoreElements()) {
        portId = (CommPortIdentifier) portList.nextElement();
        if (portId.getPortType() == CommPortIdentifier.PORT_SERIAL) {
            System.out.println("port identified is Serial.. "
                    + portId.getPortType());
            if (portId.getName().equals("COM2")) {
                System.out.println("port identified is COM2.. "
                        + portId.getName());
                // if (portId.getName().equals("/dev/term/a")) {
                SimpleRead reader = new SimpleRead();
            } else {
                System.out.println("unable to open port");
            }
        }
    }
}

public SimpleRead() {
    try {
        System.out.println("In SimpleRead() contructor");
        serialPort = (SerialPort) portId.open("SimpleReadApp1111",500);
        System.out.println(" Serial Port.. " + serialPort);
    } catch (PortInUseException e) {
        System.out.println("Port in use Exception");
    }
    try {
        inputStream = serialPort.getInputStream();
        System.out.println(" Input Stream... " + inputStream);
    } catch (IOException e) {
        System.out.println("IO Exception");
    }
    try {
        serialPort.addEventListener(this);

    } catch (TooManyListenersException e) {
        System.out.println("Tooo many Listener exception");
    }
    serialPort.notifyOnDataAvailable(true);
    try {

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

        // no handshaking or other flow control
        serialPort.setFlowControlMode(SerialPort.FLOWCONTROL_NONE);

        // timer on any read of the serial port
        serialPort.enableReceiveTimeout(500);

        System.out.println("................");

    } catch (UnsupportedCommOperationException e) {
        System.out.println("UnSupported comm operation");
    }
    readThread = new Thread(this);
    readThread.start();
}

public void run() {
    try {
        System.out.println("In run() function ");
        Thread.sleep(500);
        // System.out.println();
    } catch (InterruptedException e) {
        System.out.println("Interrupted Exception in run() method");
    }
}

public void serialEvent(SerialPortEvent event) {

    // System.out.println("In Serial Event function().. " + event +
    // event.getEventType());
    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: break;
     */
    case SerialPortEvent.DATA_AVAILABLE:
        readBuffer = new byte[8];

        try {

            while (inputStream.available()>0) {

                int numBytes = inputStream.read(readBuffer);
            //   System.out.println("Number of bytes read " + numBytes);
            }

            System.out.print(new String(readBuffer));

        } catch (IOException e) {
            System.out.println("IO Exception in SerialEvent()");
        }
        break;
    }
    // System.out.println();
/*  String one = new String(readBuffer);
    char two = one.charAt(0);
    System.out.println("Character at three: " + two);*/
}

}

Answer 1

使用以下内容：

while (inputStream.available()>0) {
  int numBytes = inputStream.read(readBuffer);
  System.out.print(new String(readBuffer));
}

您正在从while循环中打印结果。但是，循环中的代码可能会运行多次，因此会丢失大量数据。

Answer 2

在读取之前尝试刷新端口的输入缓冲区。否则，如果发送端在程序启动期间（或之前，可能由操作系统决定）发送数据，您将获得旧的缓冲数据。

此外，如果可能，请考虑将消息框架添加到协议中，这样您就可以检测到何时读取的内容实际上不是完整的消息，并将其丢弃。对于这些问题，这通常非常有用。

Answer 3

这看起来好像是在阅读在开始之前发送的其他一些消息。

尝试在启动程序时读取尽可能多的数据以清除任何硬件缓冲区。之后，开始处理。

在Java中读取串口

3 个答案: