內(nèi)容: 一個嵌入式系統(tǒng)通常需要通過串口與其主控系統(tǒng)進(jìn)行全雙工通訊，譬如一個流水線控制系統(tǒng)需要不斷的接受從主控系統(tǒng)發(fā)送來的查詢和控制信息，并將執(zhí)行結(jié)果或查詢結(jié)果發(fā)送回主控系統(tǒng)。本文介紹了一個簡單的通過串口實(shí)現(xiàn)全雙工通訊的Java類庫，該類庫大大的簡化了對串口進(jìn)行操作的過程。 本類庫主要包括：SerialBean.java (與其他應(yīng)用程序的接口), SerialBuffer.java (用來保存從串口所接收數(shù)據(jù)的緩沖區(qū)), ReadSerial.java (從串口讀取數(shù)據(jù)的程序)。另外本類庫還提供了一個例程SerialExample.java 作為示范。在下面的內(nèi)容中將逐一對這幾個部分進(jìn)行詳細(xì)介紹。 1. SerialBeanSerialBean是本類庫與其他應(yīng)用程序的接口。該類庫中定義了SerialBean的構(gòu)造方法以及初始化串口，從串口讀取數(shù)據(jù)，往串口寫入數(shù)據(jù)以及關(guān)閉串口的函數(shù)。具體介紹如下： public SerialBean(int PortID)本函數(shù)構(gòu)造一個指向特定串口的SerialBean，該串口由參數(shù)PortID所指定。PortID = 1 表示COM1，PortID = 2 表示COM2，由此類推。public int Initialize()本函數(shù)初始化所指定的串口并返回初始化結(jié)果。如果初始化成功返回1，否則返回-1。初始化的結(jié)果是該串口被SerialBean獨(dú)占性使用，其參數(shù)被設(shè)置為9600, N, 8, 1。如果串口被成功初始化，則打開一個進(jìn)程讀取從串口傳入的數(shù)據(jù)并將其保存在緩沖區(qū)中。public String ReadPort(int Length)本函數(shù)從串口(緩沖區(qū))中讀取指定長度的一個字符串。參數(shù)Length指定所返回字符串的長度。public void WritePort(String Msg)本函數(shù)向串口發(fā)送一個字符串。參數(shù)Msg是需要發(fā)送的字符串。public void ClosePort()本函數(shù)停止串口檢測進(jìn)程并關(guān)閉串口。 SerialBean的源代碼如下： package serial;import java.io.*;import java.util.*;import javax.comm.*;/**** This bean provides some basic functions to implement full dulplex* information exchange through the srial port.**/public class SerialBean{static String PortName;CommPortIdentifier portId;SerialPort serialPort;static OutputStream out;static InputStream in;SerialBuffer SB;ReadSerial RT;/**** Constructor** @param PortID the ID of the serial to be used. 1 for COM1,* 2 for COM2, etc.**/public SerialBean(int PortID){PortName = 'COM' + PortID;}/**** This function initialize the serial port for communication. It startss a* thread which consistently monitors the serial port. Any signal capturred* from the serial port is stored into a buffer area.**/public int Initialize(){int InitSuccess = 1;int InitFail = -1;try{portId = CommPortIdentifier.getPortIdentifier(PortName);try{serialPort = (SerialPort)portId.open('Serial_Communication', 2000);} catch (PortInUseException e){return InitFail;}//Use InputStream in to read from the serial port, and OutputStream//out to write to the serial port.try{in = serialPort.getInputStream();out = serialPort.getOutputStream();} catch (IOException e){return InitFail;}//Initialize the communication parameters to 9600, 8, 1, none.try{serialPort.setSerialPortParams(9600,SerialPort.DATABITS_8,SerialPort.STOPBITS_1,SerialPort.PARITY_NONE);} catch (UnsupportedCommOperationException e){return InitFail;}} catch (NoSuchPortException e){return InitFail;}// when successfully open the serial port, create a new serial buffer,// then create a thread that consistently accepts incoming signals from// the serial port. Incoming signals are stored in the serial buffer.SB = new SerialBuffer();RT = new ReadSerial(SB, in);RT.start();// return success informationreturn InitSuccess;}/**** This function returns a string with a certain length from the incomin* messages.** @param Length The length of the string to be returned.**/public String ReadPort(int Length){String Msg;Msg = SB.GetMsg(Length);return Msg;}/**** This function sends a message through the serial port.** @param Msg The string to be sent.**/public void WritePort(String Msg){int c;try{for (int i = 0; i < Msg.length(); i++)out.write(Msg.charAt(i));} catch (IOException e) {}}/**** This function closes the serial port in use.**/public void ClosePort(){RT.stop();serialPort.close();}}2. SerialBuffer SerialBuffer是本類庫中所定義的串口緩沖區(qū)，它定義了往該緩沖區(qū)中寫入數(shù)據(jù)和從該緩沖區(qū)中讀取數(shù)據(jù)所需要的函數(shù)。 public synchronized String GetMsg(int Length)本函數(shù)從串口(緩沖區(qū))中讀取指定長度的一個字符串。參數(shù)Length指定所返回字符串的長度。public synchronized void PutChar(int c)本函數(shù)望串口緩沖區(qū)中寫入一個字符，參數(shù)c 是需要寫入的字符。在往緩沖區(qū)寫入數(shù)據(jù)或者是從緩沖區(qū)讀取數(shù)據(jù)的時候，必須保證數(shù)據(jù)的同步，因此GetMsg和PutChar函數(shù)均被聲明為synchronized并在具體實(shí)現(xiàn)中采取措施實(shí)現(xiàn)的數(shù)據(jù)的同步。 SerialBuffer的源代碼如下： package serial;/**** This class implements the buffer area to store incoming data from the serial* port.**/public class SerialBuffer{private String Content = '';private String CurrentMsg, TempContent;private boolean available = false;private int LengthNeeded = 1;/**** This function returns a string with a certain length from the incomin* messages.** @param Length The length of the string to be returned.**/public synchronized String GetMsg(int Length){LengthNeeded = Length;notifyAll();if (LengthNeeded> Content.length()){available = false;while (available == false){try{wait();} catch (InterruptedException e) { }}}CurrentMsg = Content.substring(0, LengthNeeded);TempContent = Content.substring(LengthNeeded);Content = TempContent;LengthNeeded = 1;notifyAll();return CurrentMsg;}/**** This function stores a character captured from the serial port to the* buffer area.** @param t The char value of the character to be stored.**/public synchronized void PutChar(int c){Character d = new Character((char) c);Content = Content.concat(d.toString());if (LengthNeeded < Content.length()){available = true;}notifyAll();}}3. ReadSerialReadSerial是一個進(jìn)程，它不斷的從指定的串口讀取數(shù)據(jù)并將其存放到緩沖區(qū)中。 public ReadSerial(SerialBuffer SB, InputStream Port)本函數(shù)構(gòu)造一個ReadSerial進(jìn)程，參數(shù)SB指定存放傳入數(shù)據(jù)的緩沖區(qū)，參數(shù)Port指定從串口所接收的數(shù)據(jù)流。public void run()ReadSerial進(jìn)程的主函數(shù)，它不斷的從指定的串口讀取數(shù)據(jù)并將其存放到緩沖區(qū)中。 ReadSerial的源代碼如下： package serial;import java.io.*;/**** This class reads message from the specific serial port and save* the message to the serial buffer.**/public class ReadSerial extends Thread{private SerialBuffer ComBuffer;private InputStream ComPort;/**** Constructor** @param SB The buffer to save the incoming messages.* @param Port The InputStream from the specific serial port.**/public ReadSerial(SerialBuffer SB, InputStream Port){ComBuffer = SB;ComPort = Port;}public void run(){int c;try{while (true){c = ComPort.read();ComBuffer.PutChar(c);}} catch (IOException e) {}}}4. SerialExampleSerialExample是本類庫所提供的一個例程。它所實(shí)現(xiàn)的功能是打開串口COM1，對其進(jìn)行初始化，從串口讀取信息對其進(jìn)行處理后將處理結(jié)果發(fā)送到串口。 import serial.*;import java.io.*;/**** This is an example of how to use the SerialBean. It opens COM1 and reads* six messages with different length form the serial port.**/class SerialExample{public static void main(String[] args){//TO DO: Add your JAVA codes hereSerialBean SB = new SerialBean(1);String Msg;SB.Initialize();for (int i = 5; i