內容: 一個嵌入式系統通常需要通過串口與其主控系統進行全雙工通訊，譬如一個流水線控制系統需要不斷的接受從主控系統發送來的查詢和控制信息，并將執行結果或查詢結果發送回主控系統。本文介紹了一個簡單的通過串口實現全雙工通訊的Java類庫，該類庫大大的簡化了對串口進行操作的過程。 本類庫主要包括：SerialBean.java (與其他應用程序的接口), SerialBuffer.java (用來保存從串口所接收數據的緩沖區), ReadSerial.java (從串口讀取數據的程序)。另外本類庫還提供了一個例程SerialExample.java 作為示范。在下面的內容中將逐一對這幾個部分進行詳細介紹。 1. SerialBeanSerialBean是本類庫與其他應用程序的接口。該類庫中定義了SerialBean的構造方法以及初始化串口，從串口讀取數據，往串口寫入數據以及關閉串口的函數。具體介紹如下： public SerialBean(int PortID)本函數構造一個指向特定串口的SerialBean，該串口由參數PortID所指定。PortID = 1 表示COM1，PortID = 2 表示COM2，由此類推。public int Initialize()本函數初始化所指定的串口并返回初始化結果。如果初始化成功返回1，否則返回-1。初始化的結果是該串口被SerialBean獨占性使用，其參數被設置為9600, N, 8, 1。如果串口被成功初始化，則打開一個進程讀取從串口傳入的數據并將其保存在緩沖區中。public String ReadPort(int Length)本函數從串口(緩沖區)中讀取指定長度的一個字符串。參數Length指定所返回字符串的長度。public void WritePort(String Msg)本函數向串口發送一個字符串。參數Msg是需要發送的字符串。public void ClosePort()本函數停止串口檢測進程并關閉串口。 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，它定義了往該緩沖區中寫入數據和從該緩沖區中讀取數據所需要的函數。 public synchronized String GetMsg(int Length)本函數從串口(緩沖區)中讀取指定長度的一個字符串。參數Length指定所返回字符串的長度。public synchronized void PutChar(int c)本函數望串口緩沖區中寫入一個字符，參數c 是需要寫入的字符。在往緩沖區寫入數據或者是從緩沖區讀取數據的時候，必須保證數據的同步，因此GetMsg和PutChar函數均被聲明為synchronized并在具體實現中采取措施實現的數據的同步。 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是一個進程，它不斷的從指定的串口讀取數據并將其存放到緩沖區中。 public ReadSerial(SerialBuffer SB, InputStream Port)本函數構造一個ReadSerial進程，參數SB指定存放傳入數據的緩沖區，參數Port指定從串口所接收的數據流。public void run()ReadSerial進程的主函數，它不斷的從指定的串口讀取數據并將其存放到緩沖區中。 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。它所實現的功能是打開串口COM1，對其進行初始化，從串口讀取信息對其進行處理后將處理結果發送到串口。 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