用Java實現串口通信（windows系統下），須要用到sun提供的串口包 javacomm20-win32.zip。當中要用到三個文件，配置例如以下：

1.comm.jar放置到 JAVA_HOME/jre/lib/ext;
2.win32com.dll放置到 JAVA_HOME/bin;
3.javax.comm.properties 兩個地方都要放

? ??jre/lib(也就是在JAVA目錄下的jre)

?? JAVA_HOME/jre/lib

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說一下我應用的環境。電子秤稱重時，計算機通過串口給稱重控制顯示器發送一次命令“R”，控制顯示器則發送一次重量數據給串口，計算機再讀取將數據顯示在網頁上。這樣就構成了一個實時稱重系統。

讀寫串口的代碼例如以下：

package com.chengzhong.tools; import java.io.*;import javax.comm.CommPortIdentifier; import javax.comm.*;/** * * This bean provides some basic functions to implement full duplex * information exchange through the serial port. * */public class SerialBean {public static String PortName; public static CommPortIdentifier portId; public static SerialPort serialPort; public static OutputStream out; public static InputStream in;//保存讀數結果 public static String result=""; public static int openSignal=1;/** * * 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 starts a * thread which consistently monitors the serial port. Any signal captured * from the serial port is stored into a buffer area. * */public int Initialize() {openSignal=1;try{portId = CommPortIdentifier.getPortIdentifier(PortName);try{serialPort = (SerialPort)portId.open("Serial_Communication", 2000);} catch (PortInUseException e){if(!SerialBean.portId.getCurrentOwner().equals("Serial_Communication")){openSignal=2; //該串口被其他程序占用}else if(SerialBean.portId.getCurrentOwner().equals("Serial_Communication")){openSignal=1;return openSignal;}return openSignal;}//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){openSignal=3; //輸入輸出流錯誤return openSignal;}//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){openSignal=4; //參數不對return openSignal;}} catch (NoSuchPortException e){portId=null;openSignal=5; //沒有該串口return openSignal;}// 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.// return success informationreturn openSignal; }/** * * This function returns a string with a certain length from the incoming * messages. * * @param Length The length of the string to be returned. * */public static void ReadPort() {SerialBean.result=""; int c; try {if(in!=null){while(in.available()>0){c = in.read();Character d = new Character((char) c);SerialBean.result=SerialBean.result.concat(d.toString());}}} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace(); }}/** * * This function sends a message through the serial port. * * @param Msg The string to be sent. * */public static void WritePort(String Msg) {try {if(out!=null){for (int i = 0; i < Msg.length(); i++)out.write(Msg.charAt(i));}} catch (IOException e) {return;} }/** * * This function closes the serial port in use. * */public void ClosePort() {serialPort.close(); } }

這樣通過 SerialBean.result 就可得到讀數結果。

至于把數據放到網頁上，就要用到Ajax了，這里用到了一個Ajax框架dwr, dwr類Put.java 例如以下：

package com.chengzhong.dwr;import java.io.IOException;import com.chengzhong.tools.Arith; import com.chengzhong.tools.SerialBean;public class Put {//2011.9.17public String write(){//發送指令R，儀器發送一次凈重數據SerialBean.WritePort("R");//讀取數據SerialBean.ReadPort();String temp=SerialBean.result.trim(); //我這里temp是形如 wn125.000kg 的數據if(!temp.equals("") && temp.length()==11){return (change(temp)).toString();}else{return "";}}//響應開始稱重public String startWeight(String num){int n=Integer.parseInt(num.trim());SerialBean SB = new SerialBean(n);SB.Initialize();return SerialBean.openSignal+""; //返回初始化信息}//響應停止稱重public void endWeight(){try {//關閉輸入、輸出流SerialBean.in.close();SerialBean.out.close();} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();}if(SerialBean.serialPort!=null){SerialBean.serialPort.close(); //關閉串口}SerialBean.serialPort=null;SerialBean.portId=null;SerialBean.result="";}/*** 將形如 wn125.000kg 格式的重量轉換為 125.000 (kg)(四舍五入，小數點后保留兩位)*/public String change(String source){Double result=0.0;String s1=source.substring(2,9);try{result=Double.parseDouble(s1);result=Arith.round(result,2);}catch(Exception e){e.printStackTrace();return "";}return result.toString();}}

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注：Arith.java是一個java 的高精度計算文件。

package com.chengzhong.tools; import java.math.BigDecimal;/** * 因為Java的簡單類型不可以精確的對浮點數進行運算，這個工具類提供精 * 確的浮點數運算，包含加減乘除和四舍五入。 */public class Arith{//默認除法運算精度private static final int DEF_DIV_SCALE = 10;//這個類不能實例化private Arith(){}/*** 提供精確的加法運算。* @param v1 被加數* @param v2 加數* @return 兩個參數的和*/public static double add(double v1,double v2){BigDecimal b1 = new BigDecimal(Double.toString(v1));BigDecimal b2 = new BigDecimal(Double.toString(v2));return b1.add(b2).doubleValue();}/*** 提供精確的減法運算。* @param v1 被減數* @param v2 減數* @return 兩個參數的差*/public static double sub(double v1,double v2){BigDecimal b1 = new BigDecimal(Double.toString(v1));BigDecimal b2 = new BigDecimal(Double.toString(v2));return b1.subtract(b2).doubleValue();}/*** 提供精確的乘法運算。* @param v1 被乘數* @param v2 乘數* @return 兩個參數的積*/public static double mul(double v1,double v2){BigDecimal b1 = new BigDecimal(Double.toString(v1));BigDecimal b2 = new BigDecimal(Double.toString(v2));return b1.multiply(b2).doubleValue();}/*** 提供（相對）精確的除法運算，當發生除不盡的情況時，精確到* 小數點以后10位，以后的數字四舍五入。* @param v1 被除數* @param v2 除數* @return 兩個參數的商*/public static double div(double v1,double v2){return div(v1,v2,DEF_DIV_SCALE);}/*** 提供（相對）精確的除法運算。當發生除不盡的情況時，由scale參數指* 定精度，以后的數字四舍五入。* @param v1 被除數* @param v2 除數* @param scale 表示表示須要精確到小數點以后幾位。* @return 兩個參數的商*/public static double div(double v1,double v2,int scale){if(scale<0){throw new IllegalArgumentException("The scale must be a positive integer or zero");}BigDecimal b1 = new BigDecimal(Double.toString(v1));BigDecimal b2 = new BigDecimal(Double.toString(v2));return b1.divide(b2,scale,BigDecimal.ROUND_HALF_UP).doubleValue();}/*** 提供精確的小數位四舍五入處理。* @param v 須要四舍五入的數字* @param scale 小數點后保留幾位* @return 四舍五入后的結果*/public static double round(double v,int scale){if(scale<0){throw new IllegalArgumentException("The scale must be a positive integer or zero");}BigDecimal b = new BigDecimal(Double.toString(v));BigDecimal one = new BigDecimal("1");return b.divide(one,scale,BigDecimal.ROUND_HALF_UP).doubleValue();} }

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網頁頁面上：

<script type="text/javascript" src="/ChengZhong/dwr/engine.js"></script> <script type="text/javascript" src="/ChengZhong/dwr/util.js"></script> <script type='text/javascript' src='/ChengZhong/dwr/interface/ss.js' ></script> <script type='text/javascript' >var ID;function begin(){ID=window.setInterval('get()',500); //每隔半秒自己主動調用 get(),取得毛重數據填入文本框中}function get(){ ss.write(readIt); //調用dwr類 Put.java 中的write方法 }function readIt(Data){if(Data!=null && Data!=""){document.getElementById("mzBF").value=Data;}} </script>

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dwr的使用就不說了

轉載于:https://www.cnblogs.com/mfrbuaa/p/4183008.html

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