用Java实现串口通信（windows系统下），须要用到sun提供的串口包 javacomm20-win32.zip。当中要用到三个文件，配置例如以下：
m.jar放置到 JAVA_HOME/jre/lib/ext;
2.win32com.dll放置到 JAVA_HOME/bin;
m.properties 两个地方都要放
jre/lib(也就是在JAVA目录下的jre)
JAVA_HOME/jre/lib
说一下我应用的环境。电子秤称重时，计算机通过串口给称重控制显示器发送一次命令“R”，控制显示器则发送一次重量数据给串口，计算机再读取将数据显示在网页上。这样就构成了一个实时称重系统。
读写串口的代码例如以下：
package com.chengzhong.tools;import java.io.*;import mPortIdentifier;import m.*;/**** 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;//保存读数结果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; //该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; //输入输出流错误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; //參数不对return openSignal;}} catch (NoSuchPortException e){portId=null;openSignal=5; //没有该串口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();}}
这样通过 SerialBean.result 就可得到读数结果。
至于把数据放到网页上，就要用到Ajax了，这里用到了一个Ajax框架dwr, dwr类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 {//.9.17public String write(){//发送指令R，仪器发送一次净重数据SerialBean.WritePort("R");//读取数据SerialBean.ReadPort();String temp=SerialBean.result.trim(); //我这里temp是形如 wn125.000kg 的数据if(!temp.equals("") && temp.length()==11){return (change(temp)).toString();}else{return "";}}//响应開始称重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}//响应停止称重public void endWeight(){try {//关闭输入、输出流SerialBean.in.close();SerialBean.out.close();} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();}if(SerialBean.serialPort!=null){SerialBean.serialPort.close(); //关闭串口}SerialBean.serialPort=null;SerialBean.portId=null;SerialBean.result="";}/*** 将形如 wn125.000kg 格式的重量转换为 125.000 (kg)(四舍五入，小数点后保留两位)*/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();}}
注：Arith.java是一个java 的高精度计算文件。
package com.chengzhong.tools;import java.math.BigDecimal;/*** 因为Java的简单类型不可以精确的对浮点数进行运算，这个工具类提供精* 确的浮点数运算，包含加减乘除和四舍五入。*/public class Arith{//默认除法运算精度private static final int DEF_DIV_SCALE = 10;//这个类不能实例化private Arith(){}/*** 提供精确的加法运算。* @param v1 被加数* @param v2 加数* @return 两个參数的和*/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();}/*** 提供精确的减法运算。* @param v1 被减数* @param v2 减数* @return 两个參数的差*/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();}/*** 提供精确的乘法运算。* @param v1 被乘数* @param v2 乘数* @return 两个參数的积*/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（相对）精确的除法运算，当发生除不尽的情况时，精确到* 小数点以后10位，以后的数字四舍五入。* @param v1 被除数* @param v2 除数* @return 两个參数的商*/public static double div(double v1,double v2){return div(v1,v2,DEF_DIV_SCALE);}/*** 提供（相对）精确的除法运算。当发生除不尽的情况时，由scale參数指* 定精度，以后的数字四舍五入。* @param v1 被除数* @param v2 除数* @param scale 表示表示须要精确到小数点以后几位。* @return 两个參数的商*/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();}/*** 提供精确的小数位四舍五入处理。* @param v 须要四舍五入的数字* @param scale 小数点后保留几位* @return 四舍五入后的结果*/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();}}
网页页面上：
<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); //每隔半秒自己主动调用 get(),取得毛重数据填入文本框中}function get(){ ss.write(readIt); //调用dwr类 Put.java 中的write方法 }function readIt(Data){if(Data!=null && Data!=""){document.getElementById("mzBF").value=Data;}} </script>
dwr的使用就不说了
