我有一个Web应用程序，正在尝试使用Applet从客户端（浏览器）读取串行端口
HTML页面源：
<!DOCTYPE html>
<html>
<head>
<script src="http://www.java.com/js/deployJava.js"></script>
<script type="text/javascript">
var attributes = {
code : 'SampleBalanca.class',
archive : 'sampleBalanca.jar',
width : 100,
height : 100,
id : 'SampleBalanca'
};
var parameters = {
jnlp_href : 'sample-balanca.jnlp'
};
deployJava.runApplet(attributes, parameters, '1.7');
function peso() {
alert(document.SampleBalanca.peso());
}
</script>
</head>
<body>
<input type="button" name="listbutton" value="Show" onclick="peso();" />
</body>
</html>
sampleBalanca.jar的来源是：
import gnu.io.CommPortIdentifier;
import gnu.io.SerialPort;
import java.applet.Applet;
public class SampleBalanca extends Applet {
private static final long serialVersionUID = 1L;
SampleBalanca.SerialThread thread;
SerialPort serialPort;
String value;
public String peso() {
try {
CommPortIdentifier portIdentifier = CommPortIdentifier.getPortIdentifier("COM1");
serialPort = (SerialPort) portIdentifier.open("ListPortClass", 1);
serialPort.setSerialPortParams(4800, SerialPort.DATABITS_8, SerialPort.STOPBITS_1, SerialPort.PARITY_NONE);
} catch (Exception e) {
e.printStackTrace();
}
this.thread = new SampleBalanca.SerialThread();
this.thread.start();
return this.value;
}
class SerialThread extends Thread {
public void run() {
try {
CommPortIdentifier portIdentifier = CommPortIdentifier.getPortIdentifier("COM1");
if (portIdentifier.isCurrentlyOwned())
System.out.println("Port in use!");
else {
serialPort.getOutputStream().write(5);
// serialPort.getOutputStream().flush();
Thread.sleep(50);
serialPort.getInputStream().read();
byte mBytesIn[] = new byte[5];
// int n = serialPort.getInputStream().read(mBytesIn);
value = new String(mBytesIn);
serialPort.close();
}
} catch (Exception ex) {
System.out.println("Exception : " + ex.getMessage());
}
}
}
}
我的sample-balanca.jnlp文件是：
<jnlp spec="1.0+" codebase="path\\to\\project\\src\\main\\webapp\\applet\\" href="path\\to\\project\\src\\main\\webapp\\applet\\sample-balanca.jnlp">
<information>
<title>sampleBalanca</title>
<vendor>Lad</vendor>
</information>
<resources>
<j2se version="1.7" href="http://java.sun.com/products/autodl/j2se" />
<jar href="sampleBalanca.jar" main="true" />
</resources>
<security>
<all-permissions />
</security>
<applet-desc name="Sample Balanca Applet" main-class="SampleBalanca" width="100" height="100"></applet-desc>
</jnlp>
当我从浏览器打开小程序时，出现此错误：
java.lang.NullPointerException
at sun.plugin2.applet.JNLP2Manager.getAppInfo(Unknown Source)
at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
有人知道错误在哪里吗？
最佳答案
我将所有文件保存在同一目录中，因此更改了codebase=""和href="sample-balanca.jnlp"。
下一步是签署我的小程序。此后它应该工作良好。