Java IO.pdf - Nguyen Dang Binh

D:\JAVA\16>java NamedPortLister
COM1
COM2
LPT1
LPT2
Java I/O
Now you can see that I have two serial and two parallel ports. However, this same program
would fail on Unix, because it relies on hard-wired port names.
17.2.2 Getting Information About a Port
Once you have a CommPortIdentifier identifying a particular port, you can discover
information about the port by calling several accessor methods. These include:
public String getName()
public int getPortType()
public String getCurrentOwner()
public boolean isCurrentlyOwned()
The getName() method returns the platform-dependent name of the port, such as "COM1"
(Windows) "Serial A" (Solaris) or "modem" (Mac). [1] The getPortType() method returns one
of the two mnemonic constants CommPortIdentifier.PORT_SERIAL or
CommPortIdentifier.PORT_PARALLEL:
public static final int PORT_SERIAL = 1;
public static final int PORT_PARALLEL = 2;
The isCurrentlyOwned() method returns true if some process, thread, or application
currently has control of the port. It returns false otherwise. If a port is owned by another Java
program, the getCurrentOwner() returns the name supplied by the program that owns it;
otherwise, it returns null. This isn't too useful, because it doesn't handle the much more likely
case that a non-Java program like Dial-Up Networking or PPP is using the port. A comment
in the source code indicates that this should be fixed so that non-Java programs can also be
identified; this limitation may not exist by the time you read this. Example 17.3 is a revision
of the PortLister in Example 17.1 that uses these four accessor methods to provide
information about each port rather than relying on the inherited toString() method.
Example 17.3. PrettyPortLister
import javax.comm.*;
import java.util.*;
public class PrettyPortLister {
public static void main(String[] args) {
Enumeration e = CommPortIdentifier.getPortIdentifiers();
while (e.hasMoreElements()) {
CommPortIdentifier com = (CommPortIdentifier) e.nextElement();
System.out.print(com.getName());
1 That last one is hypothetical. The Comm API hasn't been ported to the Mac as of the time of this writing.
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