http://www.wellho.net/regex/javare.html

Java Regular Expressions   java.util.regex

My first encounter with regex happens when I was using String.split() function. The split char is represented by special char used by regex. I thought the function is easy to use but is spending a lot of time figuring why the string cannot be split. I was splitting the IP address which is separated by the '.' dot or period. My colleague drop me some notes from the website, and now I finally know what really happen. Great article I must say.

Class typically use for wild card search in String.

The following are some char keyword in used by the regular expressions class. In order to use the char, use \ followed by the char or insert the printable string between \Q and \E

metacharacters->   ([{\^-$|]})?*+.

There are more about regex than I thought after searching the web.

http://en.wikipedia.org/wiki/Regular_expression

package sg.com.siongboon.mypackage; //Basic java class structure

public class ClassName
{
  private int myResult;

  static
  {
    //Similar to constructor which will be executed
    //before the object is created.
    //It can be use like a constructor for your static class object,
    //where a constructor is not allowed.
         //static initializer block, it is seldom used (see example on *.dll)
  } 

  public ClassName()
  { //class constructor
  }  

  public methodOne()
  { 
  }

  final public methodOne()
  { //method cannot be overriden by other class extending it
  }

  static public methodOne()
  { //method is the only instance. It will be common to all the class object
  }

  public static void main(String args[])
  { //entry point for running this program
  }
}

//A simple illustration of Java access modifier, Private, Default, Protected, Public

Java access modifier:

public- Variables/methods using public modifier can be access easily by all objects.

protected- Protected members can be accessed by another package through inheritence. Class CC managed to access protected member C through inheritence. Class CC inherited Class AA, therefore member C becomes part of Class CC.

default- If there is no modifier specified, Java will treat it as the default modifier. Default members B gets a bit more difficult to access. Only classes within the same package can access to it. Member B using the default modifier can be access by Class BB. Class BB can creates an instance of Class AA or through static variable access to access to member B.

private- is the most restrictive modifier. The private member A can only be access within the class AA itselfs. Class AA being the creator, is able to access all it's members A, B, C and D. It is recommended to start the data/method encapsulation using private modifier. Change the modifier when neccessary. There must be a good reason why private modifier is not use.

Future research the meaning on these defination:

public interface ClassName
protected interface ClassName
private interface ClassName
public void MethodName();
protected void MethodName();
private void MethodName();
abstract..

What do these defination really means?

//Java do not have unsigned data type
//Representation of the unsigned for a signed data type.
byte temp;
int result;
result=(int)(temp[0]&0xFF);   //extract the unsigned value

long longNum = 289637082704667748;   //The literal 289637082704667748 of type int is out of range

long longNum = 289637082704667748L; //if the literal value is too big, L is required at the back

int result=(int)((1.26)+0.5);         //rounding off to the nearest integer




//declare & allocate memory for byte & char array
byte remoteIP[] = new byte[4];
byte[] dataByte = new byte[]{(byte) 0xDB, (byte) 0xA1};
char[] dataBuf = new char[100];//declare & allocate memory for byte

//converting a byte array for string use
//Please note that byte data maybe lost after converting to string using this method.  
//The conversion uses a default charsetName; 
//if charset is not able to map the data to a char, it could convert it to the data 0x3F.
String dataStr = new String(dataByte);
String dataStr = new String(dataByte,"US-ASCII");

//converting a string to byte[]
byte[] dataByte = dataStr.getBytes();
//converting a byte to char for string use (convert a byte to char)
char dataChar = (char) 0xDB;
//converting a byte to string for string use (convert a byte to String)
String str = String.valueOf((char)ch);
//more methods for dealing with bytes 
ByteBuffer byteBuffer = ByteBuffer.allocate(10);
byteBuffer.put(0x01);

//formatting a string like printf or sprintf
String str = String.format("Number=%2d, %f", 5, 1.56); //result>"Number= 5, 1.56"
String str = String.format("Leading Zero=%04d", 5); //result>"Leading Zero=0005"
String str = String.format("Hex value=0x%04x", 79 ); //result>"Hex value=0x004F"


private enum BonjourService
{    
  //use enum if there is a fix defined number of constant
  //enum can help to restrict the number input choice for
  //the programmer to feed it into the method
        CAMERA, HTTP, PRINTER, IPP, PDL_DATASTREAM
}

private String getServiceProtocolName(BonjourService service)
{
  String servStr;
        if(service==BonjourService.CAMERA)
            servStr = "_camera._tcp";
        else if(service==BonjourService.HTTP)
            servStr = "_http._tcp";
        else if(service==BonjourService.PRINTER)
            servStr = "_printer._tcp";
        else if(service==BonjourService.IPP)
            servStr = "_ipp._tcp";
        else if(service==BonjourService.PDL_DATASTREAM)
            servStr = "_pdl-datastream";       
}

String str = "(" + BonjourService.CAMERA + ")";
String str = "(" + BonjourService.CAMERA.toString() + ")";
//str="(CAMERA)", enum variables can also be used as String object.


public enum BonjourService
{
  CAMERA("camera"), HTTP("http"), PRINTER("printer");

  //constructor cannot be public
  //constructor allows multiple parameters, so that
  //the enum can represent more than 1 parameter.
  private BonjourService(String name)
  {
    this.name = name;
  }
  
  private final String name;
  public String toString()
  {
    return name;
  }
}

Toolkit.getDefaultToolkit().beep(); //error beep tone

This singleton structure will ensure that the class object can only be created once. Constructor has to be defined as private while the class variable & getInstance method is static so that they can be access with the object being created.

This is the first question that I ask myself when designing a new class object even since I learned about it; whether it can be created with multiple instance or only a single static instance of the object. In some application, especially when working with hardware devices, single instance is the only proper way to built your class. It can helps you to prevent mis-written codes, resulting in less bugs/crush program when the class is used by another programmer.

log4j
Example: FactoryLog for logging info, error, debug, etc messages.

Similar to System.out.println();

Save to project folder /lib /lib (factory logger).zip

Save to project folder /resource /resource (factory logger).zip

(Details of log file setup can be found in the file "log4j.properties".

Includes a 2nd example to config Log4j for logging in Tomcat.)

Log4j references:
http://logging.apache.org/log4j/1.2/manual.html
http://juliusdavies.ca/logging.html
http://www.laliluna.de/articles/log4j-tutorial.html

//Using LogFactory for debugging & logging example.
//Remember to include the path to "lib" & "resources" in the classpath
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

protected static transient final Log logger = LogFactory.getLog(YourClassName.class);

logger.error("");
logger.debug("Class name:<" + getClass().getSimpleName() + ">");
logger.info("Class name:<" + this.getClass().getName() + ">");  //print out the class name

//print out the method name
logger.info("Method name:<" + new Exception().getStackTrace()[0].getMethodName() + ">");

How to add *.jar library?Encountered the following errors?log4j:WARN No appenders could be found for logger (javax.swing.JApplet).
log4j:WARN Please initialize the log4j system properly.
Remember to add in the libraries in your project classpath. For Eclipse IDE the classpath is indicated in the .classpath in the project root directory.Alternative you can add the lib as follows in Eclipse:1) Right click on your project name (under "Package Explorer") and click "Properties" 2) Select "Java Build Path", and choose tab "Source". Add the folders "lib" & "resource" under your project folder. 3) Choose tab "Libraries". Click "Add JARS..." and add the "commons-logging-1.1.jar" & "log4j-1.2.14" library files. 4) Done.

//Two examples to print out error messages:
e.printStackTrace();
System.out.println("Got an IOException: " + e.getMessage());

logger.error("Got an IOException: ", e);

Example: File Write

//Reading a data stream with non-blocking mode 
private OutputStream out = null;
private InputStream out = null;
out = new DataOutputStream(sp.getOutputStream());
in = new DataInputStream(sp.getInputStream());
byte byteRead = in.read(); // -1 if there is no data 


//reading the int data stream from a binary file
import java.io.*;
import java.util.*;

public class BinOutputFileApp
{
  public static void main(String arg[])
  {
    try
    {
      FileInputStream fis = new FileInputStream("binary.dat");
      DataInputStream in = new DataInputStream(new BufferedInputStream(fis));
      int a = in.readInt();
      int b = in.readInt();
      System.out.println(a); //print int "42"
      System.out.println(b); //print int "45"
    }
    catch (IOException e)
    {
      e.printStackTrace();
    }
  }

Project example: reading_int_datastream.zipExample of the data in the binary.dat file:0x00 0x00 0x00 0x2A 0x00 0x00 0x00 0x2DActual int content represented in the binary file above:42 45

Other very good reference:- http://www3.ntu.edu.sg/home/ehchua/programming/java/J5b_IO.html (very good NTU website on data stream by Chua Hock Chuan),

Java Input & Output Stream (by Chua Hock Chuan).pdf

Note: There is another better generic methods to read *.properties. Read more about "Apache Common configuration". Commons Configuration provides a generic configuration interface which enables a Java application to read configuration data from a variety of sources. Commons Configuration provides typed access to single, and multi-valued configuration parameters.

The string user.name is the string key required to retrieve the system variables string. The following list present the other possible system variable that you can retrieve from System.getProperty(keyString);

//Threading example
public class myThreadClass extends Thread
{
  //flag to control process flow to be in syn with other critical function
  private static boolean fIsSynProcess=false;
  //object holding the reference to this thread
  private Thread thisThread = null;

  public myThreadClass()
  {
  }

  public void run()
  { //getting the thread process ID
    this.thisThread = Thread.currentThread();
    String threadName = getClass().getName() + " : " + this.thisThread.getName();
    logger.info("...thread Started: " + threadName);

    while((!isStopRequested()))
    {
        while((!isSynProcess())) 
        {
        }
    }
    logger.info("...thread Stopped: " + threadName);
  }

  private synchronized boolean isStopRequested()
  {
    if(thisThread==null)
      return(true);
    return(false);
  }
  
  public void requestStop()
  {
    Thread tempThread = thisThread;
    thisThread = null;
    //interrupt for used to exit from blocking function in the run() method's while loop
    if (tempThread != null)
      tempThread.interrupt();
  }

  private synchronized boolean isSynProcess()
  {
    return(fIsSynProcess);
  }

  private synchronized void holdThreadRun()    //prevent the run thread to terminate
  {
    fIsSynProcess=true;
  }

  private synchronized void releaseThreadRun()    //allow the run thread to terminate
  {
    fIsSynProcess=false;
  }
}

The thread example also illustrate the use of the keyword "synchronized". The java run time will ensure that those methods which are labelled as synchronized will not be excuted in parallel. This is to prevent two or more processes to access the same variable/memory which will cause data corruption or process locked issue. A program base on threading algorithm is likely to face such problems that can be resolved by implementing "synchronized".For more explaination on synchronized, please refer to the following,

http://download.oracle.com/javase/tutorial/essential/concurrency/syncmeth.html

//Another method of writing thread
Object obj = new Object();
new Thread(obj).start();
Object class must contain a method run();

//Object class must implements Runnable and that contains a method run();



this.setDaemon(true); explains: setting daemon to true, will ensure that this thread is spin off from the main's method thread. When a program execute from main entry point, main itself is actually a thread. If daemon is set to true, the sub-thread spinoff will be under the main thread. When the main thread is terminated, all sub thread will be terminated, shutdownhook can also be activated. If daemon is set to false, the thread spin off as another separated thread by its own. When the main thread is terminated, the sub thread will still exists (with daemon set to false).

public class ThreadClassShutdownHook extends Thread
{
  protected static transient final Log logger = LogFactory.getLog(ThreadClassShutdownHook.class);

  private myThreadClass tc;
  
  public ThreadClassShutdownHook(myThreadClass tc)
  {
    this.tc = tc;
    logger.info(this.getClass().getName() + " created. ShutdownHook registered.");
    Runtime.getRuntime().addShutdownHook(this);
  }
  
  public void remove()
  {
    Runtime.getRuntime().removeShutdownHook(this);
  }
  
  public void run()
  {    if(tc != null)    {
      logger.info("ShutdownHook activated for " + this.getClass().getName()
      + ". Thread: " + Thread.currentThread().getName());
      tc.requestStop();    }
    else    {
      logger.info("ShutdownHook safely release for " + this.getClass().getName()
      + ". Thread: " + Thread.currentThread().getName());
    }

  }
}

//-----------------------------------------------------------------------------
//Using Desktop class to open file, so that the code will be OS platform independent
//The default application will launch automatically with the file.
//-----------------------------------------------------------------------------
//opening a file on the project root directory
Desktop.getDesktop().open(new File("image.gif"));
//opening a file relative to the project directory
Desktop.getDesktop().open(new File("imageDir\\image.gif"));
//opening a file using absolute file name
Desktop.getDesktop().open(new File("d:\\myproject\\imageDir\\image.gif"));
//opening a pdf file
Desktop.getDesktop().open(new File("d:\\mypdf.pdf"));


//-----------------------------------------------------------------------------
//Non platform independent code. (for Window OS)
//-----------------------------------------------------------------------------
//Open gif image file
Process p1 = Runtime.getRuntime().exec("rundll32 SHELL32.DLL,ShellExec_RunDLL " + "d:\\myproject\\imageDir\\image.gif");
//Open pdf file
Process p2 = Runtime.getRuntime().exec("rundll32 url.dll,FileProtocolHandler d:\\mypdf.pdf");

Reference:http://docstore.mik.ua/orelly/java-ent/dist/ch02_01.htm

//Opening TCP/IP server socket
ServerSocket s = null;
try
{
  try
  {
    thisThread = Thread.currentThread();
    String myName = thisThread.getName();
      s = new ServerSocket(getServerListeningPort());
      logger.info("HID RFID Server ...\"START\"...   , Thread: " + myName);
    while((isSynProcess()) || (!isStopRequested()))
    {
      try
      {
        HidRfidReader hid;
        Socket incoming = s.accept();
        hid = new HidRfidReader(incoming);
        hid.setDaemon(true); //set this as a user thread. If startService thread ended, these user thread will end as well.
        hid.start();
      }
      catch(UnAuthorisedDeviceException e)
      { //ip address is not reconigze/registered. Print debug message and return to main loop to accept incoming socket connection
        logger.warn("Warning!!! <Unauthorised Access Detected> " + e);
        //detects authorised device access
        //return to check for other incoming connection
      }
    }
  }
  catch(Exception e)
  {
    logger.error("Unhandled Error: " + e, e);
  }
  finally
  {
    s.close();
  }
}
catch(IOException e)
{
  e.printStackTrace();
}
logger.info("HID RFID Server   ...\"STOP\"...");

byte[] data = LantronixDevice.queryFirmwareVer;
DatagramPacket packet = new DatagramPacket(data, data.length, bc, LantronixDevice.UDP_PORT);
DatagramSocket socket = null;

try
{
socket = new DatagramSocket();
//socket = new DatagramSocket(PORT, IP_ADDRESS); //only for communication to a particaular remote IP & PORT
//socket.setBroadcast(true);
socket.setSoTimeout(timeoutSearch);
socket.send(packet);
}
catch(SocketException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}
catch(IOException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}

UDP is a connectionless communication protocol and does not handle the integrity of the data being send. This does not mean that it cannot be implemented for communication that requires 100% error free communication. It simply means that the lower level protocol will not help you ensure that all your data bytes are being send over, and that your application will need to handle those error checking if you need it.

There are various way to setup your UDP communicates. Two methods are breifly state for your awareness.

- socket define wihtin DatagramSocket

- socket define within DatagramPacket.

For UDP communication to and only to one IP addressed device, you should define your socket in the object DatagramSocket. For packet communication with multiple UDP devices or acting as a listener, you can define your socket within the DatagramPacket object; there will be no restriction to which devices you can communicate within the network. UDP protocol is very flexible to implement.

Command Pattern: ExecutorServiceexample: ExecutorService_Queue.java, ExecutorService_QueueJob.java Command Pattern: Observerexample1: Observer command pattern.pdfexample2: Observer pattern - Wikipedia, the free encyclopedia.pdfexample3: JavaWorld - October - How-to Java_ Observer and Observable.pdf

read log4j ndc (log the individual instance of client thread connected to the server)

Design pattern reference:

- java-design-patterns.pdf

My Java Library

This utilities.zip contains my frequent/common used Java library, which contains the follow object- HexUtilities.java- ShutdownHook.java, ShutdownHookClass.java

- UtilitiesThread.java

utilities.ziputilities.jar

GUI programming notes:
- GUI programming in java.pdf
- Writing gui applications in java.pdf

int keyChar = evt.getKeyChar();
String debugStr = String.format("%1x", keyChar);
JOptionPane.showMessageDialog(null, debugStr, "Debug", JOptionPane.INFORMATION_MESSAGE);

example to load image file to JPanel.
- example- LoadAndShow (example to load image)

Inserting applet into html file, where MyApplet.class is the java class to invoke, basecode "./" is the root directory the MyApplet.class is located.
<applet code="MyApplet.class" codebase="./" height="600" width="600"></applet>

Without the *.class will also works
<applet code="MyApplet" codebase="./" height="600" width="600"></applet>

If your MyApplet.class is located in the directory /appDir
html file location -> /index.html
apps file location -> /appDir/MyApplet.class
<applet code="MyApplet.class" codebase="./appDir" height="600" width="600"></applet>

If the *.class to invoke is located inside a *.jar library archive file
<applet code=MyApplet.class archive="JarFileName.jar" codebase="./" width=width height=height> </applet>

How to signed a Java Applet for access to communication outside the server the applet reside on?

Applet

- Do not put the main Applet class in a package
- Do not do much coding in the Applet's constructor, other than GUI initialisation. Codes should be place out of the constructor.

Problem:
- Applet hangs in the browser. Need to close the broswer and terminate the browser process to shutdown/restart the Java VM
Solution:
- Applet must use a thread to open new process, especially time consuming process. GUI programming has to be very much thread base.

Problem:
- The applet is able to send out UDP packet from Eclipse applet but not the same applet on the browser.
The browser is able to use the same UDP port to sent data out, but the applet using the same port cannot send the data out.
Solution:
- Remember the applet restrictions that unsigned applets may only access the host they were loaded from, for security purpose. To overcome this security restriction, you will need to signed the applet.

Browser test for Java Applet,
- http://www.javatester.org/enabled.html

Note for Java applet,
- Defining and Using Applet Parameters.pdf
- Call a Applet Java method from Javascript.pdf
- Call Javascript from a Java applet.pdf
- Signed Applet Tutorial.pdf

Note for Java Jar file,
- JAR files revealed.pdf