Java, commonly used coding examples

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

regex example

String str = "This is a sentence. This is a question, right? Yes! It is.";
String delims = "[ .,?!]+";
String[] tokens = str.split(delims);

String str[] = result.split("HWaddr | \\. |inet addr:| \\. |Bcast:| \\. |Mask:| \\. |UP", 6);
This splits the following chunck of text into

eth0 Link encap:Ethernet HWaddr b8:27:eb:87:9e:02
 inet addr:192.168.1.97 Bcast:192.168.1.255 Mask:255.255.255.0
 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
 RX packets:4670 errors:0 dropped:0 overruns:0 frame:0
 TX packets:2034 errors:0 dropped:0 overruns:0 carrier:0
 collisions:0 txqueuelen:1000
 RX bytes:526428 (514.0 KiB) TX bytes:257010 (250.9 KiB)

str[0] -> eth0 Link encap:Ethernet
str[1] -> b8:27:eb:87:9e:02
str[2] -> 192.168.1.97
str[3] -> 192.168.1.255
str[4] -> 255.255.255.0
str[5] -> BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
 RX packets:4599 errors:0 dropped:0 overruns:0 frame:0
 TX packets:1960 errors:0 dropped:0 overruns:0 carrier:0
 collisions:0 txqueuelen:1000
 RX bytes:522426 (510.1 KiB) TX bytes:249420 (243.5 KiB)
      

package sg.com.siongboon.mypackage; //Basic java class structure. Using a domain name as your package, ensures that it will likely to be a unique namespace.

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
  }

  protected void finalize()
  { //method gets called when it is about to be delete by the garbage collector.
    //Should not be use as it is imposible to know when the object will get deletes.
  }

  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:

What do these defination really means?

//defining a common interface for objects
public interface LiftButton
{
  //define all the methods/interface in the class
  public void openLiftDoor();
  public void closeLiftDoor();
  public void pressLiftFloor(int floorLevel);
  public void alarm();
}

Very often in our physical world, we share a common interface with many different type or brand of system.

Example is our elevator lift. The interface buttons are the same/similar in each brand of lift. The user need not require training in order to use the lift, because the operating procedure is the same as what the user has used before.

The same goes for our computer system. Each computer may be run by various brand/model of CPU/hardware/OS, but the keyboard/mouse interface remains the same.

Defining an interface helps us to define a common standard, such that when it comes a day where we need to swap an object (change CPU model), we can easily change it with minimal or without any effect on the system.

It is mentioned by Jim Waldo, in his book “Java The Good Parts”, that passing parameters through the method is evetually going to be of some sort of interface. You can pass parameters using object, but later down the road, there is a high chance that it will be later change to an interface as the coding grows comre sophisticated.

//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




//'f' indicates that 1.5 is of data type float rather than a double.
//(any literal is intepreted as a double and not a float)
float x = 1.5f ;  
double x = 1.5;

//'l' indicates that 10000000000 is of data type long rather than a int .
//(any literal is intepreted as a int and not a long )
int x = 15 ;  
long x = 10000000000l;



//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
String dataStr = new String(dataByte,"ISO-8859-1");
//converting back to byte array after String manipulation
byte[] dataByte = dataStr.getBytes("ISO-8859-1"));

//Earlier method. (ineffective)
//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.
//In some case, a char 0xC2 may be inserted before a char which is > 0x7F.
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);

for information about charset encoding.

http://www.anyang-window.com.cn/tag/java-encoding/page/3/

s = s.replaceAll("\\s","");      //remove invisible \r \n char
s = s.trim();                    //remove white space

//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"


DecimalFormat formatV = new DecimalFormat("###0.00");    //floating value to 2 decimal place
String str = String.format("%6s",formatV.format(value)); //right align
//value =  0.91, result -> "  0.91"
//value = 21.91, result -> " 21.91"
//value = 12   , result -> " 12.00"

//rounding off float double value to 2 decimal place
float unround = (float) 0.34456;
double roundOff = Math.round(unround*100)/100D;    //rounding off to 2 decimal place
logger.info((float)roundOff);                      //result = 0.34
    
float unround = (float) 0.34556;
double roundOff = Math.round(unround*100)/100D;    //rounding off to 2 decimal place
logger.info((float)roundOff);               


//convert a float or double to a more precision BigDecimal
BigDecimal precision = new BigDecimal(0.34556);    //try not to use a double or float converting to a BigDecimal. It will result in additional trailing numbers because floating number is never exact. Use String instead to be accurate.
BigDecimal precision2 = new BigDecimal("0.34556");

precision = precision.setScale(2, BigDecimal.ROUND_HALF_UP);  //setup BigDecimal to 2 decimal place, and round up.

precision = precision.setScale(2, BigDecimal.ROUND_HALF_EVEN);//Banker's Rounding (rounding to the even if number is in the middle 0.5 or 0.05, etc...)
//example: 0.1265 (3 decimal place) should be round to 0.126
//example: 0.12651 (3 decimal place) should be round to 0.127
//example: 0.1275 (3 decimal place) should be round to 0.128
//example: 0.1285 (3 decimal place) should be round to 0.128

Right align a 2 decimal place floating number.

If encounter floating point error while using a variable of float data type, try changing to the data type double or use int data type instead. If precision is absolutely necessary, use the object BigDecimal.

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 final String name;

  private BonjourService(String name)
  {
    this.name = name;
  }

  public String toString()
  {
    return name;
  }
}

Toolkit.getDefaultToolkit().beep(); //error beep tone (sound, bell)

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.

Instant timestamp = Instant.now();	//newer form of Timestamp method. (Java 8)
LocalDateTime timestamp2;               //
LocalDate date;	                        //immutable object. Cannot be changed once it is created (Java 8)
LocalTime time;	                        //immutable object. Cannot be changed once it is created (Java 8)

LocalDate date = LocalDate.now();
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy MM dd");//formatter
String text = date.format(formatter);					//format date
LocalDate parsedDate = LocalDate.parse(text, formatter);		//parse date

//Timestamp string, output string "2010-03-08 14:59:30.252"
java.util.Date date= new java.util.Date();
logger.info(new Timestamp(date.getTime()));

//Calendar, Date, Time (data & formatting function)
Calendar cal;
cal = Calendar.getInstance();
int hourday = cal.get(Calendar.HOUR_OF_DAY);  //24 hour format
int hour = cal.get(Calendar.HOUR);            //12 hour format
int am_pm = cal.get(Calendar.AM_PM);          //
int minute = cal.get(Calendar.MINUTE);
int sec = cal.get(Calendar.SECOND);
int msec = cal.get(Calendar.MILLISECOND);

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MMM-dd (EEE)");
SimpleDateFormat sdf2 = new SimpleDateFormat("hh:mm:ss aaa");
String data = sdf.format(cal.getTime());               //Format string for date, time
String time = sdf2.format(cal.getTime());

DateFormat df = new SimpleDateFormat("yyyy-mm-dd");
Date dataObj = df.parse("2014-02-25");                 //Parse string for date, time


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(ClassName.class);

logger.error("");
if(logger.isDebugEnabled())
    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() + ">");
logger.info("Method name:<" + Thread.currentThread().getStackTrace()[1].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

Very often to specify a file path using a string, we need to use double slashes instead of only one in Java string.

C:\\Users\\Harald\\Folder1\\Version1\\Folder2.

This is because a slash ‘\’ is a escape char in a string. In order to indicate a ‘\’ intention, we need to put 2 slashes. This means that it will be quite odd to a typical computer user as we usually uses only one slash.

One method is to use back slash instead of forward slash. The file object classes will automatically treat ‘/’ back slash as the normal ‘\’ slash in Window OS.

Old was of specifiying the path,

processDirectory=”D:\\doc\\Expenses Invoice”

A solution of specifying the path,

processDirectory=”D:/doc/Expenses Invoice”

This solution, means that the user need not specify double slash, which can be quite confusing.

Writing an class object into a file, and reading the class obj back from the file. This acts as a means to permanently save the state or values store in the object that you have created.

There are also codes written to generate files, so that you can detect where your config files are stored in the user or project directory.

This class monitor new files added or removed from the directory. The class extends TimerTask which execute the run process every seconds.

Check out below (WatchService class) for newer methods of monitoring files and directory.

//Reading a data stream with non-blocking mode 
private OutputStream out = null;
private InputStream in = 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.

Note:
Class loader resources are often read-only; i.e. held in read-only files / read-only directories.
ClassLoader cl = getClass().getClassLoader();
Unable to obtain classloader using a static class.

Use Java Preferences API instead for configurable preferences.

Properties prop = new Properties();

try
{
  //set the properties value
  prop.setProperty("database", "localhost");
  prop.setProperty("dbuser", "mkyong");
  prop.setProperty("dbpassword", "password");

  //save properties to project root folder
  prop.store(new FileOutputStream("resource/config.properties"), null);
}
catch (IOException ex)
{
  ex.printStackTrace();
} 

//Writing or printing to PDF file.


Using PDFBox.

Download library pdfbox-app-2.0.0.jar

//Example of using Java to read excel *.xls or calc *.ods file

import org.jopendocument.dom.spreadsheet.MutableCell;
import org.jopendocument.dom.spreadsheet.Sheet;
import org.jopendocument.dom.spreadsheet.SpreadSheet;

//Getting the 0th sheet for manipulation| pass sheet name as string
spreadSheet = SpreadSheet.createFromFile(file).getSheet(0);
          
//Get row count and column count
int nColCount = spreadSheet.getColumnCount();
int nRowCount = spreadSheet.getRowCount();

System.out.println("Rows :" + nRowCount);
System.out.println("Cols :" + nColCount);
//Iterating through each row of the selected sheet
MutableCell cell = null;
for(int nRowIndex = 0;nRowIndex < nRowCount;nRowIndex++)
{
    //Iterating through each column
    int nColIndex = 0;
    for(;nColIndex < nColCount;nColIndex++)
    {
      cell = spreadSheet.getCellAt(nColIndex, nRowIndex);
      System.out.print(cell.getValue() + " ");
    }
    System.out.println();
}

This example shows how you can use java to detect the processes running under the Windows Operating System. It can a mean to detect if another Windows application or service or task is currently running.

If can even list out all the currently running processes.

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);

Add your own variables to the java environment system variables.

java YourProgram -D keyString=”mystring”.

example:
java myJavaProgram -D sg.myhomedir=”E:\myJaveProjects\”

//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());
    }

  }
}

public class Abc implements ShutdownHookClass
{
  protected static transient final Log logger = LogFactory.getLog(Abc.class);

  private myThreadClass tc;
  private Shutdownhook sdh;
  
  public Abc()
  {
    sdh.addShutdownHook(this);
  }

  @Override
  public void shutdownHookActivated()
  {
    close();
  }
  
  public void close()
  {
    if(sdh != null)
    {
      sdh.remove();
      sdh = null;
    }
  }
}

Implementing Shutdownhook using my utilities.jar file. Download the latest version from the section under “My Java Library“

//-----------------------------------------------------------------------------
//Using Desktop class to open file, so that the code will be OS platform independent
//The default application will launch automatically with the file.
//-----------------------------------------------------------------------------
String fileName = "resource/documentation/operating manual.pdf";
try
{
  Desktop.getDesktop().open(new File(fileName));
}
catch(IOException e)
{
  logger.info("Error opening file " + fileName + ". The default program to open this file may not been set. Please set the default program.");      
}

//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"));
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");

//force close the opened file
p1.destroy();

//-----------------------------------------------------------------------------
//Opening a Openoffice calc template (*.ots) as a calc file (*.ods)
//Using Desktop.getDesktop().open() will open the *.ots template file instead of a *.ods calc file
//-----------------------------------------------------------------------------

//-----------------------------------------------------------------------------
//Using Desktop class to open directory/folder, so that the code will be OS platform independent
//-----------------------------------------------------------------------------
//opening a local directory/folder.
Desktop.getDesktop().open(new File("D:\\programs\\eclipse\\_workspace\\InvoiceDataExtractor"));
//opening a remote network drive using network name/path.
Desktop.getDesktop().open(new File("\\\\BOB-PC\\Bob share folder"));
//opening a remote network drive using IP address.
Desktop.getDesktop().open(new File("\\\\192.168.1.95\\Bob share folder"));


//-----------------------------------------------------------------------------
//Non platform independent code. (for Window OS)
//-----------------------------------------------------------------------------
//open "InvoiceDataExtractor" folder
Process p = new ProcessBuilder("explorer.exe", "D:\\programs\\eclipse\\_workspace\\InvoiceDataExtractor").start();
//open "_workspace" directory and select "InvoiceDataExtractor" folder
Process p = new ProcessBuilder("explorer.exe", "/select,D:\\programs\\eclipse\\_workspace\\InvoiceDataExtractor").start();



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\"...");

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.

Compute Broadcast address from IP address and network MASK

Playing *.mp3 and *.wav audio/sound files

import java.io.File;
import javax.media.Format;
import javax.media.Manager;
import javax.media.MediaLocator;
import javax.media.Player;
import javax.media.PlugInManager;
import javax.media.format.AudioFormat;



    Format input1 = new AudioFormat(AudioFormat.MPEGLAYER3);
    Format input2 = new AudioFormat(AudioFormat.MPEG);
    Format output = new AudioFormat(AudioFormat.LINEAR);
    PlugInManager.addPlugIn("com.sun.media.codec.audio.mp3.JavaDecoder", new Format[] { input1, input2 }, new Format[] { output }, PlugInManager.CODEC);
    try
    {

      String file_location = "d:/mp3dog.mp3";
      System.out.print("start thread mp3 play: " + file_location + "\n");
      Player player = Manager.createPlayer(new MediaLocator(new File(file_location).toURI().toURL()));
      player.start();
      
      file_location = "d:/mp3siren.mp3";
      System.out.print("start thread mp3 play: " + file_location + "\n");
      Player player2 = Manager.createPlayer(new MediaLocator(new File(file_location).toURI().toURL()));
      player2.start();
      
      System.out.print("Two MP3 files playing together.\nNote that the media playing thread is still running.\n");
      
      //delay for 10sec before forcing thread to close
      try{Thread.sleep(10000);}catch(InterruptedException e){}
      
      System.out.print("Ending play thread.\n");
      player.close();
      player2.close();      
    }
    catch(Exception ex)
    {
      ex.printStackTrace();
    }

Download the following
– jmf.jar
– mp3plugin.jar
– mp3siren.mp3
– mp3dog.mp3

• Download http://java.sun.com/javase/technologies/desktop/media/jmf/2.1.1/download.html and extract the file jmf.jar (Java Media Framework, JMF). Put the jar file under your project/lib directory.
• JMF only support *.wav and *.aiff files. Download the MP3 plugin to play *.mp3 files. Download http://java.sun.com/javase/technologies/desktop/media/jmf/mp3/download.html, and extract the file “mp3plugin.jar”. Put the jar file under your project/lib directory.
• Make sure to add the jars to the compiler command or import the jar files to your project..
• add the codes (on the left) to your project to playback mp3 audio files.

Command Pattern: ExecutorService example: 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

references:
http://www.go4expert.com/articles/design-pattern-simple-examples-t5127/

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

Design pattern reference:

– java-design-patterns.pdf

GUI & Event Listener example
– Create window
– Window listener
– Mouse listener
– Keyboard listener
– Observer (command pattern)

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

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

JNI Java Native Interface

Step 1) Write your normal java class implementing a native method as an abstract.

Myclass
{
  public Myclass()
  {
  }

  public void method1() //normal java method 
  {
  }

  private native void method2(); //native method 
}

Step 3) Use the command “javah” to generate a header file from your class file. Go to your generated class directory.

example:
javah Mypackage.Myclass

A header file Mypackage_Myclass.h will be generated.

Step 5) Build the C project to generate a *.so library file.

You may encounter an error message
“error: parameter name omitted”
You may have left out the function’s (or method’s) parameter names which will not be generated in the *.h.
Provide your parametters with a variable name.

Step 6) Use the *.so file for the *.java file that you have created initially. This is for the system class loader

Reference:
Java programming with JNI.pdf
Beginning JNI with NetBeans IDE and C_C++ Plugin on Linux.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.zip

utilities (2011-03-25).jar

utilities (2013-08-11).jar