Friday, December 28, 2007

Available character sets in JAVA

A charset name must begin with either a letter or a digit. The empty string is not a legal charset name. Charset names are not case-sensitive; that is, case is always ignored when comparing charset names. Charset names generally follow the conventions documented in RFC 2278: IANA Charset Registration Procedures.

Charsets are named by strings composed of the following characters:



US-ASCIISeven-bit ASCII, a.k.a. ISO646-US,a.k.a. the Basic Latin block of the Unicode character set
ISO-8859-1 ISO Latin Alphabet No. 1, a.k.a. ISO-LATIN-1
UTF-8Eight-bit UCS Transformation Format
UTF-16BESixteen-bit UCS Transformation Format,big-endian byte order
UTF-16LESixteen-bit UCS Transformation Format,little-endian byte order
UTF-16Sixteen-bit UCS Transformation Format,byte order identified by an optional byte-order mark (BOM)

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Available Charactersets

java.lang.Charset.availableCharsets(); list all supporte character set by this JVM as like below.

{Big5=Big5, Big5-HKSCS=Big5-HKSCS, EUC-JP=EUC-JP, EUC-KR=EUC-KR, GB18030=GB18030, GB2312=GB2312, GBK=GBK, IBM-Thai=IBM-Thai, IBM00858=IBM00858, IBM01140=IBM01140, IBM01141=IBM01141, IBM01142=IBM01142, IBM01143=IBM01143, IBM01144=IBM01144, IBM01145=IBM01145, IBM01146=IBM01146, IBM01147=IBM01147, IBM01148=IBM01148, IBM01149=IBM01149, IBM037=IBM037, IBM1026=IBM1026, IBM1047=IBM1047, IBM273=IBM273, IBM277=IBM277, IBM278=IBM278, IBM280=IBM280, IBM284=IBM284, IBM285=IBM285, IBM297=IBM297, IBM420=IBM420, IBM424=IBM424, IBM437=IBM437, IBM500=IBM500, IBM775=IBM775, IBM850=IBM850, IBM852=IBM852, IBM855=IBM855, IBM857=IBM857, IBM860=IBM860, IBM861=IBM861, IBM862=IBM862, IBM863=IBM863, IBM864=IBM864, IBM865=IBM865, IBM866=IBM866, IBM868=IBM868, IBM869=IBM869, IBM870=IBM870, IBM871=IBM871, IBM918=IBM918, ISO-2022-CN=ISO-2022-CN, ISO-2022-JP=ISO-2022-JP, ISO-2022-KR=ISO-2022-KR, ISO-8859-1=ISO-8859-1, ISO-8859-13=ISO-8859-13, ISO-8859-15=ISO-8859-15, ISO-8859-2=ISO-8859-2, ISO-8859-3=ISO-8859-3, ISO-8859-4=ISO-8859-4, ISO-8859-5=ISO-8859-5, ISO-8859-6=ISO-8859-6, ISO-8859-7=ISO-8859-7, ISO-8859-8=ISO-8859-8, ISO-8859-9=ISO-8859-9, JIS_X0201=JIS_X0201, JIS_X0212-1990=JIS_X0212-1990, KOI8-R=KOI8-R, Shift_JIS=Shift_JIS, TIS-620=TIS-620, US-ASCII=US-ASCII, UTF-16=UTF-16, UTF-16BE=UTF-16BE, UTF-16LE=UTF-16LE, UTF-8=UTF-8, windows-1250=windows-1250, windows-1251=windows-1251, windows-1252=windows-1252, windows-1253=windows-1253, windows-1254=windows-1254, windows-1255=windows-1255, windows-1256=windows-1256, windows-1257=windows-1257, windows-1258=windows-1258, windows-31j=windows-31j, x-Big5-Solaris=x-Big5-Solaris, x-euc-jp-linux=x-euc-jp-linux, x-EUC-TW=x-EUC-TW, x-eucJP-Open=x-eucJP-Open, x-IBM1006=x-IBM1006, x-IBM1025=x-IBM1025, x-IBM1046=x-IBM1046, x-IBM1097=x-IBM1097, x-IBM1098=x-IBM1098, x-IBM1112=x-IBM1112, x-IBM1122=x-IBM1122, x-IBM1123=x-IBM1123, x-IBM1124=x-IBM1124, x-IBM1381=x-IBM1381, x-IBM1383=x-IBM1383, x-IBM33722=x-IBM33722, x-IBM737=x-IBM737, x-IBM834=x-IBM834, x-IBM856=x-IBM856, x-IBM874=x-IBM874, x-IBM875=x-IBM875, x-IBM921=x-IBM921, x-IBM922=x-IBM922, x-IBM930=x-IBM930, x-IBM933=x-IBM933, x-IBM935=x-IBM935, x-IBM937=x-IBM937, x-IBM939=x-IBM939, x-IBM942=x-IBM942, x-IBM942C=x-IBM942C, x-IBM943=x-IBM943, x-IBM943C=x-IBM943C, x-IBM948=x-IBM948, x-IBM949=x-IBM949, x-IBM949C=x-IBM949C, x-IBM950=x-IBM950, x-IBM964=x-IBM964, x-IBM970=x-IBM970, x-ISCII91=x-ISCII91, x-ISO-2022-CN-CNS=x-ISO-2022-CN-CNS, x-ISO-2022-CN-GB=x-ISO-2022-CN-GB, x-iso-8859-11=x-iso-8859-11, x-JIS0208=x-JIS0208, x-JISAutoDetect=x-JISAutoDetect, x-Johab=x-Johab, x-MacArabic=x-MacArabic, x-MacCentralEurope=x-MacCentralEurope, x-MacCroatian=x-MacCroatian, x-MacCyrillic=x-MacCyrillic, x-MacDingbat=x-MacDingbat, x-MacGreek=x-MacGreek, x-MacHebrew=x-MacHebrew, x-MacIceland=x-MacIceland, x-MacRoman=x-MacRoman, x-MacRomania=x-MacRomania, x-MacSymbol=x-MacSymbol, x-MacThai=x-MacThai, x-MacTurkish=x-MacTurkish, x-MacUkraine=x-MacUkraine, x-MS950-HKSCS=x-MS950-HKSCS, x-mswin-936=x-mswin-936, x-PCK=x-PCK, x-windows-50220=x-windows-50220, x-windows-50221=x-windows-50221, x-windows-874=x-windows-874, x-windows-949=x-windows-949, x-windows-950=x-windows-950, x-windows-iso2022jp=x-windows-iso2022jp}

To display file encoding character set used in JAVA:


To display default Character Set used:


Muti-byte file

Most of the text editors like Programmers Notepad, TextEdit are helps to create UTF-16 encoded file. However, We can not differenciate by opening multi-byte character files using these editors. Through command line based editors are very useful like Editor(windows) and cat(windows/linux).

Thursday, December 20, 2007

Unzipping using Package

How to unzip using Package ?
How to unzip using JAVA API ?.

Create ZipInputStream using any of the InputStream and read one by one ZIPEntry. Make if check ZIPEntry points to file object and the read bytes from ZipInputStream upto -1 byte found.


public class Unzip {

private static final String FILESEPARATOR = File.separator;

public static void storeZipStream(InputStream inputStream, 
String dir)
throws IOException {

ZipInputStream zis = new ZipInputStream(inputStream);
ZipEntry entry = null;
int countEntry = 0;
if (!dir.endsWith(FILESEPARATOR))

// check inputStream is ZIP or not
if ((entry = zis.getNextEntry()) != null) {
do {
String entryName = entry.getName();
// Directory Entry should end with FileSeparator
if (!entry.isDirectory()) {
// Directory will be created while creating file with in it.
String fileName = dir + entryName;
createFile(zis, fileName);
} while ((entry = zis.getNextEntry()) != null);
System.out.println("No of files Extracted : " + countEntry);

} else {
throw new IOException("Given file is not a Compressed one");

public static void createFile(InputStream is, 
String absoluteFileName)
throws IOException {
File f = new File(absoluteFileName);

if (!f.getParentFile().exists())
OutputStream out = new FileOutputStream(absoluteFileName);
byte[] buf = new byte[1024];
int len = 0;
while ((len = > 0) {
out.write(buf, 0, len);
// Close the streams

public static void main(String args[]) throws Exception {

if (args.length < 1) {
System.out.println("Syntax : Unzip zipfile [extractlocation]");

FileInputStream zis = new FileInputStream(new File(args[0]));
String dir = System.getProperty("");
if (args.length == 2) {
dir = args[1].replace('\\', '/');
System.out.println("Extracted to "+dir);
storeZipStream(zis, dir);

To run:

java Unzip /tmp/a content will be extracted to /tmp/a folder.

Tuesday, December 11, 2007

Create String XML without XMLDocument

How to create XML Document without using the XML Document Object ?
How to create XML Document using JAVA API ?

is there any easy way which helps to create XML Document programmatically without relying on any of the XML Parser Implementation ?.

I have created XMLDocument based on xerces, but my clients are using Oracle XDK, what to do ?.

Yes. Some features availed by giving customized methods and classes in Parser implementation. But, the same feature may not be available in other implementation.

Best and sweet approaches is, don't implement your application based on particular XML Parser implementation and try to use always the packages comes from rt.jar(javax.xml.*; org.w3c.*;). Some highly required features may not be available in these packages, hence we will force to use implementation specific features from parser implementation.

Before making use of packages which is not follows JSR 5 suggestions, do double check is that same method will be available for other parser, how they are handling the same feature.

Sometime Feature will give big head ache for us.

Here is the code how to convert XML Document Object to String xml-to-string-object.html

An Element is combination of child Elements and attributes and tagName, hence
create a class with these three components.

private String tagName;
private Map attrList = new HashMap();
private List childList = new ArrayList();

To call and get XML content as output
Tag tag = new Tag("Employees");
tag.getAttrList().put("address","ch 8509 zurich");
Tag depttag=new Tag("Department");


the output will be
<?xml version=\"1.0\"?>
<employees address="ch 8509 zurich" name="Alex">
<department name="Engineering">

To generate attribute and values to add in Element tag
for (Map.Entry attribute : attrMap.entrySet()) {
str.append(WHITE_SPACE).append(attribute.getKey()).append(EQUAL) .append(DOUBLE_QUOTE).append(attribute.getValue()).append( DOUBLE_QUOTE); }

To create Element as String object
StringBuilder str = new StringBuilder();
if (!getAttrList().isEmpty()) { str.append(generateAtribute(getAttrList()));}

if (!getChildList().isEmpty()) {
for (Tag childTag : getChildList()) {
str.append(NEWLINE).append(LT).append(BACK_SLASH).append( getTagName()).append(GT);} else { str.append(WHITE_SPACE).append(BACK_SLASH).append(GT);

Here i have explained almost all how to do implementation to get XML document without relying on any of the XML implementations. Here, you can add n number of element without worrying about the implementation of org.w3c.dom.Document object, i.e no XML Parser implementation is required to create XML document.

This implementation contains only one class with 128 line of code. This will improve performance of XML document creation(obviously less feature will do better), and eates less heap size.

Please feel free to ask implementation by sending mail or leaving your valuable comments.

Sunday, December 2, 2007

Find Class in JAR

How will i get to know which jar has required Class ?.

I do get NoClassDefFoundError or ClassNotFoundError, is there any approach to identify that the missed class is located in this jar and in which package ?.

In unix and windows(with unix utils) we have a spy(we can say) named as grep. This command used to search the specific words in a file. We can use the same command to find out the class located in jar file.

Unix :
grep -r *.jar

grep -r *

In windows, sometime wildcard only for jar will not work. This may be issue with my machine. But try for customizing wild card, if works, show little smile.

The above command will list referenced and refering jar list, we have to identify manually walkthroughwing the content of JAR using tools like WinZIP, WINRAR, Stuffit.

Saturday, December 1, 2007

XML to String Object

How to convert a XML file to string ?
How to conver the XML Node to String format ?.

Oh, my XML parser implementation does not have directly to convert as a String. toString() method just returns object information what to do?.

Yes, in this moment, we have to write a our own logic to convert the Node as a String object. Sun Microsystems javax.xml package serves transforming the XML document to String irrespective of the XML parser Implementation(refer JSR 5 and JSR 173 and etc.,)

Even upto individual Node level transformation is possible.

  • XML Document to String
  • XML element to String
  • XML Node to String

Import following package classses apart from your application class import and org.w3c.* package.

import javax.xml.transform.Result;
import javax.xml.transform.Source;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerConfigurationException;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;

Write following method and conver simply your Node as String

public static String xmlToString(Node node) {
try {
Source source = new DOMSource(node);
StringWriter stringWriter = new StringWriter();
Result result = new StreamResult(stringWriter);
TransformerFactory factory = TransformerFactory.newInstance();
Transformer transformer = factory.newTransformer();
transformer.transform(source, result);
return stringWriter.getBuffer().toString();
} catch (TransformerConfigurationException e) {
} catch (TransformerException e) {
return null;

Using Oracle implementation, we can do this XMLDocument to String by giving single command.

//any of the output stream , enjoy :)

Tuesday, November 27, 2007

Setting the class path in UNIX


Multiple path entries are separated by colons. Classpath can be either archive files or folder.To include all the Jar files in a folder/directory, include the following script to collect all the jar files from the folder and will be added to the classpath.

for i in `ls $OH/j2ee/lib/*.jar `
java -cp CP yourclass

Setting the class path in Windows

set CLASSPATH=classpath1;classpath2...

Classpath entries that are neither directories nor archives (.zip or .jar files) are ignored. If the classpath ends with a file location that should be archives. If the classpath ends with the directory then the *.class found in the path will be added in JVM CLASSPATH

Is there a way to add all the jar files in a folder / directory to CLASSPATH?.

No. There is no way of setting directly the all the jars in folder to the classpath.

set CLASSPATH=%CLASSPATH%;%LIB%/java/classes.jar
set CLASSPATH=%CLASSPATH%;%LIB%/java/rt.jar
set CLASSPATH=%CLASSPATH%;%LIB%/java/junit.jar
set CLASSPATH=%CLASSPATH%;%LIB%/java/tools.jar

Alternate approach is possible by collecting the jars from a folder and setting into CLASSPATH.

set CP=
for %%f in (%LIB%\*.jar) do set CP=!CP!;%%f
echo %CP%
java -cp %CP% yourclassname

Keep in mind:

Here ! means that variables values are expanded later.

Don't Use CLASSPATH instead of CP because it will lead you to expose these setting to environment. If you want to use CLASSPATH then the code has to be placed within setlocal and endlocal.

Delayed environment variable expansion support is always disabled by default, but may be enabled/disabled via the /V command line switch to CMD.EXE. See CMD /?

The above mentioned echo %CP% will display as !CP!;%LIB%/java/tools.jar , but this will be expanded while using in any commands like java, javac.Show text-ads on your Website or Blog with BidVertiser.

Few of Dynamic variables from Windows:

If Command Extensions are enabled, then there are several dynamic environment variables that can be expanded but which don't show up in the list of variables displayed by SET. These variable values are computed dynamically each time the value of the variable is expanded. If the user explicitly defines a variable with one of these names, then that definition will override the dynamic one described below:

expands to the current directory string.
expands to current date using same format as DATE command.
expands to current time using same format as TIME command.
expands to a random decimal number between 0 and 32767.
expands to the current ERRORLEVEL value
expands to the current Command Processor Extensions version number.
expands to the original command line that invoked the Command Processor.

Java Launcher Finds Classes

The virtual machine searches for and loads classes in this order:

Bootstrap classes
Classes that comprise the Java platform, including the classes in rt.jar and several other important jar files.
Extension classes
Classes that use the Java Extension mechanism. These are bundled as jar files located in the extensions directory.
User classes
Classes defined by developers and third parties that do not take advantage of the extension mechanism. You identify the location of these classes using the -classpath option on the command line (the preferred method) or by using the CLASSPATH environment variable.

Sunday, November 18, 2007

Default Heap Size

If not otherwise set on the command line, the sizes of the initial heap and maximum heap are calculated based on the size of the physical memory. If phys_mem is the size of the physical memory on the platform, the initial heap size will be set to phys_mem / DefaultInitialRAMFraction.

DefaultInitialRAMFraction is a command line option with a default value of 64. Similarly the maximum heap size will be set to phys_mem / DefaultMaxRAM.

DefaultMaxRAMFraction has a default value of 4.

About Generational GC
JVM heap size
Heap Size
Heap Size Options
Heap Size


The throughput collector will throw an out-of-memory exception if too much time is being spent doing garbage collection.

For example, if the JVM is spending more than 98% of the total time doing garbage collection and is recovering less than 2% of the heap, it will throw an out-of-memory expection. The implementation of this feature has changed in 1.5. The policy is the same but there may be slight differences in behavior due to the new implementation.

About Generational GC
JVM heap size
Heap Size
Heap Size Options
Heap Size

Thursday, November 15, 2007

About Generational Garbage Collection

The Java HotSpot JVM 1.3 uses generational garbage collection. While naive garbage collection examines every living object in the heap, generational garbage collection considers the lifetime of an object to avoid extra work.

The heap is divided into two general areas: New and Old. The New generation area is sub-divided further into Eden and two survivor spaces. Eden is the area where new objects are allocated. When garbage collection occurs, live objects in Eden are copied into the next survivor space. Objects are copied between survivor spaces in this way until they exceed a maximum threshold, and then they are moved out of the New area and into the Old.

Many objects become available for garbage shortly after being allocated. These objects are said to have infant mortality. The longer an object survives, the more garbage collection it goes through, and the slower garbage collection becomes. The rate at which your application creates and releases objects determines how often garbage collection occurs. Attempt to cache objects for re-use, whenever possible, rather than creating new objects

Knowing that a majority of objects die young allows you to tune for efficient garbage collection. When you manage memory in generations, you create memory pools to hold objects of different ages. Garbage collection can occur in each generation when it fills up. If you can arrange for most of your objects to survive less than one collection, garbage collection is very efficient. Poorly sized generations cause frequent garbage collection, impacting your performance.

About Generational GC
JVM heap size
Heap Size
Heap Size Options
Heap Size

About JVM Heap Size

Garbage collection is the VM process of de-allocating unused Java objects in the Java heap.The Java heap is where the objects of a Java program live. It is a repository for live objects, dead objects, and free memory. When an object can no longer be reached from any pointer in the running program, the object is garbage.

The JVM heap size determines how often and how long the VM spends collecting garbage. An acceptable rate for garbage collection is application-specific and should be adjusted after analyzing the actual time and frequency of garbage collections.

If you set a large heap size, full garbage collection is slower, but it occurs less frequently. If you set your heap size in accordance with your memory needs, full garbage collection is faster, but occurs more frequently.p>

The goal of tuning your heap size is to minimize the time that you spend doing garbage collection while maximizing the number of clients that you can handle at a given time.

To ensure maximum performance during benchmarking, you might set high heap size values to ensure that garbage collection does not occur during the entire run of the benchmark.

You might see the following java error if you are running out of heap space:

java.lang.OutOfMemoryError Exception in thread "main"
About Generational GC
JVM heap size
Heap Size
Heap Size Options
Heap Size

Specifying Heap Size Values

java ... -XX:NewSize=128m -XX:MaxNewSize=128m -XX:SurvivorRatio=8
-Xms512m -Xmx512m 

The default size for these values is measured in bytes. Append the letter `k' or `K' to the value to indicate kilobytes, `m' or `M' to indicate megabytes, and `g' or `G' to indicate gigabytes.

About Generational GC
JVM heap size
Heap Size
Heap Size Options
Heap Size

Java Heap Size Options

Setting the New generation heap size


Use this option to set the New generation Java heap size. Set this value to a multiple of 1024 that is greater than 1MB. As a general rule, set -XX:NewSize to be one-fourth the size of the maximum heap size. Increase the value of this option for larger numbers of short-lived objects.

Be sure to increase the New generation as you increase the number of processors. Memory allocation can be parallel, but garbage collection is not parallel.

Setting the maximum New generation heap size


Use this option to set the maximum New generation Java heap size. Set this value to a multiple of 1024 that is greater than 1MB.

Setting New heap size ratios


The New generation area is divided into three sub-areas: Eden, and two survivor spaces that are equal in size.

Use the -XX:SurvivorRatio=X option to configure the ratio of the Eden/survivor space size. Try setting this value to 8 and then monitor your garbage collection.

Setting minimum heap size


Use this option to set the minimum size of the memory allocation pool. Set this value to a multiple of 1024 that is greater than 1MB. As a general rule, set minimum heap size -Xms equal to the maximum heap size -Xmx.

Setting maximum heap size


Use this option to set the maximum Java heap size. Set this value to a multiple of 1024 that is greater than 1MB.

About Generational GC
JVM heap size
Heap Size
Heap Size Options
Heap Size

Monday, January 1, 2007

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