20个开发人员非常有用的Java功能代码

String a = String.valueOf(2);
//integer to numeric string
int i = Integer.parseInt(a); //numeric
string to an int
String a = String.valueOf(2);
//integer to numeric string
int i = Integer.parseInt(a); //numeric string to an
int

Updated: Thanks Simone for pointing to exception. I have

changed the code.
BufferedWriter ut = null;
try

{
out = new BufferedWriter(new FileWriter(”

filename”, true));
out.write(”

aString”);
} catch (IOException e) {
// error processing code
} finally

{
if (out != null) {
out.close();
}
}

BufferedWriter ut = null;
try {
out = new BufferedWriter(new

FileWriter(”filename”, true));
out.write(”aString”);
} catch

(IOException e) {
// error processing code
} finally {
if (out

!= null) {
out.close();
}
}

String methodName =
Thread.currentThread().getStackTrace()[1].getMethodName();
String methodName = Thread.currentThread().getStackTrace()[1].getMethodName
();

java.util.Date =
java.text.DateFormat.getDateInstance().parse(date String);
java.util.Date = java.text.DateFormat.getDateInstance().parse(date
String);or
SimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy"
);
Date date = format.parse( myString );
SimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy" );
Date date
= format.parse( myString );

public class OracleJdbcTest
{
String driverClass =

"oracle.jdbc.driver.OracleDriver";

Connection con;

public void init

(FileInputStream fs) throws ClassNotFoundException,
SQLException, FileNotFoundException, IOException
{
Properties props = new Properties();
props.load(fs);
String url = props.getProperty

("db.url");
String

userName = props.getProperty("db.user");
String password = props.getProperty

("db.password");
Class.forName(driverClass);

con=DriverManager.getConnection(url,

userName, password);
}

public void fetch() throws SQLException,

IOException
{
PreparedStatement ps =

con.prepareStatement("select SYSDATE from dual");
ResultSet rs = ps.executeQuery

();

while

(rs.next())
{
// do the

thing you do
}

rs.close();
ps.close();
}

public

static void main(String[] args)
{
OracleJdbcTest test = new

OracleJdbcTest();
test.init();
test.fetch

();
}
}

public class OracleJdbcTest
{
String driverClass =

"oracle.jdbc.driver.OracleDriver";
Connection con;
public void init(FileInputStream fs) throws ClassNotFoundException,
SQLException, FileNotFoundException, IOException
{
Properties props = new Properties();
props.load

(fs);
String url = props.getProperty

("db.url");
String userName = props.getProperty

("db.user");
String password = props.getProperty

("db.password");
Class.forName(driverClass);
con=DriverManager.getConnection(url, userName,

password);
}
public void fetch() throws SQLException, IOException
{
PreparedStatement ps = con.prepareStatement("select SYSDATE from
dual");
ResultSet rs = ps.executeQuery();
while (rs.next())
{
// do the

thing you do
}
rs.close();
ps.close

();
}
public static void main(String[] args)
{
OracleJdbcTest test = new OracleJdbcTest

();
test.init();
test.fetch();
}
}

java.util.Date utilDate = new
java.util.Date();
java.sql.Date sqlDate = new java.sql.Date
(utilDate.getTime());
java.util.Date utilDate = new java.util.Date();
java.sql.Date sqlDate =
new java.sql.Date(utilDate.getTime());

public static void fileCopy( File in, File out )

throws IOException
{
FileChannel inChannel = new

FileInputStream( in ).getChannel();
FileChannel utChannel = new

FileOutputStream( out ).getChannel();
try
{
//          inChannel.transferTo

(0, inChannel.size(), outChannel);      // original
-- apparently has trouble copying large files on Windows

// magic

number for Windows, 64Mb - 32Kb)
int maxCount

= (64 * 1024 * 1024) - (32 * 1024);
long size =

inChannel.size();
long

position = 0;
while (

position < size )
{
&

nbsp; position += inChannel.transferTo( position, maxCount, outChannel );

}

}
finally
{
if (

inChannel != null )
{
&

nbsp; inChannel.close();
}

if ( outChannel != null )
{
&

nbsp;  outChannel.close();
}

}
}

public static void fileCopy( File in, File out )
throws

IOException
{
FileChannel inChannel = new FileInputStream( in ).getChannel

();
FileChannel utChannel = new

FileOutputStream( out ).getChannel();
try
{
//          inChannel.transferTo

(0, inChannel.size(), outChannel);      // original
-- apparently has trouble copying large files on Windows
// magic

number for Windows, 64Mb - 32Kb)
int maxCount

= (64 * 1024 * 1024) - (32 *

1024);
long

size = inChannel.size

();
long

position = 0;
while ( position < size )
{
position += inChannel.transferTo( position, maxCount, outChannel

);
}
}
finally
{
if (

inChannel != null )
{
inChannel.close

();
}
if (

outChannel != null )
{
outChannel.close

();
}
}
}

private void createThumbnail(String filename, int thumbWidth,

int thumbHeight, int
quality, String outFilename)
throws InterruptedException,

FileNotFoundException, IOException
{
// load image from

filename
Image image =

Toolkit.getDefaultToolkit().getImage(filename);
MediaTracker mediaTracker = new

MediaTracker(new Container());
mediaTracker.addImage(image,

0);
mediaTracker.waitForID(0);
// use this to test for errors at

this point: System.out.println
(mediaTracker.isErrorAny());

// determine thumbnail size from

WIDTH and HEIGHT
double

thumbRatio = (double)thumbWidth / (double)thumbHeight;
int imageWidth = image.getWidth

(null);
int imageHeight

= image.getHeight(null);
double imageRatio = (double)imageWidth / (double)imageHeight;
if (thumbRatio < imageRatio)

{
thumbHeight

= (int)(thumbWidth / imageRatio);
} else {
thumbWidth =

(int)(thumbHeight * imageRatio);
}

// draw original image to thumbnail

image object and
//

scale it to the new size on-the-fly
BufferedImage thumbImage = new

BufferedImage(thumbWidth, thumbHeight,
BufferedImage.TYPE_INT_RGB);
Graphics2D graphics2D =

thumbImage.createGraphics();
graphics2D.setRenderingHint

(RenderingHints.KEY_INTERPOLATION,
RenderingHints.VALUE_INTERPOLATION_BILINEAR);
graphics2D.drawImage(image, 0, 0,

thumbWidth, thumbHeight, null);

// save thumbnail image to

outFilename
BufferedOutputStream ut = new BufferedOutputStream(new FileOutputStream
(outFilename));
JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
JPEGEncodeParam param =

encoder.getDefaultJPEGEncodeParam(thumbImage);
quality = Math.max(0, Math.min

(quality, 100));
param.setQuality((float)quality / 100.0f, false);
encoder.setJPEGEncodeParam

(param);
encoder.encode

(thumbImage);
out.close

();
}

private void createThumbnail(String filename, int thumbWidth, int

thumbHeight, int
quality, String outFilename)
throws InterruptedException,

FileNotFoundException, IOException
{
// load image from

filename
Image image = Toolkit.getDefaultToolkit().getImage

(filename);
MediaTracker mediaTracker = new MediaTracker(new

Container());
mediaTracker.addImage(image,

0);
mediaTracker.waitForID(0);
// use this to test

for errors at this point: System.out.println
(mediaTracker.isErrorAny());
// determine thumbnail size from WIDTH and

HEIGHT
double thumbRatio = (double)thumbWidth / (double)

thumbHeight;
int imageWidth = image.getWidth

(null);
int imageHeight = image.getHeight

(null);
double imageRatio = (double)imageWidth / (double)

imageHeight;
if (thumbRatio < imageRatio)

{
thumbHeight = (int)(thumbWidth /

imageRatio);
} else {
thumbWidth = (int)

(thumbHeight * imageRatio);
}
// draw original image to thumbnail image object

and
// scale it to the new size on-the-

fly
BufferedImage thumbImage = new BufferedImage(thumbWidth,
thumbHeight, BufferedImage.TYPE_INT_RGB);
Graphics2D graphics2D =

thumbImage.createGraphics();
graphics2D.setRenderingHint

(RenderingHints.KEY_INTERPOLATION,
RenderingHints.VALUE_INTERPOLATION_BILINEAR);
graphics2D.drawImag

e(image, 0, 0, thumbWidth, thumbHeight, null);
// save thumbnail image to

outFilename
BufferedOutputStream ut = new BufferedOutputStream(new
FileOutputStream(outFilename));
JPEGImageEncoder encoder =

JPEGCodec.createJPEGEncoder(out);
JPEGEncodeParam param =

encoder.getDefaultJPEGEncodeParam
(thumbImage);
quality = Math.max(0, Math.min(quality,

100));
param.setQuality((float)quality / 100.0f,

false);
encoder.setJPEGEncodeParam

(param);
encoder.encode(thumbImage);
out.close

();
}

Read this article for more details.
Download JAR file json

-rpc-1.0.jar (75 kb)

import org.json.JSONObject;
...
...
JSONObject json = new JSONObject();
json.put("city", "Mumbai");
json.put("country",

"India");
...
String utput = json.toString

();
...

import org.json.JSONObject;
...
...
JSONObject json = new

JSONObject();
json.put("city", "Mumbai");
json.put("country",

"India");
...
String utput = json.toString();
...

Read this article for more details.

import java.io.File;
import

java.io.FileOutputStream;
import java.io.OutputStream;
import java.util.Date;

import

com.lowagie.text.Document;
import

com.lowagie.text.Paragraph;
import

com.lowagie.text.pdf.PdfWriter;

public class GeneratePDF

{

public static void main(String[]

args) {
try

{
OutputStream

file = new FileOutputStream(new File("C://Test.pdf"));

Document

document = new Document();
PdfWriter.getInstance(document, file);
document.open();
document.add(new Paragraph("Hello Kiran"));
document.add(new Paragraph(new Date().toString()));

document.close();
file.close

();

} catch

(Exception e) {

e.printStackTrace();
}

}
}

import java.io.File;
import java.io.FileOutputStream;
import

java.io.OutputStream;
import java.util.Date;
import com.lowagie.text.Document;
import

com.lowagie.text.Paragraph;
import com.lowagie.text.pdf.PdfWriter;
public class GeneratePDF {
public static void main(String[] args)

{
try

{
OutputStream file = new FileOutputStream(new File("C://Test.pdf"));
Document

document = new Document

();
PdfWriter.getInstance(document,

file);
document.open

();
document.add(new Paragraph("Hello

Kiran"));
document.add(new Paragraph(new Date().toString()));
document.close

();
file.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}

System.getProperties().put("http.proxyHost",

"someProxyURL");
System.getProperties().put("http.proxyPort",

"someProxyPort");
System.getProperties().put("http.proxyUser",

"someUserName");
System.getProperties().put("http.proxyPassword",

"somePassword");

System.getProperties().put("http.proxyHost",

"someProxyURL");
System.getProperties().put("http.proxyPort",

"someProxyPort");
System.getProperties().put("http.proxyUser",

"someUserName");
System.getProperties().put("http.proxyPassword",

"somePassword");

Read this article for more

details.
Update: Thanks Markus for the comment. I have updated the code and

changed it to
more robust implementation.

public class SimpleSingleton {
private static SimpleSingleton singleInstance =  new SimpleSingleton

();

//Marking default constructor

private
//to avoid direct

instantiation.
private SimpleSingleton()

{
}

//Get instance for class SimpleSingleton
public static SimpleSingleton getInstance() {

return

singleInstance;
}
}

public class SimpleSingleton {
private static SimpleSingleton

singleInstance =  new SimpleSingleton();
//Marking default constructor private
//to avoid direct

instantiation.
private SimpleSingleton() {
}
//Get instance for class SimpleSingleton
public static

SimpleSingleton getInstance() {
return singleInstance;
}
}
One more implementation of

Singleton class. Thanks to Ralph and Lukasz Zielinski
for pointing this out.

public enum SimpleSingleton {
INSTANCE;
public void doSomething()

{
}
}

//Call the method from Singleton:
SimpleSingleton.INSTANCE.doSomething();

public enum SimpleSingleton {
INSTANCE;
public void

doSomething() {
}
}
//Call the method from Singleton:
SimpleSingleton.INSTANCE.doSomething();

Read this article for more details.

import

java.awt.Dimension;
import java.awt.Rectangle;
import java.awt.Robot;
import java.awt.Toolkit;
import java.awt.image.BufferedImage;
import

javax.imageio.ImageIO;
import java.io.File;

...

public void captureScreen(String fileName)

throws Exception {

Dimension screenSize =

Toolkit.getDefaultToolkit().getScreenSize();
Rectangle

screenRectangle = new Rectangle(screenSize);
Robot

robot = new Robot();
BufferedImage image =

robot.createScreenCapture(screenRectangle);
ImageIO.write(image, "png", new File(fileName));

}

...

import java.awt.Dimension;
import java.awt.Rectangle;
import

java.awt.Robot;
import java.awt.Toolkit;
import

java.awt.image.BufferedImage;
import javax.imageio.ImageIO;
import

java.io.File;
...
public void captureScreen(String fileName) throws Exception {
Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize

();
Rectangle screenRectangle = new Rectangle

(screenSize);
Robot robot = new Robot();
BufferedImage image = robot.createScreenCapture(screenRectangle);
ImageIO.write(image, "png", new File(fileName));
}
...

>File dir = new File("directoryName");
String[] children = dir.list();
if (children ==

null) {
// Either dir does not exist

or is not a directory
} else {
for (int i=0; i < children.length; i++)

{
// Get

filename of file or directory
String filename =

children[i];
}
}

// It is also possible to filter the

list of returned files.
// This example does not return any

files that start with `.'.
FilenameFilter filter = new

FilenameFilter() {
public boolean

accept(File dir, String name) {
return !name.startsWith

(".");
}
};
children = dir.list(filter);

// The list of files can also be retrieved as File objects
File[] files = dir.listFiles();

//

This filter only returns directories
FileFilter fileFilter =

new FileFilter() {
public boolean

accept(File file) {
return file.isDirectory

();
}
};
files = dir.listFiles(fileFilter);

File dir = new File("directoryName");
String[]

children = dir.list();
if (children == null)

{
// Either dir does not exist or is

not a directory
} else

{
for (int i=0; i <

children.length; i++)

{
// Get

filename of file or

directory
String filename = children[i];
}
}
// It is also possible to filter the list of returned

files.
// This example does not return any files that start

with `.'.
FilenameFilter filter = new FilenameFilter()

{
public boolean accept(File dir,

String name)

{
return !

name.startsWith(".");
}
};
children = dir.list(filter);
// The list of files can also be retrieved as File

objects
File[] files = dir.listFiles();
// This filter only returns directories
FileFilter fileFilter = new FileFilter()

{
public boolean accept(File file)

{
return

file.isDirectory();
}
};
files = dir.listFiles

(fileFilter);

import java.util.zip.*;
import

java.io.*;

public class ZipIt {
public static void main(String args[]) throws IOException

{
if (args.length <

2) {
System.err.println("usage: java ZipIt Zip.zip file1 file2 file3");
System.exit

(-1);
}
File zipFile = new File(args

[0]);
if

(zipFile.exists()) {
System.err.println("Zip file already exists, please try another");
System.exit

(-2);
}
FileOutputStream fos = new

FileOutputStream(zipFile);
ZipOutputStream zos = new

ZipOutputStream(fos);
int bytesRead;
byte[]

buffer = new byte[1024];
CRC32 crc = new CRC32();
for (int i=1, n=args.length; i < n; i++) {
String name

= args[i];
File file =

new File(name);
if (!

file.exists()) {
&

nbsp;  System.err.println("Skipping: " + name);
&

nbsp;  continue;
}

BufferedInputStream bis = new BufferedInputStream(
&

nbsp;  new FileInputStream(file));
crc.reset

();
while

((bytesRead = bis.read(buffer)) != -1) {
&

nbsp;  crc.update(buffer, 0, bytesRead);
}

bis.close();
// Reset to

beginning of input stream
bis = new

BufferedInputStream(
&

nbsp;  new FileInputStream(file));
ZipEntry

entry = new ZipEntry(name);
entry.setMethod(ZipEntry.STORED);
entry.setCompressedSize(file.length());
entry.setSize(file.length());
entry.setCrc(crc.getValue());
zos.putNextEntry(entry);
while

((bytesRead = bis.read(buffer)) != -1) {
&

nbsp;  zos.write(buffer, 0, bytesRead);
}

bis.close();
}

zos.close

();
}
}

import java.util.zip.*;
import java.io.*;
public class ZipIt {
public static void main(String args

[]) throws IOException {
if

(args.length < 2)

{
System.err.println("usage: java ZipIt Zip.zip file1 file2

file3");
System.exit(-1);
}
File zipFile = new File(args

[0]);
if (zipFile.exists())

{
System.err.println("Zip file already exists, please try

another");
System.exit(-2);
}
FileOutputStream fos = new

FileOutputStream(zipFile);
ZipOutputStream zos = new ZipOutputStream

(fos);
int

bytesRead;
byte[] buffer = new byte

[1024];
CRC32 crc = new CRC32

();
for (int i=1, n=args.length; i

< n; i++)

{
String name

= args[i];
File file = new File

(name);
if

(!file.exists())

{
System.err.println("Skipping: " +

name);
&

nbsp;

continue;
}
BufferedInputStream bis = new BufferedInputStream

(
new FileInputStream

(file));
crc.reset();
while ((bytesRead = bis.read(buffer)) != -1)

{
crc.update(buffer, 0,

bytesRead);
}
bis.close

();
// Reset

to beginning of input

stream
bis =

new BufferedInputStream

(
new FileInputStream

(file));
ZipEntry entry = new ZipEntry

(name);
entry.setMethod

(ZipEntry.STORED);
&

nbsp; entry.setCompressedSize(file.length

());
entry.setSize(file.length

());
entry.setCrc(crc.getValue

());
zos.putNextEntry

(entry);
while ((bytesRead = bis.read(buffer)) != -1)

{
zos.write(buffer, 0,

bytesRead);
}
bis.close

();
}
zos.close();
}
}
16. Parsing / Reading XML file in Java
Sample XML file.

John
B
12

Mary
A
11

Simon
A
18

John
B
12

Mary
A
<

AGE>11

Simon
A
18

Java code to parse above XML.

package net.viralpatel.java.xmlparser;

import java.io.File;
import

javax.xml.parsers.DocumentBuilder;
import

javax.xml.parsers.DocumentBuilderFactory;

import

org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import

org.w3c.dom.NodeList;

public class XMLParser

{

public void getAllUserNames(String

fileName) {
try

{
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
DocumentBuilder db = dbf.newDocumentBuilder();
File file =

new File(fileName);
if

(file.exists()) {
&

nbsp;  Document doc = db.parse(file);
&

nbsp;  Element docEle = doc.getDocumentElement();

&

nbsp;  // Print root element of the document
&

nbsp;  System.out.println("Root element of the document: "
&

nbsp;          + docEle.getNodeName

());

&

nbsp;  NodeList studentList = docEle.getElementsByTagName

("student");

&

nbsp;  // Print total student elements in document
&

nbsp;  System.out
&

nbsp;          .println("Total

students: " + studentList.getLength());

&

nbsp;  if (studentList != null && studentList.getLength() > 0)

{
&

nbsp;      for (int i = 0; i < studentList.getLength();

i++) {

&

nbsp;          Node node =

studentList.item(i);

&

nbsp;          if (node.getNodeType()

== Node.ELEMENT_NODE) {

&

nbsp;

System.out
&

nbsp;

.println

("=====================");

&

nbsp;

Element e = (Element) node;
&

nbsp;

NodeList nodeList = e.getElementsByTagName("name");
&

nbsp;

System.out.println("Name: "
&

nbsp;

+ nodeList.item(0).getChildNodes

().item(0)
&

nbsp;

;   .getNodeValue());

&

nbsp;

nodeList = e.getElementsByTagName("grade");
&

nbsp;

System.out.println("Grade: "
&

nbsp;

+ nodeList.item(0).getChildNodes

().item(0)
&

nbsp;

;   .getNodeValue());

&

nbsp;

nodeList = e.getElementsByTagName("age");
&

nbsp;

System.out.println("Age: "
&

nbsp;

+ nodeList.item(0).getChildNodes

().item(0)
&

nbsp;

;   .getNodeValue());
&

nbsp;          }
&

nbsp;      }
&

nbsp;  } else {
&

nbsp;      System.exit(1);
&

nbsp;  }
}

} catch (Exception e)

{
System.out.println(e);
}
}
public

static void main(String[] args) {

XMLParser parser = new XMLParser

();
parser.getAllUserNames("c://test.xml");
}

}

package net.viralpatel.java.xmlparser;
import java.io.File;
import javax.xml.parsers.DocumentBuilder;
import

javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import

org.w3c.dom.Node;
import org.w3c.dom.NodeList;
public class XMLParser {
public void getAllUserNames(String fileName) {
try

{
DocumentBuilderFactory dbf =
DocumentBuilderFactory.newInstance();
DocumentBuilder db =

dbf.newDocumentBuilder();
File file = new File

(fileName);
if (file.exists())

{
Document doc = db.parse

(file);
Element docEle = doc.getDocumentElement();
// Print root element of the

document
System.out.println("Root element of the

document: "
+ docEle.getNodeName());
NodeList studentList = docEle.getElementsByTagName
("student");
// Print total student elements in

document
System.out
&nb

sp;.println("Total students: " +
studentList.getLength());
if (studentList != null &&

studentList.getLength()
> 0) {
for (int i = 0; i <

studentList.getLength
(); i++) {
Node node = studentList.item(i);
if (node.getNodeType() ==
Node.ELEMENT_NODE) {
System.out
.println
("=====================");
Element e = (Element)

node;
NodeList nodeList =
e.getElementsByTagName

("name");
System.out.println("Name:

"
+
nodeList.item(0).getChildNodes().item(0)
.getNodeValue());
nodeList =
e.getElementsByTagName

("grade");
System.out.println("Grade:
"
+
nodeList.item(0).getChildNodes().item(0)
.getNodeValue());
nodeList =
e.getElementsByTagName

("age");
System.out.println("Age:

"
+
nodeList.item(0).getChildNodes().item(0)
.getNodeValue());
}
}
} else

{
System.exit(1);
}
}
} catch (Exception e)

{
System.out.println(e);
}
}
public static void main(String[] args) {
XMLParser parser = new XMLParser

();
parser.getAllUserNames("c://test.xml");
}
}
17.

Convert Array to Map in Java

import java.util.Map;
import

org.apache.commons.lang.ArrayUtils;

public class Main

{

public static void main(String[] args)

{
String[][] countries = { { "United States",

"New York" }, { "United Kingdom",
"London" },
{

"Netherland", "Amsterdam" }, { "Japan", "Tokyo" }, { "France", "Paris" }
};

Map countryCapitals =

ArrayUtils.toMap(countries);

System.out.println("Capital of Japan is " + countryCapitals.get

("Japan"));
System.out.println("Capital of

France is " + countryCapitals.get("France"));
}
}

import java.util.Map;
import org.apache.commons.lang.ArrayUtils;
public class Main {
public static void main(String[] args) {
String[][]

countries = { { "United States", "New York" }, { "United Kingdom",
"London" },
{ "Netherland",

"Amsterdam" }, { "Japan", "Tokyo" }, { "France", "Paris" }
};
Map countryCapitals = ArrayUtils.toMap(countries);
System.out.println("Capital of Japan is " +

countryCapitals.get("Japan"));
System.out.println("Capital of

France is " + countryCapitals.get("France"));
}
}
18. Send Email

using Java

import javax.mail.*;
import

javax.mail.internet.*;
import java.util.*;

public void postMail( String recipients[ ], String subject, String message ,

String
from) throws MessagingException
{
boolean debug = false;

//Set the host smtp address
Properties props = new Properties();
props.put("mail.smtp.host",

"smtp.example.com");

// create some

properties and get the default Session
Session

session = Session.getDefaultInstance(props, null);
session.setDebug(debug);

// create a message
Message msg = new MimeMessage(session);

// set the from and to address
InternetAddress addressFrom = new InternetAddress

(from);
msg.setFrom(addressFrom);

InternetAddress[] addressTo = new

InternetAddress[recipients.length];
for (int i =

0; i < recipients.length; i++)
{
addressTo[i] = new InternetAddress

(recipients[i]);
}
msg.setRecipients(Message.RecipientType.TO,

addressTo);

// Optional : You can

also set your custom headers in the Email if you Want
msg.addHeader("MyHeaderName", "myHeaderValue");

// Setting the Subject and Content

Type
msg.setSubject(subject);
msg.setContent(message, "text/plain");
Transport.send(msg);
}

import javax.mail.*;
import javax.mail.internet.*;
import

java.util.*;
public void postMail( String recipients[ ], String subject, String message ,

String
from) throws MessagingException
{
boolean debug =

false;
//Set the host smtp address
Properties props = new Properties();
props.put

("mail.smtp.host", "smtp.example.com");
// create some properties and get the default

Session
Session session = Session.getDefaultInstance(props,

null);
session.setDebug(debug);
// create a message
Message msg = new

MimeMessage(session);
// set the from and to address
InternetAddress addressFrom = new InternetAddress(from);
msg.setFrom(addressFrom);
InternetAddress[] addressTo = new InternetAddress

[recipients.length];
for (int i = 0; i <

recipients.length; i++)
{
addressTo[i] = new InternetAddress

(recipients[i]);
}
msg.setRecipients

(Message.RecipientType.TO, addressTo);
// Optional : You can also set your custom headers in the

Email if you Want
msg.addHeader("MyHeaderName",

"myHeaderValue");
// Setting the Subject and Content Type
msg.setSubject(subject);
msg.setContent(message,

"text/plain");
Transport.send(msg);
}
19. Send HTTP

request & fetching data using Java

import java.io.BufferedReader;
import

java.io.InputStreamReader;
import java.net.URL;

public class Main {
public static

void main(String[] args)  {
try {
URL my_url =

new URL("http://www.viralpatel.net/blogs/");&nbs

p;
BufferedReader br = new BufferedReader(new InputStreamReader
(my_url.openStream()));
String

strTemp = "";
while(null

!= (strTemp = br.readLine())){
System.out.println(strTemp);
}
} catch (Exception ex) {
ex.printStackTrace();
}

}
}

import java.io.BufferedReader;
import

java.io.InputStreamReader;
import java.net.URL;
public class Main {
public static void main(String[] args)

{
try {
URL my_url = new URL("http://www.viralpatel.net/blogs/");
BufferedReader br = new BufferedReader(new
InputStreamReader(my_url.openStream()));
String strTemp =

"";
while(null != (strTemp = br.readLine()))

{
System.out.println(strTemp);
}
} catch (Exception ex) {
ex.printStackTrace

();
}
}
}
20. Resize an Array in Java

/**
* Reallocates an array with a new size, and copies the

contents
* of the old array to the new array.
* @param

oldArray  the old array, to be reallocated.
* @param

newSize   the new array size.
*

@return          A new array with the

same contents.
*/
private static Object resizeArray (Object

oldArray, int newSize) {
int ldSize =

java.lang.reflect.Array.getLength(oldArray);
Class

elementType = oldArray.getClass().getComponentType();
Object newArray = java.lang.reflect.Array.newInstance(
elementType,newSize);
int preserveLength = Math.min

(oldSize,newSize);
if (preserveLength > 0)

System.arraycopy

(oldArray,0,newArray,0,preserveLength);
return

newArray;
}

// Test routine for

resizeArray().
public static void main (String[] args)

{
int[] a = {1,2,3};
a =

(int[])resizeArray(a,5);
a[3] = 4;
a[4] = 5;
for (int i=0; i      System.out.println (a[i]);
}

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<?xml version="1.0"?>
<students>
<student>
<name>John</name>
<grade>B</grade>
<age>12</age>
</student>
<student>
<name>Mary</name>
<grade>A</grade>
<age>11</age>
</student>
<student>
<name>Simon</name>
<grade>A</grade>
<age>18</age>
</student>
</students>

<?xml version="1.0"?>
<students>
<student>
<name>John</name>
<grade>B</grade>
<age>12</age>
</student>
<student>
<name>Mary</name>
<grade>A</grade>
<age>11</age>
</student>
<student>
<name>Simon</name>
<grade>A</grade>
<age>18</age>
</student>
</students>
Java code to parse above XML.
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package net.viralpatel.java.xmlparser;

import java.io.File;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

public class XMLParser {

public void getAllUserNames(String fileName) {
try {
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
DocumentBuilder db = dbf.newDocumentBuilder();
File file = new File(fileName);
if (file.exists()) {
Document doc = db.parse(file);
Element docEle = doc.getDocumentElement();

// Print root element of the document
System.out.println("Root element of the document: "
+ docEle.getNodeName());

NodeList studentList = docEle.getElementsByTagName("student");

// Print total student elements in document
System.out
.println("Total students: " + studentList.getLength());

if (studentList != null && studentList.getLength() > 0) {
for (int i = 0; i < studentList.getLength(); i++) {

Node node = studentList.item(i);

if (node.getNodeType() == Node.ELEMENT_NODE) {

System.out
.println("=====================");

Element e = (Element) node;
NodeList nodeList = e.getElementsByTagName("name");
System.out.println("Name: "
+ nodeList.item(0).getChildNodes().item(0)
.getNodeValue());

nodeList = e.getElementsByTagName("grade");
System.out.println("Grade: "
+ nodeList.item(0).getChildNodes().item(0)
.getNodeValue());

nodeList = e.getElementsByTagName("age");
System.out.println("Age: "
+ nodeList.item(0).getChildNodes().item(0)
.getNodeValue());
}
}
} else {
System.exit(1);
}
}
} catch (Exception e) {
System.out.println(e);
}
}
public static void main(String[] args) {

XMLParser parser = new XMLParser();
parser.getAllUserNames("c://test.xml");
}
}

package net.viralpatel.java.xmlparser;
import java.io.File;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
public class XMLParser {
public void getAllUserNames(String fileName) {
try {
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
DocumentBuilder db = dbf.newDocumentBuilder();
File file = new File(fileName);
if (file.exists()) {
Document doc = db.parse(file);
Element docEle = doc.getDocumentElement();
// Print root element of the document
System.out.println("Root element of the document: "
+ docEle.getNodeName());
NodeList studentList = docEle.getElementsByTagName("student");
// Print total student elements in document
System.out
.println("Total students: " + studentList.getLength());
if (studentList != null && studentList.getLength() > 0) {
for (int i = 0; i < studentList.getLength(); i++) {
Node node = studentList.item(i);
if (node.getNodeType() == Node.ELEMENT_NODE) {
System.out
.println("=====================");
Element e = (Element) node;
NodeList nodeList = e.getElementsByTagName("name");
System.out.println("Name: "
+ nodeList.item(0).getChildNodes().item(0)
.getNodeValue());
nodeList = e.getElementsByTagName("grade");
System.out.println("Grade: "
+ nodeList.item(0).getChildNodes().item(0)
.getNodeValue());
nodeList = e.getElementsByTagName("age");
System.out.println("Age: "
+ nodeList.item(0).getChildNodes().item(0)
.getNodeValue());
}
}
} else {
System.exit(1);
}
}
} catch (Exception e) {
System.out.println(e);
}
}
public static void main(String[] args) {
XMLParser parser = new XMLParser();
parser.getAllUserNames("c://test.xml");
}
}

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import java.util.Map;
import org.apache.commons.lang.ArrayUtils;

public class Main {

public static void main(String[] args) {
String[][] countries = { { "United States", "New York" }, { "United Kingdom", "London" },
{ "Netherland", "Amsterdam" }, { "Japan", "Tokyo" }, { "France", "Paris" } };

Map countryCapitals = ArrayUtils.toMap(countries);

System.out.println("Capital of Japan is " + countryCapitals.get("Japan"));
System.out.println("Capital of France is " + countryCapitals.get("France"));
}
}

import java.util.Map;
import org.apache.commons.lang.ArrayUtils;
public class Main {
public static void main(String[] args) {
String[][] countries = { { "United States", "New York" }, { "United Kingdom", "London" },
{ "Netherland", "Amsterdam" }, { "Japan", "Tokyo" }, { "France", "Paris" } };
Map countryCapitals = ArrayUtils.toMap(countries);
System.out.println("Capital of Japan is " + countryCapitals.get("Japan"));
System.out.println("Capital of France is " + countryCapitals.get("France"));
}
}

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import javax.mail.*;
import javax.mail.internet.*;
import java.util.*;

public void postMail( String recipients[ ], String subject, String message , String from) throws MessagingException
{
boolean debug = false;

//Set the host smtp address
Properties props = new Properties();
props.put("mail.smtp.host", "smtp.example.com");

// create some properties and get the default Session
Session session = Session.getDefaultInstance(props, null);
session.setDebug(debug);

// create a message
Message msg = new MimeMessage(session);

// set the from and to address
InternetAddress addressFrom = new InternetAddress(from);
msg.setFrom(addressFrom);

InternetAddress[] addressTo = new InternetAddress[recipients.length];
for (int i = 0; i < recipients.length; i++)
{
addressTo[i] = new InternetAddress(recipients[i]);
}
msg.setRecipients(Message.RecipientType.TO, addressTo);

// Optional : You can also set your custom headers in the Email if you Want
msg.addHeader("MyHeaderName", "myHeaderValue");

// Setting the Subject and Content Type
msg.setSubject(subject);
msg.setContent(message, "text/plain");
Transport.send(msg);
}

import javax.mail.*;
import javax.mail.internet.*;
import java.util.*;
public void postMail( String recipients[ ], String subject, String message , String from) throws MessagingException
{
boolean debug = false;
//Set the host smtp address
Properties props = new Properties();
props.put("mail.smtp.host", "smtp.example.com");
// create some properties and get the default Session
Session session = Session.getDefaultInstance(props, null);
session.setDebug(debug);
// create a message
Message msg = new MimeMessage(session);
// set the from and to address
InternetAddress addressFrom = new InternetAddress(from);
msg.setFrom(addressFrom);
InternetAddress[] addressTo = new InternetAddress[recipients.length];
for (int i = 0; i < recipients.length; i++)
{
addressTo[i] = new InternetAddress(recipients[i]);
}
msg.setRecipients(Message.RecipientType.TO, addressTo);
// Optional : You can also set your custom headers in the Email if you Want
msg.addHeader("MyHeaderName", "myHeaderValue");
// Setting the Subject and Content Type
msg.setSubject(subject);
msg.setContent(message, "text/plain");
Transport.send(msg);
}

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import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.URL;

public class Main {
public static void main(String[] args)  {
try {
URL my_url = new URL("http://www.viralpatel.net/blogs/");
BufferedReader br = new BufferedReader(new InputStreamReader(my_url.openStream()));
String strTemp = "";
while(null != (strTemp = br.readLine())){
System.out.println(strTemp);
}
} catch (Exception ex) {
ex.printStackTrace();
}
}
}

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.URL;
public class Main {
public static void main(String[] args)  {
try {
URL my_url = new URL("http://www.viralpatel.net/blogs/");
BufferedReader br = new BufferedReader(new InputStreamReader(my_url.openStream()));
String strTemp = "";
while(null != (strTemp = br.readLine())){
System.out.println(strTemp);
}
} catch (Exception ex) {
ex.printStackTrace();
}
}
}

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/**
* Reallocates an array with a new size, and copies the contents
* of the old array to the new array.
* @param oldArray  the old array, to be reallocated.
* @param newSize   the new array size.
* @return          A new array with the same contents.
*/
private static Object resizeArray (Object oldArray, int newSize) {
int ldSize = java.lang.reflect.Array.getLength(oldArray);
Class elementType = oldArray.getClass().getComponentType();