20 very useful Java code snippets for Java Developers

Following are few very useful Java code snippets for Java developers. Few of them are written by me and few are taken from other code reference. Feel free to comment about the code and also add your code snippet.


1. Converting Strings to int and int to String

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

2. Append text to file in Java

Updated: Thanks Simone for pointing to exception. I have changed the code.
BufferedWriter out = null;
try {
    out = new BufferedWriter(new FileWriter(”filename”, true));
} catch (IOException e) {
    // error processing code
} finally {
    if (out != null) {

3. Get name of current method in Java

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

4. Convert String to Date in Java

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

5. Connecting to Oracle using Java JDBC

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();
        String url = props.getProperty("db.url");
        String userName = props.getProperty("db.user");
        String password = props.getProperty("db.password");
        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
    public static void main(String[] args)
        OracleJdbcTest test = new OracleJdbcTest();

6. Convert Java util.Date to sql.Date

This snippet shows how to convert a java util Date into a sql Date for use in databases.

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

7. Java Fast File Copy using NIO

public static void fileCopy( File in, File out )
            throws IOException
        FileChannel inChannel = new FileInputStream( in ).getChannel();
        FileChannel outChannel = new FileOutputStream( out ).getChannel();
//          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 );
            if ( inChannel != null )
            if ( outChannel != null )

8. Create Thumbnail of an image in Java

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);
        // 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 out = 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);

9. Creating JSON data in Java

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 output = json.toString();

10. PDF Generation in Java using iText JAR

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.add(new Paragraph("Hello Kiran"));
            document.add(new Paragraph(new Date().toString()));
        } catch (Exception e) {

11. HTTP Proxy setting in Java

Read this article for more details.
System.getProperties().put("http.proxyHost", "someProxyURL");
System.getProperties().put("http.proxyPort", "someProxyPort");
System.getProperties().put("http.proxyUser", "someUserName");
System.getProperties().put("http.proxyPassword", "somePassword");

12. Java Singleton example

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;
One more implementation of Singleton class. Thanks to Ralph and Lukasz Zielinski for pointing this out.
public enum SimpleSingleton {
    public void doSomething() {
//Call the method from Singleton:

13. Capture screen shots in Java

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));

14. Files-Directory listing in Java

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);

15. Creating ZIP and JAR Files in Java

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");
        File zipFile = new File(args[0]);
        if (zipFile.exists()) {
            System.err.println("Zip file already exists, please try another");
        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);
            BufferedInputStream bis = new BufferedInputStream(
                new FileInputStream(file));
            while ((bytesRead = bis.read(buffer)) != -1) {
                crc.update(buffer, 0, bytesRead);
            // Reset to beginning of input stream
            bis = new BufferedInputStream(
                new FileInputStream(file));
            ZipEntry entry = new ZipEntry(name);
            while ((bytesRead = bis.read(buffer)) != -1) {
                zos.write(buffer, 0, bytesRead);

16. Parsing / Reading XML file in Java

Sample XML file.
xml version="1.0"?>
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()) {
                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
                        .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) {
                            Element e = (Element) node;
                            NodeList nodeList = e.getElementsByTagName("name");
                            System.out.println("Name: "
                                    + nodeList.item(0).getChildNodes().item(0)
                            nodeList = e.getElementsByTagName("grade");
                            System.out.println("Grade: "
                                    + nodeList.item(0).getChildNodes().item(0)
                            nodeList = e.getElementsByTagName("age");
                            System.out.println("Age: "
                                    + nodeList.item(0).getChildNodes().item(0)
                } else {
        } catch (Exception e) {
    public static void main(String[] args) {
        XMLParser parser = new XMLParser();

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"));

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);
    // create a message
    Message msg = new MimeMessage(session);
    // set the from and to address
    InternetAddress addressFrom = new InternetAddress(from);
    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.setContent(message, "text/plain");

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/");
            BufferedReader br = new BufferedReader(new InputStreamReader(my_url.openStream()));
            String strTemp = "";
            while(null != (strTemp = br.readLine())){
        } catch (Exception ex) {

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 oldSize = java.lang.reflect.Array.getLength(oldArray);
   Class elementType = oldArray.getClass().getComponentType();
   Object newArray = java.lang.reflect.Array.newInstance(
   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]);

Transfer a blog from one account to another Account

Blogger is the best place to create your own blog for absolutely free. This service is run by Google. Here you need a Google account to enter Blogger. In fact, whenever you open Blogger.com, you have to log in with your Google account.
Actually, it is a tutorial article, in which I will tell you how to transfer your blogger blog to another account. Here is a very easy procedure to transfer your blogspot blog to another Google account. So, follow the steps to know how to transfer -
STEP 1 : Go to blogger dashboard by sign in to blogger.
STEP 2 : Click on More Options button and select Settings.
Open Settings in blogger dashboard
Open Settings in blogger dashboard
STEP 3 : Now, Click on Add Authors in Permissions section.
Add authors
Add authors
STEP 4 : Now, type the another gmail id, where you want to transfer your blog.
Type another id where to transfer blog
Type another id where to transfer blog
STEP 5 : Now, sign out the blogger and open Gmail and sign in with the id where you want to transfer your blogger blog.
STEP 6 : You’ll receive a invitation link from the that blogger blog. You need to click on the link and you’ll reach to blogger dashboard. Yet, the blog has not completely transferred but you have only become a contributor for the related blogger blog.
STEP 7 : So, to transfer completely, you have to log into your blogger account again with the blog admin id and again navigate to Settings > Permissions.
STEP 8 : Now, you’ll see two blog authors one named admin and another named author. Here you need to Click on author and change it to admin and remove the old admin from the list.
So, at last sign out this blogger account and sign in with new account where you have transferred the blog. You’ll see that your blog has completely transferred from old account to this account.

How To Increase Facebook Page Likes Quickly

In this article we will show all the basic tips how to increase Facebook fan page likes instantly. Here we will discuss some major advantages of large number of facebook pages likes. Increasing the counts of facebook page likes will attract your readers more to stay on your blog. This can also help to prove that your blog is receiving decent amount of traffics. However if we have dozens of likes on facebook page you can boost our posts and share it with billions of savvy bloggers and webmasters. So it can also help in improving our post ranking in Search engine result. One of the finest advantage of having thousand of Facebook page likes we can hit up to get the attention of thousands of bloggers and webmaster. So it is also the fastest growing way to spread over voice all over the world. So in today article, we will show you how to increase facebook fan page likes quickly.

How To Increase Facebook Page Likes Quickly

Here we will discuss all the excellent tips to increase your likes instantly and show maximum counts likes on facebook page. To follow all the below tips you will be able to get massive Facebook likes. Lets See how?.

Install Facebook Likes Widget

Installing the Facebook gadget on your blog is a genuine way to increase your facebook likes. Facebook itself also gives more awesome opportunity to bloggers it provides us piece of chuck code to embed in the website which help in showing all the likes of page and give instant result if someone hit the like button which is called facebook fan page box.

To look into alternative method, we can also use the most prominent facebook popup like box which will compels our reader to hit the fb page like. But i would recommended not use this one because it will not give us positive result instead it would discourage our reader. It would also compel our blog on loading time. So by the help of Facebook widget we can build a strong facebook page likes instantly.

Buying The Facebook Likes

There are many online services available which offer sells Facebook likes at very low costs. These services include various websites to do this job one of the finest website is http://marketingwonderland.com This website offer at low cost per likes, the more you buy the likes the more you will maximize your facebook page likes. So it would give a lot of traffic from Facebook directly flow to your Facebook page.
Invite Your Common Facebook Friends

In this method you can easily grab the attention of all of your common facebook friends. Let us know how to do? to add these friend to your facebook page. Go to facebook page >> click on invite button showing at the top of the page. After clicking all your friends will listing in the drop down mode, now select your specif friends which love your brands and niche. In my case i would select only bloggers and add one by one.So in this way you can easily increase your facebook likes.

Keep Update Your Facebook Page Constantly

We all of know that every one likes new latest deadly news. So to make your facebook page more popularize we have to update our page regularly on daily basis, it would bring us more and more likes because facebook page shares our posts on theirs walls and profiles, which will automatically alert the facebook user and hence they will like our page.

Advertise Your Page On Facebook

Facebook itself gives us awesome opportunity to advertise your site, page or brands on facebook with little amount of money. some time you might have noticed that whenever to open facebook page, you will see several of pages on the right side which are also recommended to be liked. These pages are mostly publicize by bloggers and webmaster they paid a little money to facebook to share their pages.

Use AdMeFast Tools To Boost Your Facebook Page Likes

Admefast is an online tools which can multiply your likes thousands times. Admefast is the official websites design special for facebook likes. You have to get registration with addmefast site to poll your likes instantly. It work on the following criteria. After registration you will be given dozen of pages to likes from your own facebook account. So doing this in revenge the same page will also automatically like your page. 

Now it up to you how many likes you want to add to your facebook page. But i would recommended not to use this website if your website is suited only for special niche or topic. Because from this website you will get random niches likes which will give nothing. But you can only maximize your facebook page likes quickly. 

Share Your Ideas About Facebook Page Likes

We hope you find this tutorial helpful for your blogging career. This was little about how you can increase your facebook fan page likes quickly and instantly in very short duration of times. So we have shared our experienced with all of you, We are confident these tips will surely increase your Facebook page likes dramatically. i would hungry requested to kindly share your thoughts with us if you know the better way how to make increase the facebook page likes quickly. Thanks and Happy blogging day!.

How to Browse Anonymously

Although many users believe that their Web surfing activities are anonymous, a great deal of identifying information is transmitted to and from websites that you browse. A history of the sites you've visited is stored on your computer even after you close your browser, and most websites keep logs of visitors' IP addresses and other statistical data. For those who wish to surf the Web anonymously, most of the major browsers offer secure browsing modes to give users more anonymity as they travel the Web.


  1. Internet Explorer

    • Run Internet Explorer and open the "Tools" menu. Click the "InPrivate Browsing" option to open a new window that invokes this secure browsing mode. Alternately, press "Ctrl-Shift-P" on your keyboard to launch an InPrivate browsing window, or right-click a pinned Internet Explorer icon on the taskbar and select the "InPrivate Browsing" option from the context menu.
    • Browse as you normally would. If you visit websites where you have accounts, you will need to log in manually because InPrivate browsing mode does not load any cached information or cookies from previous browsing sessions. If you return to one of these websites later in a regular browsing session, your login information will be stored in the usual manner.
    • Close the InPrivate browsing window when you are finished. Make sure that you don't have any content you want to save in other tabs, as all information will be lost when your close the window.

  2. Mozilla Firefox

    • Launch Firefox. Click the "Firefox" button in the upper left corner of the window and select the "Private Browsing" option. Alternately, press "Ctrl-Shift-P" to start a private browsing session.
    • Click the "Start Private Browsing" button to begin your private browsing session when prompted. Any tabs that you currently have open will be saved and then closed, allowing you to recover your current browsing session once you have finished browsing privately. The "Firefox" button will turn purple to indicate that you are browsing privately.
    • Browse as you normally would, keeping in mind that no user data or preferences will be loaded from previous browsing sessions. Click the "Firefox" button and select the "Stop Private Browsing" option to return to standard browsing mode and reload your previously saved session. Alternately, press "Ctrl-Shift-P" again to terminate private browsing.

  3. Google Chrome

    • Launch Chrome and click the "Wrench" icon to access the options menu. Click the "New Incognito Window" option to start browsing in Chrome's Incognito Mode. A new window will open with an Incognito Mode icon that looks like a man in a trench coat and fedora. Alternately, you can launch an Incognito Mode window by pressing "Ctrl-Shift-N" on your keyboard while in Chrome.
    • Browse as you normally would. Note that user data and preferences from previous browsing sessions won't be loaded while you are browsing in Incognito Mode.
    • Close the Incognito Mode window to end your private browsing session. Any cookies or other data produced by the browsing session will be deleted when the window is closed.

Tips and Warnings
  • There are other ways to browse anonymously, such as the TOR browser that was explicitly designed to mask IP addresses and the Anomymizer.com website that routes browser traffic through its own servers to hide your IP information.
  • Plugins can add encryption features to some popular Web browsers. Firefox users can use the FoxTOR or Ultrasurf plugins to surf the Web anonymously; the latter is also available for Internet Explorer users. Chrome users can install the TOR Button plugin, which adds a toggle button to the browser that can be used to turn anonymous browsing on and off.
  • To protect your personal information, you can manually delete cookies, temporary files and other data using the "Options" or "Preferences" feature specific to your browser. Make sure that you manually log out of websites and set your browser to never remember passwords before doing this to ensure that login data isn't saved or ignored when clearing cookies and other files.
  • Turn off "third party" cookies to reduce the trail you leave as you surf the Web. Cookies are often placed on your computer when you browse a website, but some cookies can be read by other websites for advertising and similar purposes. In your browser's privacy settings, select "Customize Settings" or its equivalent and uncheck the box beside "Accept Third-party Cookies" or a similarly named option.
  • Web browsing is often not completely anonymous. Even users who deploy secure plugins and alternate browsers designed for anonymity can sometimes be tracked through the websites they visit or activities they perform online. If you post in chat rooms or on message boards, be aware that your comments may impart revealing information that defeats your efforts to surf the Web anonymously.