1. Converting Strings to int and int to String

String a = String.valueOf( 2 ); int i = Integer.parseInt(a);

2. Append text to file in Java

BufferedWriter out = null ; try { out = new BufferedWriter( new FileWriter(”filename”, true )); out.write(”aString”); } catch (IOException e) { } finally { if (out != null ) { out.close(); } }

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(); 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()) { } rs.close(); ps.close(); } public static void main (String[] args) { OracleJdbcTest test = new OracleJdbcTest(); test.init(); test.fetch(); } }

6. Convert Java util.Date to sql.Date

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(); try { 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(); } } } [/code] <h2> 8 . Create Thumbnail of an image in Java</h2> <!-- wp:code { "language" : "java" } --><pre class = "wp-block-code" ><code></code></pre><!-- /wp:code --> private void createThumbnail (String filename, int thumbWidth, int thumbHeight, int quality, String outFilename) throws InterruptedException, FileNotFoundException, IOException { Image image = Toolkit.getDefaultToolkit().getImage(filename); MediaTracker mediaTracker = new MediaTracker( new Container()); mediaTracker.addImage(image, 0 ); mediaTracker.waitForID( 0 ); 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); } 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 ); 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 ); encoder.setJPEGEncodeParam(param); encoder.encode(thumbImage); out.close(); } [/code] <h2> 9 . Creating JSON data in Java</h2> Read <a href= "https://www.viralpatel.net/creating-parsing-json-data-with-java-servlet-struts-jsp-json/" > this article</a> for more details. Download JAR file <a href= "https://www.viralpatel.net/download/json/json-rpc-1.0.jar" >json-rpc- 1.0 .jar ( 75 kb)</a> <!-- wp:code { "language" : "java" } --><pre class = "wp-block-code" ><code></code></pre><!-- /wp:code --> 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

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(); } } }

11. HTTP Proxy setting in Java

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

public class SimpleSingleton { private static SimpleSingleton singleInstance = new SimpleSingleton(); private SimpleSingleton () { } public static SimpleSingleton getInstance () { return singleInstance; } }

public enum SimpleSingleton { INSTANCE; public void doSomething () { } } SimpleSingleton.INSTANCE.doSomething();

13. Capture screen shots in Java

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 ) { } else { for ( int i= 0 ; i < children.length; i++) { String filename = children[i]; } } FilenameFilter filter = new FilenameFilter() { public boolean accept (File dir, String name) { return !name.startsWith( "." ); } }; children = dir.list(filter); File[] files = dir.listFiles(); FileFilter fileFilter = new FileFilter() { public boolean accept (File file) { return file.isDirectory(); } }; files = dir.listFiles(fileFilter); [/code] <h2> 15 . Creating ZIP and JAR Files in Java</h2> <!-- wp:code { "language" : "java" } --><pre class = "wp-block-code" ><code></code></pre><!-- /wp:code --> 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); continue ; } BufferedInputStream bis = new BufferedInputStream( new FileInputStream(file)); crc.reset(); while ((bytesRead = bis.read(buffer)) != - 1 ) { crc.update(buffer, 0 , bytesRead); } bis.close(); bis = new BufferedInputStream( 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 ) { zos.write(buffer, 0 , bytesRead); } bis.close(); } zos.close(); } } [/code] <h2> 16 . Parsing / Reading XML file in Java</h2> Sample XML file. <!-- wp:code { "language" : "xml" } --><pre class = "wp-block-code" ><code></code></pre><!-- /wp:code --> <?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>

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(); System.out.println( "Root element of the document: " + docEle.getNodeName()); NodeList studentList = docEle.getElementsByTagName( "student" ); 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" ); } } [/code] <h2> 17 . Convert Array to Map in Java</h2> <!-- wp:code { "language" : "java" } --><pre class = "wp-block-code" ><code></code></pre><!-- /wp:code --> 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 ; Properties props = new Properties(); props.put( "mail.smtp.host" , "smtp.example.com" ); Session session = Session.getDefaultInstance(props, null ); session.setDebug(debug); Message msg = new MimeMessage(session); 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); msg.addHeader( "MyHeaderName" , "myHeaderValue" ); msg.setSubject(subject); msg.setContent(message, "text/plain" ); Transport.send(msg); } [/code] <h2> 19 . Send HTTP request & fetching data using Java</h2> <!-- wp:code { "language" : "java" } --><pre class = "wp-block-code" ><code></code></pre><!-- /wp:code --> 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/" ); 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

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. [ad#singleblogtop-linkad]Updated: Thanks Simone for pointing to exception. I have changed the code.or[ad] This snippet shows how to convert a java util Date into a sql Date for use in databases.Read this article for more details.Read this article for more details.Read this article for more details. Update: Thanks Markus for the comment. I have updated the code and changed it to more robust implementation.One more implementation of Singleton class. Thanks to Ralph and Lukasz Zielinski for pointing this out.Read this article for more details.Java code to parse above XML./** * 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( 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