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20 very useful Java code snippets for Java Developers 20 very useful Java code snippets for Java Developers 20 very useful Java code snippets for Java Developers 20 very useful Java code snippets for Java Developers 20 very useful Java code snippets for Java Developers
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    Star 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

    Source Code : 
    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.

    Source Code : 
    BufferedWriter out null;
    try {
        
    out = new BufferedWriter(new FileWriter(”filename”true));
        
    out.write(”aString”);
    } catch (
    IOException e) {
        
    // error processing code
    finally {
        if (
    out != null) {
            
    out.close();
        }


    3. Get name of current method in Java

    Source Code : 
    String methodName Thread.currentThread().getStackTrace()[1].getMethodName(); 


    4. Convert String to Date in Java

    Source Code : 
    java.util.Date java.text.DateFormat.getDateInstance().parse(date String); 
    or

    Source Code : 
    SimpleDateFormat format = new SimpleDateFormat"dd.MM.yyyy" );
    Date date format.parsemyString ); 

    5. Connecting to Oracle using Java JDBC
    Source Code : 
    public class OracleJdbcTest
    {
        
    String driverClass "oracle.jdbc.driver.OracleDriver";
     
        
    Connection con;
     
        public 
    void init(FileInputStream fsthrows ClassNotFoundExceptionSQLExceptionFileNotFoundExceptionIOException
        
    {
            
    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(urluserNamepassword);
        }
     
        public 
    void fetch() throws SQLExceptionIOException
        
    {
            
    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();
        }



    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.

    Source Code : 
    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

    Source Code : 
    public static void fileCopyFile inFile out )
                
    throws IOException
        
    {
            
    FileChannel inChannel = new FileInputStreamin ).getChannel();
            
    FileChannel outChannel = new FileOutputStreamout ).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.transferTopositionmaxCountoutChannel );
                }
            }
            
    finally
            
    {
                if ( 
    inChannel != null )
                {
                   
    inChannel.close();
                }
                if ( 
    outChannel != null )
                {
                    
    outChannel.close();
                }
            }
        } 

    8. Create Thumbnail of an image in Java
    Source Code : 
    private void createThumbnail(String filenameint thumbWidthint thumbHeightint qualityString outFilename)
            
    throws InterruptedExceptionFileNotFoundExceptionIOException
        
    {
            
    // load image from filename
            
    Image image Toolkit.getDefaultToolkit().getImage(filename);
            
    MediaTracker mediaTracker = new MediaTracker(new Container());
            
    mediaTracker.addImage(image0);
            
    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(thumbWidththumbHeightBufferedImage.TYPE_INT_RGB);
            
    Graphics2D graphics2D thumbImage.createGraphics();
            
    graphics2D.setRenderingHint(RenderingHints.KEY_INTERPOLATIONRenderingHints.VALUE_INTERPOLATION_BILINEAR);
            
    graphics2D.drawImage(image00thumbWidththumbHeightnull);
     
            
    // 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(0Math.min(quality100));
            
    param.setQuality((float)quality 100.0ffalse);
            
    encoder.setJPEGEncodeParam(param);
            
    encoder.encode(thumbImage);
            
    out.close();
        } 


    9. Creating JSON data in Java
    Source 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
    Source Code : 
    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(documentfile);
                
    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
    Source Code : 
    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
    Update: Thanks Markus for the comment. I have updated the code and changed it to more robust implementation.
    Source Code : 

    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.

    Source Code : 
    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(); 


    13. Capture screen shots in Java
    Source Code : 
    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 fileNamethrows 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
    Source Code : 
    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=0children.lengthi++) {
              
    // 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 dirString 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
    Source 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=1n=args.lengthni++) {
                
    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(buffer0bytesRead);
                }
                
    bis.close();
                
    // Reset to beginning of input stream
                
    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(buffer0bytesRead);
                }
                
    bis.close();
            }
            
    zos.close();
        }



    16. Parsing / Reading XML file in Java
    Source 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>
    Java code to parse above XML.



    Source Code : 
    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: "

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    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 0studentList.getLength(); i++) {
     
                            
    Node node studentList.item(i);
     
                            if (
    node.getNodeType() == Node.ELEMENT_NODE) {
     
                                
    System.out
                                        
    .println("=====================");
     
                                
    Element e = (Elementnode;
                                
    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
    Source 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

    Source Code : 
    import javax.mail.*;
    import javax.mail.internet.*;
    import java.util.*;
     
    public 
    void postMailString recipients[ ], String subjectString message String fromthrows 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(propsnull);
        
    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 0recipients.lengthi++)
        {
            
    addressTo[i] = new InternetAddress(recipients[i]);
        }
        
    msg.setRecipients(Message.RecipientType.TOaddressTo);
     
        
    // 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
    Source 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/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
    Source Code : 
    /**
    * 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 oldArrayint 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[] = {1,2,3};
       
    = (int[])resizeArray(a,5);
       
    a[3] = 4;
       
    a[4] = 5;
       for (
    int i=0i<a.lengthi++)
          
    System.out.println (a[i]);

    Xcode Reviewed by Xcode on . 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. Rating: 5

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