20 common Java Blocks

1. The strings are converted into integers.
String a = String. valueOf (2); // integer to numeric string
Int I = Integer. parseInt (a); // numeric string to an int

2. add content to the end of the file
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. Obtain the name of the current method.
String methodName = Thread. currentThread (). getStackTrace () [1]. getMethodName ();

4. Convert string to date
Java. util. Date = java. text. DateFormat. getDateInstance (). parse (date String );
Or:
SimpleDateFormat format = new SimpleDateFormat ("dd. MM. yyyy ");
Date date = format. parse (myString );

5. Use JDBC to connect to Oracle
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.exe cuteQuery ();

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

7. Use NIO for Fast File copying
Public static void fileCopy (File in, File out)
Throws IOException
{
FileChannel inChannel = new FileInputStream (in). getChannel ();
FileChannel outChannel = new FileOutputStream (out). getChannel ();
Try
{
// InChannel. transferTo (0, inChannel. size (), outChannel); // original -- apparently has trouble copying large files on Windows

// Magic number for Windows, 64 Mb-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 ();
}
}
}

8. Create a thumbnail of the image
Private void createThumbnail (String filename, int thumbWidth, int thumbHeight, int quality, String outFilename)
Throws InterruptedException, FileNotFoundException, IOException
{
// Load image from filename
Image image = Toolkit. getdefatooltoolkit (). 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 out = new BufferedOutputStream (new FileOutputStream (outFilename ));
Required imageencoder encoder = required codec. createJPEGEncoder (out );
Export encodeparam param = encoder. getDefaultJPEGEncodeParam (thumbImage );
Quality = Math. max (0, Math. min (quality, 100 ));
Param. setQuality (float) quality/100366f, false );
Encoder. setincluencodeparam (param );
Encoder. encode (thumbImage );
Out. close ();
}

9. Create data in JSON format
Import org. json. JSONObject;
...
...
JSONObject json = new JSONObject ();
Json. put ("city", "Mumbai ");
Json. put ("country", "India ");
...
String output = json. toString ();
...

10. Use iText JAR to generate a PDF file
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=. writable writer;

Public class GeneratePDF {

Public static void main (String [] args ){
Try {
OutputStream file = new FileOutputStream (new File ("C: testpipeline "));

Document document = new Document ();
Using writer. 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 Settings
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. Singleton example for a single instance
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;
}
}

Another implementation

Public enum SimpleSingleton {
INSTANCE;
Public void doSomething (){
}
}

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

13. screen capture program
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. getdefatooltoolkit (). getScreenSize ();
Rectangle screenRectangle = new Rectangle (screenSize );
Robot robot = new Robot ();
BufferedImage image = robot. createScreenCapture (screenRectangle );
ImageIO. write (image, "png", new File (fileName ));

}
...