Java.CheatSheet.1.js

Java Snippets
Converting Strings to int and int to String
String a = String.valueOf(2); 
int i = Integer.parseInt(a);  
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 );
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());
Append text to a 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();
    }
}
Get name of current method
String methodName = Thread.currentThread().getStackTrace()[1].getMethodName();  
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()) {
            // do the thing you do
        }
        rs.close();
        ps.close();
    }
    
    public static void main(String[] args) {
        OracleJdbcTest test = new OracleJdbcTest();
        test.init();
        test.fetch();
    }
}
Create Thumbnail of an Image
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);
    System.out.println(mediaTracker.isErrorAny());
    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();
}
Generate PDF using iText
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();
        }
    }
}
HTTP Proxy setting
System.getProperties().put("http.proxyHost", "someProxyURL");
System.getProperties().put("http.proxyPort", "someProxyPort");
System.getProperties().put("http.proxyUser", "someUserName");
System.getProperties().put("http.proxyPassword", "somePassword");
Capture Screenshot
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));
}
Files-Directory listing
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);
Create ZIP and JAR files
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();
            // 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(buffer, 0, bytesRead);
            }
            bis.close();
        }
        zos.close();
    }
}
Convert Array to Map
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"));
    }
}
Send Email
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);
}
Send HTTP request and fetch data
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();
        }
    }
}