20非常有用的Java程序片段(6-10)

6. 把 Java util.Date 转成 sql.Date

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

7. 使用NIO进行快速的文件拷贝

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, 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 );
}
}
finally
{
if ( inChannel != null )
{
inChannel.close();
}
if ( outChannel != null )
{
outChannel.close();
}
}
}

8. 创建图片的缩略图

private void createThumbnail(String filename, int thumbWidth, int thumbHeight, int quality, String outFilename)
throws InterruptedException, FileNotFoundException, IOException
{
// load p_w_picpath from filename
Image p_w_picpath = Toolkit.getDefaultToolkit().getImage(filename);
MediaTracker mediaTracker = new MediaTracker( new Container());
mediaTracker.addImage(p_w_picpath, 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 p_w_picpathWidth = p_w_picpath.getWidth( null );
int p_w_picpathHeight = p_w_picpath.getHeight( null );
double p_w_picpathRatio = ( double )p_w_picpathWidth / ( double )p_w_picpathHeight;
if (thumbRatio < p_w_picpathRatio) {
thumbHeight = ( int )(thumbWidth / p_w_picpathRatio);
} else {
thumbWidth = ( int )(thumbHeight * p_w_picpathRatio);
}

// draw original p_w_picpath to thumbnail p_w_picpath 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(p_w_picpath, 0 , 0 , thumbWidth, thumbHeight, null );

// save thumbnail p_w_picpath 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 );
encoder.setJPEGEncodeParam(param);
encoder.encode(thumbImage);
out.close();
}

9. 创建 JSON 格式的数据

请先阅读这篇文章 了解一些细节，
并下面这个JAR 文件：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. 使用iText JAR生成PDF

阅读这篇文章 了解更多细节

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();
}
}
}