20个开发人员非常有用的Java功能代码(一)

1. 把Strings转换成int和把int转换成String

   String a = String.valueOf(2); //integer to numeric string   
   int i = Integer.parseInt(a); //numeric string to an int 

2. 向Java文件中添加文本

pdated: Thanks Simone for pointing to exception. I have 
changed the code.  
BufferedWriter out = null;   
try {   
    out = new BufferedWriter(new FileWriter("filename", true));   
    out.write("aString");   
} catch (IOException e) {   
    e.printStackTrace(); 
} finally {   
    if (out != null) { 
       out.close(); 
    }   
}  

3. 获取Java现在正调用的方法名

String methodName = Thread.currentThread().getStackTrace()[1].getMethodName ();

4. 在Java中将String型转换成Date型

java.util.Date = java.text.DateFormat.getDateInstance().parse(date String); 
SimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy" );  
Date date = format.parse( myString ); 

5. 通过Java JDBC链接Oracle数据库

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;
import java.util.Properties;
import java.io.InputStream;
import java.sql.DriverManager;

public class DBhelper {
	private static Properties pro;
	
	static {
		InputStream is = null;
		try{
			is = DBhelper.class.getClassLoader().getResourceAsStream("database.properties");
			pro = new Properties();
			pro.load(is);
			
			Class.forName(pro.getProperty("jdbc.driver.mysql"));
		}catch(Exception e){
			e.printStackTrace();
			
		}finally{
			try{
				is.close();
			}catch(Exception e){
				e.printStackTrace();
			}
		}
	}
	
	public static Connection getConnectionMysql(){
		Connection conn = null;
		try{
			conn = DriverManager.getConnection(
					pro.getProperty("jdbc.url.mysql"),
					pro.getProperty("jdbc.username.mysql"),
					pro.getProperty("jdbc.password.mysql"));
		}catch(Exception e){
			conn = null;			
		}
		return conn;
	}
	
	public static void close(PreparedStatement ps, Connection conn){
		if(ps != null){
			try{
				ps.close();
			}catch(SQLException e){
				e.printStackTrace();
			}
		}
		if(conn != null){
			try{
				conn.close();
			}catch(SQLException e){
				e.printStackTrace();
			}
		}
	}
	
	
}

6.将Java中的util.Date转换成sql.Date

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

7. 使用NIO快速复制Java文件

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. 在Java中创建缩略图

private void createThumbnail(String filename, int thumbWidth, int thumbHeight, int quality, String outFilename)throws InterruptedException, FileNotFoundException, IOException{
// load image from filename
Image image = Toolkit.getDefaultToolkit().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.drawImag e(image, 0, 0, thumbWidth, thumbHeight, null);

// 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(0, Math.min(quality, 100));
param.setQuality((float)quality / 100.0f, false);
encoder.setJPEGEncodeParam (param);
encoder.encode(thumbImage);
out.close ();
} 

9. 在Java中创建JSON数据

import org.json.JSONObject;  

JSONObject json = new JSONObject();  
json.put("city", "Mumbai");  
json.put("country", "India");  

String output = json.toString ();  
import org.json.JSONObject;

JSONObject json = new JSONObject();
json.put("city", "Mumbai");
json.put("country", "India");

String output = json.toString();

10.在Java中使用iText JAR打开PDF

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();
		}
	}
}