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 

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

Updated: 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) {   


// error processing code   
} finally 

{   
if (out != null) {   
out.close();  
}   
} 


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. 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); 

java.util.Date = java.text.DateFormat.getDateInstance().parse(date String);

or 
SimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy" );  
Date date = format.parse( myString ); 
SimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy" );

Date date= format.parse( myString );

5. 通过Java JDBC链接Oracle数据库

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();  
}  

} 

6.将Java中的util.Date转换成sql.Date

这一片段显示如何将一个java util Date转换成sql Date用于数据库

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 )  
{  
&nbsp; position += inChannel.transferTo( position, maxCount, outChannel );
}  
}  
finally  {  
if ( inChannel != null )  
{  
&nbsp; inChannel.close();  
}  
if ( outChannel != null )  
{  
&nbsp;  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 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. 在Java中创建JSON数据


 




Read this article for more details.
Download JAR file 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  ();   
... 
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


Read this article for more details.




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();   
}

   
}   
}