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20个开发人员非常有用的Java功能代码(1)

 
阅读更多
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(); 
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

(); 
} 
} 



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()); 
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(); 


}

 
} 


} 



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.drawImage(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

(); 
} 



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

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(); 
}

 
} 
} 



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();
}


}
}

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