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20个开发人员非常有用的Java功能代码  

2011-01-24 16:17:36|  分类: IT |  标签: |举报 |字号 订阅

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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

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

();  
}  


 


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

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();
}
}
}

11. 在Java上的HTTP代理设置

 

 

源文链接:http://developer.51cto.com/art/200905/124291_1.htm

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