（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 anint
（2）向Java文件中添加文本

 public void addFile() {
  //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) {

     try {
      out.close();
     } catch (IOException e1) {
      // TODO Auto-generated catch block
      e1.printStackTrace();
     }

    }

   }
  }
 }
（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）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());  java.util.Date utilDate = new java.util.Date();java.sql.Date sqlDate =
new java.sql.Date(utilDate.getTime());
（6）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();}
}}

(7)在Java中创建缩略图
 private void createThumbnail1(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();
 }
(8)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;......JSON
Object json = new JSONObject();
json.put("city", "Mumbai");
json.put("country", "India");
...String
output = json.toString();...

(9) 在Java中使用iText JAR打开PDF
 Read this article for more details.
import
import
import    
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.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("HelloKiran"));
document.add(new Paragraph(new Date().toString()));
document.close();
file.close();
} catch (Exception e) {
e.printStackTrace();}

}}
(10)在Java上的HTTP代理设置


System.getProperties().put("http.proxyHost", "someProxyURL");
System.getProperties().put("http.proxyPort","someProxyPort");
System.getProperties().put("http.proxyUser", "someUserName");
System.getProperties().put("http.proxyPassword", "somePassword");  
System.getProperties().put("http.proxyHost","someProxyURL");
System.getProperties().put("http.proxyPort", "someProxyPort");
System.getProperties().put("http.proxyUser","someUserName");
System.getProperties().put("http.proxyPassword","somePassword");
(11)在Java上做屏幕截图


Read this article for more details.import

java.awt.Dimension;   import java.awt.Rectangle;   

import java.awt.Robot;   import java.awt.Toolkit;   

import java.awt.image.BufferedImage;   import

javax.imageio.ImageIO;   import    ...   public void captureScreen(String fileName)

throws Exception {   Dimension screenSize =

Toolkit.getDefaultToolkit().getScreenSize();   Rectangle

screenRectangle = new Rectangle(screenSize);   Robot

robot = new Robot();
BufferedImage image = robot.createScreenCapture(screenRectangle);   
ImageIO.write(image, "png", new File(fileName));   }
   ...  
import java.awt.Dimension;import java.awt.Rectangle;import

java.awt.Robot;import java.awt.Toolkit;import

java.awt.image.BufferedImage;import javax.imageio.ImageIO;
import
...
public void captureScreen(String fileName) throws Exception {
Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
Rectangle screenRectangle = new Rectangle(screenSize);
Robot robot = new Robot();
BufferedImage image = robot.createScreenCapture(screenRectangle);
ImageIO.write(image, "png", new File(fileName));
}...
(12)在Java中创建ZIP和JAR文件
package itf;
import java.util.zip.*;
import *;
public class ZipIt {
   

 public static void main(String args[]) throws IOException

 {   if (args.length < 2) {   

 System.err.println("usage: java ZipIt Zip.zip file1 file2 file3");   

 System.exit(-1);   }   

 File zipFile = new File(args[0]);   
 if (zipFile.exists()) {   

 System.err.println("Zip file already exists, please try another");   

 System.exit(-2);   }   

 FileOutputStream fos = new FileOutputStream(zipFile);   

 ZipOutputStream zos = new ZipOutputStream(fos);  
  int bytesRead;
  byte[] buffer = new byte[1024];   
  CRC32 crc = new CRC32();  
  for (int i=1, n=args.length; i < n; i++) {   

 String name = args[i];   

 File file = new File(name);   

 if (!file.exists()) {System.err.println("Skipping: " + name);   
 continue;   
 }
 BufferedInputStream bis = new BufferedInputStream(new FileInputStream(file));   

 crc.reset();   

 while ((bytesRead = bis.read(buffer)) != -1) {crc.update(buffer, 0, bytesRead);   

 }
 bis.close();   

 // Reset to beginning of input stream   
 bis = new BufferedInputStream(new FileInputStream(file));   
 ZipEntry entry = new ZipEntry(name);   

 entry.setMethod(ZipEntry.STORED);   
 entry.setCompressedSize(file.length());   
 entry.setSize(file.length());   
 entry.setCrc(crc.getValue());   
 zos.putNextEntry(entry);   
 while

 ((bytesRead = bis.read(buffer)) != -1) {   

  zos.write(buffer, 0, bytesRead);   

 }

    bis.close();   }

    zos.close();   }   
 
 }
(13)在Java中解析/读取XML文件
view plaincopy to clipboardprint?<?xml version="1.0"?>  <students>  <student>  <name>John</name>  <grade>B</grade>  <age>12</age>  </student>  <student>  

<name>Mary</name>  <grade>A</grade>  <age>11</age>  </student>  <student>  <name>Simon</name>  <grade>A</grade>  <age>18</age>  </student>  </students>  
<?xml version="1.0"?

><students><student><name>John</name><grade>B</grade><age>12</age></student><student><name>Mary</name><grade>A</grade><age>11</age></student><student><name>S

imon</name><grade>A</grade><age>18</age></student></students>Java code to parse above XML.
view plaincopy to clipboardprint?


package itf;

import
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

public class XMLParser {
 public void getAllUserNames(String fileName) {
  try {
   DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
   DocumentBuilder db = dbf.newDocumentBuilder();
   File file = new File(fileName);
   if (file.exists()) {
    Document doc = db.parse(file);
    Element docEle = doc.getDocumentElement();
    // Print root element of the documentSystem.out.println("Root
    // element of the document: "+ docEle.getNodeName());
    NodeList studentList = docEle.getElementsByTagName("student");
    // Print total student elements in
    // documentSystem.out.println("Total students: " +
    // studentList.getLength());
    if (studentList != null && studentList.getLength() > 0) {
     for (int i = 0; i < studentList.getLength(); i++) {
      Node node = studentList.item(i);
      if (node.getNodeType() == Node.ELEMENT_NODE) {
       System.out.println("=====================");
       Element e = (Element) node;
       NodeList nodeList = e.getElementsByTagName("name");
       System.out.println("Name: "
         + nodeList.item(0).getChildNodes().item(0)
           .getNodeValue());
       nodeList = e.getElementsByTagName("grade");
       System.out.println("Grade: "
         + nodeList.item(0).getChildNodes().item(0)
           .getNodeValue());
       nodeList = e.getElementsByTagName("age");
       System.out.println("Age: "
         + nodeList.item(0).getChildNodes().item(0)
           .getNodeValue());
      }
     }
    } else {
     System.exit(1);
    }
   }
  } catch (Exception e) {
   System.out.println(e);
  }
 }

 public static void main(String[] args) {
  XMLParser parser = new XMLParser();
  parser.getAllUserNames("c:\\test.xml");
 }
}
(14)在Java中将Array转换成Map
package itf;

import java.util.Map;
import org.
public class Main {
 public static void main(String[] args) {
  String[][] countries = { { "United States", "New York" },
    { "United Kingdom", "London" }, { "Netherland", "Amsterdam" },
    { "Japan", "Tokyo" }, { "France", "Paris" } };
  Map countryCapitals = ArrayUtils.toMap(countries);
  System.out.println("Capital of Japan is "
    + countryCapitals.get("Japan"));
  System.out.println("Capital of France is "
    + countryCapitals.get("France"));
 }
}