常用java片段

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String a = String.valueOf(2);   //integer to numeric string  

3
int i = Integer.parseInt(a); //numeric string to an int

01
  
02
BufferedWriter out = null;  

03
try {  

04
    out = new BufferedWriter(new FileWriter(”filename”, true));  

05
    out.write(”aString”);  

06
} catch (IOException e) {  

07
    // error processing code  

08
} finally {  

09
    if (out != null) {  

10
        out.close();  

11
    }  

12
}

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

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2
java.util.Date = java.text.DateFormat.getDateInstance().parse(date String);

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SimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy" );  

3
Date date = format.parse( myString );

01
public class OracleJdbcTest  

02
{  

03
    String driverClass = "oracle.jdbc.driver.OracleDriver";  

04
  
05
    Connection con;  

06
  
07
    public void init(FileInputStream fs) throws ClassNotFoundException, SQLException, FileNotFoundException, IOException  

08
    {  

09
        Properties props = new Properties();  

10
        props.load(fs);  

11
        String url = props.getProperty("db.url");  

12
        String userName = props.getProperty("db.user");  

13
        String password = props.getProperty("db.password");  

14
        Class.forName(driverClass);  

15
  
16
        con=DriverManager.getConnection(url, userName, password);  

17
    }  

18
  
19
    public void fetch() throws SQLException, IOException  

20
    {  

21
        PreparedStatement ps = con.prepareStatement("select SYSDATE from dual");  

22
        ResultSet rs = ps.executeQuery();  

23
  
24
        while (rs.next())  

25
        {  

26
            // do the thing you do  

27
        }  

28
        rs.close();  

29
        ps.close();  

30
    }  

31
  
32
    public static void main(String[] args)  

33
    {  

34
        OracleJdbcTest test = new OracleJdbcTest();  

35
        test.init();  

36
        test.fetch();  

37
    }  

38
}

1
java.util.Date utilDate = new java.util.Date();  

2
java.sql.Date sqlDate = new java.sql.Date(utilDate.getTime());

01
public static void fileCopy( File in, File out )  

02
            throws IOException  

03
    {  

04
        FileChannel inChannel = new FileInputStream( in ).getChannel();  

05
        FileChannel outChannel = new FileOutputStream( out ).getChannel();  

06
        try 

07
        {  

08
//          inChannel.transferTo(0, inChannel.size(), outChannel);      // original -- apparently has trouble copying large files on Windows  

09
  
10
            // magic number for Windows, 64Mb - 32Kb)  

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            int maxCount = (64 * 1024 * 1024) - (32 * 1024);  

12
            long size = inChannel.size();  

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            long position = 0;  

14
            while ( position < size )  

15
            {  

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               position += inChannel.transferTo( position, maxCount, outChannel );  

17
            }  

18
        }  

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        finally 

20
        {  

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            if ( inChannel != null )  

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            {  

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               inChannel.close();  

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            }  

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            if ( outChannel != null )  

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            {  

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                outChannel.close();  

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            }  

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        }  

30
    }

01
private void createThumbnail(String filename, int thumbWidth, int thumbHeight,int quality, String outFilename)  

02
        throws InterruptedException, FileNotFoundException, IOException  

03
    {  

04
        // load image from filename  

05
        Image image = Toolkit.getDefaultToolkit().getImage(filename);  

06
        MediaTracker mediaTracker = new MediaTracker(new Container());  

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        mediaTracker.addImage(image, 0);  

08
        mediaTracker.waitForID(0);  

09
        // use this to test for errors at this point: System.out.println(mediaTracker.isErrorAny());  

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        // determine thumbnail size from WIDTH and HEIGHT  

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        double thumbRatio = (double)thumbWidth / (double)thumbHeight;  

13
        int imageWidth = image.getWidth(null);  

14
        int imageHeight = image.getHeight(null);  

15
        double imageRatio = (double)imageWidth / (double)imageHeight;  

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        if (thumbRatio < imageRatio) {  

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            thumbHeight = (int)(thumbWidth / imageRatio);  

18
        } else {  

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            thumbWidth = (int)(thumbHeight * imageRatio);  

20
        }  

21
  
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        // draw original image to thumbnail image object and  

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        // scale it to the new size on-the-fly  

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        BufferedImage thumbImage = new BufferedImage(thumbWidth, thumbHeight, BufferedImage.TYPE_INT_RGB);  

25
        Graphics2D graphics2D = thumbImage.createGraphics();  

26
        graphics2D.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);  

27
        graphics2D.drawImage(image, 0, 0, thumbWidth, thumbHeight, null);  

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        // save thumbnail image to outFilename  

30
        BufferedOutputStream out = new BufferedOutputStream(newFileOutputStream(outFilename));  

31
        JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);  

32
        JPEGEncodeParam param = encoder.getDefaultJPEGEncodeParam(thumbImage);  

33
        quality = Math.max(0, Math.min(quality, 100));  

34
        param.setQuality((float)quality / 100.0f, false);  

35
        encoder.setJPEGEncodeParam(param);  

36
        encoder.encode(thumbImage);  

37
        out.close();  

38
    }

1
import org.json.JSONObject;  

2
...  

3
...  

4
JSONObject json = new JSONObject();  

5
json.put("city", "Mumbai");  

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json.put("country", "India");  

7
...  

8
String output = json.toString();  

9
...

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02
import java.io.File;  

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import java.io.FileOutputStream;  

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import java.io.OutputStream;  

05
import java.util.Date;  

06
  
07
import com.lowagie.text.Document;  

08
import com.lowagie.text.Paragraph;  

09
import com.lowagie.text.pdf.PdfWriter;  

10
  
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public class GeneratePDF {  

12
  
13
    public static void main(String[] args) {  

14
        try {  

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            OutputStream file = new FileOutputStream(newFile("C:\\Test.pdf"));  

16
  
17
            Document document = new Document();  

18
            PdfWriter.getInstance(document, file);  

19
            document.open();  

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            document.add(new Paragraph("Hello Kiran"));  

21
            document.add(new Paragraph(new Date().toString()));  

22
  
23
            document.close();  

24
            file.close();  

25
  
26
        } catch (Exception e) {  

27
  
28
            e.printStackTrace();  

29
        }  

30
    }  

31
}

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System.getProperties().put("http.proxyHost", "someProxyURL");  

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System.getProperties().put("http.proxyPort", "someProxyPort");  

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System.getProperties().put("http.proxyUser", "someUserName");  

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System.getProperties().put("http.proxyPassword", "somePassword");

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public class SimpleSingleton {  

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    private static SimpleSingleton singleInstance =  new SimpleSingleton();  

04
  
05
    //Marking default constructor private  

06
    //to avoid direct instantiation.  

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    private SimpleSingleton() {  

08
    }  

09
  
10
    //Get instance for class SimpleSingleton  

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    public static SimpleSingleton getInstance() {  

12
  
13
        return singleInstance;  

14
    }  

15
}

1
public enum SimpleSingleton {  

2
    INSTANCE;  

3
    public void doSomething() {  

4
    }  

5
}  

6
  
7
//Call the method from Singleton:  

8
SimpleSingleton.INSTANCE.doSomething();

01
import java.awt.Dimension;  

02
import java.awt.Rectangle;  

03
import java.awt.Robot;  

04
import java.awt.Toolkit;  

05
import java.awt.image.BufferedImage;  

06
import javax.imageio.ImageIO;  

07
import java.io.File;  

08
  
09
...  

10
  
11
public void captureScreen(String fileName) throws Exception {  

12
  
13
   Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();  

14
   Rectangle screenRectangle = new Rectangle(screenSize);  

15
   Robot robot = new Robot();  

16
   BufferedImage image = robot.createScreenCapture(screenRectangle);  

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   ImageIO.write(image, "png", new File(fileName));  

18
  
19
}  

20
...

01
File dir = new File("directoryName");  

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  String[] children = dir.list();  

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  if (children == null) {  

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      // Either dir does not exist or is not a directory  

05
  } else {  

06
      for (int i=0; i < children.length; i++) {  

07
          // Get filename of file or directory  

08
          String filename = children[i];  

09
      }  

10
  }  

11
  
12
  // It is also possible to filter the list of returned files.  

13
  // This example does not return any files that start with `.'.  

14
  FilenameFilter filter = new FilenameFilter() {  

15
      public boolean accept(File dir, String name) {  

16
          return !name.startsWith(".");  

17
      }  

18
  };  

19
  children = dir.list(filter);  

20
  
21
  // The list of files can also be retrieved as File objects  

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  File[] files = dir.listFiles();  

23
  
24
  // This filter only returns directories  

25
  FileFilter fileFilter = new FileFilter() {  

26
      public boolean accept(File file) {  

27
          return file.isDirectory();  

28
      }  

29
  };  

30
  files = dir.listFiles(fileFilter);

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02
import java.util.zip.*;  

03
import java.io.*;  

04
  
05
public class ZipIt {  

06
    public static void main(String args[]) throws IOException {  

07
        if (args.length < 2) {  

08
            System.err.println("usage: java ZipIt Zip.zip file1 file2 file3");  

09
            System.exit(-1);  

10
        }  

11
        File zipFile = new File(args[0]);  

12
        if (zipFile.exists()) {  

13
            System.err.println("Zip file already exists, please try another");  

14
            System.exit(-2);  

15
        }  

16
        FileOutputStream fos = new FileOutputStream(zipFile);  

17
        ZipOutputStream zos = new ZipOutputStream(fos);  

18
        int bytesRead;  

19
        byte[] buffer = new byte[1024];  

20
        CRC32 crc = new CRC32();  

21
        for (int i=1, n=args.length; i < n; i++) {  

22
            String name = args[i];  

23
            File file = new File(name);  

24
            if (!file.exists()) {  

25
                System.err.println("Skipping: " + name);  

26
                continue;  

27
            }  

28
            BufferedInputStream bis = new BufferedInputStream(  

29
                new FileInputStream(file));  

30
            crc.reset();  

31
            while ((bytesRead = bis.read(buffer)) != -1) {  

32
                crc.update(buffer, 0, bytesRead);  

33
            }  

34
            bis.close();  

35
            // Reset to beginning of input stream  

36
            bis = new BufferedInputStream(  

37
                new FileInputStream(file));  

38
            ZipEntry entry = new ZipEntry(name);  

39
            entry.setMethod(ZipEntry.STORED);  

40
            entry.setCompressedSize(file.length());  

41
            entry.setSize(file.length());  

42
            entry.setCrc(crc.getValue());  

43
            zos.putNextEntry(entry);  

44
            while ((bytesRead = bis.read(buffer)) != -1) {  

45
                zos.write(buffer, 0, bytesRead);  

46
            }  

47
            bis.close();  

48
        }  

49
        zos.close();  

50
    }  

51
}

01
<?xml version="1.0"?> 

02
<students> 

03
    <student> 

04
        <name>John</name> 

05
        <grade>B</grade> 

06
        <age>12</age> 

07
    </student> 

08
    <student> 

09
        <name>Mary</name> 

10
        <grade>A</grade> 

11
        <age>11</age> 

12
    </student> 

13
    <student> 

14
        <name>Simon</name> 

15
        <grade>A</grade> 

16
        <age>18</age> 

17
    </student> 

18
</students>

01
  
02
package net.viralpatel.java.xmlparser;  

03
  
04
import java.io.File;  

05
import javax.xml.parsers.DocumentBuilder;  

06
import javax.xml.parsers.DocumentBuilderFactory;  

07
  
08
import org.w3c.dom.Document;  

09
import org.w3c.dom.Element;  

10
import org.w3c.dom.Node;  

11
import org.w3c.dom.NodeList;  

12
  
13
public class XMLParser {  

14
  
15
    public void getAllUserNames(String fileName) {  

16
        try {  

17
            DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();  

18
            DocumentBuilder db = dbf.newDocumentBuilder();  

19
            File file = new File(fileName);  

20
            if (file.exists()) {  

21
                Document doc = db.parse(file);  

22
                Element docEle = doc.getDocumentElement();  

23
  
24
                // Print root element of the document  

25
                System.out.println("Root element of the document: " 

26
                        + docEle.getNodeName());  

27
  
28
                NodeList studentList = docEle.getElementsByTagName("student");  

29
  
30
                // Print total student elements in document  

31
                System.out  

32
                        .println("Total students: " + studentList.getLength());  

33
  
34
                if (studentList != null && studentList.getLength() > 0) {  

35
                    for (int i = 0; i < studentList.getLength(); i++) {  

36
  
37
                        Node node = studentList.item(i);  

38
  
39
                        if (node.getNodeType() == Node.ELEMENT_NODE) {  

40
  
41
                            System.out  

42
                                    .println("=====================");  

43
  
44
                            Element e = (Element) node;  

45
                            NodeList nodeList = e.getElementsByTagName("name");  

46
                            System.out.println("Name: " 

47
                                    + nodeList.item(0).getChildNodes().item(0)  

48
                                            .getNodeValue());  

49
  
50
                            nodeList = e.getElementsByTagName("grade");  

51
                            System.out.println("Grade: " 

52
                                    + nodeList.item(0).getChildNodes().item(0)  

53
                                            .getNodeValue());  

54
  
55
                            nodeList = e.getElementsByTagName("age");  

56
                            System.out.println("Age: " 

57
                                    + nodeList.item(0).getChildNodes().item(0)  

58
                                            .getNodeValue());  

59
                        }  

60
                    }  

61
                } else {  

62
                    System.exit(1);  

63
                }  

64
            }  

65
        } catch (Exception e) {  

66
            System.out.println(e);  

67
        }  

68
    }  

69
    public static void main(String[] args) {  

70
  
71
        XMLParser parser = new XMLParser();  

72
        parser.getAllUserNames("c:\\test.xml");  

73
    }  

74
}

01
  
02
import java.util.Map;  

03
import org.apache.commons.lang.ArrayUtils;  

04
  
05
public class Main {  

06
  
07
  public static void main(String[] args) {  

08
    String[][] countries = { { "United States", "New York" }, { "United Kingdom", "London" },  

09
        { "Netherland", "Amsterdam" }, { "Japan", "Tokyo" }, { "France", "Paris"} };  

10
  
11
    Map countryCapitals = ArrayUtils.toMap(countries);  

12
  
13
    System.out.println("Capital of Japan is " + countryCapitals.get("Japan"));  

14
    System.out.println("Capital of France is " + countryCapitals.get("France"));  

15
  }  

16
}

01
import javax.mail.*;  

02
import javax.mail.internet.*;  

03
import java.util.*;  

04
  
05
public void postMail( String recipients[ ], String subject, String message , String from) throws MessagingException  

06
{  

07
    boolean debug = false;  

08
  
09
     //Set the host smtp address  

10
     Properties props = new Properties();  

11
     props.put("mail.smtp.host", "smtp.example.com");  

12
  
13
    // create some properties and get the default Session  

14
    Session session = Session.getDefaultInstance(props, null);  

15
    session.setDebug(debug);  

16
  
17
    // create a message  

18
    Message msg = new MimeMessage(session);  

19
  
20
    // set the from and to address  

21
    InternetAddress addressFrom = new InternetAddress(from);  

22
    msg.setFrom(addressFrom);  

23
  
24
    InternetAddress[] addressTo = new InternetAddress[recipients.length];  

25
    for (int i = 0; i < recipients.length; i++)  

26
    {  

27
        addressTo[i] = new InternetAddress(recipients[i]);  

28
    }  

29
    msg.setRecipients(Message.RecipientType.TO, addressTo);  

30
  
31
    // Optional : You can also set your custom headers in the Email if you Want  

32
    msg.addHeader("MyHeaderName", "myHeaderValue");  

33
  
34
    // Setting the Subject and Content Type  

35
    msg.setSubject(subject);  

36
    msg.setContent(message, "text/plain");  

37
    Transport.send(msg);  

38
}

01
  
02
import java.io.BufferedReader;  

03
import java.io.InputStreamReader;  

04
import java.net.URL;  

05
  
06
public class Main {  

07
    public static void main(String[] args)  {  

08
        try {  

09
            URL my_url = new URL("http://google.com.hk/");  

10
            BufferedReader br = new BufferedReader(newInputStreamReader(my_url.openStream()));  

11
            String strTemp = "";  

12
            while(null != (strTemp = br.readLine())){  

13
            System.out.println(strTemp);  

14
        }  

15
        } catch (Exception ex) {  

16
            ex.printStackTrace();  

17
        }  

18
    }  

19
}

01
  
02
/** 

03
* Reallocates an array with a new size, and copies the contents 

04
* of the old array to the new array. 

05
* @param oldArray  the old array, to be reallocated. 

06
* @param newSize   the new array size. 

07
* @return          A new array with the same contents. 

08
*/ 

09
private static Object resizeArray (Object oldArray, int newSize) {  

10
   int oldSize = java.lang.reflect.Array.getLength(oldArray);  

11
   Class elementType = oldArray.getClass().getComponentType();  

12
   Object newArray = java.lang.reflect.Array.newInstance(  

13
         elementType,newSize);  

14
   int preserveLength = Math.min(oldSize,newSize);  

15
   if (preserveLength > 0)  

16
      System.arraycopy (oldArray,0,newArray,0,preserveLength);  

17
   return newArray;  

18
}  

19
  
20
// Test routine for resizeArray().  

21
public static void main (String[] args) {  

22
   int[] a = {1,2,3};  

23
   a = (int[])resizeArray(a,5);  

24
   a[3] = 4;  

25
   a[4] = 5;  

26
   for (int i=0; i<a.length; i++)  

27
      System.out.println (a[i]);  

28
}

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