常用java代码段有哪些

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

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

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(); 

    } 

}

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

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

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

Date date = format.parse( myString );

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(); 

    } 

}

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

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

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 = ; 

            while ( position < size ) 

            { 

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

            } 

        } 

        finally

        { 

            if ( inChannel != null ) 

            { 

               inChannel.close(); 

            } 

            if ( outChannel != null ) 

            { 

                outChannel.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, ); 

        mediaTracker.waitForID(); 

        // 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, , , 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(, Math.min(quality, 100)); 

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

        encoder.setJPEGEncodeParam(param); 

        encoder.encode(thumbImage); 

        out.close(); 

    }

import org.json.JSONObject; 

... 

... 

JSONObject json = new JSONObject(); 

json.put("city", "Mumbai"); 

json.put("country", "India"); 

... 

String output = json.toString(); 

...

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(); 

        } 

    } 

}

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

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

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

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

public class SimpleSingleton { 

    private static SimpleSingleton singleInstance =  new SimpleSingleton(); 

    //Marking default constructor private 

    //to avoid direct instantiation. 

    private SimpleSingleton() { 

    } 

    //Get instance for class SimpleSingleton 

    public static SimpleSingleton getInstance() { 

        return singleInstance; 

    } 

}

public enum SimpleSingleton { 

    INSTANCE; 

    public void doSomething() { 

    } 

} 

//Call the method from Singleton: 

SimpleSingleton.INSTANCE.doSomething();

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 java.io.File; 

... 

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)); 

} 

...

File dir = new File("directoryName"); 

  String[] children = dir.list(); 

  if (children == null) { 

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

  } else { 

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

          // Get filename of file or directory 

          String filename = children[i]; 

      } 

  } 

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

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

  FilenameFilter filter = new FilenameFilter() { 

      public boolean accept(File dir, String name) { 

          return !name.startsWith("."); 

      } 

  }; 

  children = dir.list(filter); 

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

  File[] files = dir.listFiles(); 

  // This filter only returns directories 

  FileFilter fileFilter = new FileFilter() { 

      public boolean accept(File file) { 

          return file.isDirectory(); 

      } 

  }; 

  files = dir.listFiles(fileFilter);

import java.util.zip.*; 

import java.io.*; 

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[]); 

        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, , 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, , bytesRead); 

            } 

            bis.close(); 

        } 

        zos.close(); 

    } 

}

<?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>

package net.viralpatel.java.xmlparser; 

import java.io.File; 

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 document 

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

                        + docEle.getNodeName()); 

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

                // Print total student elements in document 

                System.out 

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

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

                    for (int i = ; 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().getChildNodes().item() 

                                            .getNodeValue()); 

                            nodeList = e.getElementsByTagName("grade"); 

                            System.out.println("Grade: "

                                    + nodeList.item().getChildNodes().item() 

                                            .getNodeValue()); 

                            nodeList = e.getElementsByTagName("age"); 

                            System.out.println("Age: "

                                    + nodeList.item().getChildNodes().item() 

                                            .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"); 

    } 

}

import java.util.Map; 

import org.apache.commons.lang.ArrayUtils; 

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")); 

  } 

}

import javax.mail.*; 

import javax.mail.internet.*; 

import java.util.*; 

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

{ 

    boolean debug = false; 

     //Set the host smtp address 

     Properties props = new Properties(); 

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

    // create some properties and get the default Session 

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

    session.setDebug(debug); 

    // create a message 

    Message msg = new MimeMessage(session); 

    // set the from and to address 

    InternetAddress addressFrom = new InternetAddress(from); 

    msg.setFrom(addressFrom); 

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

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

    { 

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

    } 

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

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

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

    // Setting the Subject and Content Type 

    msg.setSubject(subject); 

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

    Transport.send(msg); 

}

import java.io.BufferedReader; 

import java.io.InputStreamReader; 

import java.net.URL; 

public class Main { 

    public static void main(String[] args)  { 

        try { 

            URL my_url = new URL("http://coolshell.cn/"); 

            BufferedReader br = new BufferedReader(new InputStreamReader(my_url.openStream())); 

            String strTemp = ""; 

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

            System.out.println(strTemp); 

        } 

        } catch (Exception ex) { 

            ex.printStackTrace(); 

        } 

    } 

}

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

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

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

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

         elementType,newSize); 

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

   if (preserveLength > ) 

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

   return newArray; 

} 

// Test routine for resizeArray(). 

public static void main (String[] args) { 

   int[] a = {1,2,3}; 

   a = (int[])resizeArray(a,5); 

   a[3] = 4; 

   a[4] = 5; 

   for (int i=; i<a.length; i++) 

      System.out.println (a[i]); 

}