java 零碎知识点

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

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

BufferedWriter out = null; 

try{ 

    out = newBufferedWriter(newFileWriter(”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 = newSimpleDateFormat( "dd.MM.yyyy"); 

Date date = format.parse( myString );

publicclassOracleJdbcTest 

{ 

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

    Connection con; 

    publicvoidinit(FileInputStream fs) throwsClassNotFoundException, SQLException, FileNotFoundException, IOException 

    { 

        Properties props = newProperties(); 

        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); 

    } 

    publicvoidfetch() throwsSQLException, 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(); 

    } 

    publicstaticvoidmain(String[] args) 

    { 

        OracleJdbcTest test = newOracleJdbcTest(); 

        test.init(); 

        test.fetch(); 

    } 

}

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

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

publicstaticvoidfileCopy( File in, File out ) 

            throwsIOException 

    { 

        FileChannel inChannel = newFileInputStream( in ).getChannel(); 

        FileChannel outChannel = newFileOutputStream( out ).getChannel(); 

        try

        { 

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

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

            intmaxCount = (64* 1024* 1024) - (32* 1024); 

            longsize = inChannel.size(); 

            longposition = 0; 

            while( position < size ) 

            { 

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

            } 

        } 

        finally

        { 

            if( inChannel != null) 

            { 

               inChannel.close(); 

            } 

            if( outChannel != null) 

            { 

                outChannel.close(); 

            } 

        } 

    }

privatevoidcreateThumbnail(String filename, intthumbWidth, intthumbHeight, intquality, String outFilename) 

        throwsInterruptedException, FileNotFoundException, IOException 

    { 

        // load image from filename 

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

        MediaTracker mediaTracker = newMediaTracker(newContainer()); 

        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 

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

        intimageWidth = image.getWidth(null); 

        intimageHeight = image.getHeight(null); 

        doubleimageRatio = (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 = newBufferedImage(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 = newBufferedOutputStream(newFileOutputStream(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(); 

    }

importorg.json.JSONObject; 

... 

... 

JSONObject json = newJSONObject(); 

json.put("city", "Mumbai"); 

json.put("country", "India"); 

... 

String output = json.toString(); 

...

importjava.io.File; 

importjava.io.FileOutputStream; 

importjava.io.OutputStream; 

importjava.util.Date; 

importcom.lowagie.text.Document; 

importcom.lowagie.text.Paragraph; 

importcom.lowagie.text.pdf.PdfWriter; 

publicclassGeneratePDF { 

    publicstaticvoidmain(String[] args) { 

        try{ 

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

            Document document = newDocument(); 

            PdfWriter.getInstance(document, file); 

            document.open(); 

            document.add(newParagraph("Hello Kiran")); 

            document.add(newParagraph(newDate().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");

publicclassSimpleSingleton { 

    privatestaticSimpleSingleton singleInstance =  newSimpleSingleton(); 

    //Marking default constructor private 

    //to avoid direct instantiation. 

    privateSimpleSingleton() { 

    } 

    //Get instance for class SimpleSingleton 

    publicstaticSimpleSingleton getInstance() { 

        returnsingleInstance; 

    } 

}

publicenumSimpleSingleton { 

    INSTANCE; 

    publicvoiddoSomething() { 

    } 

} 

//Call the method from Singleton: 

SimpleSingleton.INSTANCE.doSomething();

importjava.awt.Dimension; 

importjava.awt.Rectangle; 

importjava.awt.Robot; 

importjava.awt.Toolkit; 

importjava.awt.image.BufferedImage; 

importjavax.imageio.ImageIO; 

importjava.io.File; 

... 

publicvoidcaptureScreen(String fileName) throwsException { 

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

   Rectangle screenRectangle = newRectangle(screenSize); 

   Robot robot = newRobot(); 

   BufferedImage image = robot.createScreenCapture(screenRectangle); 

   ImageIO.write(image, "png", newFile(fileName)); 

} 

...

File dir = newFile("directoryName"); 

  String[] children = dir.list(); 

  if(children == null) { 

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

  } else{ 

      for(inti=0; 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 = newFilenameFilter() { 

      publicbooleanaccept(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 = newFileFilter() { 

      publicbooleanaccept(File file) { 

          returnfile.isDirectory(); 

      } 

  }; 

  files = dir.listFiles(fileFilter);

importjava.util.zip.*; 

importjava.io.*; 

publicclassZipIt { 

    publicstaticvoidmain(String args[]) throwsIOException { 

        if(args.length < 2) { 

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

            System.exit(-1); 

        } 

        File zipFile = newFile(args[0]); 

        if(zipFile.exists()) { 

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

            System.exit(-2); 

        } 

        FileOutputStream fos = newFileOutputStream(zipFile); 

        ZipOutputStream zos = newZipOutputStream(fos); 

        intbytesRead; 

        byte[] buffer = newbyte[1024]; 

        CRC32 crc = newCRC32(); 

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

            String name = args[i]; 

            File file = newFile(name); 

            if(!file.exists()) { 

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

                continue; 

            } 

            BufferedInputStream bis = newBufferedInputStream( 

                newFileInputStream(file)); 

            crc.reset(); 

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

                crc.update(buffer, 0, bytesRead); 

            } 

            bis.close(); 

            // Reset to beginning of input stream 

            bis = newBufferedInputStream( 

                newFileInputStream(file)); 

            ZipEntry entry = newZipEntry(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(); 

    } 

}

<?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>

packagenet.viralpatel.java.xmlparser; 

importjava.io.File; 

importjavax.xml.parsers.DocumentBuilder; 

importjavax.xml.parsers.DocumentBuilderFactory; 

importorg.w3c.dom.Document; 

importorg.w3c.dom.Element; 

importorg.w3c.dom.Node; 

importorg.w3c.dom.NodeList; 

publicclassXMLParser { 

    publicvoidgetAllUserNames(String fileName) { 

        try{ 

            DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance(); 

            DocumentBuilder db = dbf.newDocumentBuilder(); 

            File file = newFile(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() > 0) { 

                    for(inti = 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); 

        } 

    } 

    publicstaticvoidmain(String[] args) { 

        XMLParser parser = newXMLParser(); 

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

    } 

}

importjava.util.Map; 

importorg.apache.commons.lang.ArrayUtils; 

publicclassMain { 

  publicstaticvoidmain(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")); 

  } 

}

importjavax.mail.*; 

importjavax.mail.internet.*; 

importjava.util.*; 

publicvoidpostMail( String recipients[ ], String subject, String message , String from) throwsMessagingException 

{ 

    booleandebug = false; 

     //Set the host smtp address 

     Properties props = newProperties(); 

     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 = newMimeMessage(session); 

    // set the from and to address 

    InternetAddress addressFrom = newInternetAddress(from); 

    msg.setFrom(addressFrom); 

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

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

    { 

        addressTo[i] = newInternetAddress(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); 

}

importjava.io.BufferedReader; 

importjava.io.InputStreamReader; 

importjava.net.URL; 

publicclassMain { 

    publicstaticvoidmain(String[] args)  { 

        try{ 

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

            BufferedReader br = newBufferedReader(newInputStreamReader(my_url.openStream())); 

            String strTemp = ""; 

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

            System.out.println(strTemp); 

        } 

        } catch(Exception ex) { 

            ex.printStackTrace(); 

        } 

    } 

}

/**

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

* of the old array to the new array.

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

* @param newSize   the new array size.

* @return          A new array with the same contents.

*/

privatestaticObject resizeArray (Object oldArray, intnewSize) { 

   intoldSize = java.lang.reflect.Array.getLength(oldArray); 

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

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

         elementType,newSize); 

   intpreserveLength = Math.min(oldSize,newSize); 

   if(preserveLength > 0) 

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

   returnnewArray; 

} 

// Test routine for resizeArray(). 

publicstaticvoidmain (String[] args) { 

   int[] a = {1,2,3}; 

   a = (int[])resizeArray(a,5); 

   a[3] = 4; 

   a[4] = 5; 

   for(inti=0; i<a.length; i++) 

      System.out.println (a[i]); 

}