1. 字符串有整型的相互转换
String a = String.valueOf(2); //integer to numeric string
int i = Integer.parseInt(a); //numeric string to an int2. 向文件末尾添加内容
| 1 2 3 4 5 6 7 8 9 10 11 | 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. 得到当前方法的名字
String methodName = Thread.currentThread().getStackTrace()[1].getMethodName();
4. 转字符串到日期
java.util.Date = java.text.DateFormat.getDateInstance().parse(date String);
或者是： SimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy" ); Date date = format.parse( myString );5. 使用JDBC链接Oracle
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 | 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. 把 Java util.Date 转成 sql.Date
| 1 2 | java.util.Date utilDate = new java.util.Date(); java.sql.Date sqlDate = new java.sql.Date(utilDate.getTime()); |
7. 使用NIO进行快速的文件拷贝
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 | 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(); } } } |
8. 创建图片的缩略图
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 | 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(); } |
9.创建 JSON 格式的数据
并下面这个JAR 文件：json-rpc-1.0.jar (75 kb)/http://t.cn/Rz0bhUA
| 1 2 3 4 5 6 7 8 9 | import org.json.JSONObject; ... ... JSONObject json = new JSONObject(); json.put( "city" , "Mumbai" ); json.put( "country" , "India" ); ... String output = json.toString(); ... |
10. 使用iText JAR生成PDF
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 | 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. HTTP 代理设置
| 1 2 3 4 | System.getProperties().put( "http.proxyHost" , "someProxyURL" ); System.getProperties().put( "http.proxyPort" , "someProxyPort" ); System.getProperties().put( "http.proxyUser" , "someUserName" ); System.getProperties().put( "http.proxyPassword" , "somePassword" ); |
12. 单实例Singleton 示例
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 | 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; } } |
13. 抓屏程序
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 | 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)); } ... |
14. 列出文件和目录
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 | 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= 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 = 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); |
15. 创建ZIP和JAR文件
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 | 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[ 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(); } } |
16. 解析/读取XML 文件
XML文件
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 | <?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> |
Java代码
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 | <span style= "font-family:Arial;font-size:14px;" > 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() > 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" ); } } |
17. 把 Array 转换成 Map
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 | 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" )); } } |
18. 发送邮件
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 | 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 = 0 ; 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); } |
19. 发送代数据的HTTP 请求
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 | 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( "" ); 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(); } } } |
20. 改变数组的大小
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 | /** * 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. */ 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 > 0 ) System.arraycopy (oldArray, 0 ,newArray, 0 ,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= 0 ; i<a.length; i++) System.out.println (a[i]); } |