Shulou(Shulou.com)06/03 Report--

20个有用的java代码分别是什么，很多新手对此不是很清楚，为了帮助大家解决这个难题，下面小编将为大家详细讲解，有这方面需求的人可以来学习下，希望你能有所收获。

20个有用的java代码

1. Strings转int和int转String

String a = String.valueOf(2); //integer to numeric stringint i = Integer.parseInt(a); //numeric string to an int

2.在文件内追加文字

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.获取当前的方法名

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

4.String转换为Date

java.util.Date = java.text.DateFormat.getDateInstance().parse(date String);//orSimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy" );Date date = format.parse( myString );

5.JDBC连接Oracle数据库

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util.Date转换为sql.Date

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

7.Java Fast File Copy using NIO

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.创建一个图片的缩略图 private void createThumbnail(String filename, int thumbWidth, int thumbHeight, int quality, String outFilename)throws InterruptedException, FileNotFoundException, IOException {// load image from filenameImage 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 HEIGHTdouble 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-flyBufferedImage 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 outFilenameBufferedOutputStream 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.生成JSON数据 // 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();... 10.生成PDF 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 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.单例 public class SimpleSingleton {private static SimpleSingleton singleInstance = new SimpleSingleton(); //Marking default constructor private//to avoid direct instantiation.private SimpleSingleton() { } //Get instance for class SimpleSingletonpublic static SimpleSingleton getInstance() { return singleInstance; }}// One more implementation of Singleton class. Thanks to Ralph and Lukasz Zielinski for pointing this out.public enum SimpleSingleton { INSTANCE;public void doSomething() { }} //Call the method from Singleton:SimpleSingleton.INSTANCE.doSomething(); 13.截屏 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.文件监控 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.生成.jar,.zip文件 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 streambis = 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.操作XML JohnB12MaryA11SimonA18 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 documentSystem.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.Array转化为Map 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.发邮件 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 SessionSession session = Session.getDefaultInstance(props, null); session.setDebug(debug); // create a messageMessage msg = new MimeMessage(session); // set the from and to addressInternetAddress 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 Wantmsg.addHeader("MyHeaderName", "myHeaderValue"); // Setting the Subject and Content Type msg.setSubject(subject); msg.setContent(message, "text/plain"); Transport.send(msg);} 19.远程抓取数据 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://www.viralpatel.net/blogs/"); 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.重新定义数组大小 /*** 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

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