10个开发人员非常有用的Java功能代码

来自：http://developer.51cto.com/art/200905/124291.htm

本文将为大家介绍20人员非常有用的Java功能代码。这20段代码，可以成为大家在今后的开发过程中，Java编程手册的重要部分。

1. 把Strings转换成int和把int转换成String

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

2. 向Java文件中添加文本

BufferedWriter out = null;try {out = new BufferedWriter(new FileWriter("filename", true));out.write("aString");} catch (IOException e) {// error processing code} finally {if (out != null) {try {out.close();} catch (IOException e) {// error processing code}}}

3. 获取Java现在正调用的方法名

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

4. 在Java中将String型转换成Date型

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

5. 通过Java JDBC链接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();//}}public class OracleJdbcTest1 {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.将Java中的util.Date转换成sql.Date

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

7. 使用NIO快速复制Java文件

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();  }   }  }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. 在Java中创建缩略图

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 ();  } private void createThumbnail(String filename, int thumbWidth, int thumbHeight, intquality, 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.drawImag e(image, 0, 0, thumbWidth, thumbHeight, null);// save thumbnail image to outFilenameBufferedOutputStream out = new BufferedOutputStream(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 ();} 

9. 在Java中创建JSON数据

Read this article for more details.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 ();   ... import org.json.JSONObject; ... ... JSONObject json = new JSONObject(); json.put("city", "Mumbai"); json.put("country", "India"); ... String output = json.toString(); ...

10. 在Java中使用iText JAR打开PDF

Read this article for more details.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();  }   }  } 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();}}}