下面是20个非常有用的Java程序片段，希望能对你有用。

1. 字符串有整型的相互转换

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

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

2. 向文件末尾添加内容

1. BufferedWriter out = null;

2. try {

3. out = new BufferedWriter(new FileWriter(”filename”, true));

4. out.write(”aString”);

5. } catch (IOException e) {

6. // error processing code

7. } finally {

8. if (out != null) {

9. out.close();

10. }

11. }

3. 得到当前方法的名字

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

4. 转字符串到日期

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

或者是：

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

2. Date date = format.parse( myString );

5. 使用JDBC链接Oracle

1. publicclass OracleJdbcTest

2. {

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

4. Connection con;

5. publicvoid init(FileInputStream fs) throws ClassNotFoundException, SQLException, FileNotFoundException, IOException

6. {

7. Properties props = new Properties();

8. props.load(fs);

9. String url = props.getProperty("db.url");

10. String userName = props.getProperty("db.user");

11. String password = props.getProperty("db.password");

12. Class.forName(driverClass);

13. con=DriverManager.getConnection(url, userName, password);

14. }

15. publicvoid fetch() throws SQLException, IOException

16. {

17. PreparedStatement ps = con.prepareStatement("select SYSDATE from dual");

18. ResultSet rs = ps.executeQuery();

19. while (rs.next())

20. {

21. // do the thing you do

22. }

23. rs.close();

24. ps.close();

25. }

26. publicstaticvoid main(String[] args)

27. {

28. OracleJdbcTest test = new OracleJdbcTest();

29. test.init();

30. test.fetch();

31. }

32. }

6. 把 Java util.Date 转成 sql.Date

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

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

7. 使用NIO进行快速的文件拷贝

1. publicstaticvoid fileCopy( File in, File out )

2. throws IOException

3. {

4. FileChannel inChannel = new FileInputStream( in ).getChannel();

5. FileChannel outChannel = new FileOutputStream( out ).getChannel();

6. try

7. {

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

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

10. int maxCount = (64 * 1024 * 1024) - (32 * 1024);

11. long size = inChannel.size();

12. long position = 0;

13. while ( position < size )

14. {

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

16. }

17. }

18. finally

19. {

20. if ( inChannel != null )

21. {

22. inChannel.close();

23. }

24. if ( outChannel != null )

25. {

26. outChannel.close();

27. }

28. }

29. }

8. 创建图片的缩略图

1. privatevoid createThumbnail(String filename, int thumbWidth, int thumbHeight, int quality, String outFilename)

2. throws InterruptedException, FileNotFoundException, IOException

3. {

4. // load p_w_picpath from filename

5. Image p_w_picpath = Toolkit.getDefaultToolkit().getImage(filename);

6. MediaTracker mediaTracker = new MediaTracker(new Container());

7. mediaTracker.addImage(p_w_picpath, 0);

8. mediaTracker.waitForID(0);

9. // use this to test for errors at this point: System.out.println(mediaTracker.isErrorAny());

10. // determine thumbnail size from WIDTH and HEIGHT

11. double thumbRatio = (double)thumbWidth / (double)thumbHeight;

12. int p_w_picpathWidth = p_w_picpath.getWidth(null);

13. int p_w_picpathHeight = p_w_picpath.getHeight(null);

14. double p_w_picpathRatio = (double)p_w_picpathWidth / (double)p_w_picpathHeight;

15. if (thumbRatio < p_w_picpathRatio) {

16. thumbHeight = (int)(thumbWidth / p_w_picpathRatio);

17. } else {

18. thumbWidth = (int)(thumbHeight * p_w_picpathRatio);

19. }

20. // draw original p_w_picpath to thumbnail p_w_picpath object and

21. // scale it to the new size on-the-fly

22. BufferedImage thumbImage = new BufferedImage(thumbWidth, thumbHeight, BufferedImage.TYPE_INT_RGB);

23. Graphics2D graphics2D = thumbImage.createGraphics();

24. graphics2D.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);

25. graphics2D.drawImage(p_w_picpath, 0, 0, thumbWidth, thumbHeight, null);

26. // save thumbnail p_w_picpath to outFilename

27. BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream(outFilename));

28. JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);

29. JPEGEncodeParam param = encoder.getDefaultJPEGEncodeParam(thumbImage);

30. quality = Math.max(0, Math.min(quality, 100));

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

32. encoder.setJPEGEncodeParam(param);

33. encoder.encode(thumbImage);

34. out.close();

35. }