原文出处：
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.public class OracleJdbcTest
2.{
3. String driverClass = "oracle.jdbc.driver.OracleDriver";
4.
5. Connection con;
6.
7. public void init(FileInputStream fs) throws ClassNotFoundException, SQLException, FileNotFoundException, IOException
8. {
9. Properties props = new Properties();
10. props.load(fs);
11. String url = props.getProperty("db.url");
12. String userName = props.getProperty("db.user");
13. String password = props.getProperty("db.password");
14. Class.forName(driverClass);
15.
16. con=DriverManager.getConnection(url, userName, password);
17. }
18.
19. public void fetch() throws SQLException, IOException
20. {
21. PreparedStatement ps = con.prepareStatement("select SYSDATE from dual");
22. ResultSet rs = ps.executeQuery();
23.
24. while (rs.next())
25. {
26. // do the thing you do
27. }
28. rs.close();
29. ps.close();
30. }
31.
32. public static void main(String[] args)
33. {
34. OracleJdbcTest test = new OracleJdbcTest();
35. test.init();
36. test.fetch();
37. }
38.}
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.public static void 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.
10. // magic number for Windows, 64Mb - 32Kb)
11. int maxCount = (64 * 1024 * 1024) - (32 * 1024);
12. long size = inChannel.size();
13. long position = 0;
14. while ( position < size )
15. {
16. position += inChannel.transferTo( position, maxCount, outChannel );
17. }
18. }
19. finally
20. {
21. if ( inChannel != null )
22. {
23. inChannel.close();
24. }
25. if ( outChannel != null )
26. {
27. outChannel.close();
28. }
29. }
30. }
8. 创建图片的缩略图
1.private void 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.
11. // determine thumbnail size from WIDTH and HEIGHT
12. double thumbRatio = (double)thumbWidth / (double)thumbHeight;
13. int p_w_picpathWidth = p_w_picpath.getWidth(null);
14. int p_w_picpathHeight = p_w_picpath.getHeight(null);
15. double p_w_picpathRatio = (double)p_w_picpathWidth / (double)p_w_picpathHeight;
16. if (thumbRatio < p_w_picpathRatio) {
17. thumbHeight = (int)(thumbWidth / p_w_picpathRatio);
18. } else {
19. thumbWidth = (int)(thumbHeight * p_w_picpathRatio);
20. }
21.
22. // draw original p_w_picpath to thumbnail p_w_picpath object and
23. // scale it to the new size on-the-fly
24. BufferedImage thumbImage = new BufferedImage(thumbWidth, thumbHeight, BufferedImage.TYPE_INT_RGB);
25. Graphics2D graphics2D = thumbImage.createGraphics();
26. graphics2D.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);
27. graphics2D.drawImage(p_w_picpath, 0, 0, thumbWidth, thumbHeight, null);
28.
29. // save thumbnail p_w_picpath to outFilename
30. BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream(outFilename));
31. JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
32. JPEGEncodeParam param = encoder.getDefaultJPEGEncodeParam(thumbImage);
33. quality = Math.max(0, Math.min(quality, 100));
34. param.setQuality((float)quality / 100.0f, false);
35. encoder.setJPEGEncodeParam(param);
36. encoder.encode(thumbImage);
37. out.close();
38. }
9. 创建 JSON 格式的数据
请先阅读了解一些细节，并下面这个JAR 文件：
1.import org.json.JSONObject;
2....
3....
4.JSONObject json = new JSONObject();
5.json.put("city", "Mumbai"); 6.json.put("country", "India"); 7....
8.String output = json.toString();
9....
10. 使用iTextJAR生成PDF
阅读这篇了解更多细节
1.import java.io.File;
2.import java.io.FileOutputStream;
3.import java.io.OutputStream;
4.import java.util.Date;
5.
6.import com.lowagie.text.Document;
7.import com.lowagie.text.Paragraph;
8.import com.lowagie.text.pdf.PdfWriter;
9.
10.publicclass GeneratePDF { 11.
12.publicstaticvoid main(String[] args) { 13.try { 14. OutputStream file = new FileOutputStream(new File("C:\\Test.pdf")); 15.
16. Document document = new Document();
17. PdfWriter.getInstance(document, file);
18. document.open();
19. document.add(new Paragraph("Hello Kiran")); 20. document.add(new Paragraph(new Date().toString()));
21.
22. document.close();
23. file.close();
24.
25. } catch (Exception e) { 26.
27. e.printStackTrace();
28. }
29. }
30.}