20非常有用的Java程序片段 (上)

xiaoxiao2026-06-14 6

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

view source <embed id="highlighter_685098_clipboard" title="copy to clipboard" type="application/x-shockwave-flash" width="16" height="16" src="http://cocre.com/wp-content/plugins/syntaxhighlighter/syntaxhighlighter/scripts/clipboard.swf" lk_media="yes" lk_mediaid="lk_juiceapp_mediaPopup_1243315888969" allowscriptaccess="always" wmode="transparent" flashvars="highlighterId=highlighter_685098" menu="false"></embed> print ? 1. 2. String a = String.valueOf( 2 ); //integer to numeric string 3. int i = Integer.parseInt(a); //numeric string to an int

2. 向文件末尾添加内容

view source <embed id="highlighter_886302_clipboard" title="copy to clipboard" type="application/x-shockwave-flash" width="16" height="16" src="http://cocre.com/wp-content/plugins/syntaxhighlighter/syntaxhighlighter/scripts/clipboard.swf" lk_media="yes" lk_mediaid="lk_juiceapp_mediaPopup_1243315888976" allowscriptaccess="always" wmode="transparent" flashvars="highlighterId=highlighter_886302" menu="false"></embed> print ? 01. 02. BufferedWriter out = null ; 03. try { 04. out = new BufferedWriter( new FileWriter(”filename”, true )); 05. out.write(”aString”); 06. } catch (IOException e) { 07. // error processing code 08. } finally { 09. if (out != null ) { 10. out.close(); 11. } 12. }

3. 得到当前方法的名字

view source <embed id="highlighter_90532_clipboard" title="copy to clipboard" type="application/x-shockwave-flash" width="16" height="16" src="http://cocre.com/wp-content/plugins/syntaxhighlighter/syntaxhighlighter/scripts/clipboard.swf" lk_media="yes" lk_mediaid="lk_juiceapp_mediaPopup_1243315888980" allowscriptaccess="always" wmode="transparent" flashvars="highlighterId=highlighter_90532" menu="false"></embed> print ? 1. String methodName = Thread.currentThread().getStackTrace()[ 1 ].getMethodName();

4. 转字符串到日期

view source <embed id="highlighter_366714_clipboard" title="copy to clipboard" type="application/x-shockwave-flash" width="16" height="16" src="http://cocre.com/wp-content/plugins/syntaxhighlighter/syntaxhighlighter/scripts/clipboard.swf" lk_media="yes" lk_mediaid="lk_juiceapp_mediaPopup_1243315888984" allowscriptaccess="always" wmode="transparent" flashvars="highlighterId=highlighter_366714" menu="false"></embed> print ? 1. 2. java.util.Date = java.text.DateFormat.getDateInstance().parse(date String);

或者是：

view source <embed id="highlighter_544817_clipboard" title="copy to clipboard" type="application/x-shockwave-flash" width="16" height="16" src="http://cocre.com/wp-content/plugins/syntaxhighlighter/syntaxhighlighter/scripts/clipboard.swf" lk_media="yes" lk_mediaid="lk_juiceapp_mediaPopup_1243315888988" allowscriptaccess="always" wmode="transparent" flashvars="highlighterId=highlighter_544817" menu="false"></embed> print ? 1. 2. SimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy" ); 3. Date date = format.parse( myString );

5. 使用JDBC链接Oracle

view source <embed id="highlighter_694591_clipboard" title="copy to clipboard" type="application/x-shockwave-flash" width="16" height="16" src="http://cocre.com/wp-content/plugins/syntaxhighlighter/syntaxhighlighter/scripts/clipboard.swf" lk_media="yes" lk_mediaid="lk_juiceapp_mediaPopup_1243315888991" allowscriptaccess="always" wmode="transparent" flashvars="highlighterId=highlighter_694591" menu="false"></embed> print ? 01. public class OracleJdbcTest 02. { 03. String driverClass = "oracle.jdbc.driver.OracleDriver" ; 04. 05. Connection con; 06. 07. public void init(FileInputStream fs) throws ClassNotFoundException, SQLException, FileNotFoundException, IOException 08. { 09. 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

view source <embed id="highlighter_65942_clipboard" title="copy to clipboard" type="application/x-shockwave-flash" width="16" height="16" src="http://cocre.com/wp-content/plugins/syntaxhighlighter/syntaxhighlighter/scripts/clipboard.swf" lk_media="yes" lk_mediaid="lk_juiceapp_mediaPopup_1243315888995" allowscriptaccess="always" wmode="transparent" flashvars="highlighterId=highlighter_65942" menu="false"></embed> print ? 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

view source <embed id="highlighter_484357_clipboard" title="copy to clipboard" type="application/x-shockwave-flash" width="16" height="16" src="http://cocre.com/wp-content/plugins/syntaxhighlighter/syntaxhighlighter/scripts/clipboard.swf" lk_media="yes" lk_mediaid="lk_juiceapp_mediaPopup_1243315888999" allowscriptaccess="always" wmode="transparent" flashvars="highlighterId=highlighter_484357" menu="false"></embed> print ? 01. public static void fileCopy( File in, File out ) 02. throws IOException 03. { 04. FileChannel inChannel = new FileInputStream( in ).getChannel(); 05. FileChannel outChannel = new FileOutputStream( out ).getChannel(); 06. try 07. { 08. // inChannel.transferTo(0, inChannel.size(), outChannel); // original -- apparently has trouble copying large files on Windows 09. 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

view source <embed id="highlighter_236268_clipboard" title="copy to clipboard" type="application/x-shockwave-flash" width="16" height="16" src="http://cocre.com/wp-content/plugins/syntaxhighlighter/syntaxhighlighter/scripts/clipboard.swf" lk_media="yes" lk_mediaid="lk_juiceapp_mediaPopup_1243315889003" allowscriptaccess="always" wmode="transparent" flashvars="highlighterId=highlighter_236268" menu="false"></embed> print ? 01. private void createThumbnail(String filename, int thumbWidth, int thumbHeight, int quality, String outFilename) 02. throws InterruptedException, FileNotFoundException, IOException 03. { 04. // load image from filename 05. Image image = Toolkit.getDefaultToolkit().getImage(filename); 06. MediaTracker mediaTracker = new MediaTracker( new Container()); 07. mediaTracker.addImage(image, 0 ); 08. mediaTracker.waitForID( 0 ); 09. // 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 imageWidth = image.getWidth( null ); 14. int imageHeight = image.getHeight( null ); 15. double imageRatio = ( double )imageWidth / ( double )imageHeight; 16. if (thumbRatio < imageRatio) { 17. thumbHeight = ( int )(thumbWidth / imageRatio); 18. } else { 19. thumbWidth = ( int )(thumbHeight * imageRatio); 20. } 21. 22. // draw original image to thumbnail image 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(image, 0 , 0 , thumbWidth, thumbHeight, null ); 28. 29. // save thumbnail image 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

请先阅读这篇文章了解一些细节，并下面这个JAR 文件：json-rpc-1.0.jar (75 kb)

view source <embed id="highlighter_808034_clipboard" title="copy to clipboard" type="application/x-shockwave-flash" width="16" height="16" src="http://cocre.com/wp-content/plugins/syntaxhighlighter/syntaxhighlighter/scripts/clipboard.swf" lk_media="yes" lk_mediaid="lk_juiceapp_mediaPopup_1243315889007" allowscriptaccess="always" wmode="transparent" flashvars="highlighterId=highlighter_808034" menu="false"></embed> print ? 01. import org.json.JSONObject; 02. ... 03. ... 04. JSONObject json = new JSONObject(); 05. json.put( "city" , "Mumbai" ); 06. json.put( "country" , "India" ); 07. ... 08. String output = json.toString(); 09. ...

10. 使用iText JAR生成PDF

阅读这篇文章了解更多细节

view source <embed id="highlighter_651063_clipboard" title="copy to clipboard" type="application/x-shockwave-flash" width="16" height="16" src="http://cocre.com/wp-content/plugins/syntaxhighlighter/syntaxhighlighter/scripts/clipboard.swf" lk_media="yes" lk_mediaid="lk_juiceapp_mediaPopup_1243315889011" allowscriptaccess="always" wmode="transparent" flashvars="highlighterId=highlighter_651063" menu="false"></embed> print ? 01. 02. import java.io.File; 03. import java.io.FileOutputStream; 04. import java.io.OutputStream; 05. import java.util.Date; 06. 07. import com.lowagie.text.Document; 08. import com.lowagie.text.Paragraph; 09. import com.lowagie.text.pdf.PdfWriter; 10. 11. public class GeneratePDF { 12. 13. public static void main(String[] args) { 14. try { 15. OutputStream file = new FileOutputStream( new File( "C:\\Test.pdf" )); 16. 17. Document document = new Document(); 18. PdfWriter.getInstance(document, file); 19. document.open(); 20. document.add( new Paragraph( "Hello Kiran" )); 21. document.add( new Paragraph( new Date().toString())); 22. 23. document.close(); 24. file.close(); 25. 26. } catch (Exception e) { 27. 28. e.printStackTrace(); 29. } 30. } 31. }

11. HTTP 代理设置

阅读这篇文章了解更多细节。

view source <embed id="highlighter_44581_clipboard" title="copy to clipboard" type="application/x-shockwave-flash" width="16" height="16" src="http://cocre.com/wp-content/plugins/syntaxhighlighter/syntaxhighlighter/scripts/clipboard.swf" lk_media="yes" lk_mediaid="lk_juiceapp_mediaPopup_1243315889015" allowscriptaccess="always" wmode="transparent" flashvars="highlighterId=highlighter_44581" menu="false"></embed> print ? 1. 2. System.getProperties().put( "http.proxyHost" , "someProxyURL" ); 3. System.getProperties().put( "http.proxyPort" , "someProxyPort" ); 4. System.getProperties().put( "http.proxyUser" , "someUserName" ); 5. System.getProperties().put( "http.proxyPassword" , "somePassword" );

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