非常有用的java代码段.doc

20非常有用的Java程序片段(1)2013-06-14 14:57 陈皓 酷壳网我要评论(0)字号：T|T下面是20个非常有用的Java程序片段，希望能对你有用。AD：2013大数据全球技术峰会课程PPT下载下面是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. Stringa=String.valueOf(2);/integertonumericstring2. inti=Integer.parseInt(a);/numericstringtoanint2. 向文件末尾添加内容1. BufferedWriterout=null;2. try3. out=newBufferedWriter(newFileWriter(”filename”,true);4. out.write(”aString”);5. catch(IOExceptione)6. /errorprocessingcode7. finally8. if(out!=null)9. out.close();10. 11. 3. 得到当前方法的名字1. StringmethodName=Thread.currentThread().getStackTrace()1.getMethodName();4. 转字符串到日期1. java.util.Date=java.text.DateFormat.getDateInstance().parse(dateString);或者是：1. SimpleDateFormatformat=newSimpleDateFormat(dd.MM.yyyy);2. Datedate=format.parse(myString);5. 使用JDBC链接Oracle1. publicclassOracleJdbcTest2. 3. StringdriverClass=oracle.jdbc.driver.OracleDriver;4. 5. Connectioncon;6. 7. publicvoidinit(FileInputStreamfs)throwsClassNotFoundException,SQLException,FileNotFoundException,IOException8. 9. Propertiesprops=newProperties();10. props.load(fs);11. Stringurl=props.getProperty(db.url);12. StringuserName=props.getProperty(db.user);13. Stringpassword=props.getProperty(db.password);14. Class.forName(driverClass);15. 16. con=DriverManager.getConnection(url,userName,password);17. 18. 19. publicvoidfetch()throwsSQLException,IOException20. 21. PreparedStatementps=con.prepareStatement(selectSYSDATEfromdual);22. ResultSetrs=ps.executeQuery();23. 24. while(rs.next()25. 26. /dothethingyoudo27. 28. rs.close();29. ps.close();30. 31. 32. publicstaticvoidmain(Stringargs)33. 34. OracleJdbcTesttest=newOracleJdbcTest();35. test.init();36. test.fetch();37. 38. 6.把 Java util.Date转成 sql.Date1. java.util.DateutilDate=newjava.util.Date();2. java.sql.DatesqlDate=newjava.sql.Date(utilDate.getTime();7. 使用NIO进行快速的文件拷贝1. publicstaticvoidfileCopy(Filein,Fileout)2. throwsIOException3. 4. FileChannelinChannel=newFileInputStream(in).getChannel();5. FileChanneloutChannel=newFileOutputStream(out).getChannel();6. try7. 8. /inChannel.transferTo(0,inChannel.size(),outChannel);/original-apparentlyhastroublecopyinglargefilesonWindows9. 10. /magicnumberforWindows,64Mb-32Kb)11. intmaxCount=(64*1024*1024)-(32*1024);12. longsize=inChannel.size();13. longposition=0;14. while(positionsize)15. 16. position+=inChannel.transferTo(position,maxCount,outChannel);17. 18. 19. finally20. 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. privatevoidcreateThumbnail(Stringfilename,intthumbWidth,intthumbHeight,intquality,StringoutFilename)2. throwsInterruptedException,FileNotFoundException,IOException3. 4. /loadimagefromfilename5. Imageimage=Toolkit.getDefaultToolkit().getImage(filename);6. MediaTrackermediaTracker=newMediaTracker(newContainer();7. mediaTracker.addImage(image,0);8. mediaTracker.waitForID(0);9. /usethistotestforerrorsatthispoint:System.out.println(mediaTracker.isErrorAny();10. 11. /determinethumbnailsizefromWIDTHandHEIGHT12. doublethumbRatio=(double)thumbWidth/(double)thumbHeight;13. intimageWidth=image.getWidth(null);14. intimageHeight=image.getHeight(null);15. doubleimageRatio=(double)imageWidth/(double)imageHeight;16. if(thumbRatioimageRatio)17. thumbHeight=(int)(thumbWidth/imageRatio);18. else19. thumbWidth=(int)(thumbHeight*imageRatio);20. 21. 22. /draworiginalimagetothumbnailimageobjectand23. /scaleittothenewsizeon-the-fly24. BufferedImagethumbImage=newBufferedImage(thumbWidth,thumbHeight,BufferedImage.TYPE_INT_RGB);25. Graphics2Dgraphics2D=thumbImage.createGraphics();26. graphics2D.setRenderingHint(RenderingHints.KEY_INTERPOLATION,RenderingHints.VALUE_INTERPOLATION_BILINEAR);27. graphics2D.drawImage(image,0,0,thumbWidth,thumbHeight,null);28. 29. /savethumbnailimagetooutFilename30. BufferedOutputStreamout=newBufferedOutputStream(newFileOutputStream(outFilename);31. JPEGImageEncoderencoder=JPEGCodec.createJPEGEncoder(out);32. JPEGEncodeParamparam=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)1. importorg.json.JSONObject;2. .3. .4. JSONObjectjson=newJSONObject();5. json.put(city,Mumbai);6. json.put(country,India);7. .8. Stringoutput=json.toString();9. .10. 使用iText JAR生成PDF阅读这篇文章了解更多细节1. importjava.io.File;2. importjava.io.FileOutputStream;3. importjava.io.OutputStream;4. importjava.util.Date;5. 6. importcom.lowagie.text.Document;7. importcom.lowagie.text.Paragraph;8. importcom.lowagie.text.pdf.PdfWriter;9. 10. publicclassGeneratePDF11. 12. publicstaticvoidmain(Stringargs)13. try14. OutputStreamfile=newFileOutputStream(newFile(C:Test.pdf);15. 16. Documentdocument=newDocument();17. PdfWriter.getInstance(document,file);18. document.open();19. document.add(newParagraph(HelloKiran);20. document.add(newParagraph(newDate().toString();21. 22. document.close();23. file.close();24. 25. catch(Exceptione)26. 27. e.printStackTrace();28. 29. 30. 11. HTTP 代理设置阅读这篇文章了解更多细节。1. System.getProperties().put(xyHost,someProxyURL);2. System.getProperties().put(xyPort,someProxyPort);3. System.getProperties().put(xyUser,someUserName);4. System.getProperties().put(xyPassword,somePassword);2. 单实例Singleton 示例请先阅读这篇文章了解更多信息1. publicclassSimpleSingleton2. privatestaticSimpleSingletonsingleInstance=newSimpleSingleton();3. 4. /Markingdefaultconstructorprivate5. /toavoiddirectinstantiation.6. privateSimpleSingleton()7. 8. 9. /GetinstanceforclassSimpleSingleton10. publicstaticSimpleSingletongetInstance()11. 12. returnsingleInstance;13. 14. 另一种实现1. publicenumSimpleSingleton2. INSTANCE;3. publicvoiddoSomething()4. 5. 6. 7. /CallthemethodfromSingleton:8. SimpleSingleton.INSTANCE.doSomething();13. 抓屏程序阅读这篇文章获得更多信息。1. importjava.awt.Dimension;2. importjava.awt.Rectangle;3. importjava.awt.Robot;4. importjava.awt.Toolkit;5. importjava.awt.image.BufferedImage;6. importjavax.imageio.ImageIO;7. importjava.io.File;8. 9. .10. 11. publicvoidcaptureScreen(StringfileName)throwsException12. 13. DimensionscreenSize=Toolkit.getDefaultToolkit().getScreenSize();14. RectanglescreenRectangle=newRectangle(screenSize);15. Robotrobot=newRobot();16. BufferedImageimage=robot.createScreenCapture(screenRectangle);17. ImageIO.write(image,png,newFile(fileName);18. 19. 20. .14. 列出文件和目录1. Filedir=newFile(directoryName);2. Stringchildren=dir.list();3. if(children=null)4. /Eitherdirdoesnotexistorisnotadirectory5. else6. for(inti=0;ichildren.length;i+)7. /Getfilenameoffileordirectory8. Stringfilename=childreni;9. 10. 11. 12. /Itisalsopossibletofilterthelistofreturnedfiles.13. /Thisexampledoesnotreturnanyfilesthatstartwith.14. FilenameFilterfilter=newFilenameFilter()15. publicbooleanaccept(Filedir,Stringname)16. return!name.startsWith(.);17. 18. ;19. children=dir.list(filter);20. 21. /ThelistoffilescanalsoberetrievedasFileobjects22. Filefiles=dir.listFiles();23. 24. /Thisfilteronlyreturnsdirectories25. FileFilterfileFilter=newFileFilter()26. publicbooleanaccept(Filefile)27. returnfile.isDirectory();28. 29. ;30. files=dir.listFiles(fileFilter);15. 创建ZIP和JAR文件1. importjava.util.zip.*;2. importjava.io.*;3. 4. publicclassZipIt5. publicstaticvoidmain(Stringargs)throwsIOException6. if(args.length2)7. System.err.println(usage:javaZipItZip.zipfile1file2file3);8. System.exit(-1);9. 10. FilezipFile=newFile(args0);11. if(zipFile.exists()12. System.err.println(Zipfilealreadyexists,pleasetryanother);13. System.exit(-2);14. 15. FileOutputStreamfos=newFileOutputStream(zipFile);16. ZipOutputStreamzos=newZipOutputStream(fos);17. intbytesRead;18. bytebuffer=newbyte1024;19. CRC32crc=newCRC32();20. for(inti=1,n=args.length;in;i+)21. Stringname=argsi;22. Filefile=newFile(name);23. if(!file.exists()24. System.err.println(Skipping:+name);25. continue;26. 27. BufferedInputStreambis=newBufferedInputStream(28. newFileInputStream(file);29. crc.reset();30. while(bytesRead=bis.read(buffer)!=-1)31. crc.update(buffer,0,bytesRead);32. 33. bis.close();34. /Resettobeginningofinputstream35. bis=newBufferedInputStream(36. newFileInputStream(file);37. ZipEntryentry=newZipEntry(name);38. entry.setMethod(ZipEntry.STORED);39. entry.setCompressedSize(file.length();40. entry.setSize(file.length();41. entry.setCrc(crc.getValue();42. zos.putNextEntry(entry);43. while(bytesRead=bis.read(buffer)!=-1)44. zos.write(buffer,0,bytesRead);45. 46. bis.close();47. 48. zos.close();49. 50. 16. 解析/读取XML 文件XML文件1. 2. 3. 4. John5. B6. 127. 8. 9. Mary10. A11. 1112. 13. 14. Simon15. A16. 1817. 18. Java代码：1. ackagenet.viralpatel.java.xmlparser;2. 3. importjava.io.File;4. importjavax.xml.parsers.DocumentBuilder;5. importjavax.xml.parsers.DocumentBuilderFactory;6. 7. importorg.w3c.dom.Document;8. importorg.w3c.dom.Element;9. importorg.w3c.dom.Node;10. importorg.w3c.dom.NodeList;11. 12. publicclassXMLParser13. 14. publicvoidgetAllUserNames(StringfileName)15. try16. DocumentBuilderFactorydbf=DocumentBuilderFactory.newInstance();17. DocumentBuilderdb=dbf.newDocumentBuilder();18. Filefile=newFile(fileName);19. if(file.exists()20. Documentdoc=db.parse(file);21. ElementdocEle=doc.getDocumentElement();22. 23. /Printrootelementofthedocument24. System.out.println(Rootelementofthedocument:25. +docEle.getNodeName();26. 27. NodeListstudentList=docEle.getElementsByTagName(student);28. 29. /Printtotalstudentelementsindocument30. System.out31. .println(Totalstudents:+studentList.getLength();32. 33. if(studentList!=null&studentList.getLength()0)34. for(inti=0;istudentList.getLength();i+)35. 36. Nodenode=studentList.item(i);37. 38. if(node.getNodeType()=Node.ELEMENT_NODE)39. 40. System.out41. .println(=);42. 43. Elemente=(Element)node;44. NodeListnodeList=e.getElementsByTagName(name);45. System.out.println(Name:46. +nodeList.item(0).getChildNodes().item(0)47. .getNodeValue();48. 49. nodeList=e.getElementsByTagName(grade);50. System.out.println(Grade:51. +nodeList.item(0).getChildNodes().item(0)52. .getNodeValue();53. 54. nodeList=e.getElementsByTagName(age);55. System.out.println(Age:56. +nodeList.item(0).getChildNodes().item(0)57. .getNodeValue();58. 59. 60. else61. System.exit(1);62. 63. 64. catch(Exceptione)65. System.out.println(e);66. 67. 68. publicstaticvoidmain(Stringargs)69. 70. XMLParserparser=newXMLParser();71. parser.getAllUserNames(c:test.xml);72. 73. 17.把 Array转换成 Map1. importjava.util.Map;2. mons.lang.ArrayUt