20个有用的java片段.docx
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- 上传时间:2022-11-24
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20个有用的java片段.docx
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20个有用的java片段
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
Stringa=String.valueOf
(2);//integertonumericstring
inti=Integer.parseInt(a);//numericstringtoanint
2.向文件末尾添加内容
BufferedWriterout=null;
try{
out=newBufferedWriter(newFileWriter(”filename”,true));
out.write(”aString”);
}catch(IOExceptione){
//errorprocessingcode
}finally{
if(out!
=null){
out.close();
}
}
3.得到当前方法的名字
StringmethodName=Thread.currentThread().getStackTrace()[1].getMethodName();
4.转字符串到日期
java.util.Date=java.text.DateFormat.getDateInstance().parse(dateString);
或者是:
SimpleDateFormatformat=newSimpleDateFormat("dd.MM.yyyy");
Datedate=format.parse(myString);
5.使用JDBC链接Oracle
publicclassOracleJdbcTest
{
StringdriverClass="oracle.jdbc.driver.OracleDriver";
Connectioncon;
publicvoidinit(FileInputStreamfs)throwsClassNotFoundException,SQLException,FileNotFoundException,IOException
{
Propertiesprops=newProperties();
props.load(fs);
Stringurl=props.getProperty("db.url");
StringuserName=props.getProperty("db.user");
Stringpassword=props.getProperty("db.password");
Class.forName(driverClass);
con=DriverManager.getConnection(url,userName,password);
}
publicvoidfetch()throwsSQLException,IOException
{
PreparedStatementps=con.prepareStatement("selectSYSDATEfromdual");
ResultSetrs=ps.executeQuery();
while(rs.next())
{
//dothethingyoudo
}
rs.close();
ps.close();
}
publicstaticvoidmain(String[]args)
{
OracleJdbcTesttest=newOracleJdbcTest();
test.init();
test.fetch();
}
}
6. 把Javautil.Date 转成sql.Date
java.util.DateutilDate=newjava.util.Date();
java.sql.DatesqlDate=newjava.sql.Date(utilDate.getTime());
7.使用NIO进行快速的文件拷贝
publicstaticvoidfileCopy(Filein,Fileout)
throwsIOException
{
FileChannelinChannel=newFileInputStream(in).getChannel();
FileChanneloutChannel=newFileOutputStream(out).getChannel();
try
{
//inChannel.transferTo(0,inChannel.size(),outChannel);//original--apparentlyhastroublecopyinglargefilesonWindows
//magicnumberforWindows,64Mb-32Kb)
intmaxCount=(64*1024*1024)-(32*1024);
longsize=inChannel.size();
longposition=0;
while(position { position+=inChannel.transferTo(position,maxCount,outChannel); } } finally { if(inChannel! =null) { inChannel.close(); } if(outChannel! =null) { outChannel.close(); } } } 8.创建图片的缩略图 privatevoidcreateThumbnail(Stringfilename,intthumbWidth,intthumbHeight,intquality,StringoutFilename) throwsInterruptedException,FileNotFoundException,IOException { //loadimagefromfilename Imageimage=Toolkit.getDefaultToolkit().getImage(filename); MediaTrackermediaTracker=newMediaTracker(newContainer()); mediaTracker.addImage(image,0); mediaTracker.waitForID(0); //usethistotestforerrorsatthispoint: System.out.println(mediaTracker.isErrorAny()); //determinethumbnailsizefromWIDTHandHEIGHT doublethumbRatio=(double)thumbWidth/(double)thumbHeight; intimageWidth=image.getWidth(null); intimageHeight=image.getHeight(null); doubleimageRatio=(double)imageWidth/(double)imageHeight; if(thumbRatio thumbHeight=(int)(thumbWidth/imageRatio); }else{ thumbWidth=(int)(thumbHeight*imageRatio); } //draworiginalimagetothumbnailimageobjectand //scaleittothenewsizeon-the-fly BufferedImagethumbImage=newBufferedImage(thumbWidth,thumbHeight,BufferedImage.TYPE_INT_RGB); Graphics2Dgraphics2D=thumbImage.createGraphics(); graphics2D.setRenderingHint(RenderingHints.KEY_INTERPOLATION,RenderingHints.VALUE_INTERPOLATION_BILINEAR); graphics2D.drawImage(image,0,0,thumbWidth,thumbHeight,null); //savethumbnailimagetooutFilename BufferedOutputStreamout=newBufferedOutputStream(newFileOutputStream(outFilename)); JPEGImageEncoderencoder=JPEGCodec.createJPEGEncoder(out); JPEGEncodeParamparam=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. 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(75kb) importorg.json.JSONObject; ... ... JSONObjectjson=newJSONObject(); json.put("city","Mumbai"); json.put("country","India"); ... Stringoutput=json.toString(); ... 10.使用iTextJAR生成PDF 阅读这篇文章了解更多细节 importjava.io.File; importjava.io.FileOutputStream; importjava.io.OutputStream; importjava.util.Date; importcom.lowagie.text.Document; importcom.lowagie.text.Paragraph; importcom.lowagie.text.pdf.PdfWriter; publicclassGeneratePDF{ publicstaticvoidmain(String[]args){ try{ OutputStreamfile=newFileOutputStream(newFile("C: \\Test.pdf")); Documentdocument=newDocument(); PdfWriter.getInstance(document,file); document.open(); document.add(newParagraph("HelloKiran")); document.add(newParagraph(newDate().toString())); document.close(); file.close(); }catch(Exceptione){ e.printStackTrace(); } } } 11.HTTP代理设置 阅读这篇 文章了解更多细节。 System.getProperties().put("http.proxyHost","someProxyURL"); System.getProperties().put("http.proxyPort","someProxyPort"); System.getProperties().put("http.proxyUser","someUserName"); System.getProperties().put("http.proxyPassword","somePassword"); 12.单实例Singleton示例 请先阅读这篇文章了解更多信息 publicclassSimpleSingleton{ privatestaticSimpleSingletonsingleInstance=newSimpleSingleton(); //Markingdefaultconstructorprivate //toavoiddirectinstantiation. privateSimpleSingleton(){ } //GetinstanceforclassSimpleSingleton publicstaticSimpleSingletongetInstance(){ returnsingleInstance; } } 另一种实现 publicenumSimpleSingleton{ INSTANCE; publicvoiddoSomething(){ } } //CallthemethodfromSingleton: SimpleSingleton.INSTANCE.doSomething(); 13.抓屏程序 阅读这篇文章获得更多信息。 importjava.awt.Dimension; importjava.awt.Rectangle; importjava.awt.Robot; importjava.awt.Toolkit; importjava.awt.image.BufferedImage; importjavax.imageio.ImageIO; importjava.io.File; ... publicvoidcaptureScreen(StringfileName)throwsException{ DimensionscreenSize=Toolkit.getDefaultToolkit().getScreenSize(); RectanglescreenRectangle=newRectangle(screenSize); Robotrobot=newRobot(); BufferedImageimage=robot.createScreenCapture(screenRectangle); ImageIO.write(image,"png",newFile(fileName)); } ... 14.列出文件和目录 Filedir=newFile("directoryName"); String[]children=dir.list(); if(children==null){ //Eitherdirdoesnotexistorisnotadirectory }else{ for(inti=0;i //Getfilenameoffileordirectory Stringfilename=children[i]; } } //Itisalsopossibletofilterthelistofreturnedfiles. //Thisexampledoesnotreturnanyfilesthatstartwith`.'. FilenameFilterfilter=newFilenameFilter(){ publicbooleanaccept(Filedir,Stringname){ return! name.startsWith("."); } }; children=dir.list(filter); //ThelistoffilescanalsoberetrievedasFileobjects File[]files=dir.listFiles(); //Thisfilteronlyreturnsdirectories FileFilterfileFilter=newFileFilter(){ publicbooleanaccept(Filefile){ returnfile.isDirectory(); } }; files=dir.listFiles(fileFilter); 15.创建ZIP和JAR文件 importjava.util.zip.*; importjava.io.*; publicclassZipIt{ publicstaticvoidmain(Stringargs[])throwsIOException{ if(args.length<2){ System.err.println("usage: javaZipItZip.zipfile1file2file3"); System.exit(-1); } FilezipFile=newFile(args[0]); if(zipFile.exists()){ System.err.println("Zipfilealreadyexists,pleasetryanother"); System.exit(-2); } FileOutputStreamfos=newFileOutputStream(zipFile); ZipOutputStreamzos=newZipOutputStream(fos); intbytesRead; byte[]buffer=newbyte[1024]; CRC32crc=newCRC32(); for(inti=1,n=args.length;i Stringname=args[i]; Filefile=newFile(name); if(! file.exists()){ System.err.println("Skipping: "+name); continue; } BufferedInputStreambis=newBufferedInputStream( newFileInputStream(file)); crc.reset(); while((bytesRead=bis.read(buffer))! =-1){ crc.update(buffer,0,bytesRead); } bis.close(); //Resettobeginningofinputstream bis=newBufferedInputStream( newFileInputStream(file)); ZipEntryentry=newZipEntry(name); entry.setMethod(ZipEntry.STORED); entry.setCompressedSize(file.length()); entry.setSize(file.length()); entry.setCrc(crc.getValue()); zos.putNextEntry(entry); while((bytesRead=bis.read(buffer))! =-1){ zos.write(buffer,0,bytesRead); } bis.close(); } zos.close(); } } 16.解析/读取XML文件 XML文件 xmlversion="1.0"? > Java代码 packagenet.viralpatel.java.xmlparser; importjava.io.File; importjavax.xml.parsers.DocumentBuilder; importjavax.xml.parsers.DocumentBuilderFactory; importorg.w3c.dom.Document; importorg.w3c.dom.Element; importorg.w3c.dom.Node; importorg.w3c.dom.NodeList; publicclassXMLParser{ publicvoidgetAllUserNames(StringfileName){ try{ DocumentBuilderFactorydbf=DocumentBuilderFactory.newInstance(); DocumentBuilderdb=dbf.newDocumentBuilder(); Filefile=newFile(fileName); if(file.exists()){ Documentdoc=db.parse(file); ElementdocEle=doc.getDocumentElement(); //Printrootelementofthedocume
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