本文给大家分享了 20 个常用的 java 代码，都是别人项目中使用过的代码，这里推荐给大家，有需要的小伙伴可以参考下.
1. 字符串有整型的相互转换
String a = String.valueOf(2); //integer to numeric string
int i = Integer.parseInt(a); //numeric string to an int
2. 向文件末尾添加内容
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BufferedWriter out = null; try{ out = newBufferedWriter(newFileWriter(”filename”, true)); out.write(”aString”); } catch(IOException e) { // error processing code } finally{ if(out != null) { out.close(); } } |
3. 得到当前方法的名字
String methodName = Thread.currentThread().getStackTrace()[1].getMethodName();
4. 转字符串到日期
java.util.Date = java.text.DateFormat.getDateInstance().parse(date String);
或者是：
SimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy" );
Date date = format.parse( myString );
5. 使用 JDBC 链接 Oracle
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publicclassOracleJdbcTest { String driverClass = "oracle.jdbc.driver.OracleDriver"; Connection con; publicvoidinit(FileInputStream fs) throwsClassNotFoundException, SQLException, FileNotFoundException, IOException { Properties props = newProperties(); props.load(fs); String url = props.getProperty("db.url"); String userName = props.getProperty("db.user"); String password = props.getProperty("db.password"); Class.forName(driverClass); con=DriverManager.getConnection(url, userName, password); } publicvoidfetch() throwsSQLException, IOException { PreparedStatement ps = con.prepareStatement("select SYSDATE from dual"); ResultSet rs = ps.executeQuery(); while(rs.next()) { // do the thing you do } rs.close(); ps.close(); } publicstaticvoidmain(String[] args) { OracleJdbcTest test = newOracleJdbcTest(); test.init(); test.fetch(); } } |
6. 把 Java util.Date 转成 sql.Date
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java.util.Date utilDate = newjava.util.Date(); java.sql.Date sqlDate = newjava.sql.Date(utilDate.getTime()); |
7. 使用 NIO 进行快速的文件拷贝
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publicstaticvoidfileCopy( File in, File out ) throwsIOException { FileChannel inChannel = newFileInputStream( in ).getChannel(); FileChannel outChannel = newFileOutputStream( out ).getChannel(); try { // inChannel.transferTo(0, inChannel.size(), outChannel); // original -- apparently has trouble copying large files on Windows // magic number for Windows, 64Mb - 32Kb) intmaxCount = (64* 1024* 1024) - (32* 1024); longsize = inChannel.size(); longposition = 0; while( position < size ) { 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
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privatevoidcreateThumbnail(String filename, intthumbWidth, intthumbHeight, intquality, String outFilename) throwsInterruptedException, FileNotFoundException, IOException { // load image from filename Image image = Toolkit.getDefaultToolkit().getImage(filename); MediaTracker mediaTracker = newMediaTracker(newContainer()); mediaTracker.addImage(image, 0); mediaTracker.waitForID(0); // use this to test for errors at this point: System.out.println(mediaTracker.isErrorAny()); // determine thumbnail size from WIDTH and HEIGHT doublethumbRatio = (double)thumbWidth / (double)thumbHeight; intimageWidth = image.getWidth(null); intimageHeight = image.getHeight(null); doubleimageRatio = (double)imageWidth / (double)imageHeight; if(thumbRatio < imageRatio) { thumbHeight = (int)(thumbWidth / imageRatio); } else{ thumbWidth = (int)(thumbHeight * imageRatio); } // draw original image to thumbnail image object and // scale it to the new size on-the-fly BufferedImage thumbImage = newBufferedImage(thumbWidth, thumbHeight, BufferedImage.TYPE_INT_RGB); Graphics2D graphics2D = thumbImage.createGraphics(); graphics2D.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR); graphics2D.drawImage(image, 0, 0, thumbWidth, thumbHeight, null); // save thumbnail image to outFilename BufferedOutputStream out = newBufferedOutputStream(newFileOutputStream(outFilename)); JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out); JPEGEncodeParam param = 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
并下面这个 JAR 文件：json-rpc-1.0.jar (75 kb)/http://t.cn/Rz0bhUA
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importorg.json.JSONObject; ... ... JSONObject json = newJSONObject(); json.put("city", "Mumbai"); json.put("country", "India"); ... String output = json.toString(); ... |
10. 使用 iText JAR 生成 PDF
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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{ OutputStream file = newFileOutputStream(newFile("C:\\Test.pdf")); Document document = newDocument(); PdfWriter.getInstance(document, file); document.open(); document.add(newParagraph("Hello Kiran")); document.add(newParagraph(newDate().toString())); document.close(); file.close(); } catch(Exception e) { e.printStackTrace(); } } } |
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