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20个常用的java开发块
- //1. 字符串有整型的相互转换
- 002 String a = String.valueOf(2); //integer to numeric string
- 003 int i = Integer.parseInt(a); //numeric string to an int
- 004
- 005 //2. 向文件末尾添加内容
- 006 BufferedWriter out = null;
- 007 try {
- 008 out = new BufferedWriter(new FileWriter(”filename”, true));
- 009 out.write(”aString”);
- 010 } catch (IOException e) {
- 011 // error processing code
- 012
- 013 } finally {
- 014 if (out != null) {
- 015 out.close();
- 016 }
- 017
- 018 }
- 019
- 020 //3. 得到当前方法的名字
- 021 String methodName = Thread.currentThread().getStackTrace()[1].getMethodName();
-
- 022
- 023 //4. 转字符串到日期
- 024 java.util.Date = java.text.DateFormat.getDateInstance().parse(date String);
-
- 025 //或者是：
- 026 SimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy" );
- 027 Date date = format.parse( myString );
- 028
- 029 //5. 使用JDBC链接Oracle
- 030 public class OracleJdbcTest
- 031 {
- 032 String driverClass = "oracle.jdbc.driver.OracleDriver";
- 033
- 034 Connection con;
- 035
- 036 public void init(FileInputStream fs) throws ClassNotFoundException, SQLException, FileNotFoundException, IOException
-
- 037 {
- 038 Properties props = new Properties();
- 039 props.load(fs);
- 040 String url = props.getProperty("db.url");
- 041 String userName = props.getProperty("db.user");
- 042 String password = props.getProperty("db.password");
- 043 Class.forName(driverClass);
- 044
- 045 con=DriverManager.getConnection(url, userName, password);
- 046 }
- 047
- 048 public void fetch() throws SQLException, IOException
- 049 {
- 050 PreparedStatement ps = con.prepareStatement("select SYSDATE from dual");
- 051 ResultSet rs = ps.executeQuery();
- 052
- 053 while (rs.next())
- 054 {
- 055 // do the thing you do
- 056 }
- 057 rs.close();
- 058 ps.close();
- 059 }
- 060
- 061 public static void main(String[] args)
- 062 {
- 063 OracleJdbcTest test = new OracleJdbcTest();
- 064 test.init();
- 065 test.fetch();
- 066 }
- 067 }
- 068
- 069 6. 把 Java util.Date 转成 sql.Date
- 070 java.util.Date utilDate = new java.util.Date();
- 071 java.sql.Date sqlDate = new java.sql.Date(utilDate.getTime());
- 072
- 073 //7. 使用NIO进行快速的文件拷贝
- 074 public static void fileCopy( File in, File out )
- 075 throws IOException
- 076 {
- 077 FileChannel inChannel = new FileInputStream( in ).getChannel();
- 078 FileChannel outChannel = new FileOutputStream( out ).getChannel();
- 079 try
- 080 {
- 081 // inChannel.transferTo(0, inChannel.size(), outChannel); // original -- apparently has trouble copying large files on Windows
-
- 082
- 083 // magic number for Windows, 64Mb - 32Kb)
- 084 int maxCount = (64 * 1024 * 1024) - (32 * 1024);
- 085 long size = inChannel.size();
- 086 long position = 0;
- 087 while ( position < size )
- 088 {
- 089 position += inChannel.transferTo( position, maxCount, outChannel );
- 090 }
- 091 }
- 092 finally
- 093 {
- 094 if ( inChannel != null )
- 095 {
- 096 inChannel.close();
- 097 }
- 098 if ( outChannel != null )
- 099 {
- 100 outChannel.close();
- 101 }
- 102 }
- 103 }
- 104
- 105 //8. 创建图片的缩略图
- 106 private void createThumbnail(String filename, int thumbWidth, int thumbHeight, int quality, String outFilename)
-
- 107 throws InterruptedException, FileNotFoundException, IOException
- 108 {
- 109 // load image from filename
- 110 Image image = Toolkit.getDefaultToolkit().getImage(filename);
- 111 MediaTracker mediaTracker = new MediaTracker(new Container());
- 112 mediaTracker.addImage(image, 0);
- 113 mediaTracker.waitForID(0);
- 114 // use this to test for errors at this point: System.out.println(mediaTracker.isErrorAny());
-
- 115
- 116 // determine thumbnail size from WIDTH and HEIGHT
- 117 double thumbRatio = (double)thumbWidth / (double)thumbHeight;
- 118 int imageWidth = image.getWidth(null);
- 119 int imageHeight = image.getHeight(null);
- 120 double imageRatio = (double)imageWidth / (double)imageHeight;
- 121 if (thumbRatio < imageRatio) {
- 122 thumbHeight = (int)(thumbWidth / imageRatio);
- 123 } else {
- 124 thumbWidth = (int)(thumbHeight * imageRatio);
- 125 }
- 126
- 127 // draw original image to thumbnail image object and
- 128 // scale it to the new size on-the-fly
- 129 BufferedImage thumbImage = new BufferedImage(thumbWidth, thumbHeight, BufferedImage.TYPE_INT_RGB);
-
- 130 Graphics2D graphics2D = thumbImage.createGraphics();
- 131 graphics2D.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);
-
- 132 graphics2D.drawImage(image, 0, 0, thumbWidth, thumbHeight, null);
- 133
- 134 // save thumbnail image to outFilename
- 135 BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream(outFilename));
-
- 136 JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
- 137 JPEGEncodeParam param = encoder.getDefaultJPEGEncodeParam(thumbImage);
- 138 quality = Math.max(0, Math.min(quality, 100));
- 139 param.setQuality((float)quality / 100.0f, false);
- 140 encoder.setJPEGEncodeParam(param);
- 141 encoder.encode(thumbImage);
- 142 out.close();
- 143 }
- 144
- 145 //9. 创建 JSON 格式的数据
- 146 import org.json.JSONObject;
- 147 ...
- 148 ...
- 149 JSONObject json = new JSONObject();
- 150 json.put("city", "Mumbai");
- 151 json.put("country", "India");
- 152 ...
- 153 String output = json.toString();
- 154 ...
- 155
- 156 //10. 使用iText JAR生成PDF
- 157 import java.io.File;
- 158 import java.io.FileOutputStream;
- 159 import java.io.OutputStream;
- 160 import java.util.Date;
- 161
- 162 import com.lowagie.text.Document;
- 163 import com.lowagie.text.Paragraph;
- 164 import com.lowagie.text.pdf.PdfWriter;
- 165
- 166 public class GeneratePDF {
- 167
- 168 public static void main(String[] args) {
- 169 try {
- 170 OutputStream file = new FileOutputStream(new File("C:\\Test.pdf"));
- 171
- 172 Document document = new Document();
- 173 PdfWriter.getInstance(document, file);
- 174 document.open();
- 175 document.add(new Paragraph("Hello Kiran"));
- 176 document.add(new Paragraph(new Date().toString()));
- 177
- 178 document.close();
- 179 file.close();
- 180
- 181 } catch (Exception e) {
- 182
- 183 e.printStackTrace();
- 184 }
- 185 }
- 186 }
- 187
- 188 //11. HTTP 代理设置
- 189 System.getProperties().put("http.proxyHost", "someProxyURL");
- 190 System.getProperties().put("http.proxyPort", "someProxyPort");
- 191 System.getProperties().put("http.proxyUser", "someUserName");
- 192 System.getProperties().put("http.proxyPassword", "somePassword");
- 193
- 194 //12. 单实例Singleton 示例
- 195 public class SimpleSingleton {
- 196 private static SimpleSingleton singleInstance = new SimpleSingleton();
- 197
- 198 //Marking default constructor private
- 199 //to avoid direct instantiation.
- 200 private SimpleSingleton() {
- 201 }
- 202
- 203 //Get instance for class SimpleSingleton
- 204 public static SimpleSingleton getInstance() {
- 205
- 206 return singleInstance;
- 207 }
- 208 }
- 209
- 210 //另一种实现
- 211
- 212 public enum SimpleSingleton {
- 213 INSTANCE;
- 214 public void doSomething() {
- 215 }
- 216 }
- 217
- 218 //Call the method from Singleton:
- 219 SimpleSingleton.INSTANCE.doSomething();
- 220
- 221 //13. 抓屏程序
- 222 import java.awt.Dimension;
- 223 import java.awt.Rectangle;
- 224 import java.awt.Robot;
- 225 import java.awt.Toolkit;
- 226 import java.awt.image.BufferedImage;
- 227 import javax.imageio.ImageIO;
- 228 import java.io.File;
- 229
- 230 ...
- 231 public void captureScreen(String fileName) throws Exception {
- 232
- 233 Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
- 234 Rectangle screenRectangle = new Rectangle(screenSize);
- 235 Robot robot = new Robot();
- 236 BufferedImage image = robot.createScreenCapture(screenRectangle);
- 237 ImageIO.write(image, "png", new File(fileName));
- 238
- 239 }
- 240 //14. 列出文件和目录
- 241 File dir = new File("directoryName");
- 242 String[] children = dir.list();
- 243 if (children == null) {
- 244 // Either dir does not exist or is not a directory
- 245 } else {
- 246 for (int i=0; i < children.length; i++) {
- 247 // Get filename of file or directory
- 248 String filename = children[i];
- 249 }
- 250 }
- 251
- 252 // It is also possible to filter the list of returned files.
- 253 // This example does not return any files that start with `.’.
- 254 FilenameFilter filter = new FilenameFilter() {
- 255 public boolean accept(File dir, String name) {
- 256 return !name.startsWith(".");
- 257 }
- 258 };
- 259 children = dir.list(filter);
- 260
- 261 // The list of files can also be retrieved as File objects
- 262 File[] files = dir.listFiles();
- 263
- 264 // This filter only returns directories
- 265 FileFilter fileFilter = new FileFilter() {
- 266 public boolean accept(File file) {
- 267 return file.isDirectory();
- 268 }
- 269 };
- 270 files = dir.listFiles(fileFilter);
- 271
- 272 //15. 创建ZIP和JAR文件
- 273
- 274 import java.util.zip.*;
- 275 import java.io.*;
- 276
- 277 public class ZipIt {
- 278 public static void main(String args[]) throws IOException {
- 279 if (args.length < 2) {
- 280 System.err.println("usage: java ZipIt Zip.zip file1 file2 file3");
- 281 System.exit(-1);
- 282 }
- 283 File zipFile = new File(args[0]);
- 284 if (zipFile.exists()) {
- 285 System.err.println("Zip file already exists, please try another");
- 286 System.exit(-2);
- 287 }
- 288 FileOutputStream fos = new FileOutputStream(zipFile);
- 289 ZipOutputStream zos = new ZipOutputStream(fos);
- 290 int bytesRead;
- 291 byte[] buffer = new byte[1024];
- 292 CRC32 crc = new CRC32();
- 293 for (int i=1, n=args.length; i < n; i++) {
- 294 String name = args[i];
- 295 File file = new File(name);
- 296 if (!file.exists()) {
- 297 System.err.println("Skipping: " + name);
- 298 continue;
- 299 }
- 300 BufferedInputStream bis = new BufferedInputStream(
- 301 new FileInputStream(file));
- 302 crc.reset();
- 303 while ((bytesRead = bis.read(buffer)) != -1) {
- 304 crc.update(buffer, 0, bytesRead);
- 305 }
- 306 bis.close();
- 307 // Reset to beginning of input stream
- 308 bis = new BufferedInputStream(
- 309 new FileInputStream(file));
- 310 ZipEntry entry = new ZipEntry(name);
- 311 entry.setMethod(ZipEntry.STORED);
- 312 entry.setCompressedSize(file.length());
- 313 entry.setSize(file.length());
- 314 entry.setCrc(crc.getValue());
- 315 zos.putNextEntry(entry);
- 316 while ((bytesRead = bis.read(buffer)) != -1) {
- 317 zos.write(buffer, 0, bytesRead);
- 318 }
- 319 bis.close();
- 320 }
- 321 zos.close();
- 322 }
- 323 }
- 324
- 325 //16. 解析/读取XML 文件
- 326 XML文件
- 327 <?xml version="1.0"?>
- 328 <students>
- 329 <student>
- 330 <name>John</name>
- 331 <grade>B</grade>
- 332 <age>12</age>
- 333 </student>
- 334 <student>
- 335 <name>Mary</name>
- 336 <grade>A</grade>
- 337 <age>11</age>
- 338 </student>
- 339 <student>
- 340 <name>Simon</name>
- 341 <grade>A</grade>
- 342 <age>18</age>
- 343 </student>
- 344 </students>
- 345
- 346 //Java代码
- 347 package net.viralpatel.java.xmlparser;
- 348
- 349 import java.io.File;
- 350 import javax.xml.parsers.DocumentBuilder;
- 351 import javax.xml.parsers.DocumentBuilderFactory;
- 352
- 353 import org.w3c.dom.Document;
- 354 import org.w3c.dom.Element;
- 355 import org.w3c.dom.Node;
- 356 import org.w3c.dom.NodeList;
- 357
- 358 public class XMLParser {
- 359
- 360 public void getAllUserNames(String fileName) {
- 361 try {
- 362 DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
- 363 DocumentBuilder db = dbf.newDocumentBuilder();
- 364 File file = new File(fileName);
- 365 if (file.exists()) {
- 366 Document doc = db.parse(file);
- 367 Element docEle = doc.getDocumentElement();
- 368
- 369 // Print root element of the document
- 370 System.out.println("Root element of the document: "
- 371 + docEle.getNodeName());
- 372
- 373 NodeList studentList = docEle.getElementsByTagName("student");
- 374
- 375 // Print total student elements in document
- 376 System.out
- 377 .println("Total students: " + studentList.getLength());
- 378
- 379 if (studentList != null && studentList.getLength() > 0) {
- 380 for (int i = 0; i < studentList.getLength(); i++) {
- 381
- 382 Node node = studentList.item(i);
- 383
- 384 if (node.getNodeType() == Node.ELEMENT_NODE) {
- 385
- 386 System.out
- 387 .println("=====================");
- 388
- 389 Element e = (Element) node;
- 390 NodeList nodeList = e.getElementsByTagName("name");
- 391 System.out.println("Name: "
- 392 + nodeList.item(0).getChildNodes().item(0)
- 393 .getNodeValue());
- 394
- 395 nodeList = e.getElementsByTagName("grade");
- 396 System.out.println("Grade: "
- 397 + nodeList.item(0).getChildNodes().item(0)
- 398 .getNodeValue());
- 399
- 400 nodeList = e.getElementsByTagName("age");
- 401 System.out.println("Age: "
- 402 + nodeList.item(0).getChildNodes().item(0)
- 403 .getNodeValue());
- 404 }
- 405 }
- 406 } else {
- 407 System.exit(1);
- 408 }
- 409 }
- 410 } catch (Exception e) {
- 411 System.out.println(e);
- 412 }
- 413 }
- 414 public static void main(String[] args) {
- 415
- 416 XMLParser parser = new XMLParser();
- 417 parser.getAllUserNames("c:\\test.xml");
- 418 }
- 419 }
- 420 //17. 把 Array 转换成 Map
- 421 import java.util.Map;
- 422 import org.apache.commons.lang.ArrayUtils;
- 423
- 424 public class Main {
- 425
- 426 public static void main(String[] args) {
- 427 String[ ][ ] countries = { { "United States", "New York" }, { "United Kingdom", "London" },
-
- 428 { "Netherland", "Amsterdam" }, { "Japan", "Tokyo" }, { "France", "Paris" } };
-
- 429
- 430 Map countryCapitals = ArrayUtils.toMap(countries);
- 431
- 432 System.out.println("Capital of Japan is " + countryCapitals.get("Japan"));
-
- 433 System.out.println("Capital of France is " + countryCapitals.get("France"));
-
- 434 }
- 435 }
- 436
- 437 //18. 发送邮件
- 438 import javax.mail.*;
- 439 import javax.mail.internet.*;
- 440 import java.util.*;
- 441
- 442 public void postMail( String recipients[ ], String subject, String message , String from) throws MessagingException
-
- 443 {
- 444 boolean debug = false;
- 445
- 446 //Set the host smtp address
- 447 Properties props = new Properties();
- 448 props.put("mail.smtp.host", "smtp.example.com");
- 449
- 450 // create some properties and get the default Session
- 451 Session session = Session.getDefaultInstance(props, null);
- 452 session.setDebug(debug);
- 453
- 454 // create a message
- 455 Message msg = new MimeMessage(session);
- 456
- 457 // set the from and to address
- 458 InternetAddress addressFrom = new InternetAddress(from);
- 459 msg.setFrom(addressFrom);
- 460
- 461 InternetAddress[] addressTo = new InternetAddress[recipients.length];
- 462 for (int i = 0; i < recipients.length; i++)
- 463 {
- 464 addressTo[i] = new InternetAddress(recipients[i]);
- 465 }
- 466 msg.setRecipients(Message.RecipientType.TO, addressTo);
- 467
- 468 // Optional : You can also set your custom headers in the Email if you Want
-
- 469 msg.addHeader("MyHeaderName", "myHeaderValue");
- 470
- 471 // Setting the Subject and Content Type
- 472 msg.setSubject(subject);
- 473 msg.setContent(message, "text/plain");
- 474 Transport.send(msg);
- 475 }
- 476
- 477 //19. 发送代数据的HTTP 请求
- 478 import java.io.BufferedReader;
- 479 import java.io.InputStreamReader;
- 480 import java.net.URL;
- 481
- 482 public class Main {
- 483 public static void main(String[] args) {
- 484 try {
- 485 URL my_url = new URL("http://cocre.com/");
- 486 BufferedReader br = new BufferedReader(new InputStreamReader(my_url.openStream()));
-
- 487 String strTemp = "";
- 488 while(null != (strTemp = br.readLine())){
- 489 System.out.println(strTemp);
- 490 }
- 491 } catch (Exception ex) {
- 492 ex.printStackTrace();
- 493 }
- 494 }
- 495 }
- 496
- 497 //20. 改变数组的大小
- 498 /**
- 499 * Reallocates an array with a new size, and copies the contents
- 500 * of the old array to the new array.
- 501 * @param oldArray the old array, to be reallocated.
- 502 * @param newSize the new array size.
- 503 * @return A new array with the same contents.
- 504 */
- 505 private static Object resizeArray (Object oldArray, int newSize) {
- 506 int oldSize = java.lang.reflect.Array.getLength(oldArray);
- 507 Class elementType = oldArray.getClass().getComponentType();
- 508 Object newArray = java.lang.reflect.Array.newInstance(
- 509 elementType,newSize);
- 510 int preserveLength = Math.min(oldSize,newSize);
- 511 if (preserveLength > 0)
- 512 System.arraycopy (oldArray,0,newArray,0,preserveLength);
- 513 return newArray;
- 514 }
- 515
- 516 // Test routine for resizeArray().
- 517 public static void main (String[] args) {
- 518 int[] a = {1,2,3};
- 519 a = (int[])resizeArray(a,5);
- 520 a[3] = 4;
- 521 a[4] = 5;
- 522 for (int i=0; i<a.length; i++)
- 523 System.out.println (a[i]);
- 524 }
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发表于 2012-03-15 20:57
