20个常用的Java程序块

001 	//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 	}