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().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 {
032String driverClass = "oracle.jdbc.driver.OracleDriver";
033
034Connection con;
035
036public void init(FileInputStream fs) throws ClassNotFoundException, SQLException, FileNotFoundException, IOException
037{
038Properties props = new Properties();
039props.load(fs);
040String url = props.getProperty("db.url");
041String userName = props.getProperty("db.user");
042String password = props.getProperty("db.password");
043Class.forName(driverClass);
044
045con=DriverManager.getConnection(url, userName, password);
046}
047
048public void fetch() throws SQLException, IOException
049{
050PreparedStatement ps = con.prepareStatement("select SYSDATE from dual");
051ResultSet rs = ps.executeQuery();
052
053while (rs.next())
054{
055// do the thing you do
056}
057rs.close();
058ps.close();
059}
060
061public static void main(String[] args)
062{
063OracleJdbcTest test = new OracleJdbcTest();
064test.init();
065test.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
074public static void fileCopy( File in, File out )
075throws IOException
076{
077FileChannel inChannel = new FileInputStream( in ).getChannel();
078FileChannel outChannel = new FileOutputStream( out ).getChannel();
079try
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)
084int maxCount = (64 * 1024 * 1024) - (32 * 1024);
085long size = inChannel.size();
086long position = 0;
087while ( position < size )
088{
089position += inChannel.transferTo( position, maxCount, outChannel );
090}
091}
092finally
093{
094if ( inChannel != null )
095{
096inChannel.close();
097}
098if ( outChannel != null )
099{
100outChannel.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)
107throws InterruptedException, FileNotFoundException, IOException
108{
109// load image from filename
110Image image = Toolkit.getDefaultToolkit().getImage(filename);
111MediaTracker mediaTracker = new MediaTracker(new Container());
112mediaTracker.addImage(image, 0);
113mediaTracker.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
117double thumbRatio = (double)thumbWidth / (double)thumbHeight;
118int imageWidth = image.getWidth(null);
119int imageHeight = image.getHeight(null);
120double imageRatio = (double)imageWidth / (double)imageHeight;
121if (thumbRatio < imageRatio) {
122thumbHeight = (int)(thumbWidth / imageRatio);
123} else {
124thumbWidth = (int)(thumbHeight * imageRatio);
125}
126
127// draw original image to thumbnail image object and
128// scale it to the new size on-the-fly
129BufferedImage thumbImage = new BufferedImage(thumbWidth, thumbHeight, BufferedImage.TYPE_INT_RGB);
130Graphics2D graphics2D = thumbImage.createGraphics();
131graphics2D.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);
132graphics2D.drawImage(image, 0, 0, thumbWidth, thumbHeight, null);
133
134// save thumbnail image to outFilename
135BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream(outFilename));
136JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
137JPEGEncodeParam param = encoder.getDefaultJPEGEncodeParam(thumbImage);
138quality = Math.max(0, Math.min(quality, 100));
139param.setQuality((float)quality / 100.0f, false);
140encoder.setJPEGEncodeParam(param);
141encoder.encode(thumbImage);
142out.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
168public static void main(String[] args) {
169try {
170OutputStream file = new FileOutputStream(new File("C:\\Test.pdf"));
171
172Document document = new Document();
173PdfWriter.getInstance(document, file);
174document.open();
175document.add(new Paragraph("Hello Kiran"));
176document.add(new Paragraph(new Date().toString()));
177
178document.close();
179file.close();
180
181} catch (Exception e) {
182
183e.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 {
196private static SimpleSingleton singleInstance = new SimpleSingleton();
197
198//Marking default constructor private
199//to avoid direct instantiation.
200private SimpleSingleton() {
201}
202
203//Get instance for class SimpleSingleton
204public static SimpleSingleton getInstance() {
205
206return singleInstance;
207}
208 }
209
210 //另一种实现
211
212 public enum SimpleSingleton {
213INSTANCE;
214public 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
233Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
234Rectangle screenRectangle = new Rectangle(screenSize);
235Robot robot = new Robot();
236BufferedImage image = robot.createScreenCapture(screenRectangle);
237ImageIO.write(image, "png", new File(fileName));
238
239 }
240 //14. 列出文件和目录
241 File dir = new File("directoryName");
242String[] children = dir.list();
243if (children == null) {
244// Either dir does not exist or is not a directory
245} else {
246for (int i=0; i < children.length; i++) {
247// Get filename of file or directory
248String filename = children;
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 `.’.
254FilenameFilter filter = new FilenameFilter() {
255public boolean accept(File dir, String name) {
256return !name.startsWith(".");
257}
258};
259children = dir.list(filter);
260
261// The list of files can also be retrieved as File objects
262File[] files = dir.listFiles();
263
264// This filter only returns directories
265FileFilter fileFilter = new FileFilter() {
266public boolean accept(File file) {
267return file.isDirectory();
268}
269};
270files = 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 {
278public static void main(String args[]) throws IOException {
279if (args.length < 2) {
280System.err.println("usage: java ZipIt Zip.zip file1 file2 file3");
281System.exit(-1);
282}
283File zipFile = new File(args);
284if (zipFile.exists()) {
285System.err.println("Zip file already exists, please try another");
286System.exit(-2);
287}
288FileOutputStream fos = new FileOutputStream(zipFile);
289ZipOutputStream zos = new ZipOutputStream(fos);
290int bytesRead;
291byte[] buffer = new byte;
292CRC32 crc = new CRC32();
293for (int i=1, n=args.length; i < n; i++) {
294String name = args;
295File file = new File(name);
296if (!file.exists()) {
297System.err.println("Skipping: " + name);
298continue;
299}
300BufferedInputStream bis = new BufferedInputStream(
301new FileInputStream(file));
302crc.reset();
303while ((bytesRead = bis.read(buffer)) != -1) {
304crc.update(buffer, 0, bytesRead);
305}
306bis.close();
307// Reset to beginning of input stream
308bis = new BufferedInputStream(
309new FileInputStream(file));
310ZipEntry entry = new ZipEntry(name);
311entry.setMethod(ZipEntry.STORED);
312entry.setCompressedSize(file.length());
313entry.setSize(file.length());
314entry.setCrc(crc.getValue());
315zos.putNextEntry(entry);
316while ((bytesRead = bis.read(buffer)) != -1) {
317zos.write(buffer, 0, bytesRead);
318}
319bis.close();
320}
321zos.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
360public void getAllUserNames(String fileName) {
361try {
362DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
363DocumentBuilder db = dbf.newDocumentBuilder();
364File file = new File(fileName);
365if (file.exists()) {
366Document doc = db.parse(file);
367Element docEle = doc.getDocumentElement();
368
369// Print root element of the document
370System.out.println("Root element of the document: "
371+ docEle.getNodeName());
372
373NodeList studentList = docEle.getElementsByTagName("student");
374
375// Print total student elements in document
376System.out
377.println("Total students: " + studentList.getLength());
378
379if (studentList != null && studentList.getLength() > 0) {
380for (int i = 0; i < studentList.getLength(); i++) {
381
382Node node = studentList.item(i);
383
384if (node.getNodeType() == Node.ELEMENT_NODE) {
385
386System.out
387.println("=====================");
388
389Element e = (Element) node;
390NodeList nodeList = e.getElementsByTagName("name");
391System.out.println("Name: "
392+ nodeList.item(0).getChildNodes().item(0)
393.getNodeValue());
394
395nodeList = e.getElementsByTagName("grade");
396System.out.println("Grade: "
397+ nodeList.item(0).getChildNodes().item(0)
398.getNodeValue());
399
400nodeList = e.getElementsByTagName("age");
401System.out.println("Age: "
402+ nodeList.item(0).getChildNodes().item(0)
403.getNodeValue());
404}
405}
406} else {
407System.exit(1);
408}
409}
410} catch (Exception e) {
411System.out.println(e);
412}
413}
414public static void main(String[] args) {
415
416XMLParser parser = new XMLParser();
417parser.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
426public static void main(String[] args) {
427String[ ][ ] countries = { { "United States", "New York" }, { "United Kingdom", "London" },
428{ "Netherland", "Amsterdam" }, { "Japan", "Tokyo" }, { "France", "Paris" } };
429
430Map countryCapitals = ArrayUtils.toMap(countries);
431
432System.out.println("Capital of Japan is " + countryCapitals.get("Japan"));
433System.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 {
444boolean debug = false;
445
446//Set the host smtp address
447Properties props = new Properties();
448props.put("mail.smtp.host", "smtp.example.com");
449
450// create some properties and get the default Session
451Session session = Session.getDefaultInstance(props, null);
452session.setDebug(debug);
453
454// create a message
455Message msg = new MimeMessage(session);
456
457// set the from and to address
458InternetAddress addressFrom = new InternetAddress(from);
459msg.setFrom(addressFrom);
460
461InternetAddress[] addressTo = new InternetAddress;
462for (int i = 0; i < recipients.length; i++)
463{
464addressTo = new InternetAddress(recipients);
465}
466msg.setRecipients(Message.RecipientType.TO, addressTo);
467
468// Optional : You can also set your custom headers in the Email if you Want
469msg.addHeader("MyHeaderName", "myHeaderValue");
470
471// Setting the Subject and Content Type
472msg.setSubject(subject);
473msg.setContent(message, "text/plain");
474Transport.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 {
483public static void main(String[] args) {
484try {
485URL my_url = new URL("http://cocre.com/");
486BufferedReader br = new BufferedReader(new InputStreamReader(my_url.openStream()));
487String strTemp = "";
488while(null != (strTemp = br.readLine())){
489System.out.println(strTemp);
490}
491} catch (Exception ex) {
492ex.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) {
506int oldSize = java.lang.reflect.Array.getLength(oldArray);
507Class elementType = oldArray.getClass().getComponentType();
508Object newArray = java.lang.reflect.Array.newInstance(
509elementType,newSize);
510int preserveLength = Math.min(oldSize,newSize);
511if (preserveLength > 0)
512System.arraycopy (oldArray,0,newArray,0,preserveLength);
513return newArray;
514 }
515
516 // Test routine for resizeArray().
517 public static void main (String[] args) {
518int[] a = {1,2,3};
519a = (int[])resizeArray(a,5);
520a = 4;
521a = 5;
522for (int i=0; i<a.length; i++)
523System.out.println (a);
524 }
页:
[1]