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多個有用的程序

1. 字符串有整型的相互轉換

1

`2`	`String a = String.valueOf(2);` `//integer to numeric string`

`3`	`int` `i = Integer.parseInt(a);` `//numeric string to an int`

2. 向文件末尾添加內容

01

`02`	`BufferedWriter out =` `null;`

03 try {

`04`	`out =` `new` `BufferedWriter(new` `FileWriter(”filename”,` `true));`

`05`	`out.write(”aString”);`

`06`	`}` `catch` `(IOException e) {`

`07`	`// error processing code`

`08`	`}` `finally` `{`

`09`	`if` `(out !=` `null) {`

`10`	`out.close();`

11 }

12 }

3. 得到當前方法的名字

`1`	`String methodName = Thread.currentThread().getStackTrace()[1].getMethodName();`

4. 轉字符串到日期

1

`2`	`java.util.Date = java.text.DateFormat.getDateInstance().parse(date String);`

或者是：

1

`2`	`SimpleDateFormat format =` `new` `SimpleDateFormat(` `"dd.MM.yyyy"` `);`

`3`	`Date date = format.parse( myString );`

5. 使用JDBC鏈接Oracle

`01`	`public` `class` `OracleJdbcTest`

02 {

`03`	`String driverClass =` `"oracle.jdbc.driver.OracleDriver";`

04

`05`	`Connection con;`

06

`07`	`public` `void` `init(FileInputStream fs)` `throws` `ClassNotFoundException, SQLException, FileNotFoundException, IOException`

08 {

`09`	`Properties props =` `new` `Properties();`

`10`	`props.load(fs);`

`11`	`String url = props.getProperty("db.url");`

`12`	`String userName = props.getProperty("db.user");`

`13`	`String password = props.getProperty("db.password");`

`14`	`Class.forName(driverClass);`

15

`16`	`con=DriverManager.getConnection(url, userName, password);`

17 }

18

`19`	`public` `void` `fetch()` `throws` `SQLException, IOException`

20 {

`21`	`PreparedStatement ps = con.prepareStatement("select SYSDATE from dual");`

`22`	`ResultSet rs = ps.executeQuery();`

23

`24`	`while` `(rs.next())`

25 {

`26`	`// do the thing you do`

27 }

`28`	`rs.close();`

`29`	`ps.close();`

30 }

31

`32`	`public` `static` `void` `main(String[] args)`

33 {

`34`	`OracleJdbcTest test =` `new` `OracleJdbcTest();`

`35`	`test.init();`

`36`	`test.fetch();`

37 }

38 }

6. 把 Java util.Date 轉成 sql.Date

`1`	`java.util.Date utilDate =` `new` `java.util.Date();`

`2`	`java.sql.Date sqlDate =` `new` `java.sql.Date(utilDate.getTime());`

7. 使用NIO進行快速的文件拷貝

`01`	`public` `static` `void` `fileCopy( File in, File out )`

`02`	`throws` `IOException`

03 {

`04`	`FileChannel inChannel =` `new` `FileInputStream( in ).getChannel();`

`05`	`FileChannel outChannel =` `new` `FileOutputStream( out ).getChannel();`

06 try

07 {

`08`	`// inChannel.transferTo(0, inChannel.size(), outChannel); // original -- apparently has trouble copying large files on Windows`

09

`10`	`// magic number for Windows, 64Mb - 32Kb)`

`11`	`int` `maxCount = (64` `` `1024` `` `1024) - (32` `*` `1024);`

`12`	`long` `size = inChannel.size();`

`13`	`long` `position =` `0;`

`14`	`while` `( position < size )`

15 {

`16`	`position += inChannel.transferTo( position, maxCount, outChannel );`

17 }

18 }

19 finally

20 {

`21`	`if` `( inChannel !=` `null` `)`

22 {

`23`	`inChannel.close();`

24 }

`25`	`if` `( outChannel !=` `null` `)`

26 {

`27`	`outChannel.close();`

28 }

29 }

30 }

8. 創建圖片的縮略圖

`01`	`private` `void` `createThumbnail(String filename,` `int` `thumbWidth,` `int` `thumbHeight,` `int` `quality, String outFilename)`

`02`	`throws` `InterruptedException, FileNotFoundException, IOException`

03 {

`04`	`// load image from filename`

`05`	`Image image = Toolkit.getDefaultToolkit().getImage(filename);`

`06`	`MediaTracker mediaTracker =` `new` `MediaTracker(new` `Container());`

`07`	`mediaTracker.addImage(image,` `0);`

`08`	`mediaTracker.waitForID(0);`

`09`	`// use this to test for errors at this point: System.out.println(mediaTracker.isErrorAny());`

10

`11`	`// determine thumbnail size from WIDTH and HEIGHT`

`12`	`double` `thumbRatio = (double)thumbWidth / (double)thumbHeight;`

`13`	`int` `imageWidth = image.getWidth(null);`

`14`	`int` `imageHeight = image.getHeight(null);`

`15`	`double` `imageRatio = (double)imageWidth / (double)imageHeight;`

`16`	`if` `(thumbRatio < imageRatio) {`

`17`	`thumbHeight = (int)(thumbWidth / imageRatio);`

`18`	`}` `else` `{`

`19`	`thumbWidth = (int)(thumbHeight * imageRatio);`

20 }

21

`22`	`// draw original image to thumbnail image object and`

`23`	`// scale it to the new size on-the-fly`

`24`	`BufferedImage thumbImage =` `new` `BufferedImage(thumbWidth, thumbHeight, BufferedImage.TYPE_INT_RGB);`

`25`	`Graphics2D graphics2D = thumbImage.createGraphics();`

`26`	`graphics2D.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);`

`27`	`graphics2D.drawImage(image,` `0,` `0, thumbWidth, thumbHeight,` `null);`

28

`29`	`// save thumbnail image to outFilename`

`30`	`BufferedOutputStream out =` `new` `BufferedOutputStream(new` `FileOutputStream(outFilename));`

`31`	`JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);`

`32`	`JPEGEncodeParam param = encoder.getDefaultJPEGEncodeParam(thumbImage);`

`33`	`quality = Math.max(0, Math.min(quality,` `100));`

`34`	`param.setQuality((float)quality /` `100.0f,` `false);`

`35`	`encoder.setJPEGEncodeParam(param);`

`36`	`encoder.encode(thumbImage);`

`37`	`out.close();`

38 }

9. 創建 JSON 格式的數據

請先閱讀這篇文章了解一些細節，
并下面這個JAR 文件：json-rpc-1.0.jar (75 kb)

`1`	`import` `org.json.JSONObject;`

2 ...

3 ...

`4`	`JSONObject json =` `new` `JSONObject();`

`5`	`json.put("city",` `"Mumbai");`

`6`	`json.put("country",` `"India");`

7 ...

`8`	`String output = json.toString();`

9 ...

10. 使用iText JAR生成PDF

閱讀這篇文章了解更多細節

01

`02`	`import` `java.io.File;`

`03`	`import` `java.io.FileOutputStream;`

`04`	`import` `java.io.OutputStream;`

`05`	`import` `java.util.Date;`

06

`07`	`import` `com.lowagie.text.Document;`

`08`	`import` `com.lowagie.text.Paragraph;`

`09`	`import` `com.lowagie.text.pdf.PdfWriter;`

10

`11`	`public` `class` `GeneratePDF {`

12

`13`	`public` `static` `void` `main(String[] args) {`

14 try {

`15`	`OutputStream file =` `new` `FileOutputStream(new` `File("C:\\Test.pdf"));`

16

`17`	`Document document =` `new` `Document();`

`18`	`PdfWriter.getInstance(document, file);`

`19`	`document.open();`

`20`	`document.add(new` `Paragraph("Hello Kiran"));`

`21`	`document.add(new` `Paragraph(new` `Date().toString()));`

22

`23`	`document.close();`

`24`	`file.close();`

25

`26`	`}` `catch` `(Exception e) {`

27

`28`	`e.printStackTrace();`

29 }

30 }

31 }

11. HTTP 代理設置

閱讀這篇文章了解更多細節。

1

`2`	`System.getProperties().put("http.proxyHost",` `"someProxyURL");`

`3`	`System.getProperties().put("http.proxyPort",` `"someProxyPort");`

`4`	`System.getProperties().put("http.proxyUser",` `"someUserName");`

`5`	`System.getProperties().put("http.proxyPassword",` `"somePassword");`

12. 單實例Singleton 示例

請先閱讀這篇文章了解更多信息

01

`02`	`public` `class` `SimpleSingleton {`

`03`	`private` `static` `SimpleSingleton singleInstance =` `new` `SimpleSingleton();`

04

`05`	`//Marking default constructor private`

`06`	`//to avoid direct instantiation.`

`07`	`private` `SimpleSingleton() {`

08 }

09

`10`	`//Get instance for class SimpleSingleton`

`11`	`public` `static` `SimpleSingleton getInstance() {`

12

`13`	`return` `singleInstance;`

14 }

15 }

另一種實現

`1`	`public` `enum` `SimpleSingleton {`

`2`	`INSTANCE;`

`3`	`public` `void` `doSomething() {`

4 }

5 }

6

`7`	`//Call the method from Singleton:`

`8`	`SimpleSingleton.INSTANCE.doSomething();`

13. 抓屏程序

閱讀這篇文章獲得更多信息。

`01`	`import` `java.awt.Dimension;`

`02`	`import` `java.awt.Rectangle;`

`03`	`import` `java.awt.Robot;`

`04`	`import` `java.awt.Toolkit;`

`05`	`import` `java.awt.image.BufferedImage;`

`06`	`import` `javax.imageio.ImageIO;`

`07`	`import` `java.io.File;`

08

09 ...

10

`11`	`public` `void` `captureScreen(String fileName)` `throws` `Exception {`

12

`13`	`Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();`

`14`	`Rectangle screenRectangle =` `new` `Rectangle(screenSize);`

`15`	`Robot robot =` `new` `Robot();`

`16`	`BufferedImage image = robot.createScreenCapture(screenRectangle);`

`17`	`ImageIO.write(image,` `"png",` `new` `File(fileName));`

18

19 }

20 ...

14. 列出文件和目錄

`01`	`File dir =` `new` `File("directoryName");`

`02`	`String[] children = dir.list();`

`03`	`if` `(children ==` `null) {`

`04`	`// Either dir does not exist or is not a directory`

`05`	`}` `else` `{`

`06`	`for` `(int` `i=0; i < children.length; i++) {`

`07`	`// Get filename of file or directory`

`08`	`String filename = children[i];`

09 }

10 }

11

`12`	`// It is also possible to filter the list of returned files.`

`13`	// This example does not return any files that start with `.'.

`14`	`FilenameFilter filter =` `new` `FilenameFilter() {`

`15`	`public` `boolean` `accept(File dir, String name) {`

`16`	`return` `!name.startsWith(".");`

17 }

18 };

`19`	`children = dir.list(filter);`

20

`21`	`// The list of files can also be retrieved as File objects`

`22`	`File[] files = dir.listFiles();`

23

`24`	`// This filter only returns directories`

`25`	`FileFilter fileFilter =` `new` `FileFilter() {`

`26`	`public` `boolean` `accept(File file) {`

`27`	`return` `file.isDirectory();`

28 }

29 };

`30`	`files = dir.listFiles(fileFilter);`

15. 創建ZIP和JAR文件

01

`02`	`import` `java.util.zip.*;`

`03`	`import` `java.io.*;`

04

`05`	`public` `class` `ZipIt {`

`06`	`public` `static` `void` `main(String args[])` `throws` `IOException {`

`07`	`if` `(args.length <` `2) {`

`08`	`System.err.println("usage: java ZipIt Zip.zip file1 file2 file3");`

`09`	`System.exit(-1);`

10 }

`11`	`File zipFile =` `new` `File(args[0]);`

`12`	`if` `(zipFile.exists()) {`

`13`	`System.err.println("Zip file already exists, please try another");`

`14`	`System.exit(-2);`

15 }

`16`	`FileOutputStream fos =` `new` `FileOutputStream(zipFile);`

`17`	`ZipOutputStream zos =` `new` `ZipOutputStream(fos);`

`18`	`int` `bytesRead;`

`19`	`byte[] buffer =` `new` `byte[1024];`

`20`	`CRC32 crc =` `new` `CRC32();`

`21`	`for` `(int` `i=1, n=args.length; i < n; i++) {`

`22`	`String name = args[i];`

`23`	`File file =` `new` `File(name);`

`24`	`if` `(!file.exists()) {`

`25`	`System.err.println("Skipping: "` `+ name);`

`26`	`continue;`

27 }

`28`	`BufferedInputStream bis =` `new` `BufferedInputStream(`

`29`	`new` `FileInputStream(file));`

`30`	`crc.reset();`

`31`	`while` `((bytesRead = bis.read(buffer)) != -1) {`

`32`	`crc.update(buffer,` `0, bytesRead);`

33 }

`34`	`bis.close();`

`35`	`// Reset to beginning of input stream`

`36`	`bis =` `new` `BufferedInputStream(`

`37`	`new` `FileInputStream(file));`

`38`	`ZipEntry entry =` `new` `ZipEntry(name);`

`39`	`entry.setMethod(ZipEntry.STORED);`

`40`	`entry.setCompressedSize(file.length());`

`41`	`entry.setSize(file.length());`

`42`	`entry.setCrc(crc.getValue());`

`43`	`zos.putNextEntry(entry);`

`44`	`while` `((bytesRead = bis.read(buffer)) != -1) {`

`45`	`zos.write(buffer,` `0, bytesRead);`

46 }

`47`	`bis.close();`

48 }

`49`	`zos.close();`

50 }

51 }

16. 解析/讀取XML 文件

XML文件

`01`	`<?xml` `version="1.0"?>`

`02`	`<students>`

`03`	`<student>`

`04`	`<name>John</name>`

`05`	`<grade>B</grade>`

`06`	`<age>12</age>`

`07`	`</student>`

`08`	`<student>`

`09`	`<name>Mary</name>`

`10`	`<grade>A</grade>`

`11`	`<age>11</age>`

`12`	`</student>`

`13`	`<student>`

`14`	`<name>Simon</name>`

`15`	`<grade>A</grade>`

`16`	`<age>18</age>`

`17`	`</student>`

`18`	`</students>`

Java代碼

01

`02`	`package` `net.viralpatel.java.xmlparser;`

03

`04`	`import` `java.io.File;`

`05`	`import` `javax.xml.parsers.DocumentBuilder;`

`06`	`import` `javax.xml.parsers.DocumentBuilderFactory;`

07

`08`	`import` `org.w3c.dom.Document;`

`09`	`import` `org.w3c.dom.Element;`

`10`	`import` `org.w3c.dom.Node;`

`11`	`import` `org.w3c.dom.NodeList;`

12

`13`	`public` `class` `XMLParser {`

14

`15`	`public` `void` `getAllUserNames(String fileName) {`

16 try {

`17`	`DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();`

`18`	`DocumentBuilder db = dbf.newDocumentBuilder();`

`19`	`File file =` `new` `File(fileName);`

`20`	`if` `(file.exists()) {`

`21`	`Document doc = db.parse(file);`

`22`	`Element docEle = doc.getDocumentElement();`

23

`24`	`// Print root element of the document`

`25`	`System.out.println("Root element of the document: "`

`26`	`+ docEle.getNodeName());`

27

`28`	`NodeList studentList = docEle.getElementsByTagName("student");`

29

`30`	`// Print total student elements in document`

`31`	`System.out`

`32`	`.println("Total students: "` `+ studentList.getLength());`

33

`34`	`if` `(studentList !=` `null` `&& studentList.getLength() >` `0) {`

`35`	`for` `(int` `i =` `0; i < studentList.getLength(); i++) {`

36

`37`	`Node node = studentList.item(i);`

38

`39`	`if` `(node.getNodeType() == Node.ELEMENT_NODE) {`

40

`41`	`System.out`

`42`	`.println("=====================");`

43

`44`	`Element e = (Element) node;`

`45`	`NodeList nodeList = e.getElementsByTagName("name");`

`46`	`System.out.println("Name: "`

`47`	`+ nodeList.item(0).getChildNodes().item(0)`

`48`	`.getNodeValue());`

49

`50`	`nodeList = e.getElementsByTagName("grade");`

`51`	`System.out.println("Grade: "`

`52`	`+ nodeList.item(0).getChildNodes().item(0)`

`53`	`.getNodeValue());`

54

`55`	`nodeList = e.getElementsByTagName("age");`

`56`	`System.out.println("Age: "`

`57`	`+ nodeList.item(0).getChildNodes().item(0)`

`58`	`.getNodeValue());`

59 }

60 }

`61`	`}` `else` `{`

`62`	`System.exit(1);`

63 }

64 }

`65`	`}` `catch` `(Exception e) {`

`66`	`System.out.println(e);`

67 }

68 }

`69`	`public` `static` `void` `main(String[] args) {`

70

`71`	`XMLParser parser =` `new` `XMLParser();`

`72`	`parser.getAllUserNames("c:\\test.xml");`

73 }

74 }

17. 把 Array 轉換成 Map

01

`02`	`import` `java.util.Map;`

`03`	`import` `org.apache.commons.lang.ArrayUtils;`

04

`05`	`public` `class` `Main {`

06

`07`	`public` `static` `void` `main(String[] args) {`

`08`	`String[][] countries = { {` `"United States",` `"New York"` `}, {` `"United Kingdom",` `"London"` `},`

`09`	`{` `"Netherland",` `"Amsterdam"` `}, {` `"Japan",` `"Tokyo"` `}, {` `"France",` `"Paris"` `} };`

10

`11`	`Map countryCapitals = ArrayUtils.toMap(countries);`

12

`13`	`System.out.println("Capital of Japan is "` `+ countryCapitals.get("Japan"));`

`14`	`System.out.println("Capital of France is "` `+ countryCapitals.get("France"));`

15 }

16 }

18. 發送郵件

`01`	`import` `javax.mail.*;`

`02`	`import` `javax.mail.internet.*;`

`03`	`import` `java.util.*;`

04

`05`	`public` `void` `postMail( String recipients[ ], String subject, String message , String from)` `throws` `MessagingException`

06 {

`07`	`boolean` `debug =` `false;`

08

`09`	`//Set the host smtp address`

`10`	`Properties props =` `new` `Properties();`

`11`	`props.put("mail.smtp.host",` `"smtp.example.com");`

12

`13`	`// create some properties and get the default Session`

`14`	`Session session = Session.getDefaultInstance(props,` `null);`

`15`	`session.setDebug(debug);`

16

`17`	`// create a message`

`18`	`Message msg =` `new` `MimeMessage(session);`

19

`20`	`// set the from and to address`

`21`	`InternetAddress addressFrom =` `new` `InternetAddress(from);`

`22`	`msg.setFrom(addressFrom);`

23

`24`	`InternetAddress[] addressTo =` `new` `InternetAddress[recipients.length];`

`25`	`for` `(int` `i =` `0; i < recipients.length; i++)`

26 {

`27`	`addressTo[i] =` `new` `InternetAddress(recipients[i]);`

28 }

`29`	`msg.setRecipients(Message.RecipientType.TO, addressTo);`

30

`31`	`// Optional : You can also set your custom headers in the Email if you Want`

`32`	`msg.addHeader("MyHeaderName",` `"myHeaderValue");`

33

`34`	`// Setting the Subject and Content Type`

`35`	`msg.setSubject(subject);`

`36`	`msg.setContent(message,` `"text/plain");`

`37`	`Transport.send(msg);`

38 }

19. 發送代數據的HTTP 請求

01

`02`	`import` `java.io.BufferedReader;`

`03`	`import` `java.io.InputStreamReader;`

`04`	`import` `java.net.URL;`

05

`06`	`public` `class` `Main {`

`07`	`public` `static` `void` `main(String[] args) {`

08 try {

`09`	`URL my_url =` `new` `URL(");`

`10`	`BufferedReader br =` `new` `BufferedReader(new` `InputStreamReader(my_url.openStream()));`

`11`	`String strTemp =` `"";`

`12`	`while(null` `!= (strTemp = br.readLine())){`

`13`	`System.out.println(strTemp);`

14 }

`15`	`}` `catch` `(Exception ex) {`

`16`	`ex.printStackTrace();`

17 }

18 }

19 }

20. 改變數組的大小

01

02 /**

`03`	`* Reallocates an array with a new size, and copies the contents`

`04`	`* of the old array to the new array.`

`05`	`* @param oldArray the old array, to be reallocated.`

`06`	`* @param newSize the new array size.`

`07`	`* @return A new array with the same contents.`

08 */

`09`	`private` `static` `Object resizeArray (Object oldArray,` `int` `newSize) {`

`10`	`int` `oldSize = java.lang.reflect.Array.getLength(oldArray);`

`11`	`Class elementType = oldArray.getClass().getComponentType();`

`12`	`Object newArray = java.lang.reflect.Array.newInstance(`

`13`	`elementType,newSize);`

`14`	`int` `preserveLength = Math.min(oldSize,newSize);`

`15`	`if` `(preserveLength >` `0)`

`16`	`System.arraycopy (oldArray,0,newArray,0,preserveLength);`

`17`	`return` `newArray;`

18 }

19

`20`	`// Test routine for resizeArray().`

`21`	`public` `static` `void` `main (String[] args) {`

`22`	`int[] a = {1,2,3};`

`23`	`a = (int[])resizeArray(a,5);`

`24`	`a[3] =` `4;`

`25`	`a[4] =` `5;`

`26`	`for` `(int` `i=0; i<a.length; i++)`

`27`	`System.out.println (a[i]);`

28 }

posted on 2013-01-18 15:08 楊軍威閱讀(161) 評論(0) 編輯收藏

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