20个非常有用的Java程序片段

下面是20个非常有用的Java程序片段，希望能对你有用。 1. 字符串有整型的相互转换 Java代码 1. 2.String a = String.valueOf(2); //integer to numeric string 3.int i = Integer.parseInt(a); //numeric string to an int 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 Java代码 1. 2.BufferedWriter out = null; 3.try { 4. out = new BufferedWriter(new FileWriter(”filename”, true)); 5. out.write(”aString”); 6.} catch (IOException e) { 7. // error processing code 8.} finally { 9. if (out != null) { 10. out.close(); 11. } 12.} BufferedWriter out = null; try { out = new BufferedWriter(new FileWriter(”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 Java代码 1.String methodName = Thread.currentThread().getStackTrace()[1].getMethodName(); String methodName = Thread.currentThread().getStackTrace()[1].getMethodName(); 4. 转字符串到日期 Java代码 1. 2.java.util.Date = java.text.DateFormat.getDateInstance().parse(date String); 3.或者是： 4. 5. 6.SimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy" ); 7.Date date = format.parse( myString ); 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 Java代码 1.public class OracleJdbcTest 2.{ 3. String driverClass = "oracle.jdbc.driver.OracleDriver"; 4. 5. Connection con; 6. 7. public void init(FileInputStream fs) throws ClassNotFoundException, SQLException, FileNotFoundException, IOException 8. { 9. 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.} public class OracleJdbcTest { String driverClass = "oracle.jdbc.driver.OracleDriver"; Connection con; public void init(FileInputStream fs) throws ClassNotFoundException, SQLException, FileNotFoundException, IOException { Properties props = new Properties(); 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); } public void fetch() throws SQLException, 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(); } public static void main(String[] args) { OracleJdbcTest test = new OracleJdbcTest(); test.init(); test.fetch(); } } 6. 把 Java util.Date 转成 sql.Date Java代码 1.java.util.Date utilDate = new java.util.Date(); 2.java.sql.Date sqlDate = new java.sql.Date(utilDate.getTime()); java.util.Date utilDate = new java.util.Date(); java.sql.Date sqlDate = new java.sql.Date(utilDate.getTime()); 7. 使用NIO进行快速的文件拷贝 Java代码 1. 2. 3.public static void fileCopy( File in, File out ) 4. throws IOException 5. { 6. FileChannel inChannel = new FileInputStream( in ).getChannel(); 7. FileChannel outChannel = new FileOutputStream( out ).getChannel(); 8. try 9. { 10.// inChannel.transferTo(0, inChannel.size(), outChannel); // original -- apparently has trouble copying large files on Windows 11. 12. // magic number for Windows, 64Mb - 32Kb) 13. int maxCount = (64 * 1024 * 1024) - (32 * 1024); 14. long size = inChannel.size(); 15. long position = 0; 16. while ( position < size ) 17. { 18. position += inChannel.transferTo( position, maxCount, outChannel ); 19. } 20. } 21. finally 22. { 23. if ( inChannel != null ) 24. { 25. inChannel.close(); 26. } 27. if ( outChannel != null ) 28. { 29. outChannel.close(); 30. } 31. } 32. } public static void fileCopy( File in, File out ) throws IOException { FileChannel inChannel = new FileInputStream( in ).getChannel(); FileChannel outChannel = new FileOutputStream( out ).getChannel(); try { // inChannel.transferTo(0, inChannel.size(), outChannel); // original -- apparently has trouble copying large files on Windows // magic number for Windows, 64Mb - 32Kb) int maxCount = (64 * 1024 * 1024) - (32 * 1024); long size = inChannel.size(); long position = 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 Java代码 1.private void createThumbnail(String filename, int thumbWidth, int thumbHeight, int quality, String outFilename) 2. throws InterruptedException, FileNotFoundException, IOException 3. { 4. // load image from filename 5. Image image = Toolkit.getDefaultToolkit().getImage(filename); 6. MediaTracker mediaTracker = new MediaTracker(new Container()); 7. mediaTracker.addImage(image, 0); 8. mediaTracker.waitForID(0); 9. // 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. } private void createThumbnail(String filename, int thumbWidth, int thumbHeight, int quality, String outFilename) throws InterruptedException, FileNotFoundException, IOException { // load image from filename Image image = Toolkit.getDefaultToolkit().getImage(filename); MediaTracker mediaTracker = new MediaTracker(new Container()); 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 double thumbRatio = (double)thumbWidth / (double)thumbHeight; int imageWidth = image.getWidth(null); int imageHeight = image.getHeight(null); double imageRatio = (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 = new BufferedImage(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 = new BufferedOutputStream(new FileOutputStream(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 Java代码 1.请先阅读这篇文章 了解一些细节， 2.并下面这个JAR 文件：json-rpc-1.0.jar (75 kb) 3. 4.import org.json.JSONObject; 5.... 6.... 7.JSONObject json = new JSONObject(); 8.json.put("city", "Mumbai"); 9.json.put("country", "India"); 10.... 11.String output = json.toString(); 12.... 请先阅读这篇文章 了解一些细节， 并下面这个JAR 文件：json-rpc-1.0.jar (75 kb) import org.json.JSONObject; ... ... JSONObject json = new JSONObject(); json.put("city", "Mumbai"); json.put("country", "India"); ... String output = json.toString(); ... 10. 使用iText JAR生成PDF Java代码 1.阅读这篇文章 了解更多细节 2. 3. 4.import java.io.File; 5.import java.io.FileOutputStream; 6.import java.io.OutputStream; 7.import java.util.Date; 8. 9.import com.lowagie.text.Document; 10.import com.lowagie.text.Paragraph; 11.import com.lowagie.text.pdf.PdfWriter; 12. 13.public class GeneratePDF { 14. 15. public static void main(String[] args) { 16. try { 17. OutputStream file = new FileOutputStream(new File("C://Test.pdf")); 18. 19. Document document = new Document(); 20. PdfWriter.getInstance(document, file); 21. document.open(); 22. document.add(new Paragraph("Hello Kiran")); 23. document.add(new Paragraph(new Date().toString())); 24. 25. document.close(); 26. file.close(); 27. 28. } catch (Exception e) { 29. 30. e.printStackTrace(); 31. } 32. } 33.} 阅读这篇文章 了解更多细节 import java.io.File; import java.io.FileOutputStream; import java.io.OutputStream; import java.util.Date; import com.lowagie.text.Document; import com.lowagie.text.Paragraph; import com.lowagie.text.pdf.PdfWriter; public class GeneratePDF { public static void main(String[] args) { try { OutputStream file = new FileOutputStream(new File("C://Test.pdf")); Document document = new Document(); PdfWriter.getInstance(document, file); document.open(); document.add(new Paragraph("Hello Kiran")); document.add(new Paragraph(new Date().toString())); document.close(); file.close(); } catch (Exception e) { e.printStackTrace(); } } } 11. HTTP 代理设置 Java代码 1.阅读这篇 文章 了解更多细节。 2. 3. 4.System.getProperties().put("http.proxyHost", "someProxyURL"); 5.System.getProperties().put("http.proxyPort", "someProxyPort"); 6.System.getProperties().put("http.proxyUser", "someUserName"); 7.System.getProperties().put("http.proxyPassword", "somePassword"); 阅读这篇 文章 了解更多细节。 System.getProperties().put("http.proxyHost", "someProxyURL"); System.getProperties().put("http.proxyPort", "someProxyPort"); System.getProperties().put("http.proxyUser", "someUserName"); System.getProperties().put("http.proxyPassword", "somePassword"); 12. 单实例Singleton 示例 Java代码 1.请先阅读这篇文章 了解更多信息 2. 3. 4.public class SimpleSingleton { 5. private static SimpleSingleton singleInstance = new SimpleSingleton(); 6. 7. //Marking default constructor private 8. //to avoid direct instantiation. 9. private SimpleSingleton() { 10. } 11. 12. //Get instance for class SimpleSingleton 13. public static SimpleSingleton getInstance() { 14. 15. return singleInstance; 16. } 17.} 18.另一种实现 19. 20.public enum SimpleSingleton { 21. INSTANCE; 22. public void doSomething() { 23. } 24.} 25. 26.//Call the method from Singleton: 27.SimpleSingleton.INSTANCE.doSomething(); 请先阅读这篇文章 了解更多信息 public class SimpleSingleton { private static SimpleSingleton singleInstance = new SimpleSingleton(); //Marking default constructor private //to avoid direct instantiation. private SimpleSingleton() { } //Get instance for class SimpleSingleton public static SimpleSingleton getInstance() { return singleInstance; } } 另一种实现 public enum SimpleSingleton { INSTANCE; public void doSomething() { } } //Call the method from Singleton: SimpleSingleton.INSTANCE.doSomething(); 13. 抓屏程序 Java代码 1.阅读这篇文章 获得更多信息。 2. 3.import java.awt.Dimension; 4.import java.awt.Rectangle; 5.import java.awt.Robot; 6.import java.awt.Toolkit; 7.import java.awt.image.BufferedImage; 8.import javax.imageio.ImageIO; 9.import java.io.File; 10. 11.... 12. 13.public void captureScreen(String fileName) throws Exception { 14. 15. Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize(); 16. Rectangle screenRectangle = new Rectangle(screenSize); 17. Robot robot = new Robot(); 18. BufferedImage image = robot.createScreenCapture(screenRectangle); 19. ImageIO.write(image, "png", new File(fileName)); 20. 21.} 22.... 23. 24. 25. 阅读这篇文章 获得更多信息。 import java.awt.Dimension; import java.awt.Rectangle; import java.awt.Robot; import java.awt.Toolkit; import java.awt.image.BufferedImage; import javax.imageio.ImageIO; import java.io.File; ... public void captureScreen(String fileName) throws Exception { Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize(); Rectangle screenRectangle = new Rectangle(screenSize); Robot robot = new Robot(); BufferedImage image = robot.createScreenCapture(screenRectangle); ImageIO.write(image, "png", new File(fileName)); } ... 14. 列出文件和目录 Java代码 1.File dir = new File("directoryName"); 2. String[] children = dir.list(); 3. if (children == null) { 4. // Either dir does not exist or is not a directory 5. } else { 6. for (int i=0; i < children.length; i++) { 7. // Get filename of file or directory 8. String filename = children[i]; 9. } 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); File dir = new File("directoryName"); String[] children = dir.list(); if (children == null) { // Either dir does not exist or is not a directory } else { for (int i=0; i < children.length; i++) { // Get filename of file or directory String filename = children[i]; } } // It is also possible to filter the list of returned files. // This example does not return any files that start with `.'. FilenameFilter filter = new FilenameFilter() { public boolean accept(File dir, String name) { return !name.startsWith("."); } }; children = dir.list(filter); // The list of files can also be retrieved as File objects File[] files = dir.listFiles(); // This filter only returns directories FileFilter fileFilter = new FileFilter() { public boolean accept(File file) { return file.isDirectory(); } }; files = dir.listFiles(fileFilter); 15. 创建ZIP和JAR文件 Java代码 1. 2.import java.util.zip.*; 3.import java.io.*; 4. 5.public class ZipIt { 6. public static void main(String args[]) throws IOException { 7. if (args.length < 2) { 8. System.err.println("usage: java ZipIt Zip.zip file1 file2 file3"); 9. 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.} import java.util.zip.*; import java.io.*; public class ZipIt { public static void main(String args[]) throws IOException { if (args.length < 2) { System.err.println("usage: java ZipIt Zip.zip file1 file2 file3"); System.exit(-1); } File zipFile = new File(args[0]); if (zipFile.exists()) { System.err.println("Zip file already exists, please try another"); System.exit(-2); } FileOutputStream fos = new FileOutputStream(zipFile); ZipOutputStream zos = new ZipOutputStream(fos); int bytesRead; byte[] buffer = new byte[1024]; CRC32 crc = new CRC32(); for (int i=1, n=args.length; i < n; i++) { String name = args[i]; File file = new File(name); if (!file.exists()) { System.err.println("Skipping: " + name); continue; } BufferedInputStream bis = new BufferedInputStream( new FileInputStream(file)); crc.reset(); while ((bytesRead = bis.read(buffer)) != -1) { crc.update(buffer, 0, bytesRead); } bis.close(); // Reset to beginning of input stream bis = new BufferedInputStream( new FileInputStream(file)); ZipEntry entry = new ZipEntry(name); entry.setMethod(ZipEntry.STORED); entry.setCompressedSize(file.length()); entry.setSize(file.length()); entry.setCrc(crc.getValue()); zos.putNextEntry(entry); while ((bytesRead = bis.read(buffer)) != -1) { zos.write(buffer, 0, bytesRead); } bis.close(); } zos.close(); } } 16. 解析/读取XML 文件 Java代码 1.XML文件 2. 3. 4.<?xml version="1.0"?> 5.<students> 6. <student> 7. <name>John</name> 8. <grade>B</grade> 9. <age>12</age> 10. </student> 11. <student> 12. <name>Mary</name> 13. <grade>A</grade> 14. <age>11</age> 15. </student> 16. <student> 17. <name>Simon</name> 18. <grade>A</grade> 19. <age>18</age> 20. </student> 21.</students> 22.Java代码 23. 24. 25.package net.viralpatel.java.xmlparser; 26. 27.import java.io.File; 28.import javax.xml.parsers.DocumentBuilder; 29.import javax.xml.parsers.DocumentBuilderFactory; 30. 31.import org.w3c.dom.Document; 32.import org.w3c.dom.Element; 33.import org.w3c.dom.Node; 34.import org.w3c.dom.NodeList; 35. 36.public class XMLParser { 37. 38. public void getAllUserNames(String fileName) { 39. try { 40. DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance(); 41. DocumentBuilder db = dbf.newDocumentBuilder(); 42. File file = new File(fileName); 43. if (file.exists()) { 44. Document doc = db.parse(file); 45. Element docEle = doc.getDocumentElement(); 46. 47. // Print root element of the document 48. System.out.println("Root element of the document: " 49. + docEle.getNodeName()); 50. 51. NodeList studentList = docEle.getElementsByTagName("student"); 52. 53. // Print total student elements in document 54. System.out 55. .println("Total students: " + studentList.getLength()); 56. 57. if (studentList != null && studentList.getLength() > 0) { 58. for (int i = 0; i < studentList.getLength(); i++) { 59. 60. Node node = studentList.item(i); 61. 62. if (node.getNodeType() == Node.ELEMENT_NODE) { 63. 64. System.out 65. .println("====================="); 66. 67. Element e = (Element) node; 68. NodeList nodeList = e.getElementsByTagName("name"); 69. System.out.println("Name: " 70. + nodeList.item(0).getChildNodes().item(0) 71. .getNodeValue()); 72. 73. nodeList = e.getElementsByTagName("grade"); 74. System.out.println("Grade: " 75. + nodeList.item(0).getChildNodes().item(0) 76. .getNodeValue()); 77. 78. nodeList = e.getElementsByTagName("age"); 79. System.out.println("Age: " 80. + nodeList.item(0).getChildNodes().item(0) 81. .getNodeValue()); 82. } 83. } 84. } else { 85. System.exit(1); 86. } 87. } 88. } catch (Exception e) { 89. System.out.println(e); 90. } 91. } 92. public static void main(String[] args) { 93. 94. XMLParser parser = new XMLParser(); 95. parser.getAllUserNames("c://test.xml"); 96. } 97.} XML文件 <?xml version="1.0"?> <students> <student> <name>John</name> <grade>B</grade> <age>12</age> </student> <student> <name>Mary</name> <grade>A</grade> <age>11</age> </student> <student> <name>Simon</name> <grade>A</grade> <age>18</age> </student> </students> Java代码 package net.viralpatel.java.xmlparser; import java.io.File; import javax.xml.parsers.DocumentBuilder; import javax.xml.parsers.DocumentBuilderFactory; import org.w3c.dom.Document; import org.w3c.dom.Element; import org.w3c.dom.Node; import org.w3c.dom.NodeList; public class XMLParser { public void getAllUserNames(String fileName) { try { DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance(); DocumentBuilder db = dbf.newDocumentBuilder(); File file = new File(fileName); if (file.exists()) { Document doc = db.parse(file); Element docEle = doc.getDocumentElement(); // Print root element of the document System.out.println("Root element of the document: " + docEle.getNodeName()); NodeList studentList = docEle.getElementsByTagName("student"); // Print total student elements in document System.out .println("Total students: " + studentList.getLength()); if (studentList != null && studentList.getLength() > 0) { for (int i = 0; i < studentList.getLength(); i++) { Node node = studentList.item(i); if (node.getNodeType() == Node.ELEMENT_NODE) { System.out .println("====================="); Element e = (Element) node; NodeList nodeList = e.getElementsByTagName("name"); System.out.println("Name: " + nodeList.item(0).getChildNodes().item(0) .getNodeValue()); nodeList = e.getElementsByTagName("grade"); System.out.println("Grade: " + nodeList.item(0).getChildNodes().item(0) .getNodeValue()); nodeList = e.getElementsByTagName("age"); System.out.println("Age: " + nodeList.item(0).getChildNodes().item(0) .getNodeValue()); } } } else { System.exit(1); } } } catch (Exception e) { System.out.println(e); } } public static void main(String[] args) { XMLParser parser = new XMLParser(); parser.getAllUserNames("c://test.xml"); } } 17. 把 Array 转换成 Map Java代码 1. 2.import java.util.Map; 3.import org.apache.commons.lang.ArrayUtils; 4. 5.public class Main { 6. 7. public static void main(String[] args) { 8. String[][] countries = { { "United States", "New York" }, { "United Kingdom", "London" }, 9. { "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.} import java.util.Map; import org.apache.commons.lang.ArrayUtils; public class Main { public static void main(String[] args) { String[][] countries = { { "United States", "New York" }, { "United Kingdom", "London" }, { "Netherland", "Amsterdam" }, { "Japan", "Tokyo" }, { "France", "Paris" } }; Map countryCapitals = ArrayUtils.toMap(countries); System.out.println("Capital of Japan is " + countryCapitals.get("Japan")); System.out.println("Capital of France is " + countryCapitals.get("France")); } } 18. 发送邮件 Java代码 1.import javax.mail.*; 2.import javax.mail.internet.*; 3.import java.util.*; 4. 5.public void postMail( String recipients[ ], String subject, String message , String from) throws MessagingException 6.{ 7. boolean debug = false; 8. 9. //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.} import javax.mail.*; import javax.mail.internet.*; import java.util.*; public void postMail( String recipients[ ], String subject, String message , String from) throws MessagingException { boolean debug = false; //Set the host smtp address Properties props = new Properties(); props.put("mail.smtp.host", "smtp.example.com"); // create some properties and get the default Session Session session = Session.getDefaultInstance(props, null); session.setDebug(debug); // create a message Message msg = new MimeMessage(session); // set the from and to address InternetAddress addressFrom = new InternetAddress(from); msg.setFrom(addressFrom); InternetAddress[] addressTo = new InternetAddress[recipients.length]; for (int i = 0; i < recipients.length; i++) { addressTo[i] = new InternetAddress(recipients[i]); } msg.setRecipients(Message.RecipientType.TO, addressTo); // Optional : You can also set your custom headers in the Email if you Want msg.addHeader("MyHeaderName", "myHeaderValue"); // Setting the Subject and Content Type msg.setSubject(subject); msg.setContent(message, "text/plain"); Transport.send(msg); } 19. 发送代数据的HTTP 请求 Java代码 1. 2.import java.io.BufferedReader; 3.import java.io.InputStreamReader; 4.import java.net.URL; 5. 6.public class Main { 7. public static void main(String[] args) { 8. try { 9. URL my_url = new URL("http://coolshell.cn/"); 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.} import java.io.BufferedReader; import java.io.InputStreamReader; import java.net.URL; public class Main { public static void main(String[] args) { try { URL my_url = new URL("http://coolshell.cn/"); BufferedReader br = new BufferedReader(new InputStreamReader(my_url.openStream())); String strTemp = ""; while(null != (strTemp = br.readLine())){ System.out.println(strTemp); } } catch (Exception ex) { ex.printStackTrace(); } } } 20. 改变数组的大小 Java代码 1.查看源代码打印帮助 2. 3./** 4.* Reallocates an array with a new size, and copies the contents 5.* of the old array to the new array. 6.* @param oldArray the old array, to be reallocated. 7.* @param newSize the new array size. 8.* @return A new array with the same contents. 9.*/ 10.private static Object resizeArray (Object oldArray, int newSize) { 11. int oldSize = java.lang.reflect.Array.getLength(oldArray); 12. Class elementType = oldArray.getClass().getComponentType(); 13. Object newArray = java.lang.reflect.Array.newInstance( 14. elementType,newSize); 15. int preserveLength = Math.min(oldSize,newSize); 16. if (preserveLength > 0) 17. System.arraycopy (oldArray,0,newArray,0,preserveLength); 18. return newArray; 19.} 20. 21.// Test routine for resizeArray(). 22.public static void main (String[] args) { 23. int[] a = {1,2,3}; 24. a = (int[])resizeArray(a,5); 25. a[3] = 4; 26. a[4] = 5; 27. for (int i=0; i<a.length; i++) 28. System.out.println (a[i]); 29.} 查看源代码打印帮助 /** * Reallocates an array with a new size, and copies the contents * of the old array to the new array. * @param oldArray the old array, to be reallocated. * @param newSize the new array size. * @return A new array with the same contents. */ private static Object resizeArray (Object oldArray, int newSize) { int oldSize = java.lang.reflect.Array.getLength(oldArray); Class elementType = oldArray.getClass().getComponentType(); Object newArray = java.lang.reflect.Array.newInstance( elementType,newSize); int preserveLength = Math.min(oldSize,newSize); if (preserveLength > 0) System.arraycopy (oldArray,0,newArray,0,preserveLength); return newArray; } // Test routine for resizeArray(). public static void main (String[] args) { int[] a = {1,2,3}; a = (int[])resizeArray(a,5); a[3] = 4; a[4] = 5; for (int i=0; i<a.length; i++) System.out.println (a[i]); }