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关于JAVA的二十个经典应用案例

责任编辑:宏鹏来源:武汉北大青鸟鲁广校区时间:2013-02-15 10:53:31
导读:JAVA的二十个经典应用案例, 字符串有整型的相互转换, 向文件末尾添加内容等等。    

1. 字符串有整型的相互转换

  Java代码 String a = String.valueOf(2); 或者 String a=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 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 String methodName = Thread.currentThread().getStackTrace()[1].getMethodName(); 4. 转字符串到日期

  Java代码 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 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 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 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 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   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   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   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   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   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));   }   ...   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   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   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   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   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   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   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("//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   查看源代码打印帮助   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]);   }

本文标题:关于JAVA的二十个经典应用案例,责任编辑:宏鹏,来源:武汉北大青鸟鲁广校区栏目,于2013-02-15 10:53:31发布于北大青鸟鲁广校区。JAVA的二十个经典应用案例, 字符串有整型的相互转换, 向文件末尾添加内容等等。    

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