java代碼例子(java中有哪些常用的代碼示例)

java常用代碼有:1、 字符串有整型的相互轉換;2、向文件末尾添加內容;3、得到當前方法的名字 ;4、轉字符串到日期;5、使用JDBC鏈接Oracle;6、使用NIO進行快速的文件拷貝。

java常用代碼有:

1. 字符串有整型的相互轉換

String a = String.valueOf(2);   //integer to numeric string  int i = Integer.parseInt(a); //numeric string to an int

2. 向文件末尾添加內容

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. 得到當前方法的名字

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

4. 轉字符串到日期

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鏈接Oracle

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 轉成 sql.Date

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

7. 使用NIO進行快速的文件拷貝

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. 創建圖片的縮略圖

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.創建 JSON 格式的數據

并下面這個JAR 文件:json-rpc-1.0.jar (75 kb)/http://t.cn/Rz0bhUA

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

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 代理設置

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. 單實例Singleton 示例

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;   } }

13. 抓屏程序

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. 列出文件和目錄

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. 創建ZIP和JAR文件

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/讀取XML 文件

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代碼

<span style="font-family:Arial;font-size:14px;">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 轉換成 Map

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. 發送郵件

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. 發送代數據的HTTP 請求

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. 改變數組的大小

/** * 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]); }

感謝各位的閱讀!看完上述內容,你們對java中有哪些常用的代碼示例大概了解了嗎?希望文章內容對大家有所幫助。如果想了解更多相關文章內容,歡迎關注本站行業資訊頻道。