常用的Java代码汇总

1 <font face="Arial" size="3">String a = String.valueOf(2);   //integer to numeric string  
2 int i = Integer.parseInt(a); //numeric string to an int</font>

 1 <font face="Arial" size="3">]BufferedWriter out = null;  
 2 try {  
 3     out = new BufferedWriter(new FileWriter(”filename”, true));  
 4     out.write(”aString”);  
 5 } catch (IOException e) {  
 6     // error processing code  
 7 } finally {  
 8     if (out != null) {  
 9         out.close();  
10     }  
11 }</font>

1 <font face="Arial" size="3"><span style="font-family:Arial;font-size:14px;">String methodName = Thread.currentThread().getStackTrace()[1].getMethodName(); </span></font>

1 <font face="Arial" size="3">java.util.Date = java.text.DateFormat.getDateInstance().parse(date String);</font>

1 <font face="Arial" size="3">SimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy" );  
2 Date date = format.parse( myString );</font>

 1 <font face="Arial" size="3">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 }</font>

1 <font face="Arial" size="3"><span style="font-family:Arial;font-size:14px;">java.util.Date utilDate = new java.util.Date();  
2 java.sql.Date sqlDate = new java.sql.Date(utilDate.getTime());</span></font>

 1 <font face="Arial" size="3">public static void fileCopy( File in, File out )  
 2             throws IOException  
 3     {  
 4         FileChannel inChannel = new FileInputStream( in ).getChannel();  
 5         FileChannel outChannel = new FileOutputStream( out ).getChannel();  
 6         try 
 7         {  
 8 //          inChannel.transferTo(0, inChannel.size(), outChannel);      // original -- apparently has trouble copying large files on Windows  
 9   
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     }</font>

 1 <font face="Arial" size="3">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     }</font>

1 <font face="Arial" size="3">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 ...</font>

 1 <font face="Arial" size="3">import java.io.File;  
 2 import java.io.FileOutputStream;  
 3 import java.io.OutputStream;  
 4 import java.util.Date;  
 5   
 6 import com.lowagie.text.Document;  
 7 import com.lowagie.text.Paragraph;  
 8 import com.lowagie.text.pdf.PdfWriter;  
 9   
10 public class GeneratePDF {  
11   
12     public static void main(String[] args) {  
13         try {  
14             OutputStream file = new FileOutputStream(new File("C:\\Test.pdf"));  
15   
16             Document document = new Document();  
17             PdfWriter.getInstance(document, file);  
18             document.open();  
19             document.add(new Paragraph("Hello Kiran"));  
20             document.add(new Paragraph(new Date().toString()));  
21   
22             document.close();  
23             file.close();  
24   
25         } catch (Exception e) {  
26   
27             e.printStackTrace();  
28         }  
29     }  
30 }</font>

1 <font face="Arial" size="3">System.getProperties().put("http.proxyHost", "someProxyURL");  
2 System.getProperties().put("http.proxyPort", "someProxyPort");  
3 System.getProperties().put("http.proxyUser", "someUserName");  
4 System.getProperties().put("http.proxyPassword", "somePassword");</font>

 1 <font face="Arial" size="3">public class SimpleSingleton {  
 2     private static SimpleSingleton singleInstance =  new SimpleSingleton();  
 3   
 4     //Marking default constructor private  
 5     //to avoid direct instantiation.  
 6     private SimpleSingleton() {  
 7     }  
 8   
 9     //Get instance for class SimpleSingleton  
10     public static SimpleSingleton getInstance() {  
11   
12         return singleInstance;  
13     }  
14 }</font>

 1 <font face="Arial" size="3">import java.awt.Dimension;  
 2 import java.awt.Rectangle;  
 3 import java.awt.Robot;  
 4 import java.awt.Toolkit;  
 5 import java.awt.image.BufferedImage;  
 6 import javax.imageio.ImageIO;  
 7 import java.io.File;  
 8   
 9 ...  
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 ...</font>

 1 <font face="Arial" size="3">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;  
 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);</font>

 1 <font face="Arial" size="3"><span style="font-family:Arial;font-size:14px;">import java.util.zip.*;  
 2 import java.io.*;  
 3   
 4 public class ZipIt {  
 5     public static void main(String args[]) throws IOException {  
 6         if (args.length < 2) {  
 7             System.err.println("usage: java ZipIt Zip.zip file1 file2 file3");  
 8             System.exit(-1);  
 9         }  
10         File zipFile = new File(args[0]);  
11         if (zipFile.exists()) {  
12             System.err.println("Zip file already exists, please try another");  
13             System.exit(-2);  
14         }  
15         FileOutputStream fos = new FileOutputStream(zipFile);  
16         ZipOutputStream zos = new ZipOutputStream(fos);  
17         int bytesRead;  
18         byte[] buffer = new byte[1024];  
19         CRC32 crc = new CRC32();  
20         for (int i=1, n=args.length; i < n; i++) {  
21             String name = args;  
22             File file = new File(name);  
23             if (!file.exists()) {  
24                 System.err.println("Skipping: " + name);  
25                 continue;  
26             }  
27             BufferedInputStream bis = new BufferedInputStream(  
28                 new FileInputStream(file));  
29             crc.reset();  
30             while ((bytesRead = bis.read(buffer)) != -1) {  
31                 crc.update(buffer, 0, bytesRead);  
32             }  
33             bis.close();  
34             // Reset to beginning of input stream  
35             bis = new BufferedInputStream(  
36                 new FileInputStream(file));  
37             ZipEntry entry = new ZipEntry(name);  
38             entry.setMethod(ZipEntry.STORED);  
39             entry.setCompressedSize(file.length());  
40             entry.setSize(file.length());  
41             entry.setCrc(crc.getValue());  
42             zos.putNextEntry(entry);  
43             while ((bytesRead = bis.read(buffer)) != -1) {  
44                 zos.write(buffer, 0, bytesRead);  
45             }  
46             bis.close();  
47         }  
48         zos.close();  
49     }  
50 } </span></font>

 1 <font face="Arial" size="3"><?xml version="1.0"?> 
 2 <students> 
 3     <student> 
 4         <name>John</name> 
 5         <grade>B</grade> 
 6         <age>12</age> 
 7     </student> 
 8     <student> 
 9         <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></font>

 1 <font face="Arial" size="3"><span style="font-family:Arial;font-size:14px;">package net.viralpatel.java.xmlparser;  
 2   
 3 import java.io.File;  
 4 import javax.xml.parsers.DocumentBuilder;  
 5 import javax.xml.parsers.DocumentBuilderFactory;  
 6   
 7 import org.w3c.dom.Document;  
 8 import org.w3c.dom.Element;  
 9 import org.w3c.dom.Node;  
10 import org.w3c.dom.NodeList;  
11   
12 public class XMLParser {  
13   
14     public void getAllUserNames(String fileName) {  
15         try {  
16             DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();  
17             DocumentBuilder db = dbf.newDocumentBuilder();  
18             File file = new File(fileName);  
19             if (file.exists()) {  
20                 Document doc = db.parse(file);  
21                 Element docEle = doc.getDocumentElement();  
22   
23                 // Print root element of the document  
24                 System.out.println("Root element of the document: " 
25                         + docEle.getNodeName());  
26   
27                 NodeList studentList = docEle.getElementsByTagName("student");  
28   
29                 // Print total student elements in document  
30                 System.out  
31                         .println("Total students: " + studentList.getLength());  
32   
33                 if (studentList != null && studentList.getLength() > 0) {  
34                     for (int i = 0; i < studentList.getLength(); i++) {  
35   
36                         Node node = studentList.item(i);  
37   
38                         if (node.getNodeType() == Node.ELEMENT_NODE) {  
39   
40                             System.out  
41                                     .println("=====================");  
42   
43                             Element e = (Element) node;  
44                             NodeList nodeList = e.getElementsByTagName("name");  
45                             System.out.println("Name: " 
46                                     + nodeList.item(0).getChildNodes().item(0)  
47                                             .getNodeValue());  
48   
49                             nodeList = e.getElementsByTagName("grade");  
50                             System.out.println("Grade: " 
51                                     + nodeList.item(0).getChildNodes().item(0)  
52                                             .getNodeValue());  
53   
54                             nodeList = e.getElementsByTagName("age");  
55                             System.out.println("Age: " 
56                                     + nodeList.item(0).getChildNodes().item(0)  
57                                             .getNodeValue());  
58                         }  
59                     }  
60                 } else {  
61                     System.exit(1);  
62                 }  
63             }  
64         } catch (Exception e) {  
65             System.out.println(e);  
66         }  
67     }  
68     public static void main(String[] args) {  
69   
70         XMLParser parser = new XMLParser();  
71         parser.getAllUserNames("c:\\test.xml");  
72     }  
73 }</span></font>

 1 <font face="Arial" size="3">import java.util.Map;  
 2 import org.apache.commons.lang.ArrayUtils;  
 3   
 4 public class Main {  
 5   
 6   public static void main(String[] args) {  
 7     String[][] countries = { { "United States", "New York" }, { "United Kingdom", "London" },  
 8         { "Netherland", "Amsterdam" }, { "Japan", "Tokyo" }, { "France", "Paris" } };  
 9   
10     Map countryCapitals = ArrayUtils.toMap(countries);  
11   
12     System.out.println("Capital of Japan is " + countryCapitals.get("Japan"));  
13     System.out.println("Capital of France is " + countryCapitals.get("France"));  
14   }  
15 }</font>

 1 <font face="Arial" size="3">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 = new InternetAddress(recipients);  
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 }</font>

 1 <font face="Arial" size="3">import java.io.BufferedReader;  
 2 import java.io.InputStreamReader;  
 3 import java.net.URL;  
 4   
 5 public class Main {  
 6     public static void main(String[] args)  {  
 7         try {  
 8             URL my_url = new URL("http://coolshell.cn/");  
 9             BufferedReader br = new BufferedReader(new InputStreamReader(my_url.openStream()));  
10             String strTemp = "";  
11             while(null != (strTemp = br.readLine())){  
12             System.out.println(strTemp);  
13         }  
14         } catch (Exception ex) {  
15             ex.printStackTrace();  
16         }  
17     }  
18 }</font>

 1 <font face="Arial" size="3">/** 
 2 * Reallocates an array with a new size, and copies the contents 
 3 * of the old array to the new array. 
 4 * @param oldArray  the old array, to be reallocated. 
 5 * @param newSize   the new array size. 
 6 * @return          A new array with the same contents. 
 7 */ 
 8 private static Object resizeArray (Object oldArray, int newSize) {  
 9    int oldSize = java.lang.reflect.Array.getLength(oldArray);  
10    Class elementType = oldArray.getClass().getComponentType();  
11    Object newArray = java.lang.reflect.Array.newInstance(  
12          elementType,newSize);  
13    int preserveLength = Math.min(oldSize,newSize);  
14    if (preserveLength > 0)  
15       System.arraycopy (oldArray,0,newArray,0,preserveLength);  
16    return newArray;  
17 }  
18   
19 // Test routine for resizeArray().  
20 public static void main (String[] args) {  
21    int[] a = {1,2,3};  
22    a = (int[])resizeArray(a,5);  
23    a[3] = 4;  
24    a[4] = 5;  
25    for (int i=0; i<a.length; i++)  
26       System.out.println (a);  
27 }</font>