1. 字符串有整型的相互转换

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

2. 向文件末尾添加内容

1. 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. } 

3. 得到当前方法的名字

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

4. 转字符串到日期

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

或者是：

1. SimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy" );  
2. Date date = format.parse( myString ); 

5. 使用JDBC链接Oracle

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. } 

6. 把 Java util.Date 转成 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进行快速的文件拷贝

1. 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.     } 

8. 创建图片的缩略图

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.     } 

9. 创建ZIP和JAR文件

1. 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[i];  
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. } 

10. 解析/读取XML 文件

XML文件

1. <?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> 

Java代码：

1. ackage 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. } 

11. 把 Array 转换成 Map

1. 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. } 

12. 发送邮件

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. } 

13. 发送代数据的HTTP 请求

1. 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. }

14. 改变数组的大小

1. /**
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[i]);  
27. }