常用java片段

1. 字符串有整型的相互转换

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

2. 向文件末尾添加内容

01
02 BufferedWriter out = null;
03 try {
04     out = new BufferedWriter(new FileWriter(”filename”, true));
05     out.write(”aString”);
06 } catch (IOException e) {
07     // error processing code
08 } finally {
09     if (out != null) {
10         out.close();
11     }
12 }

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

或者是：

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

5. 使用JDBC链接Oracle

01 public class OracleJdbcTest
02 {
03     String driverClass = "oracle.jdbc.driver.OracleDriver";
04
05     Connection con;
06
07     public void init(FileInputStream fs) throws ClassNotFoundException, SQLException, FileNotFoundException, IOException
08     {
09         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

01 public static void fileCopy( File in, File out )
02             throws IOException
03     {
04         FileChannel inChannel = new FileInputStream( in ).getChannel();
05         FileChannel outChannel = new FileOutputStream( out ).getChannel();
06         try
07         {
08 //          inChannel.transferTo(0, inChannel.size(), outChannel);      // original -- apparently has trouble copying large files on Windows
09
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

01 private void createThumbnail(String filename, int thumbWidth, int thumbHeight,int quality, String outFilename)
02         throws InterruptedException, FileNotFoundException, IOException
03     {
04         // load image from filename
05         Image image = Toolkit.getDefaultToolkit().getImage(filename);
06         MediaTracker mediaTracker = new MediaTracker(new Container());
07         mediaTracker.addImage(image, 0);
08         mediaTracker.waitForID(0);
09         // 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(newFileOutputStream(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);