20非常有用的Java程序片段(1)

下面是20个非常有用的Java程序片段，希望能对你有用。

1. 字符串有整型的相互转换

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

2. 向文件末尾添加内容

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. 得到当前方法的名字

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

4. 转字符串到日期

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链接Oracle

publicclass OracleJdbcTest
{
    String driverClass = "oracle.jdbc.driver.OracleDriver";

    Connection con;

publicvoid 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);
    }

publicvoid 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();
    }

publicstaticvoid main(String[] args)
    {
        OracleJdbcTest test = new OracleJdbcTest();
        test.init();
        test.fetch();
    }
}

6. 把 Java util.Date 转成 sql.Date

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

7. 使用NIO进行快速的文件拷贝

publicstaticvoid 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

privatevoid 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();
    }