Java常用代码

 

1.String型转换成int型与int型转换成String型

//integer to numeric string
 String a = String.valueOf(2); 

 //numeric string to an int
 int i = Integer.parseInt(a);

 

2.向Java文件中添加文本

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.获取Java正在调用的方法名

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

 

4.在Java中将String型转换为Date型

//method one
 java.util.Date = java.text.DateFormat.getDateInstance().parse(date String);

 //method two
 SimpleDateFormat format = new SimpleDateFormat("dd.MM.yyyy");
Date date = format.parse( myString );

 

5.通过JDBC连接数据库

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.将java中的util.Date转换成sql.Date这一片段显示如何将一个java util Date转换成sql Date用于数据库

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

 

7.使用NIO快速复制Java文件

public static void fileCopy( File in, File out) throws IOException {
    FileChannel inChannel = new FileInputStream( in ).getChannel(); 
    FileChannel utChannel = 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.在Java中使用缩略图

private void createThumbnail(String filename, int thumbWidth,int thumbHeight, int quality, String outFilename) throws InterruptedException, FileNotFoundException, IOException {
    // load image fromfilename
    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 fromWIDTH 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 = newBufferedImage(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 ut = 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.在Java中使用iText JAR打开PDF文

//Read this article for more details.
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(); 
        }
    }
}

 

10.在Java上做屏幕截

//Read this article for more details. 
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)); 
}

 

11.接收键盘输入

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));