Java中常用的代码汇总_轻课堂-网络学习平台

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 = newBufferedWriter(newFileWriter(”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

publicclassOracleJdbcTest 
{ 
  String driverClass = "oracle.jdbc.driver.OracleDriver"; 
  
  Connection con; 
  
  publicvoidinit(FileInputStream fs) throwsClassNotFoundException, SQLException, FileNotFoundException, IOException 
  { 
    Properties props = newProperties(); 
    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); 
  } 
  
  publicvoidfetch() throwsSQLException, 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(); 
  } 
  
  publicstaticvoidmain(String[] args) 
  { 
    OracleJdbcTest test = newOracleJdbcTest(); 
    test.init(); 
    test.fetch(); 
  } 
}

6. 把 Java util.Date 转成 sql.Date

1 2	`java.util.Date utilDate =` `newjava.util.Date();` `java.sql.Date sqlDate =` `newjava.sql.Date(utilDate.getTime());`

7. 使用 NIO 进行快速的文件拷贝

publicstaticvoidfileCopy( File in, File out ) 
      throwsIOException 
  { 
    FileChannel inChannel = newFileInputStream( in ).getChannel(); 
    FileChannel outChannel = newFileOutputStream( out ).getChannel(); 
    try
    { 
//     inChannel.transferTo(0, inChannel.size(), outChannel);   // original -- apparently has trouble copying large files on Windows 
  
      // magic number for Windows, 64Mb - 32Kb) 
      intmaxCount = (64* 1024* 1024) - (32* 1024); 
      longsize = inChannel.size(); 
      longposition = 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

privatevoidcreateThumbnail(String filename, intthumbWidth, intthumbHeight, intquality, String outFilename) 
    throwsInterruptedException, FileNotFoundException, IOException 
  { 
    // load image from filename 
    Image image = Toolkit.getDefaultToolkit().getImage(filename); 
    MediaTracker mediaTracker = newMediaTracker(newContainer()); 
    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 
    doublethumbRatio = (double)thumbWidth / (double)thumbHeight; 
    intimageWidth = image.getWidth(null); 
    intimageHeight = image.getHeight(null); 
    doubleimageRatio = (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 out = newBufferedOutputStream(newFileOutputStream(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.创建 JSON 格式的数据

并下面这个 JAR 文件：json-rpc-1.0.jar (75 kb)/http://t.cn/Rz0bhUA

importorg.json.JSONObject; 
... 
... 
JSONObject json = newJSONObject(); 
json.put("city", "Mumbai"); 
json.put("country", "India"); 
... 
String output = json.toString(); 
...

10. 使用 iText JAR 生成 PDF

importjava.io.File; 
importjava.io.FileOutputStream; 
importjava.io.OutputStream; 
importjava.util.Date; 
  
importcom.lowagie.text.Document; 
importcom.lowagie.text.Paragraph; 
importcom.lowagie.text.pdf.PdfWriter; 
  
publicclassGeneratePDF { 
  
  publicstaticvoidmain(String[] args) { 
    try{ 
      OutputStream file = newFileOutputStream(newFile("C:\\Test.pdf")); 
  
      Document document = newDocument(); 
      PdfWriter.getInstance(document, file); 
      document.open(); 
      document.add(newParagraph("Hello Kiran")); 
      document.add(newParagraph(newDate().toString())); 
  
      document.close(); 
      file.close(); 
  
    } catch(Exception e) { 
  
      e.printStackTrace(); 
    } 
  } 
}

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Java中常用的代码汇总