Java常用代码段你都了解多少？

这篇文章给大家分享的是Java常用代码段。小编觉得挺实用的，因此分享给大家做个参考，文中的示例代码介绍得很详细，有需要的朋友可以参考，接下来就跟随小编一起了解看看吧。

本教程操作环境：windows7系统、java10版，DELL G3电脑。

常用的Java代码段有：

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

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. 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

public static void 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

private void 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();
  
    }
    

9. 创建 JSON 格式的数据

请先阅读这篇文章 了解一些细节，

并下面这个JAR 文件：json-rpc-1.0.jar (75 kb)

import org.json.JSONObject;
      
...  
...  
JSONObject json = new JSONObject();
      
json.put("city", "Mumbai");
      
json.put("country", "India");
      
...  
String output = json.toString();
      
...

10. 使用iText JAR生成PDF

阅读这篇文章 了解更多细节

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();
  
        }
  
    }
  
}
    

关于Java常用代码段就介绍到这，上述示例具有一定的借鉴价值，感兴趣的朋友可以参考，希望能对大家有帮助，想要了解更多大家可以关注网络其它的相关文章。

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