这么简单的问题用得着那么难的想法么?
import java.io.File;
import java.io.FileOutputStream;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.image.BufferedImage;
import com.sun.image.codec.jpeg.JPEGCodec;
import com.sun.image.codec.jpeg.JPEGImageEncoder;
  
  public class JpgTest {
  
  public void JpgTset() throws Exception{
  File _file = new File("/Order005-0001.jpg"); 
  Image src = javax.imageio.ImageIO.read(_file); 
  int wideth=src.getWidth(null); 
  int height=src.getHeight(null); 
  BufferedImage tag = new BufferedImage(wideth/2,height/2,BufferedImage.TYPE_INT_RGB);
  tag.getGraphics().drawImage(src,0,0,wideth/2,height/2,null);   FileOutputStream out=new FileOutputStream("newfile.jpg"); 
  JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out); 
  encoder.encode(tag); //近JPEG??
  //System.out.print(width+"*"+height); 
  out.close();
  }
  }