1. 使用第三方库，比如OpenCV、ImageMagick等进行图片格式转换。 示例代码：

import org.opencv.core.Core; import org.opencv.core.Mat; import org.opencv.highgui.Highgui;

public class ConvertJpgToPng {

public static void main( String[] args ) { System.loadLibrary( Core.NATIVE_LIBRARY_NAME );

   String inputFilePath = "input.jpg";
   String outputFilePath = "output.png";

   Mat image = Highgui.imread(inputFilePath);

   if(image == null) {
       System.out.println("Error: Could not read image file " + inputFilePath);
       return;
   }

   boolean success = Highgui.imwrite(outputFilePath, image);

   if(success) {
       System.out.println("Image saved as " + outputFilePath);
   } else {
       System.out.println("Error: Could not save image file " + outputFilePath);
   }

}

}

2. 使用Java内置的ImageIO类，但是需要自己实现JPG解码器。 示例代码：

import java.awt.image.BufferedImage; import java.io.File; import java.io.IOException;

import javax.imageio.ImageIO;

public class ConvertJpgToPng {

public static void main( String[] args ) { String inputFilePath = "input.jpg"; String outputFilePath = "output.png";

   try {
       BufferedImage image = readJpg(inputFilePath);
       if(image == null) {
           System.out.println("Error: Could not read image file " + inputFilePath);
           return;
       }

       boolean success = ImageIO.write(image, "png", new File(outputFilePath));

       if(success) {
           System.out.println("Image saved as " + outputFilePath);
       } else {
           System.out.println("Error: Could not save image file " + outputFilePath);
       }
   } catch (IOException e) {
       e.printStackTrace();
   }

}

private static BufferedImage readJpg(String filename) throws IOException { byte[] data = org.apache.commons.io.FileUtils.readFileToByteArray(new File(filename)); BufferedImage img = readJpg(data); return img; }

private static BufferedImage readJpg(byte[] data) throws IOException { int len = data.length;