使用java修改图片DPI

修改以后可以直接用PS打开看效果

全部使用rt下的类，无需下载其他jar包

import com.sun.image.codec.jpeg.JPEGCodec;  
import com.sun.image.codec.jpeg.JPEGEncodeParam;  
import com.sun.image.codec.jpeg.JPEGImageEncoder;  
  
import javax.imageio.ImageIO;  
import java.awt.image.BufferedImage;  
import java.io.File;  
import java.io.FileOutputStream;  
import java.io.IOException;  
  
public class DPIHandleHelper {  
    private static int DPI = 300;  
  
    public static void main(String[] args) {  
        String path = "C:\\test.jpg";  
        File file = new File(path);  
        handleDpi(file, 300, 300);  
    }  
  
    /** 
     * 改变图片DPI 
     * 
     * @param file 
     * @param xDensity 
     * @param yDensity 
     */  
    public static void handleDpi(File file, int xDensity, int yDensity) {  
        try {  
            BufferedImage image = ImageIO.read(file);  
            JPEGImageEncoder jpegEncoder = JPEGCodec.createJPEGEncoder(new FileOutputStream(file));  
            JPEGEncodeParam jpegEncodeParam = jpegEncoder.getDefaultJPEGEncodeParam(image);  
            jpegEncodeParam.setDensityUnit(JPEGEncodeParam.DENSITY_UNIT_DOTS_INCH);  
            jpegEncoder.setJPEGEncodeParam(jpegEncodeParam);  
            jpegEncodeParam.setQuality(0.75f, false);  
            jpegEncodeParam.setXDensity(xDensity);  
            jpegEncodeParam.setYDensity(yDensity);  
            jpegEncoder.encode(image, jpegEncodeParam);  
            image.flush();  
        } catch (IOException e) {  
            e.printStackTrace();  
        }  
    }  
}