java jpg dpi_Java 设置图片的DPI（com.sun.image.codec.jpeg does not exist）

图片DPI：图像每英寸长度内的像素点数。( density is dots per inch)

一开始使用jpeg code包编写，代码如下：public static String setImgDpi(MultipartFile file, int xDensity, int yDensity) {

try {

BufferedImage image = ImageIO.read(file.getInputStream());

ByteArrayOutputStream bo = new ByteArrayOutputStream();

JPEGImageEncoder jpegEncoder = JPEGCodec.createJPEGEncoder(bo);

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);

return Base64.getEncoder().encodeToString(bo.toByteArray());

} catch (IOException e) {

e.printStackTrace();

}

return null;

}

本地测试没问题，但是在发布时编译提示错误：package com.sun.image.codec.jpeg does not exist

度娘上解释说：因为版权原因，jdk1.7后将不会自动包含sun.*的类库，也不建议我们直接使用sun下的类库。

基于这个原因，我们可以手动的将需要的rt.jar导入到我们的项目中即可解决问题。

1.手动将rt.jar放到项目的lib下

2.maven项目可参考(注意windows和linux下的路径格式不一样)

maven-compiler-plugin

UTF-8

${java.home}/lib/rt.jar${path.separator}${java.home}/lib/jce.jar

但是既然已经不提倡使用sun，所以我没有采用上述方法解决问题，而是找了新的类(ImageIO)代替此功能的实现。import org.w3c.dom.Element;

import javax.imageio.IIOImage;

import javax.imageio.ImageIO;

import javax.imageio.ImageTypeSpecifier;

import javax.imageio.ImageWriteParam;

import javax.imageio.ImageWriter;

import javax.imageio.metadata.IIOMetadata;

import javax.imageio.stream.ImageOutputStream;

import java.awt.image.BufferedImage;

import java.io.ByteArrayOutputStream;

import java.io.IOException;

import java.util.Iterator;

public class ImageUtils {

/**

* 设置图片DPI

* @param image

* @param dpi

* @return

* @throws IOException

*/

public static byte[] setImgDpi(BufferedImage image, int dpi) throws IOException {

for (Iterator iw = ImageIO.getImageWritersByFormatName("jpeg"); iw.hasNext();) {

ImageWriter writer = iw.next();

ImageWriteParam writeParams = writer.getDefaultWriteParam();

writeParams.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);

//调整图片质量

writeParams.setCompressionQuality(1f);

IIOMetadata data = writer.getDefaultImageMetadata(new ImageTypeSpecifier(image), writeParams);

Element tree = (Element) data.getAsTree("javax_imageio_jpeg_image_1.0");

Element jfif = (Element) tree.getElementsByTagName("app0JFIF").item(0);

//设置图片dpi

jfif.setAttribute("resUnits", "1"); // density is dots per inch

jfif.setAttribute("Xdensity", dpi + "");

jfif.setAttribute("Ydensity", dpi + "");

ByteArrayOutputStream out = new ByteArrayOutputStream();

ImageOutputStream stream = null;

try {

stream = ImageIO.createImageOutputStream(out);

writer.setOutput(stream);

writer.write(data, new IIOImage(image, null, null), writeParams);

} finally {

stream.close();

}

return out.toByteArray();

}

return null;

}

}