Java：类与继承

添加依赖

<dependency>
  <groupId>net.coobird</groupId>
  <artifactId>thumbnailator</artifactId>
  <version>0.4.8</version>
</dependency>

按质量压缩
 
import java.io.File;
import java.io.FileOutputStream;
import net.coobird.thumbnailator.Thumbnails;

public class Client {

  public static void main(String[] args) throws Exception {
    Thumbnails.of(new File("D:/showqrcode.jpg"))
        .scale(1f) //图片大小（长宽）压缩比例 从0-1，1表示原图
        .outputQuality(0.5f) //图片质量压缩比例 从0-1，越接近1质量越好
        .toOutputStream(new FileOutputStream("D:/showqrcode_50.jpg"));
  }

}

按比例缩放

import java.io.File;
import java.io.FileOutputStream;
import net.coobird.thumbnailator.Thumbnails;

public class Client2 {

  public static void main(String[] args) throws Exception {
    Thumbnails.of(new File("D:/showqrcode.jpg"))
        .scale(0.5f) //图片大小（长宽）压缩 从0按照
        .outputQuality(0.5f) //图片质量压缩比例 从0-1，越接近1质量越好
        .toOutputStream(new FileOutputStream("D:/showqrcode_50%.jpg"));
  }

}

按大小和比例缩放

import java.io.File;
import java.io.FileOutputStream;
import net.coobird.thumbnailator.Thumbnails;

public class Client21 {

  public static void main(String[] args) throws Exception {
    Thumbnails.of(new File("D:/showqrcode.jpg"))
        .size(500, 300) // 图片比例不变
        .toOutputStream(new FileOutputStream("D:/showqrcode_500_300.jpg"));
  }

}

按大小缩放

import java.io.File;
import java.io.FileOutputStream;
import net.coobird.thumbnailator.Thumbnails;

public class Client22 {

  public static void main(String[] args) throws Exception {
    Thumbnails.of(new File("D:/showqrcode.jpg"))
        .forceSize(500, 300) //不保持图片比例
        .toOutputStream(new FileOutputStream("D:/showqrcode_500_300.jpg"));
  }

}

旋转 
import java.io.File;
import java.io.FileOutputStream;
import net.coobird.thumbnailator.Thumbnails;

public class Client3 {

  public static void main(String[] args) throws Exception {
    Thumbnails.of(new File("D:/showqrcode.jpg"))
        .forceSize(500, 300)
        .rotate(90f) //向右旋转
        .toOutputStream(new FileOutputStream("D:/showqrcode+90.jpg"));
  }

}

加水印
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import net.coobird.thumbnailator.Thumbnails;
import net.coobird.thumbnailator.geometry.Positions;

public class Client4 {

  public static void main(String[] args) throws IOException {
    Thumbnails.of("D:/showqrcode.jpg")
        .size(1280, 1024)
        .watermark(Positions.BOTTOM_RIGHT, ImageIO.read(new File("D:/watermark.jpg")),
            0.5f) //位置，水印来源，透明度
        .outputQuality(0.8f)
        .toFile("D:/showqrcode_watermark_bottom_right.jpg");
  }

}

裁剪

import java.io.IOException;
import net.coobird.thumbnailator.Thumbnails;
import net.coobird.thumbnailator.geometry.Positions;

public class Client5 {

  public static void main(String[] args) throws IOException {
    Thumbnails.of("D:/showqrcode.jpg")
        .sourceRegion(Positions.CENTER, 800, 600) //位置，宽，高
        .size(800, 600)
        .keepAspectRatio(false)
        .toFile("D:/showqrcode_region_center.jpg");
  }

}

拼接

import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Objects;
import javax.imageio.ImageIO;

public class Client6 {

  public static void main(String[] args) throws Exception {
    byte[] bytes = joinImages(false, new File("D:/showqrcode.jpg"), new File("D:/showqrcode.jpg"));
    if (Objects.nonNull(bytes)) {
      new ByteArrayInputStream(bytes).transferTo(new FileOutputStream("D:/showqrcode_join.jpg"));
    }
  }

  /**
   * 将多张图片拼接成一张
   *
   * @param horizontal 是否为水平拼接
   * @param files 文件列表
   * @return 拼接后的文件字节数组
   */
  private static byte[] joinImages(boolean horizontal, File... files) throws IOException {
    if (Objects.isNull(files) || files.length == 0) {
      return null;
    }
    List<BufferedImage> imageList = new ArrayList<>();
    for (File file : files) {
      BufferedImage image = ImageIO.read(file);
      imageList.add(image);
    }
    int height = imageList.get(0).getHeight();
    int width = imageList.get(0).getWidth();
    if (horizontal) {
      width = imageList.stream().mapToInt(BufferedImage::getWidth).sum();
    } else {
      height = imageList.stream().mapToInt(BufferedImage::getHeight).sum();
    }
    //创建拼接后的图片画布，参数分别为宽，高，类型，这里我们使用RGB3元色类型
    BufferedImage resultImage = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
    Graphics graphics = resultImage.getGraphics();
    int previousWidth = 0;
    int previousHeight = 0;
    for (BufferedImage image : imageList) {
      //向画布上画图片
      graphics.drawImage(image, previousWidth, previousHeight, null);
      if (horizontal) {
        previousWidth += image.getWidth();
      } else {
        previousHeight += image.getHeight();
      }
    }
    ByteArrayOutputStream output = new ByteArrayOutputStream();
    ImageIO.write(resultImage, "jpg", output);
    return output.toByteArray();
  }
}