Java图片拼接

最近遇到一个挺离谱的功能，某个表单只让上传一张图，多图上传会使导出失败。跟开发沟通后表示，这个问题处理不了。我...

遂自己思考，能否以曲线救国的方式拯救一下，即不伤及代码之根本，又能解决燃眉之急。灵光一闪，想到了美图救救的图片拼接功能。于是就想着尝试一下是否可行。

考虑到图片拼接界限等，目标实现：白色图片背景（默认是黑色），以最大图片的宽为最终拼接图片的宽，图片纵向拼接，图与图之间间隔35px。代码如下（异常捕获、空值判断、权限判断等需自行完善）：

import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.multipart.MultipartFile;

import javax.imageio.ImageIO;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

@RestController
public class ImagePinJie {

    @PostMapping("/imgPinJie")
    public String imageUpload(@RequestParam("files") MultipartFile[] files) throws IOException {
        if (files.length == 0) {
            return "没有文件被上传";
        }
        List<BufferedImage> bufferedImages = new ArrayList<>();
        List<Integer> widths = new ArrayList<>();
        List<Integer> heights = new ArrayList<>();

        for (MultipartFile file : files) {
            if (!file.isEmpty()) {
                try {
                    BufferedImage bi = ImageIO.read(file.getInputStream());
                    bufferedImages.add(bi);
                    widths.add(bi.getWidth());
                    heights.add(bi.getHeight());
                } catch (Exception e) {
                    return "上传失败: " + e.getMessage();
                }
            }
        }

        BufferedImage bufferedImage = imgPinJie(bufferedImages, widths, heights);
        createImage(bufferedImage);
        return "上传成功";
    }

    public BufferedImage imgPinJie(List<BufferedImage> bufferedImages, List<Integer> widths, List<Integer> heights) {
        int maxWidth = widths.stream().mapToInt(Integer::intValue).max().getAsInt();
        int totalHeight = heights.stream().mapToInt(Integer::intValue).sum() + (heights.size() - 1) * 35;
        BufferedImage bufferedImage = new BufferedImage(maxWidth, totalHeight, BufferedImage.TYPE_INT_RGB);
        int offset = 0;

        Graphics2D graphics = bufferedImage.createGraphics();
        graphics.setColor(Color.WHITE);
        graphics.fillRect(0, 0, maxWidth, totalHeight);
        for(BufferedImage bi : bufferedImages) {
            graphics.drawImage(bi, 0, offset, bi.getWidth(), bi.getHeight(), null);
            offset += bi.getHeight() + 35;
        }
        graphics.dispose();
        return bufferedImage;
    }

    public void createImage(BufferedImage bufferedImage) throws IOException {
        File file = new File("C:/Users/iTcys/Pictures/pinjie.png");
        ImageIO.write(bufferedImage, "png", file);
    }
}