Java实现多张图片合并一张，这个还是挺常用到的。

public class ImageUtil {
    public static boolean merge(String[] imgs, String type, String mergePic) {
        int dstHeight = 0;
        int dstWidth = 0;
        // 获取需要拼接的图片长度
        int len = imgs.length;
        // 判断长度是否大于0
        if (len < 1) {
            return false;
        }
        File[] file = new File[len];
        BufferedImage[] images = new BufferedImage[len];
        int[][] ImageArrays = new int[len][];
        for (int i = 0; i < len; i++) {
            try {
                file[i] = new File(imgs[i]);
                images[i] = ImageIO.read(file[i]);
            } catch (Exception e) {
                e.printStackTrace();
                return false;
            }

            int width = images[i].getWidth();
            int height = images[i].getHeight();

            // 从图片中读取RGB 像素
            ImageArrays[i] = new int[width * height];
            ImageArrays[i] = images[i].getRGB(0, 0, width, height, ImageArrays[i], 0, width);

            // 计算合并的宽度和高度
            dstWidth = dstWidth > width ? dstWidth : width;
            dstHeight += height;
        }

        // 合成图片像素
        System.out.println("宽度:" + dstWidth);
        System.out.println("高度:" + dstHeight);

        if (dstHeight < 1) {
            System.out.println("dstHeight < 1");
            return false;
        }
        // 生成新图片
        try {
            BufferedImage imageNew = new BufferedImage(dstWidth, dstHeight, BufferedImage.TYPE_INT_RGB);
            int width_i = 0;
            int height_i = 0;
            for (int i = 0; i < images.length; i++) {
                int width = images[i].getWidth();
                int height = images[i].getHeight();
                imageNew.setRGB(0, height_i, width, height, ImageArrays[i], 0, width);
                height_i += height;
            }

            File outFile = new File(mergePic);
            // 写图片，输出到硬盘
            ImageIO.write(imageNew, type, outFile);
        } catch (Exception e) {
            e.printStackTrace();
            return false;
        }
        return true;
    }

    public static void main(String[] args) throws Exception {
        String saveFile = "E:\\tmp\\avatar2.png";
        String images[] = {"E:\\tmp\\avatar.png", "E:\\tmp\\avatar.png"};
        ImageUtil.merge(images, "png", saveFile);
    }
}

效果如下：