Java中base64转multipartFile工具类

由于Base64编码的数据是字符串形式的，需要将其转换为二进制数据才能保存为文件。因此，需要先将Base64编码的字符串转换为byte数组，再将byte数组转换为MultipartFile格式的文件。

以下是Java中将Base64编码的字符串转换为MultipartFile格式的工具类：

import org.springframework.web.multipart.MultipartFile;
import sun.misc.BASE64Decoder;

import java.io.IOException;
import java.util.Base64;

public class Base64ToMultipartFileUtil {

    public static MultipartFile base64ToMultipart(String base64) throws IOException {
        String[] baseStrs = base64.split(",");
        byte[] bytes = new BASE64Decoder().decodeBuffer(baseStrs[1]);

        for (int i = 0; i < bytes.length; ++i) {
            if (bytes[i] < 0) {
                bytes[i] += 256;
            }
        }

        return new Base64MultipartFile(bytes, baseStrs[0]);
    }

    private static class Base64MultipartFile implements MultipartFile {

        private final byte[] imgContent;
        private final String header;

        public Base64MultipartFile(byte[] imgContent, String header) {
            this.imgContent = imgContent;
            this.header = header.split(";")[0];
        }

        @Override
        public String getName() {
            return System.currentTimeMillis() + Math.random() + "." + header.split("/")[1];
        }

        @Override
        public String getOriginalFilename() {
            return System.currentTimeMillis() + (int) Math.random() * 10000 + "." + header.split("/")[1];
        }

        @Override
        public String getContentType() {
            return header.split(":")[1];
        }

        @Override
        public boolean isEmpty() {
            return imgContent == null || imgContent.length == 0;
        }

        @Override
        public long getSize() {
            return imgContent.length;
        }

        @Override
        public byte[] getBytes() throws IOException {
            return imgContent;
        }

        @Override
        public InputStream getInputStream() throws IOException {
            return new ByteArrayInputStream(imgContent);
        }

        @Override
        public void transferTo(File dest) throws IOException, IllegalStateException {
            FileUtils.writeByteArrayToFile(dest, imgContent);
        }
    }
}

使用方法如下：

MultipartFile multipartFile = Base64ToMultipartFileUtil.base64ToMultipart(base64String);