将File转化为MultipartFile

以下是将File转化为MultipartFile的两种方法：
1. 使用MockMultipartFile实现：

from org.springframework.mock.web import MockMultipartFile
import java.io.File
import java.io.FileInputStream

file = File("example.txt")
fileInputStream = FileInputStream(file)
multipartFile = MockMultipartFile("file", file.getName(), "text/plain", fileInputStream)

2. 使用html5的file api里的readAsDataURL函数实现转换：

function fileToMultipartFile(file) {
  var reader = new FileReader();
  reader.readAsDataURL(file);
  reader.onload = function () {
    var arrayBuffer = this.result;
    var bytes = new Uint8Array(arrayBuffer);
    var blob = new Blob([bytes], {type: "application/octet-stream"});
    var multipartFile = new File([blob], file.name, {type: file.type});
    return multipartFile;
  };
}