InputStream 转 MultipartFile

将 `InputStream` 转换为 `MultipartFile` 可以通过创建一个自定义的 `MultipartFile` 实现。以下是一个示例代码：

import org.springframework.web.multipart.MultipartFile;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;

public class InputStreamMultipartFile implements MultipartFile {

    private final String name;
    private final String originalFileName;
    private final String contentType;
    private final byte[] content;

    public InputStreamMultipartFile(String name, String originalFileName, String contentType, byte[] content) {
        this.name = name;
        this.originalFileName = originalFileName;
        this.contentType = contentType;
        this.content = content;
    }

    @Override
    public String getName() {
        return name;
    }

    @Override
    public String getOriginalFilename() {
        return originalFileName;
    }

    @Override
    public String getContentType() {
        return contentType;
    }

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

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

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

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

    @Override
    public void transferTo(java.io.File file) throws IOException, IllegalStateException {
        throw new UnsupportedOperationException("Not implemented");
    }
}

然后，您可以使用以下代码将 `InputStream` 转换为 `MultipartFile`：

InputStream inputStream = ...;
MultipartFile multipartFile = new InputStreamMultipartFile("file", "filename.txt", "text/plain", inputStream.readAllBytes());

请注意，上述示例中的 `transferTo` 方法未实现。如果需要支持此方法，您可以在自定义 `MultipartFile` 类中实现该方法。