java把图片链接转换成MultipartFile

你可以使用`URL`类来下载图片，并将其转换为`byte[]`数组，然后将该数组转换为`MultipartFile`对象。以下是一个示例代码：

import org.springframework.web.multipart.MultipartFile;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;

public class ImageConverter {
    public static MultipartFile convertToMultipartFile(String imageUrl) throws IOException {
        URL url = new URL(imageUrl);
        try (InputStream inputStream = url.openStream();
             ByteArrayOutputStream outputStream = new ByteArrayOutputStream()) {
            byte[] buffer = new byte[4096];
            int bytesRead;
            while ((bytesRead = inputStream.read(buffer)) != -1) {
                outputStream.write(buffer, 0, bytesRead);
            }
            byte[] imageBytes = outputStream.toByteArray();
            return new InMemoryMultipartFile(imageBytes, url.getFile());
        }
    }
}

class InMemoryMultipartFile implements MultipartFile {
    private final byte[] content;
    private final String name;

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

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

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

    @Override
    public String getContentType() {
        // 设置图片的 Content-Type
        return "image/jpeg";
    }

    @Override
    public boolean isEmpty() {
        return false;
    }

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

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

    @Override
    public InputStream getInputStream() throws IOException {
        return null;
    }

    @Override
    public void transferTo(java.io.File file) throws IOException, IllegalStateException {
        // 可以选择将文件保存到本地
    }
}

你可以通过调用`convertToMultipartFile`方法并传入图片链接来获得对应的`MultipartFile`对象。请确保在使用该代码时导入了所需的依赖，如`org.springframework.web.multipart.MultipartFile`。