spring boot3 构造自定义MultipartFile

package ***;

import org.springframework.web.multipart.MultipartFile;

import java.io.*;
import java.nio.file.Files;
import java.nio.file.Path;

public class CustomMultipartFile implements MultipartFile {

    private final byte[] fileContent;
    private final String fileName;
    private final String contentType;

    public CustomMultipartFile(byte[] fileContent, String fileName) {
        this.fileContent = fileContent != null ? fileContent : new byte[0];
        this.fileName = fileName;
        this.contentType = detectContentType(fileName);
    }

    public CustomMultipartFile(byte[] fileContent, String fileName, String contentType) {
        this.fileContent = fileContent != null ? fileContent : new byte[0];
        this.fileName = fileName;
        this.contentType = contentType != null ? contentType : detectContentType(fileName);
    }

    private String detectContentType(String fileName) {
        if (fileName == null) {
            return "application/octet-stream";
        }

        try {
            // 使用 JDK 的 Files.probeContentType 检测类型
            Path tempFile = Files.createTempFile("temp", fileName);
            Files.write(tempFile, new byte[0]);
            String detectedType = Files.probeContentType(tempFile);
            Files.deleteIfExists(tempFile);

            if (detectedType != null) {
                return detectedType;
            }
        } catch (IOException e) {
            // 忽略异常，使用默认类型
        }

        // 手动检测常见类型
        String lowerName = fileName.toLowerCase();
        if (lowerName.endsWith(".jpg") || lowerName.endsWith(".jpeg")) {
            return "image/jpeg";
        } else if (lowerName.endsWith(".png")) {
            return "image/png";
        } else if (lowerName.endsWith(".gif")) {
            return "image/gif";
        } else if (lowerName.endsWith(".pdf")) {
            return "application/pdf";
        } else if (lowerName.endsWith(".txt")) {
            return "text/plain";
        }

        return "application/octet-stream";
    }

    @Override
    public String getName() {
        return "file";
    }

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

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

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

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

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

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

    @Override
    public void transferTo(File dest) throws IOException, IllegalStateException {
        if (dest == null) {
            throw new IllegalArgumentException("目标文件不能为空");
        }

        if (!dest.getParentFile().exists() && !dest.getParentFile().mkdirs()) {
            throw new IOException("无法创建目录: " + dest.getParent());
        }

        try (FileOutputStream fos = new FileOutputStream(dest)) {
            fos.write(fileContent);
        }
    }

    @Override
    public void transferTo(Path dest) throws IOException, IllegalStateException {
        if (dest == null) {
            throw new IllegalArgumentException("目标路径不能为空");
        }

        Files.createDirectories(dest.getParent());
        Files.write(dest, fileContent);
    }
}