SpringBoot实现自定义注解用于文件验证的详细过程(大小、扩展名、MIME类型)

import javax.validation.Constraint;
import javax.validation.Payload;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Documented
@Constraint(validatedBy = FileValidator.class)
@Target({ ElementType.METHOD, ElementType.FIELD })
@Retention(RetentionPolicy.RUNTIME)
public @interface ValidFile {
    String message() default "{constraints.ValidFileMimeType.message}";
    Class<?>[] groups() default {};
    Class<? extends Payload>[] payload() default {};

    String[] extensions() default {};
    String[] mimeTypes() default {};
    long maxSize() default 1024 * 1024; // 默认最大1MB
}

import org.springframework.web.multipart.MultipartFile;

import javax.validation.ConstraintValidator;
import javax.validation.ConstraintValidatorContext;
import java.io.IOException;

public class FileValidator implements ConstraintValidator<ValidFile, MultipartFile> {
    private final Tika tika = new Tika();
    private List<String> extensions;
    private List<String> mimeTypes;
    private long maxSize;

    @Override
    public void initialize(ValidFile constraintAnnotation) {
        extensions = List.of(constraintAnnotation.extensions());
        mimeTypes = List.of(constraintAnnotation.mimeTypes());
        maxSize = constraintAnnotation.maxSize();
    }

    @Override
    public boolean isValid(MultipartFile file, ConstraintValidatorContext context) {
        if (file == null || file.isEmpty()) {
            return true;
        }
        // 文件大小验证
        if (file.getSize() > maxSize) {
            return false;
        }
        // 文件扩展名验证
        // String fileName = file.getOriginalFilename();
        // String fileExtension = fileName.substring(fileName.lastIndexOf(".") + 1);
        String fileExtension = FilenameUtils.getExtension(file.getOriginalFilename());
        if( StringUtils.isNotBlank(fileExtension) && extensions.contains(fileExtension .toLowerCase())){
            retrun true;
        }
        // 这里使用apache tika验证文件mime,实际是通过文件头内容中的魔法数来验证的
        var detect = tika.detect(TikaInputStream.get(file.getInputStream()));
        return mimeTypes.contains(detect);
    }
}

import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.multipart.MultipartFile;

import javax.validation.constraints.NotNull;

@RestController
public class FileUploadController {

    @PostMapping("/upload")
    public ResponseEntity<?> uploadFile(@RequestParam("file") @NotNull @ValidFile(extensions = {"jpg", "png"}, mimeTypes = {"image/jpeg", "image/png"}, maxSize = 2 * 1024 * 1024) MultipartFile file) {
        // 文件处理逻辑
        return ResponseEntity.ok("File uploaded successfully");
    }
}