异常

java.io.FileNotFoundException: Byte array resource [resource loaded from byte array] cannot be resolved to absolute file path
    at org.springframework.core.io.AbstractResource.getFile(AbstractResource.java:114)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(NativeMethodAccessorImpl.java)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at com.alibaba.fastjson.util.FieldInfo.get(FieldInfo.java:453)
    at com.alibaba.fastjson.serializer.FieldSerializer.getPropertyValueDirect(FieldSerializer.java:110)
    at com.alibaba.fastjson.serializer.JavaBeanSerializer.write(JavaBeanSerializer.java:196)
    at com.alibaba.fastjson.serializer.JSONSerializer.writeWithFieldName(JSONSerializer.java:304)
    at com.alibaba.fastjson.serializer.ASMSerializer_1_HttpEntity.write
    at com.alibaba.fastjson.serializer.ListSerializer.write(ListSerializer.java:126)
    at com.alibaba.fastjson.serializer.MapSerializer.write(MapSerializer.java:243)
    at com.alibaba.fastjson.serializer.JSONSerializer.write(JSONSerializer.java:275)
    at com.alibaba.fastjson.JSON.toJSONString(JSON.java:648)
    at com.alibaba.fastjson.JSON.toJSONString(JSON.java:590)
    at com.alibaba.fastjson.JSON.toJSONString(JSON.java:555)

上下文

其中file为MultipartFile

MultiValueMap<String, Object> map = new LinkedMultiValueMap<String, Object>();
        final String filename = file.getName();
        Path path = file.toPath();
        map.add("name", filename);
        map.add("filename", filename);

        HttpHeaders fileHeaders = new HttpHeaders();
        fileHeaders.setContentDispositionFormData("file",filename);
        ByteArrayResource contentsAsResource = new ByteArrayResource(Files.readAllBytes(path)){
            @Override
            public String getFilename(){
                return filename;
            }
        };
        map.add("file", new HttpEntity<>(contentsAsResource, fileHeaders));
     

报错的地方

JSON.toJSONString(map)

toJSONString也不是所有类型的都可以使用，要慎重一点，这里遇到file要去序列化，然后就报错了。