Obtaining Data Metadata

Updated at：2025-11-03

Overview

Object metadata refers to the attribute descriptions of files uploaded to BOS and is categorized into two types: system-defined metadata and user-defined metadata. Metadata can be configured during various upload methods or file copying processes.

System-defined Metadata

Each object is associated with a set of metadata. Metadata identifies the attributes of an object, such as the date and content length, which is used for object management.

System-defined metadata is further divided into two categories: modifiable by users and unmodifiable by users. Inherent attributes of an object, such as creation date, content length, last modification time, and MD5 checksum, are unmodifiable metadata. Attributes like Content-Type, Cache-Control, and storage-class can be modified by users when creating the object or as required. For a detailed description of system-defined metadata, please refer to the table below:

Name	Type	Description	Whether it can be modified by users
Cache-Control	String	Cache settings for downloading the object. Common values include private, no-cache, max-age, must-revalidate.	Yes
Content-Disposition	String	Specify whether the browser should download the file. Possible values are inline and attachment, e.g., filename="download.txt".	Yes
Content-MD5	String	The MD5 checksum of the HTTP request content as defined in RFC 2616, used to ensure consistency between the file stored on BOS and the file expected by the user.	No
Content-Length	Long Int	The size of the data returned to the object.	No
Content-Type	String	The object's type and encoding method.	Yes
Expires	String	Set the cache expiration time when the object is downloaded.	Yes
ETag	String	The HTTP protocol entity tag of the object.	No
x-bce-storage-class	String	Standard storage returns STANDARD, infrequent access storage returns STANDARD_IA, cold storage returns COLD, and archive storage returns ARCHIVE.	No
x-bce-object-type	String	Determine whether an object is appendable or regular. Appendable objects can have data appended, while regular ones cannot. Archive storage does not support appendable objects.	No
x-bce-tagging-count	Long Int	Specify the number of tags associated with an object.	No

User-defined metadata

Enable users to add additional descriptions to an object. In BOS, all parameters prefixed with x-bce-meta- are considered user-defined metadata, such as x-bce-meta-tag. An object can have multiple user-defined metadata entries, which will be returned in the HTTP header during downloads using GetObject or HeadObject.

Description:

The size limit for the PUT request header is 8 KB. Within the PUT request header, user-defined metadata has a size limit of 2 KB.

Operation types

BOS supports obtaining object meta information through various SDKs, as follows:

[Java SDK](BOS/SDK/Java-SDK/File management/Get and update file meta information.md)
[Python SDK](BOS/SDK/Python-SDK/File management/Get and update file meta information.md)
PHP SDK
[C++ SDK](BOS/SDK/C++-SDK/File management/Get and update file meta information.md)

Example

Take the Java SDK as an example

Plain Text

1String EndPoint = "bj.bce.bos.com"
2public static void GetObjectMeta(BosClient bosClient, String bucketname, String objectkey)
3    {
4        ObjectMetadata objectMetadata；
5        objectMetadata = bosClient.getObjectMetadata(bucketname, objectkey);
6        System.out.println(objectMetadata.getContentType());
7        System.out.println(objectMetadata.getUserMetadata());
8    }

Delete data

Viewing File List