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Querying Object Metadata
Last updated: 2024-02-02 16:24:05
Querying Object Metadata
Last updated: 2024-02-02 16:24:05

Overview

This document provides an overview of APIs and SDK code samples related to querying object metadata.
API
Operation
Description
Querying object metadata
Queries the metadata of an object.

Simple Operations

Requests for simple operations need to be initiated through COSClient instances. You need to create a COSClient instance before performing simple operations.
COSClient instances are concurrency safe. You are advised to create only one COSClient instance for a process and then close it when it is no longer used to initiate requests.

Creating a COSClient instance

Before calling the COS API, you need to create a COSClient instance.
// Create a COSClient instance, which is used to initiate requests later.
COSClient createCOSClient() {
// Set the user identity information.
// Log in to the [CAM console](https://console.tencentcloud.com/cam/capi) to view and manage the `SecretId` and `SecretKey` of your project.
String secretId = "SECRETID";
String secretKey = "SECRETKEY";
COSCredentials cred = new BasicCOSCredentials(secretId, secretKey);

// `ClientConfig` contains the COS client configuration for subsequent COS requests.
ClientConfig clientConfig = new ClientConfig();

// Set the bucket region.
// For more information on COS regions, please visit https://www.tencentcloud.com/document/product/436/6224.
clientConfig.setRegion(new Region("COS_REGION"));

// Set the request protocol, `http` or `https`.
// For 5.6.53 and earlier versions, HTTPS is recommended.
// Starting from 5.6.54, HTTPS is used by default.
clientConfig.setHttpProtocol(HttpProtocol.https);

// The following settings are optional.

// Set the read timeout period, which is 30s by default.
clientConfig.setSocketTimeout(30*1000);
// Set the connection timeout period, which is 30s by default.
clientConfig.setConnectionTimeout(30*1000);

// If necessary, set the HTTP proxy, IP, and port.
clientConfig.setHttpProxyIp("httpProxyIp");
clientConfig.setHttpProxyPort(80);

// Generate a COS client.
return new COSClient(cred, clientConfig);
}

Creating a COSClient client with a temporary key

If you want to request COS with a temporary key, you need to create a COSClient instance with the temporary key. This SDK does not generate temporary keys. For how to generate a temporary key, please see Generating a Temporary Keys.

// Create a COSClient instance, which is used to initiate requests later.
COSClient createCOSClient() {
// Here, the temporary key information is needed.
// For how to generate temporary keys, please visit https://www.tencentcloud.com/document/product/436/14048.
String tmpSecretId = "TMPSECRETID";
String tmpSecretKey = "TMPSECRETKEY";
String sessionToken = "SESSIONTOKEN";

COSCredentials cred = new BasicSessionCredentials(tmpSecretId, tmpSecretKey, sessionToken);

// `ClientConfig` contains the COS client configuration for subsequent COS requests.
ClientConfig clientConfig = new ClientConfig();

// Set the bucket region.
// For more information on COS regions, please visit https://www.tencentcloud.com/document/product/436/6224.
clientConfig.setRegion(new Region("COS_REGION"));

// Set the request protocol, `http` or `https`.
// For 5.6.53 and earlier versions, HTTPS is recommended.
// Starting from 5.6.54, HTTPS is used by default.
clientConfig.setHttpProtocol(HttpProtocol.https);

// The following settings are optional.

// Set the read timeout period, which is 30s by default.
clientConfig.setSocketTimeout(30*1000);
// Set the connection timeout period, which is 30s by default.
clientConfig.setConnectionTimeout(30*1000);

// If necessary, set the HTTP proxy, IP, and port.
clientConfig.setHttpProxyIp("httpProxyIp");
clientConfig.setHttpProxyPort(80);

// Generate a COS client.
return new COSClient(cred, clientConfig);
}

Querying object metadata

This API (HEAD Object) is used to query object metadata.

Method prototype

public ObjectMetadata getObjectMetadata(String bucketName, String key)
throws CosClientException, CosServiceException;

Sample request

// Before using the COS API, ensure that the process contains a COSClient instance. If such an instance does not exist, create one.
// For the detailed code, see "Simple Operations -> Creating a COSClient instance" on the current page.
COSClient cosClient = createCOSClient();

// Enter the bucket name in the format of `BucketName-APPID`.
String bucketName = "examplebucket-1250000000";
// Object key, the unique ID of an object in a bucket. For more information, please see [Object Key](https://www.tencentcloud.com/document/product/436/13324).
String key = "exampleobject";

try {
ObjectMetadata objectMetadata = cosClient.getObjectMetadata(bucketName, key);
System.out.println(objectMetadata.getCrc64Ecma());
System.out.println(objectMetadata.getLastModified());
} catch (CosServiceException e) {
e.printStackTrace();
} catch (CosClientException e) {
e.printStackTrace();
}

// After confirming that the process does not use the COSClient instance anymore, close it.
cosClient.shutdown();

Parameter description

Parameter
Description
Type
bucketName
Bucket name in the format of BucketName-APPID. For details, see Naming Conventions
String
key
Object key, the unique identifier of an object in a bucket. For example, in the object endpoint examplebucket-1250000000.cos.ap-guangzhou.myqcloud.com/do/picture.jpg, the object key is doc/picture.jpg. For details, see ObjectKey
String

Response description

Success: returns ObjectMetadata, including the user-defined headers and object metadata such as the ETag.
Failure: if an error (such as authentication failure) occurs, the CosClientException or CosServiceException exception will be thrown. For more information, please see Troubleshooting.

Response parameters

The ObjectMetadata class is used to record the metadata of an object. The main members are described as follows:
Member Name
Description
Type
httpExpiresDate
Cache expiration time, which is the same value as that of the Expires field in HTTP response header
Date
ongoingRestore
Indicates the object is being restored from ARCHIVE
Boolean
userMetadata
User-defined metadata prefixed with x-cos-meta-
Map<String, String>
metadata
Headers other than user-defined metadata
Map<String, String>
restoreExpirationTime
Expiration time for an object copy restored from ARCHIVE
Date
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