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Checking Whether Objects Exist

Last updated: 2022-01-27 13:10:20

    Overview

    This document provides an overview of the API and sample code for quickly checking whether an object exists in a bucket. The sample code actually calls the HEAD Object COS API and is a simplified version of the API.

    In addition to checking whether an object exists, HEAD Object returns object metadata. To view the SDK API that contains the full functionality of HEAD Object, please see Querying Object Metadata.

    API Operation Description
    HEAD Object 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.cloud.tencent.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://intl.cloud.tencent.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://intl.cloud.tencent.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://intl.cloud.tencent.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);
    }
    

    Checking whether an object exists

    This API calls the object metadata query API to check whether an object exists.

    Method prototype

    public boolean doesObjectExist(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://intl.cloud.tencent.com/document/product/436/13324).
    String key = "exampleobject";
    try {
      boolean objectExists = cosClient.doesObjectExist(bucketName, key);
    } 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: return a Boolean value. true: the object exists. false: the object does not exist.
    • Failure: if an error (such as authentication failure) occurs, the CosClientException or CosServiceException exception will be thrown. For more information, please see Troubleshooting.
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