# Listing Buckets

#### Scenarios

If you want to view information about all buckets created by yourself, you can call the API for listing buckets.

The following describes how to call the API for listing buckets. For details about how to call an API, see Calling APIs.

#### Prerequisites

- You have obtained the AK and SK. For details about how to obtain the AK and SK, see Obtaining Access Keys (AK/SK).
- You have specified the region where you want to list buckets and obtained the endpoint required for API calls. For details, see Regions and Endpoints.

#### Obtaining the Bucket List in the a1 Region

In this example, an Apache HttpClient is used.

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    package com.obsclient;

    import java.io.*;
    import java.util.ArrayList;
    import java.util.List;

    import org.apache.http.Header;
    import org.apache.http.HttpEntity;
    import org.apache.http.NameValuePair;
    import org.apache.http.client.entity.UrlEncodedFormEntity;
    import org.apache.http.client.methods.CloseableHttpResponse;
    import org.apache.http.client.methods.HttpGet;
    import org.apache.http.client.methods.HttpPost;
    import org.apache.http.client.methods.HttpPut;
    import org.apache.http.entity.InputStreamEntity;
    import org.apache.http.entity.StringEntity;
    import org.apache.http.impl.client.CloseableHttpClient;
    import org.apache.http.impl.client.HttpClients;
    import org.apache.http.message.BasicNameValuePair;

    public class TestMain {

        public static String accessKey = "UDSIAMSTUBTEST000012"; //The value of this parameter is the AK obtained.
         public static String securityKey = "Udsiamstubtest000000UDSIAMSTUBTEST000012";  //The value of this parameter is the SK obtained.

        public static void main(String[] str) {

            listAllMyBuckets();

        }

        private static void listAllMyBuckets() {
            CloseableHttpClient httpClient = HttpClients.createDefault();
            String requesttime = DateUtils.formatDate(System.currentTimeMillis());

            HttpGet httpGet = new HttpGet("http://obs.a1.example.com");
            httpGet.addHeader("Date", requesttime);

            /**Calculate the signature based on the request.**/
            String contentMD5 = "";
            String contentType = "";
            String canonicalizedHeaders = "";
            String canonicalizedResource = "/";
            // Content-MD5 and Content-Type fields do not contain line breaks. The data format is RFC 1123, which is the same as the time in the request.
            String canonicalString = "GET" + "\n" + contentMD5 + "\n" + contentType + "\n" + requesttime + "\n" + canonicalizedHeaders + canonicalizedResource;
            System.out.println("StringToSign:[" + canonicalString + "]");
            String signature = null;
            try {
                signature = Signature.signWithHmacSha1(securityKey, canonicalString);

                 // Added the Authorization: OBS AccessKeyID:signature field to the header.
                httpGet.addHeader("Authorization", "OBS " + accessKey + ":" + signature);
                CloseableHttpResponse httpResponse = httpClient.execute(httpGet);

                // Prints the sending request information and the received response message.
                System.out.println("Request Message:");
                System.out.println(httpGet.getRequestLine());
                for (Header header : httpGet.getAllHeaders()) {
                    System.out.println(header.getName() + ":" + header.getValue());
                }

                System.out.println("Response Message:");
                System.out.println(httpResponse.getStatusLine());
                for (Header header : httpResponse.getAllHeaders()) {
                    System.out.println(header.getName() + ":" + header.getValue());
                }
                BufferedReader reader = new BufferedReader(new InputStreamReader(
                        httpResponse.getEntity().getContent()));

                String inputLine;
                StringBuffer response = new StringBuffer();

                while ((inputLine = reader.readLine()) != null) {
                    response.append(inputLine);
                }
                reader.close();
                // print result
                System.out.println(response.toString());
            } catch (UnsupportedEncodingException e) {
                e.printStackTrace();

            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                try {
                    httpClient.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }

        }

    }

The format of the Date header field DateUtils is as follows:

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    package com.obsclient;

    import java.text.DateFormat;
    import java.text.SimpleDateFormat;
    import java.util.Locale;
    import java.util.TimeZone;

    public class DateUtils {

        public static String formatDate(long time)
        {
            DateFormat serverDateFormat = new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss z", Locale.ENGLISH);
            serverDateFormat.setTimeZone(TimeZone.getTimeZone("GMT"));
            return serverDateFormat.format(time);
        }
    }

The method of calculating the signature character string is as follows:

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    package com.obsclient;

    import javax.crypto.Mac;
    import javax.crypto.spec.SecretKeySpec;
    import java.io.UnsupportedEncodingException;
    import java.security.NoSuchAlgorithmException;
    import java.security.InvalidKeyException;
    import java.util.Base64;

    public class Signature {
        public static String signWithHmacSha1(String sk, String canonicalString) throws UnsupportedEncodingException {

            try {
                SecretKeySpec signingKey = new SecretKeySpec(sk.getBytes("UTF-8"), "HmacSHA1");
                Mac mac = Mac.getInstance("HmacSHA1");
                mac.init(signingKey);
                return Base64.getEncoder().encodeToString(mac.doFinal(canonicalString.getBytes("UTF-8")));
            } catch (NoSuchAlgorithmException | InvalidKeyException | UnsupportedEncodingException e) {
                e.printStackTrace();
            }
            return null;
        }
    }

Parent topic: Getting Started