步驟 2：測試分類帳的連線

在此步驟中，您確認可以使用交易資料 API 端點連接到 Amazon QLDB 中的vehicle-registration總帳。

測試分類帳的連線

1. 複查下列程式 (ConnectToLedger.java)，此程式會建立與vehicle-registration分類帳的資料階段作業連線。

   2.x

   /*
    * Copyright 2019 Amazon.com, Inc. or its affiliates. All Rights Reserved.
    * SPDX-License-Identifier: MIT-0
    *
    * Permission is hereby granted, free of charge, to any person obtaining a copy of this
    * software and associated documentation files (the "Software"), to deal in the Software
    * without restriction, including without limitation the rights to use, copy, modify,
    * merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
    * permit persons to whom the Software is furnished to do so.
    *
    * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
    * INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
    * PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
    * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
    * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
    * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
    */
   
   package software.amazon.qldb.tutorial;
   
   import java.net.URI;
   import java.net.URISyntaxException;
   import org.slf4j.Logger;
   import org.slf4j.LoggerFactory;
   import software.amazon.awssdk.auth.credentials.AwsCredentialsProvider;
   import software.amazon.awssdk.services.qldbsession.QldbSessionClient;
   import software.amazon.awssdk.services.qldbsession.QldbSessionClientBuilder;
   import software.amazon.qldb.QldbDriver;
   import software.amazon.qldb.RetryPolicy;
   
   /**
    * Connect to a session for a given ledger using default settings.
    * <p>
    * This code expects that you have AWS credentials setup per:
    * http://docs.aws.amazon.com/java-sdk/latest/developer-guide/setup-credentials.html
    */
   public final class ConnectToLedger {
       public static final Logger log = LoggerFactory.getLogger(ConnectToLedger.class);
       public static AwsCredentialsProvider credentialsProvider;
       public static String endpoint = null;
       public static String ledgerName = Constants.LEDGER_NAME;
       public static String region = null;
       public static QldbDriver driver;
   
       private ConnectToLedger() {
       }
   
       /**
        * Create a pooled driver for creating sessions.
        *
        * @param retryAttempts How many times the transaction will be retried in
        * case of a retryable issue happens like Optimistic Concurrency Control exception,
        * server side failures or network issues.
        * @return The pooled driver for creating sessions.
        */
       public static QldbDriver createQldbDriver(int retryAttempts) {
           QldbSessionClientBuilder builder = getAmazonQldbSessionClientBuilder();
           return QldbDriver.builder()
                                .ledger(ledgerName)
                                .transactionRetryPolicy(RetryPolicy
                                      .builder()
                                      .maxRetries(retryAttempts)
                                      .build())
                                .sessionClientBuilder(builder)
                                .build();
       }
   
       /**
        * Create a pooled driver for creating sessions.
        *
        * @return The pooled driver for creating sessions.
        */
       public static QldbDriver createQldbDriver() {
           QldbSessionClientBuilder builder = getAmazonQldbSessionClientBuilder();
           return QldbDriver.builder()
               .ledger(ledgerName)
               .transactionRetryPolicy(RetryPolicy.builder()
                                                  .maxRetries(Constants.RETRY_LIMIT).build())
               .sessionClientBuilder(builder)
               .build();
       }
   
       /**
        * Creates a QldbSession builder that is passed to the QldbDriver to connect to the Ledger.
        *
        * @return An instance of the AmazonQLDBSessionClientBuilder
        */
       public static QldbSessionClientBuilder getAmazonQldbSessionClientBuilder() {
           QldbSessionClientBuilder builder = QldbSessionClient.builder();
           if (null != endpoint && null != region) {
               try {
                   builder.endpointOverride(new URI(endpoint));
               } catch (URISyntaxException e) {
                   throw new IllegalArgumentException(e);
               }
           }
           if (null != credentialsProvider) {
               builder.credentialsProvider(credentialsProvider);
           }
           return builder;
       }
   
       /**
        * Create a pooled driver for creating sessions.
        *
        * @return The pooled driver for creating sessions.
        */
       public static QldbDriver getDriver() {
           if (driver == null) {
               driver = createQldbDriver();
           }
           return driver;
       }
   
   
       public static void main(final String... args) {
           Iterable<String> tables = ConnectToLedger.getDriver().getTableNames();
           log.info("Existing tables in the ledger:");
           for (String table : tables) {
               log.info("- {} ", table);
           }
       }
   }
   

   注意

   • 若要在分類帳上執行資料作業，您必須建立QldbDriver類別的執行環境，以連線至特定分類帳。這與您在上一個步驟中用來建立分類帳的用AmazonQLDB戶端不同的用戶端物件。先前的用戶端僅用於執行中列出的管理 API 作業Amazon QLDB API 參考參考。

   • 首先，創建一個QldbDriver對象。建立此動因時，您必須指定分類帳名稱。

     然後，您可以使用此驅動程式的execute方法來執行 PartiQL 陳述式。

   • 您可以選擇性地指定異動例外的重試次數上限。此方execute法會自動重試樂觀並行控制 (OCC) 衝突及其他常見暫態例外狀況，達到此可設定的限制。預設值為 4。

     如果達到限制後交易仍然失敗，則驅動程序拋出異常。如需進一步了解，請參閱 瞭解亞馬遜 QLDB 中的驅動程序的重試策略。

   1.x

   /*
    * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
    * SPDX-License-Identifier: MIT-0
    *
    * Permission is hereby granted, free of charge, to any person obtaining a copy of this
    * software and associated documentation files (the "Software"), to deal in the Software
    * without restriction, including without limitation the rights to use, copy, modify,
    * merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
    * permit persons to whom the Software is furnished to do so.
    *
    * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
    * INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
    * PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
    * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
    * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
    * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
    */
   
   package software.amazon.qldb.tutorial;
   
   import com.amazonaws.auth.AWSCredentialsProvider;
   import com.amazonaws.client.builder.AwsClientBuilder;
   import com.amazonaws.services.qldbsession.AmazonQLDBSessionClientBuilder;
   import org.slf4j.Logger;
   import org.slf4j.LoggerFactory;
   import software.amazon.qldb.PooledQldbDriver;
   import software.amazon.qldb.QldbDriver;
   import software.amazon.qldb.QldbSession;
   import software.amazon.qldb.exceptions.QldbClientException;
   
   /**
    * Connect to a session for a given ledger using default settings.
    * <p>
    * This code expects that you have AWS credentials setup per:
    * http://docs.aws.amazon.com/java-sdk/latest/developer-guide/setup-credentials.html
    */
   public final class ConnectToLedger {
       public static final Logger log = LoggerFactory.getLogger(ConnectToLedger.class);
       public static AWSCredentialsProvider credentialsProvider;
       public static String endpoint = null;
       public static String ledgerName = Constants.LEDGER_NAME;
       public static String region = null;
       private static PooledQldbDriver driver;
   
       private ConnectToLedger() {
       }
   
       /**
        * Create a pooled driver for creating sessions.
        *
        * @return The pooled driver for creating sessions.
        */
       public static PooledQldbDriver createQldbDriver() {
           AmazonQLDBSessionClientBuilder builder = AmazonQLDBSessionClientBuilder.standard();
           if (null != endpoint && null != region) {
               builder.setEndpointConfiguration(new AwsClientBuilder.EndpointConfiguration(endpoint, region));
           }
           if (null != credentialsProvider) {
               builder.setCredentials(credentialsProvider);
           }
           return PooledQldbDriver.builder()
                   .withLedger(ledgerName)
                   .withRetryLimit(Constants.RETRY_LIMIT)
                   .withSessionClientBuilder(builder)
                   .build();
       }
   
       /**
        * Create a pooled driver for creating sessions.
        *
        * @return The pooled driver for creating sessions.
        */
       public static PooledQldbDriver getDriver() {
           if (driver == null) {
               driver = createQldbDriver();
           }
           return driver;
       }
   
       /**
        * Connect to a ledger through a {@link QldbDriver}.
        *
        * @return {@link QldbSession}.
        */
       public static QldbSession createQldbSession() {
           return getDriver().getSession();
       }
   
       public static void main(final String... args) {
           try (QldbSession qldbSession = createQldbSession()) {
               log.info("Listing table names ");
               for (String tableName : qldbSession.getTableNames()) {
                   log.info(tableName);
               }
           } catch (QldbClientException e) {
               log.error("Unable to create session.", e);
           }
       }
   }

   注意

   • 若要在分類帳上執行資料作業，您必須建立PooledQldbDriver或QldbDriver類別的執行環境，以連線至特定分類帳。這與您在上一個步驟中用來建立分類帳的用AmazonQLDB戶端不同的用戶端物件。先前的用戶端僅用於執行中列出的管理 API 作業Amazon QLDB API 參考參考。

     我們建議您使用，PooledQldbDriver除非您需要使用QldbDriver. 的預設集區大小PooledQldbDriver是工作階段用戶端允許的開啟 HTTP 連線數目上限。

   • 首先，創建一個PooledQldbDriver對象。建立此動因時，您必須指定分類帳名稱。

     然後，您可以使用此驅動程式的execute方法來執行 PartiQL 陳述式。或者，您可以從此池驅動程序對象手動創建會話，並使用會話的execute方法。會話表示與分類帳的單個連接。

   • 您可以選擇性地指定異動例外的重試次數上限。此方execute法會自動重試樂觀並行控制 (OCC) 衝突及其他常見暫態例外狀況，達到此可設定的限制。預設值為 4。

     如果達到限制後交易仍然失敗，則驅動程序拋出異常。如需進一步了解，請參閱 瞭解亞馬遜 QLDB 中的驅動程序的重試策略。

2. 編譯並執行ConnectToLedger.java程式，以測試資料階段作業與vehicle-registration分類帳的連線。

覆寫AWS 區域

範例應用程式會以預設值連線至 QLDBAWS 區域，您可以按照先決條件步驟中的說明進行設定設定您的預設AWS憑證和區域。您也可以透過修改 QLDB 工作階段用戶端產生器屬性來變更區域。

2.x

下列程式碼範例會實體化新QldbSessionClientBuilder物件。

import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.qldbsession.QldbSessionClientBuilder;

// This client builder will default to US East (Ohio)
QldbSessionClientBuilder builder = QldbSessionClient.builder()
    .region(Region.US_EAST_2);

您可以使用此region方法，對 QLDB 執行程式碼。如需完整清單，請參閱中的 Amazon QLDB 端點和配額AWS 一般參考。

1.x

下列程式碼範例會實體化新AmazonQLDBSessionClientBuilder物件。

import com.amazonaws.regions.Regions;
import com.amazonaws.services.qldbsession.AmazonQLDBSessionClientBuilder;

// This client builder will default to US East (Ohio)
AmazonQLDBSessionClientBuilder builder = AmazonQLDBSessionClientBuilder.standard()
    .withRegion(Regions.US_EAST_2); 

您可以使用此withRegion方法，對 QLDB 執行程式碼。如需完整清單，請參閱中的 Amazon QLDB 端點和配額AWS 一般參考。

若要在vehicle-registration分類帳中建立表格，請繼續執行步驟 3：建立資料表、索引和範例資料。