aws java api_例如：使用 AWS SDK for Java 文档 API 的批量操作 - Amazon DynamoDB
本文属于机器翻译版本。若本译文内容与英语原文存在差异，则一律以英文原文为准。
例如：使用 AWS SDK for Java 文档 API 的批量操作
本部分提供在 Amazon DynamoDB 中使用AWS SDK for Java文档 API 执行批量写入和批量获取操作的示例。
注意
适用于 Java 的开发工具包还提供一个对象持久化模型，可用来将客户端类映射到 DynamoDB 表。该方法可以减少您必须编写的代码数量。有关更多信息，请参阅AWS 开发工具包: DynamoDBMapper。
例如：使用 AWS SDK for Java 文档 API 的批量写入操作
以下 Java 代码示例使用 batchWriteItem 方法执行以下放置和删除操作：
在 Forum 表中放置一个项目。
在 Thread 表中放置一个项目并删除一个项目。
在创建批量写入请求时，您可以就一个或多个表指定任意数量的放置和删除请求。但是，batchWriteItem 对批量写入请求的大小，以及单个批量写入操作中的放置和删除操作数量有限制。如果您的请求超出这些限制，请求会遭到拒绝。如果您的表的预置吞吐量不足，无法处理此请求，那么响应将返回未处理的请求项目。
以下示例查看响应，了解响应是否包含任何未处理的请求项目。如果存在，则循环返回，并重新发送包含请求中的未处理项目的 batchWriteItem 请求。如果您已按照为 DynamoDB 中的代码示例创建表和加载数据部分进行操作，您应当已经创建了 Forum 和 Thread 表。您还能够以编程方式创建这些表和上传示例数据。有关更多信息，请参阅使用适用于 Java 的 AWS 开发工具包创建示例表并上传数据。
有关测试以下示例的分步说明，请参阅 Java 代码示例。
例
/**
* Copyright 2010-2019 Amazon.com, Inc. or its affiliates. All Rights Reserved.
*
* This file is licensed under the Apache License, Version 2.0 (the "License").
* You may not use this file except in compliance with the License. A copy of
* the License is located at
*
* http://aws.amazon.com/apache2.0/
*
* This file is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
* CONDITIONS OF ANY KIND, either express or implied. See the License for the
* specific language governing permissions and limitations under the License.
*/
package com.amazonaws.codesamples.document;
import java.io.IOException;
import java.util.Arrays;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import com.amazonaws.services.dynamodbv2.AmazonDynamoDB;
import com.amazonaws.services.dynamodbv2.AmazonDynamoDBClientBuilder;
import com.amazonaws.services.dynamodbv2.document.BatchWriteItemOutcome;
import com.amazonaws.services.dynamodbv2.document.DynamoDB;
import com.amazonaws.services.dynamodbv2.document.Item;
import com.amazonaws.services.dynamodbv2.document.TableWriteItems;
import com.amazonaws.services.dynamodbv2.model.WriteRequest;
public class DocumentAPIBatchWrite {
static AmazonDynamoDB client = AmazonDynamoDBClientBuilder.standard().build();
static DynamoDB dynamoDB = new DynamoDB(client);
static String forumTableName = "Forum";
static String threadTableName = "Thread";
public static void main(String[] args) throws IOException {
writeMultipleItemsBatchWrite();
}
private static void writeMultipleItemsBatchWrite() {
try {
// Add a new item to Forum
TableWriteItems forumTableWriteItems = new TableWriteItems(forumTableName) // Forum
.withItemsToPut(new Item().withPrimaryKey("Name", "Amazon RDS").withNumber("Threads", 0));
// Add a new item, and delete an existing item, from Thread
// This table has a partition key and range key, so need to specify
// both of them
TableWriteItems threadTableWriteItems = new TableWriteItems(threadTableName)
.withItemsToPut(new Item().withPrimaryKey("ForumName", "Amazon RDS", "Subject", "Amazon RDS Thread 1")
.withString("Message", "ElastiCache Thread 1 message")
.withStringSet("Tags", new HashSet(Arrays.asList("cache", "in-memory"))))
.withHashAndRangeKeysToDelete("ForumName", "Subject", "Amazon S3", "S3 Thread 100");
System.out.println("Making the request.");
BatchWriteItemOutcome outcome = dynamoDB.batchWriteItem(forumTableWriteItems, threadTableWriteItems);
do {
// Check for unprocessed keys which could happen if you exceed
// provisioned throughput
Map> unprocessedItems = outcome.getUnprocessedItems();
if (outcome.getUnprocessedItems().size() == 0) {
System.out.println("No unprocessed items found");
}
else {
System.out.println("Retrieving the unprocessed items");
outcome = dynamoDB.batchWriteItemUnprocessed(unprocessedItems);
}
} while (outcome.getUnprocessedItems().size() > 0);
}
catch (Exception e) {
System.err.println("Failed to retrieve items: ");
e.printStackTrace(System.err);
}
}
}
例如：使用 AWS SDK for Java 文档 API 的批量获取操作
以下 Java 代码示例使用 batchGetItem 方法检索 Forum 和 Thread 表中的多个项目。BatchGetItemRequest 为每个要获取的项目指定表名称和键列表。示例介绍通过打印检索到的项目来处理响应。
注意
此代码示例假定您已按照 为 DynamoDB 中的代码示例创建表和加载数据部分的说明，为您的账户将数据加载到 DynamoDB 中。
有关运行以下示例的分步说明，请参阅 Java 代码示例。
例
/**
* Copyright 2010-2019 Amazon.com, Inc. or its affiliates. All Rights Reserved.
*
* This file is licensed under the Apache License, Version 2.0 (the "License").
* You may not use this file except in compliance with the License. A copy of
* the License is located at
*
* http://aws.amazon.com/apache2.0/
*
* This file is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
* CONDITIONS OF ANY KIND, either express or implied. See the License for the
* specific language governing permissions and limitations under the License.
*/
package com.amazonaws.codesamples.document;
import java.io.IOException;
import java.util.List;
import java.util.Map;
import com.amazonaws.services.dynamodbv2.AmazonDynamoDB;
import com.amazonaws.services.dynamodbv2.AmazonDynamoDBClientBuilder;
import com.amazonaws.services.dynamodbv2.document.BatchGetItemOutcome;
import com.amazonaws.services.dynamodbv2.document.DynamoDB;
import com.amazonaws.services.dynamodbv2.document.Item;
import com.amazonaws.services.dynamodbv2.document.TableKeysAndAttributes;
import com.amazonaws.services.dynamodbv2.model.KeysAndAttributes;
public class DocumentAPIBatchGet {
static AmazonDynamoDB client = AmazonDynamoDBClientBuilder.standard().build();
static DynamoDB dynamoDB = new DynamoDB(client);
static String forumTableName = "Forum";
static String threadTableName = "Thread";
public static void main(String[] args) throws IOException {
retrieveMultipleItemsBatchGet();
}
private static void retrieveMultipleItemsBatchGet() {
try {
TableKeysAndAttributes forumTableKeysAndAttributes = new TableKeysAndAttributes(forumTableName);
// Add a partition key
forumTableKeysAndAttributes.addHashOnlyPrimaryKeys("Name", "Amazon S3", "Amazon DynamoDB");
TableKeysAndAttributes threadTableKeysAndAttributes = new TableKeysAndAttributes(threadTableName);
// Add a partition key and a sort key
threadTableKeysAndAttributes.addHashAndRangePrimaryKeys("ForumName", "Subject", "Amazon DynamoDB",
"DynamoDB Thread 1", "Amazon DynamoDB", "DynamoDB Thread 2", "Amazon S3", "S3 Thread 1");
System.out.println("Making the request.");
BatchGetItemOutcome outcome = dynamoDB.batchGetItem(forumTableKeysAndAttributes,
threadTableKeysAndAttributes);
Map unprocessed = null;
do {
for (String tableName : outcome.getTableItems().keySet()) {
System.out.println("Items in table " + tableName);
List items = outcome.getTableItems().get(tableName);
for (Item item : items) {
System.out.println(item.toJSONPretty());
}
}
// Check for unprocessed keys which could happen if you exceed
// provisioned
// throughput or reach the limit on response size.
unprocessed = outcome.getUnprocessedKeys();
if (unprocessed.isEmpty()) {
System.out.println("No unprocessed keys found");
}
else {
System.out.println("Retrieving the unprocessed keys");
outcome = dynamoDB.batchGetItemUnprocessed(unprocessed);
}
} while (!unprocessed.isEmpty());
}
catch (Exception e) {
System.err.println("Failed to retrieve items.");
System.err.println(e.getMessage());
}
}
}