Example: Handling binary type attributes using the Amazon SDK for Java document API - Amazon DynamoDB
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Example: Handling binary type attributes using the Amazon SDK for Java document API

The following Java code example illustrates handling binary type attributes. The example adds an item to the Reply table. The item includes a binary type attribute (ExtendedMessage) that stores compressed data. The example then retrieves the item and prints all the attribute values. For illustration, the example uses the GZIPOutputStream class to compress a sample stream and assign it to the ExtendedMessage attribute. When the binary attribute is retrieved, it is decompressed using the GZIPInputStream class.


The SDK for Java also provides an object persistence model, enabling you to map your client-side classes to DynamoDB tables. This approach can reduce the amount of code that you have to write. For more information, see Java: DynamoDBMapper.

If you followed the Creating tables and loading data for code examples in DynamoDB section, you should already have created the Reply table. You can also create this table programmatically. For more information, see Creating example tables and uploading data using the Amazon SDK for Java.

For step-by-step instructions for testing the following sample, see Java code examples.


/** * 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.ByteArrayInputStream; import java.io.ByteArrayOutputStream; import java.io.IOException; import java.nio.ByteBuffer; import java.text.SimpleDateFormat; import java.util.Date; import java.util.TimeZone; import java.util.zip.GZIPInputStream; import java.util.zip.GZIPOutputStream; import com.amazonaws.services.dynamodbv2.AmazonDynamoDB; import com.amazonaws.services.dynamodbv2.AmazonDynamoDBClientBuilder; import com.amazonaws.services.dynamodbv2.document.DynamoDB; import com.amazonaws.services.dynamodbv2.document.Item; import com.amazonaws.services.dynamodbv2.document.Table; import com.amazonaws.services.dynamodbv2.document.spec.GetItemSpec; public class DocumentAPIItemBinaryExample { static AmazonDynamoDB client = AmazonDynamoDBClientBuilder.standard().build(); static DynamoDB dynamoDB = new DynamoDB(client); static String tableName = "Reply"; static SimpleDateFormat dateFormatter = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSS'Z'"); public static void main(String[] args) throws IOException { try { // Format the primary key values String threadId = "Amazon DynamoDB#DynamoDB Thread 2"; dateFormatter.setTimeZone(TimeZone.getTimeZone("UTC")); String replyDateTime = dateFormatter.format(new Date()); // Add a new reply with a binary attribute type createItem(threadId, replyDateTime); // Retrieve the reply with a binary attribute type retrieveItem(threadId, replyDateTime); // clean up by deleting the item deleteItem(threadId, replyDateTime); } catch (Exception e) { System.err.println("Error running the binary attribute type example: " + e); e.printStackTrace(System.err); } } public static void createItem(String threadId, String replyDateTime) throws IOException { Table table = dynamoDB.getTable(tableName); // Craft a long message String messageInput = "Long message to be compressed in a lengthy forum reply"; // Compress the long message ByteBuffer compressedMessage = compressString(messageInput.toString()); table.putItem(new Item().withPrimaryKey("Id", threadId).withString("ReplyDateTime", replyDateTime) .withString("Message", "Long message follows").withBinary("ExtendedMessage", compressedMessage) .withString("PostedBy", "User A")); } public static void retrieveItem(String threadId, String replyDateTime) throws IOException { Table table = dynamoDB.getTable(tableName); GetItemSpec spec = new GetItemSpec().withPrimaryKey("Id", threadId, "ReplyDateTime", replyDateTime) .withConsistentRead(true); Item item = table.getItem(spec); // Uncompress the reply message and print String uncompressed = uncompressString(ByteBuffer.wrap(item.getBinary("ExtendedMessage"))); System.out.println("Reply message:\n" + " Id: " + item.getString("Id") + "\n" + " ReplyDateTime: " + item.getString("ReplyDateTime") + "\n" + " PostedBy: " + item.getString("PostedBy") + "\n" + " Message: " + item.getString("Message") + "\n" + " ExtendedMessage (uncompressed): " + uncompressed + "\n"); } public static void deleteItem(String threadId, String replyDateTime) { Table table = dynamoDB.getTable(tableName); table.deleteItem("Id", threadId, "ReplyDateTime", replyDateTime); } private static ByteBuffer compressString(String input) throws IOException { // Compress the UTF-8 encoded String into a byte[] ByteArrayOutputStream baos = new ByteArrayOutputStream(); GZIPOutputStream os = new GZIPOutputStream(baos); os.write(input.getBytes("UTF-8")); os.close(); baos.close(); byte[] compressedBytes = baos.toByteArray(); // The following code writes the compressed bytes to a ByteBuffer. // A simpler way to do this is by simply calling // ByteBuffer.wrap(compressedBytes); // However, the longer form below shows the importance of resetting the // position of the buffer // back to the beginning of the buffer if you are writing bytes directly // to it, since the SDK // will consider only the bytes after the current position when sending // data to DynamoDB. // Using the "wrap" method automatically resets the position to zero. ByteBuffer buffer = ByteBuffer.allocate(compressedBytes.length); buffer.put(compressedBytes, 0, compressedBytes.length); buffer.position(0); // Important: reset the position of the ByteBuffer // to the beginning return buffer; } private static String uncompressString(ByteBuffer input) throws IOException { byte[] bytes = input.array(); ByteArrayInputStream bais = new ByteArrayInputStream(bytes); ByteArrayOutputStream baos = new ByteArrayOutputStream(); GZIPInputStream is = new GZIPInputStream(bais); int chunkSize = 1024; byte[] buffer = new byte[chunkSize]; int length = 0; while ((length = is.read(buffer, 0, chunkSize)) != -1) { baos.write(buffer, 0, length); } String result = new String(baos.toByteArray(), "UTF-8"); is.close(); baos.close(); bais.close(); return result; } }