Query.java - AWS Code Sample


Query.java demonstrates how to query an Amazon DynamoDB table.

/* Copyright 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.example.dynamodb; import software.amazon.awssdk.services.dynamodb.model.AttributeValue; import software.amazon.awssdk.services.dynamodb.model.QueryRequest; import software.amazon.awssdk.services.dynamodb.model.QueryResponse; import software.amazon.awssdk.services.dynamodb.DynamoDbClient; import java.util.HashMap; import software.amazon.awssdk.services.dynamodb.model.DynamoDbException; import software.amazon.awssdk.regions.Region; /** * Query an Amazon DynamoDB table * * * This code expects that you have AWS credentials set up, as described here: * http://docs.aws.amazon.com/java-sdk/latest/developer-guide/setup-credentials.html */ public class Query { public static void main(String[] args) { final String USAGE = "\n" + "Usage:\n" + " Query <table> <partitionkey> <partitionkeyvalue>\n\n" + "Where:\n" + " table - the table to put the item in (i.e., Music3)\n" + " partitionkey - the partition key name of the table (i.e., Artist)\n" + " partitionkeyvalue - the value of the partition key that should match (i.e., Famous Band)\n\n" + "Example:\n" + " Query Music3 Artist Famous Band \n"; if (args.length < 3) { System.out.println(USAGE); System.exit(1); } String tableName = args[0]; String partitionKeyName = args[1]; String partitionKeyVal = args[2]; String partitionAlias = "#a"; System.out.format("Querying %s", tableName); System.out.println(""); Region region = Region.US_EAST_1; DynamoDbClient ddb = DynamoDbClient.builder() .region(region) .build(); int count = queryTable(ddb, tableName, partitionKeyName, partitionKeyVal,partitionAlias ) ; System.out.println("There were "+count + "record(s) returned"); } public static int queryTable(DynamoDbClient ddb, String tableName, String partitionKeyName, String partitionKeyVal, String partitionAlias) { // Set up an alias for the partition key name in case it's a reserved word HashMap<String,String> attrNameAlias = new HashMap<String,String>(); attrNameAlias.put(partitionAlias, partitionKeyName); // Set up mapping of the partition name with the value HashMap<String, AttributeValue> attrValues = new HashMap<String,AttributeValue>(); attrValues.put(":"+partitionKeyName, AttributeValue.builder().s(partitionKeyVal).build()); // Cretae a QueryRequest object QueryRequest queryReq = QueryRequest.builder() .tableName(tableName) .keyConditionExpression(partitionAlias + " = :" + partitionKeyName) .expressionAttributeNames(attrNameAlias) .expressionAttributeValues(attrValues) .build(); try { QueryResponse response = ddb.query(queryReq); return response.count(); } catch (DynamoDbException e) { System.err.println(e.getMessage()); System.exit(1); } return -1; } }

Sample Details

Service: Amazon Dynamodb

Last tested: 2/5/2020

Author: scmacdon-aws

Type: full-example