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In this tutorial, we will learn about how to get an item from dynamoDB (GetItem) using java language.

DynamoDB

Amazon DynamoDB is a fully managed NoSQL database services offered by Amazon as part of its Amazon Web Service (AWS) portfolio. It provides fast and predictable performance with seamless scalability. DynamoDB is a key-value datastore, where each item (row) in a table is a key-value pair.

Project Setup

Create a simple maven project in your favorite IDE and add below mentioned dependency in your pom.xml file.

<dependency>
  <groupId>com.amazonaws</groupId>
  <artifactId>aws-java-sdk</artifactId>
  <version>1.11.524</version>
</dependency>

For latest version of aws library, check this page.

Table Schema

In this example, we will get an item from JOB table. Schema of this table is as follows:-

1. CountryName (Partition Key) :- It represents name of the country for which job is posted. It is stored as String data type (ScalarAttributeType S).
2. JobId (Sort Key) :- It represents unique id of the posted job. It is of Number datatype (ScalarAttributeType N).
3. CompanyName :- It represents name of the company by which job is posted. It is of String datatype (ScalarAttributeType S).
4. JobTitle :- As the name suggest, it represents tile of the job. It is of String datatype (ScalarAttributeType S).
5. JobDescription :- It represents details job description. It is of String datatype (ScalarAttributeType S).

DynamoDB Connection

Create an object of AmazonDynamoDB ( com.amazonaws.services.dynamodbv2.AmazonDynamoDB ) class for sending a client request to dynamoDB. To get instance of this class, we will use AmazonDynamoDBClientBuilder builder class. It requires three important parameters :- 

1. Region :- It is a region where dynamoDB table will be stored.
2. ACCESS_KEY :- It is a access key for using dynamoDB. You can generate this key, using aws management console.
3. SECRET_KEY :- It is a secret key of above mentioned access key.

Here is a code example :-

AmazonDynamoDB dynamoDB = AmazonDynamoDBClientBuilder.standard()
				.withRegion(Regions.AP_SOUTH_1)
				.withCredentials(new AWSStaticCredentialsProvider
                                                    (new BasicAWSCredentials("ACCESS_KEY","SECRET_KEY")))
				.build();

GetItem

Steps to create and send GetItemRequest to dynamoDB are as follows:-

1. Instantiate GetItemRequest object, this object will send the client request to dynamoDB.
2. Set name of the table. In our case JOB.
3. Set return consumed capacity as TOTAL, this returns aggregate consumed capacity.
4. Set projection expression by passing comma separated attribute names
5. Set Consistent Read as True, this will return strong consistent result.
6. Create a map of primary key attributes and their values.
7. Invoke the getItem method on AmazonDynamoDB object by passing GetItemRequest object as an argument.

Example

import java.util.HashMap;
import java.util.Map;

import com.amazonaws.AmazonServiceException;
import com.amazonaws.auth.AWSStaticCredentialsProvider;
import com.amazonaws.auth.BasicAWSCredentials;
import com.amazonaws.regions.Regions;
import com.amazonaws.services.dynamodbv2.AmazonDynamoDB;
import com.amazonaws.services.dynamodbv2.AmazonDynamoDBClientBuilder;
import com.amazonaws.services.dynamodbv2.model.AttributeValue;
import com.amazonaws.services.dynamodbv2.model.GetItemRequest;
import com.amazonaws.services.dynamodbv2.model.GetItemResult;
import com.amazonaws.services.dynamodbv2.model.ReturnConsumedCapacity;

public class GetItem {
	
public static void main(String[] args) {
		
		/* Create DynamoDB Client Object */
		AmazonDynamoDB dynamoDB = AmazonDynamoDBClientBuilder
				.standard()
				.withRegion(Regions.AP_SOUTH_1)
				.withCredentials(new AWSStaticCredentialsProvider(
                                     new BasicAWSCredentials("ACCESS_KEY","SECRET_KEY")))
				.build();
		
		/* Create an Object of GetItemRequest */
		GetItemRequest request = new GetItemRequest();
		
		/* Setting Table Name */
		request.setTableName("JOB");
		
		/* Setting Consumed Capacity */
		request.setReturnConsumedCapacity(ReturnConsumedCapacity.TOTAL);
		
		/* Setting Name of attributes to Get */
		request.setProjectionExpression("CountryId, CompanyName");
		
		/* Setting Consistency Models */
		/* true for Strong Consistent & false for Eventually Consistent */
		request.setConsistentRead(true);
		
		/* Create a Map of Primary Key attributes */
		Map<String, AttributeValue> keysMap = new HashMap<>();
		keysMap.put("CountryId", new AttributeValue("18"));
		keysMap.put("JobId", (new AttributeValue()).withN("1"));		
		request.setKey(keysMap);
		
        try {
        	/* Send Get Item Request */
            GetItemResult result = dynamoDB.getItem(request);
            
            System.out.println("Status : " +  result.getSdkHttpMetadata().getHttpStatusCode());
            
            System.out.println("Read Consumed Capacity : " +  result.getConsumedCapacity().getReadCapacityUnits());
            
            /* Printing Attributes Name and Values */
			if (result.getItem() != null) {
				result.getItem().entrySet().stream()
						.forEach(e -> System.out.println(e.getKey() + " " + e.getValue().toString()));
			}          
            
        } catch (AmazonServiceException e) {
        	
            System.out.println(e.getErrorMessage());
            
        }
	}

}

References :-

1. GetItemRequest Java Docs
2. GetItemResult Java Docs

That’s all for how to get an item from dynamoDB (GetItem) using java language. If you liked it, please share your thoughts in comments section and share it with others too.