Learning AWS SDK for Java and basic S3 operations with sample code

AWS SDK for Java is a Java API for AWS and contains AWS the Java library, code samples, and Eclipse IDE support. You can easily build scalable applications by working with Amazon S3, Amazon Glacier, and more.

To get started with AWS SDK for Java, it is necessary to install the following on your development machine:

First, we set up an IAM user, create a user policy, and attach the policy to the IAM user in the IAM management console in order to securely allow the IAM user to access the S3 bucket. We can define the access control for the IAM user by configuring the IAM policy. Then, we install AWS SDK for Java by using Apache Maven and git.

There are two ways to install AWS SDK for Java, one is to get the source code from GitHub, and the other is to use Apache Maven. We use the latter because the official site recommends this way and it is much easier.

Next, we clone a repository for the S3 Java sample application and run the application by using the Maven command (mvn). First, we set up the AWS credentials to operate S3, clone the sample application repository from GitHub, and then build and run the sample application using the mvn command:

The sample code works as shown in the following diagram; initiating the credentials to allow access Amazon S3, creating and listing a bucket in a region, putting, getting, and listing objects into the bucket, and then finally deleting the objects, and then the bucket:

Now, let's run the sample application and see the output of the preceding command, as shown in the following screenshot, and then follow the source code step by step:

Then, let's examine the sample code at aws-java-sample/src/main/java/com/amazonaws/samples/S3Sample.java.

The AmazonS3Client method instantiates an AWS service client with the default credential provider chain (~/.aws/credentials). Then, the Region.getRegion method retrieves a region object, and chooses the US West (Oregon) region for the AWS client:

AmazonS3 s3 = new AmazonS3Client();
Region usWest2 = Region.getRegion(Regions.US_WEST_2);
s3.setRegion(usWest2);

The createBucket method creates an S3 bucket with the specified name in the specified region:

s3.createBucket(bucketName);

The listBuckets method lists and gets the bucket name:

for (Bucket bucket : s3.listBuckets()) {
System.out.println(" - " + bucket.getName());

The putObject method uploads objects into the specified bucket. The objects consist of the following code:

s3.putObject(new PutObjectRequest(bucketName, key, createSampleFile()));

The getObject method gets the object stored in the specified bucket:

S3Object object = s3.getObject(new GetObjectRequest(bucketName, key));

The ListObjects method returns a list of summary information of the object in the specified bucket:

ObjectListing objectListing = s3.listObjects(new ListObjectsRequest()

The deleteObject method deletes the specified object in the specified bucket.

The reason to clean up objects before deleting the S3 bucket is that, it is unable to remove an S3 bucket with objects. We need to remove all objects in an S3 bucket first and then delete the bucket:

s3.deleteObject(bucketName, key);

The deleteBucket method deletes the specified bucket in the region.

The AmazonServiceException class provides the error messages, for example, the request ID, HTTP status code, the AWS error code, for a failed request from the client in order to examine the request. On the other hand, the AmazonClientException class can be used for mainly providing error responses when the client is unable to get a response from AWS resources or successfully make the service call, for example, a client failed to make a service call because no network was present:

s3.deleteBucket(bucketName);
} catch (AmazonServiceException ase) {
  System.out.println("Caught an AmazonServiceException, which means your request made it " + "to Amazon S3, but was rejected with an error response for some reason.");
  System.out.println("Error Message:  " + ase.getMessage());
  System.out.println("HTTP Status Code:  " + ase.getStatusCode());
  System.out.println("AWS Error Code:  " + ase.getErrorCode());
  System.out.println("Error Type:  " + ase.getErrorType());
  System.out.println("Request ID:  " + ase.getRequestId());
  } catch (AmazonClientException ace) {
    System.out.println("Caught an AmazonClientException, which means the client encountered " + "a serious internal problem while trying to communicate with S3," + "such as not being able to access the network.");
    System.out.println("Error Message: " + ace.getMessage());