Generic Wrapper for AWSClient Builder to override the endpoint URL using environment variables

AWSClientEnvConfig.java

package com.britive.util;

import static org.apache.commons.lang3.ObjectUtils.defaultIfNull;

import com.amazonaws.auth.AWSCredentialsProvider;
import com.amazonaws.auth.AWSStaticCredentialsProvider;
import com.amazonaws.auth.BasicAWSCredentials;
import com.amazonaws.client.builder.AwsClientBuilder;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;

/**
 * This class allows global and selective endpoint override for the following services via
 * an environment variable
 * 
 *      DynamoDB - AWS_DYNAMO_ENDPOINT_URL
 *      SNS - AWS_SNS_ENDPOINT_URL
 *      SQS - AWS_SQS_ENDPOINT_URL
 *      SES - AWS_SES_ENDPOINT_URL
 *      S3 - AWS_S3_ENDPOINT_URL
 *      KMS - AWS_KMS_ENDPOINT_URL
 *      Cognito - AWS_IAM_ENDPOINT_URL
 *      
 * You can globally override for all services by setting AWS_ENDPOINT_URL, but the specific
 * ones above will override when necessary.   For example:
 *
 *      AWS_ENDPOINT_URL=http://localstack:4566
 *      AWS_S3_ENDPOINT_URL=http://s3.localhost.localstack.cloud:4566
 *
 * The region for each endpoint can be set as well:
 *
 *     AWS_IAM_REGION=us-west-2
 *     AWS_KMS_REGION=us-east-1
 *
 * Otherwise the value of AWS_REGION is used.
 *
 *  Note you must wrap your current code with this decorator as described below in the build() method.
**/
public class AWSClientEnvConfig {
    private AWSClientEnvConfig() {};
    private static Map<String, String> envMap = Collections.unmodifiableMap(
            new HashMap<String, String>() {{
                // By not using <classname>.class.getSimpleName() we avoid the need
                // to import all the packages and dependencies into this module
                put("AmazonDynamoDBClientBuilder", "AWS_DYNAMO_ENDPOINT_URL");
                put("AmazonIdentityManagementClientBuilder", "AWS_IAM_ENDPOINT_URL");
                put("AWSCognitoIdentityProviderClientBuilder", "AWS_IAM_ENDPOINT_URL");
                put("AmazonKinesisFirehoseClientBuilder", "AWS_KFIRE_ENDPOINT_URL");
                put("AmazonS3ClientBuilder", "AWS_S3_ENDPOINT_URL");
                put("AmazonSNSAsyncClientBuilder", "AWS_SNS_ENDPOINT_URL");
                put("AmazonSNSClientBuilder", "AWS_SNS_ENDPOINT_URL");
                put("AmazonSQSAsyncClientBuilder", "AWS_SQS_ENDPOINT_URL");
                put("AmazonSQSClientBuilder", "AWS_SQS_ENDPOINT_URL");
                put("AmazonSimpleEmailServiceClientBuilder", "AWS_SES_ENDPOINT_URL");
                put("AWSKMSClientBuilder", "AWS_KMS_ENDPOINT_URL");
                put("AWSSimpleSystemsManagementClientBuilder", "AWS_SSM_ENDPOINT_URL");
                // The above was determined by grepping all our source.  Feel free to add more as needed
            }});

    private static String getEnvEndpoint(String classname) {
        String globalEndpoint = System.getenv("AWS_ENDPOINT_URL");
        if (envMap.containsKey(classname)) {
            String serviceEndpoint = System.getenv(envMap.get(classname));
            if (serviceEndpoint != null && !serviceEndpoint.isEmpty()) {
                if (serviceEndpoint.contentEquals("default")) {
                    return null;
                }
                return serviceEndpoint;
            }
        }
        return globalEndpoint;
    }
    /**
     * Allow for environment endpoint URL override when creating an Amazon client (Dynamo, Dax, SNS, etc..)
     *
     * Example old code
     *      dynamoDB = AmazonDynamoDBClientBuilder.standard().build()
     *      snsClient = AmazonSNSAsyncClientBuilder.standard().build()
     *      sqs = AmazonSQSClientBuilder.defaultClient();
     * New code
     *      dynamoDB = AWSClientEnvConfig.build(AmazonDynamoDBClientBuilder.standard());
     *      snsClient = AWSClientEnvConfig.build(AmazonSNSAsyncClientBuilder.standard());
     *      sqs = AWSClientEnvConfig.build(AmazonSQSClientBuilder.standard());
     *
     * @param builder
     * @return an AWS Client of the desired type
     * @param <T> The return type (IE: AWSDynamoDB)
     * @param <B> The builder for the type.  Typically the return from AWS*ClientBuilder.standard()
     */
    public static <T, B extends AwsClientBuilder<B, T>> T build(B builder) {
        String endpointURL = getEnvEndpoint(builder.getClass().getSimpleName());
        if (endpointURL != null && !endpointURL.isEmpty()) {
            if (endpointURL.contains("localstack")) {
                // Reset the credentials.
                // XXX: This should check an environment variable for the case where you want to test localstack IAM
                AWSCredentialsProvider creds = new AWSStaticCredentialsProvider(new BasicAWSCredentials("none", "none"));
                builder.setCredentials(creds);
            }
            String region = getEnvRegion(builder.getClass().getSimpleName());
            AwsClientBuilder.EndpointConfiguration epc = new AwsClientBuilder.EndpointConfiguration(endpointURL, region);
            return builder.withEndpointConfiguration(epc).build();
        } else {
            return builder.build();
        }
    }

    private static String getEnvRegion(String classname) {
        String envVarName = envMap.get(classname);
        String region = null;
        if (envVarName != null) {
            envVarName = envVarName.replace("ENDPOINT_URL", "REGION");
            region = System.getenv(envVarName);
        }
        return defaultIfNull(region,
            defaultIfNull(System.getenv("AWS_REGION"), "us-east-1")
        );
    }
}

Added per-service region support