.js

package com.serverless.dal;
...

public class DynamoDBAdapter {
    ...
    private DynamoDBAdapter() {
        this.client = AmazonDynamoDBClientBuilder.standard()
            .withRegion(Regions.US_EAST_1)
            .build();
    }
    public static DynamoDBAdapter getInstance() {
        if (db_adapter == null)
          db_adapter = new DynamoDBAdapter();

        return db_adapter;
    }
    ...
    public DynamoDBMapper createDbMapper(DynamoDBMapperConfig mapperConfig) {
        if (this.client != null)
            mapper = new DynamoDBMapper(this.client, mapperConfig);

        return this.mapper;
    }
}