Read File from S3 in Java

Function.java

public static final String TYPE_QUERY_PARAM = "type";
public static final String JSON_FILE_EXTENSION = ".json";
public static final String PAGE_PREFIX = "_p";

private S3Client s3Client = S3Client.builder()
        .region(Region.EU_WEST_1)
        .httpClient(UrlConnectionHttpClient.builder().build())
        .credentialsProvider(EnvironmentVariableCredentialsProvider.create())
        .build();

@Override
public APIGatewayProxyResponseEvent handleRequest(APIGatewayProxyRequestEvent input, Context context) {
    Map<String, String> queryStringParameters = input.getQueryStringParameters();

    String page = queryStringParameters.getOrDefault("page", "1");
    String type;

    if(!queryStringParameters.containsKey(TYPE_QUERY_PARAM)){
        throw new MissingTypeException("Parameter Type cannot be null");
    } else {
        type = queryStringParameters.get(TYPE_QUERY_PARAM);
    }

    String key = type + PAGE_PREFIX + page + JSON_FILE_EXTENSION;

    ResponseInputStream<GetObjectResponse> s3ClientObject = s3Client
            .getObject(GetObjectRequest
                    .builder()
                    .bucket("apigatelambdas3integrationdemo")
                    .key(key)
                    .build());

    return new APIGatewayProxyResponseEvent()
            .withStatusCode(200)
            .withHeaders(
                    Map.of("Content-Type", s3ClientObject.response().contentType(),
                            "Content-Length", s3ClientObject.response().contentLength().toString()))
            .withBody(getFileContentAsString(context, s3ClientObject));
}

private String getFileContentAsString(Context context, ResponseInputStream<GetObjectResponse> s3ClientObject) {
    String fileAsString = "";
    try (BufferedReader reader = new BufferedReader(new InputStreamReader(s3ClientObject))) {
        fileAsString = reader.lines().collect(Collectors.joining(System.lineSeparator()));
    } catch (IOException e) {
        context.getLogger().log("Oops! Something went wrong while converting the file from S3 to a String");
        e.printStackTrace();
    }
    return fileAsString;
}

mapping-template.vm

#set($type = $input.params('type')
#set($page = $input.params('page'))
#if( $page == '') 
  #set($context.requestOverride.path.fileName = $type + '_p1.json')
#else
  #set($context.requestOverride.path.fileName = $type + '_p'+ $page + '.json')
#end

parameter-mapping.csv