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The Amazon Web Services SDK for Java provides Java APIs for building software on AWS' cost-effective, scalable, and reliable infrastructure products. The AWS Java SDK allows developers to code against APIs for all of Amazon's infrastructure web services (Amazon S3, Amazon EC2, Amazon SQS, Amazon Relational Database Service, Amazon AutoScaling, etc).

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/*
 * Copyright 2010-2014 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License").
 * You may not use this file except in compliance with the License.
 * A copy of the License is located at
 *
 *  http://aws.amazon.com/apache2.0
 *
 * or in the "license" file accompanying this file. This file is distributed
 * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
 * express or implied. See the License for the specific language governing
 * permissions and limitations under the License.
 */
package com.amazonaws.metrics.internal.cloudwatch.spi;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * Service specific metric transformer factory.
 */
public enum AWSMetricTransformerFactory {
    DynamoDB,
    ;
    private static final String REQUEST_TRANSFORMER_CLASSNAME_SUFFIX = "RequestMetricTransformer";
    public static final String DEFAULT_METRIC_TRANSFORM_PROVIDER_PACKAGE = 
        "com.amazonaws.metrics.internal.cloudwatch.provider.transform";
    public static volatile String transformerPackage = DEFAULT_METRIC_TRANSFORM_PROVIDER_PACKAGE;

    public static String getTransformerPackage() {
        return transformerPackage;
    }

    public static void setTransformerPackage(
            String transformPackage) {
        if (transformPackage == null)
            throw new IllegalArgumentException();
        AWSMetricTransformerFactory.transformerPackage = transformPackage;
    }

    /**
     * By default, the transformer class for each AWS specific service is
     * assumed to reside in the Java package
     * {@link #DEFAULT_METRIC_TRANSFORM_PROVIDER_PACKAGE} and follow the naming
     * convention of <AwsPrefix>MetricTransformer. The "AwsPrefix" is the
     * same as the enum literal name. Since each service specific request metric
     * transformer internally contains static reference to service specific
     * classes, this dynamic class loading mechansim allows service specific
     * transformers to be skipped in case some service specific class files are
     * absent in the classpath.
     */
    private volatile RequestMetricTransformer requestMetricTransformer;

    /**
     * Returns the fully qualified class name of the request metric
     * transformer, given the specific AWS prefix.
     */
    public static String buildRequestMetricTransformerFQCN(String awsPrefix, String packageName) {
        return packageName + "." 
             + awsPrefix + REQUEST_TRANSFORMER_CLASSNAME_SUFFIX
             ;
    }

    /**
     * @param fqcn fully qualified class name.
     */
    private RequestMetricTransformer loadRequestMetricTransformer(String fqcn) {
       Log log = LogFactory.getLog(AWSMetricTransformerFactory.class);
       if (log.isDebugEnabled()) {
           log.debug("Loading " + fqcn);
       }
        try {
            Class c = Class.forName(fqcn);
            return (RequestMetricTransformer)c.newInstance();
        } catch (Throwable e) {
            if (log.isDebugEnabled()) {
                log.debug("Failed to load " + fqcn
                        + "; therefore ignoring " + this.name()
                        + " specific predefined metrics", e);
            }
        }
        return RequestMetricTransformer.NONE;
   }

    public RequestMetricTransformer getRequestMetricTransformer() {
        RequestMetricTransformer transformer = requestMetricTransformer;
        String packageName = transformerPackage;
        if (transformer != null
        &&  packageName.equals(transformer.getClass().getPackage().getName())) {
            return transformer;
        }
        String fqcn = AWSMetricTransformerFactory
            .buildRequestMetricTransformerFQCN(name(), packageName);
        return this.requestMetricTransformer = loadRequestMetricTransformer(fqcn);
    }
}