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LegacyJavaClients.md

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Legacy Java Clients

The current version of EmoDB uses DropWizard 7.1. The Java clients returned by the [Data Store] (https://github.com/bazaarvoice/emodb/blob/master/sor-client/src/main/java/com/bazaarvoice/emodb/sor/client/DataStoreClientFactory.java), [Blob Store] (https://github.com/bazaarvoice/emodb/blob/master/blob-client/src/main/java/com/bazaarvoice/emodb/blob/client/BlobStoreClientFactory.java), [Databus] (https://github.com/bazaarvoice/emodb/blob/master/databus-client/src/main/java/com/bazaarvoice/emodb/databus/client/DatabusClientFactory.java), [Queue] (https://github.com/bazaarvoice/emodb/blob/master/queue-client/src/main/java/com/bazaarvoice/emodb/queue/client/QueueClientFactory.java), and [Dedup Queue] (https://github.com/bazaarvoice/emodb/blob/master/queue-client/src/main/java/com/bazaarvoice/emodb/queue/client/DedupQueueClientFactory.java) client factories use dependencies matching that version of DropWizard.

Historically EmoDB version up to and including 3.33 used DropWizard 6.2. There have been numerous API updates and bug fixes since that release and all projects using older versions of EmoDB are encouraged to upgrade. However, this would also require those projects to upgrade to DropWizard 7 -- or at least upgrade to using the same shared dependencies. As an intermediate solution EmoDB provides a set of legacy clients. These clients receive the same updates as the standard EmoDB clients and use a nearly identical API (the differences will be explained shortly).

Shading

The legacy clients are a slightly-modified version of the standard EmoDB clients with all dependencies shaded into a single uber-jar. The package names in the shaded jar have been relocated so they should not conflict with your project's declared dependencies. For the most part these relocated classes are used only internally by EmoDB; the few places they are exposed through the EmoDB client API are addressed later in this document.

Maven Dependency

Unlike with the standard EmoDB client libraries all shaded clients are included in a single Maven dependency.

<dependency>
    <groupId>com.bazaarvoice.emodb</groupId>
    <artifactId>emodb-shaded-clients-dropwizard6</artifactId>
    <!-- Replace the following with the actual latest version -->
    <version>4.14</version>
</dependency>

This project includes clients for the system of record, blob store, databus, and queues.

Creating a Client

Creating a client using the shaded project is nearly identical to the process for creating a standard client. For example considering the following example for creating a system of record client:

import com.bazaarvoice.shaded.emodb.sor.client.DataStoreClientFactory;
import com.bazaarvoice.shaded.ostrich.EmoServicePoolBuilder;
import com.bazaarvoice.shaded.ostrich.ServiceFactory;
import com.bazaarvoice.shaded.ostrich.EmoZooKeeperHostDiscovery;
import com.bazaarvoice.shaded.ostrich.pool.ServiceCachingPolicyBuilder;
import com.bazaarvoice.shaded.ostrich.retry.ExponentialBackoffRetry;


ServiceFactory<DataStore> dataStoreFactory =
    DataStoreClientFactory.forClusterAndHttpClient("local_default", jerseyClient).usingCredentials(apiKey);
DataStore dataStore = EmoServicePoolBuilder.create(DataStore.class)
        .withHostDiscovery(new EmoZooKeeperHostDiscovery(curator, dataStoreFactory.getServiceName()))
        .withServiceFactory(dataStoreFactory)
        .buildProxy(new ExponentialBackoffRetry(5, 50, 1000, TimeUnit.MILLISECONDS));

Notice the key differences from using the standard client:

  • DataStoreClientFactory is in a different package that starts with com.bazaarvoice.shaded.emodb.
  • Ostrich classes such as ServiceFactory are unchanged but have been relocated to com.bazaarvoice.shaded.ostrich.
  • EmoServicePoolBuilder is used instead of ServicePoolBuilder. This isn't required but it helpfully initializes several required attributes that you will not use, such as the metric registry.
  • EmoZooKeeperHostDiscovery is used instead of ZooKeeperHostDiscovery for the same reason as above.

Using a Client

From this point forward the API for each client matches that for the standard client. However, due to shading the following classes have been relocated:

Original Class Shaded Class Usages
com.google.common.io.InputSupplier com.google.shaded.common.io.InputSupplier BlobStore.put()