hadoop/hadoop-hdds/docs/content/JavaApi.md

---
title: "Java API"
date: "2017-09-14"
menu:
   main:
      parent: "Client"
---
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Introduction
-------------

Ozone ships with its own client library that supports RPC. For generic use cases the S3 
compatible REST interface also can be used instead of the Ozone client. 


## Creating an Ozone client
The Ozone client factory creates the ozone client. To get a RPC client we can call

{{< highlight java >}}
OzoneClient ozClient = OzoneClientFactory.getRpcClient();
{{< /highlight >}}

If the user want to create a client based on the configuration, then they can
call.

{{< highlight java >}}
OzoneClient ozClient = OzoneClientFactory.getClient();
{{< /highlight >}}

and an appropriate client based on configuration will be returned.

## Writing data using Ozone Client

The hierarchy of data inside ozone is a volume, bucket and a key. A volume
is a collection of buckets. A bucket is a collection of keys. To write data
to the ozone, you need a volume, bucket and a key.

### Creating a Volume

Once we have a client, we need to get a reference to the ObjectStore.  This
is done via

{{< highlight java >}}
ObjectStore objectStore = ozClient.getObjectStore();
{{< /highlight >}}

An object store represents an active cluster against which the client is working.

{{< highlight java >}}
// Let us create a volume to store our game assets.
// This uses default arguments for creating that volume.
objectStore.createVolume("assets");

// Let us verify that the volume got created.
OzoneVolume assets = objectStore.getVolume("assets");
{{< /highlight >}}


It is possible to pass an array of arguments to the createVolume by creating volume arguments.

### Creating a Bucket

Once you have a volume, you can create buckets inside the volume.

{{< highlight bash >}}
// Let us create a bucket called videos.
assets.createBucket("videos");
OzoneBucket video = assets.getBucket("videos");
{{< /highlight >}}

At this point we have a usable volume and a bucket. Our volume is called assets and bucket is called videos.

Now we can create a Key.

### Reading and Writing a Key

With a bucket object the users can now read and write keys. The following code reads a video called intro.mp4 from the local disk and stores in the video bucket that we just created.

{{< highlight bash >}}
// read data from the file, this is a user provided function.
byte [] videoData = readFile("intro.mp4");

// Create an output stream and write data.
OzoneOutputStream videoStream = video.createKey("intro.mp4", 1048576);
videoStream.write(videoData);

// Close the stream when it is done.
videoStream.close();


// We can use the same bucket to read the file that we just wrote, by creating an input Stream.
// Let us allocate a byte array to hold the video first.
byte[] data = new byte[(int)1048576];
OzoneInputStream introStream = video.readKey("intro.mp4");
// read intro.mp4 into the data buffer
introStream.read(data);
introStream.close();
{{< /highlight >}}


Here is a complete example of the code that we just wrote. Please note the close functions being called in this program.

{{< highlight java >}}
// Let us create a client
OzoneClient ozClient = OzoneClientFactory.getClient();

// Get a reference to the ObjectStore using the client
ObjectStore objectStore = ozClient.getObjectStore();

// Let us create a volume to store our game assets.
// This default arguments for creating that volume.
objectStore.createVolume("assets");

// Let us verify that the volume got created.
OzoneVolume assets = objectStore.getVolume("assets");

// Let us create a bucket called videos.
assets.createBucket("videos");
OzoneBucket video = assets.getBucket("videos");

// read data from the file, this is assumed to be a user provided function.
byte [] videoData = readFile("intro.mp4");

// Create an output stream and write data.
OzoneOutputStream videoStream = video.createKey("intro.mp4", 1048576);
videoStream.write(videoData);

// Close the stream when it is done.
videoStream.close();


// We can use the same bucket to read the file that we just wrote, by creating an input Stream.
// Let us allocate a byte array to hold the video first.

byte[] data = new byte[(int)1048576];
OzoneInputStream introStream = video.readKey("intro.mp4");
introStream.read(data);

// Close the stream when it is done.
introStream.close();

// Close the client.
ozClient.close();
{{< /highlight >}}