153 lines
4.6 KiB
Markdown
153 lines
4.6 KiB
Markdown
---
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title: "Java API"
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date: "2017-09-14"
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menu:
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main:
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parent: "Client"
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---
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Introduction
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-------------
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Ozone ships with it own client library, that supports both RPC(Remote
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Procedure call) and REST(Representational State Transfer). This library is
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the primary user interface to ozone.
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It is trivial to switch from RPC to REST or vice versa, by setting the
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property _ozone.client.protocol_ in the configuration or by calling the
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appropriate factory method.
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## Creating an Ozone client
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The Ozone client factory creates the ozone client. It allows the user to
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specify the protocol of communication. For example, to get an REST client, we
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can use
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{{< highlight java >}}
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OzoneClient ozClient = OzoneClientFactory.getRestClient();
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{{< /highlight >}}
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And to get a a RPC client we can call
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{{< highlight java >}}
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OzoneClient ozClient = OzoneClientFactory.getRpcClient();
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{{< /highlight >}}
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If the user want to create a client based on the configuration, then they can
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call
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{{< highlight java >}}
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OzoneClient ozClient = OzoneClientFactory.getClient();
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{{< /highlight >}}
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and an appropriate client based on configuration will be returned.
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## Writing data using Ozone Client
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The hierarchy of data inside ozone is a volume, bucket and a key. A volume
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is a collection of buckets. A bucket is a collection of keys. To write data
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to the ozone, you need a volume, bucket and a key.
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### Creating a Volume
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Once we have a client, we need to get a reference to the ObjectStore. This
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is done via
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{{< highlight java >}}
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ObjectStore objectStore = ozClient.getObjectStore();
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{{< /highlight >}}
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An object store represents an active cluster against which the client is working.
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{{< highlight java >}}
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// Let us create a volume to store our game assets.
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// This uses default arguments for creating that volume.
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objectStore.createVolume(“assets”);
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// Let us verify that the volume got created.
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OzoneVolume assets = objectStore.getVolume(“assets”);
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{{< /highlight >}}
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It is possible to pass an array of arguments to the createVolume by creating volume arguments.
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### Creating a Bucket
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Once you have a volume, you can create buckets inside the volume.
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{{< highlight bash >}}
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// Let us create a bucket called videos.
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assets.createBucket(“videos”);
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Ozonebucket video = assets.getBucket(“videos”);
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{{< /highlight >}}
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At this point we have a usable volume and a bucket. Our volume is called assets and bucket is called videos.
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Now we can create a Key.
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### Reading and Writing a Key
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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.
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{{< highlight bash >}}
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// read data from the file, this is a user provided function.
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byte [] vidoeData = readFile(“into.mp4”);
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// Create an output stream and write data.
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OzoneOutputStream videoStream = video.createKey(“intro.mp4”, 1048576);
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videoStream.write(videoData);
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// Close the stream when it is done.
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videoStream.close();
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// We can use the same bucket to read the file that we just wrote, by creating an input Stream.
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// Let us allocate a byte array to hold the video first.
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byte[] data = new byte[(int)1048576];
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OzoneInputStream introStream = video.readKey(“intro.mp4”);
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// read intro.mp4 into the data buffer
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introStream.read(data);
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introStream.close();
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{{< /highlight >}}
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Here is a complete example of the code that we just wrote. Please note the close functions being called in this program.
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{{< highlight java >}}
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OzoneClient ozClient = OzoneClientFactory.getClient();
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// Let us create a volume to store our game assets.
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// This default arguments for creating that volume.
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objectStore.createVolume(“assets”);
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// Let us verify that the volume got created.
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OzoneVolume assets = objectStore.getVolume(“assets”);
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// Let us create a bucket called videos.
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assets.createBucket(“videos”);
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Ozonebucket video = assets.getBucket(“videos”);
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// read data from the file, this is assumed to be a user provided function.
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byte [] vidoeData = readFile(“into.mp4”);
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// Create an output stream and write data.
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OzoneOutputStream videoStream = video.createKey(“intro.mp4”, 1048576);
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videoStream.write(videoData);
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// Close the stream when it is done.
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videoStream.close();
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// We can use the same bucket to read the file that we just wrote, by creating an input Stream.
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// Let us allocate a byte array to hold the video first.
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byte[] data = new byte[(int)1048576];
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OzoneInputStream introStream = video.readKey(“into.mp4”);
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introStream.read(data);
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// Close the stream when it is done.
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introStream.close();
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// Close the client.
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ozClient.close();
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{{< /highlight >}}
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