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<h1>Java API</h1>
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<p>Ozone 自带了支持 RPC 的客户端库，对于一般的应用场景也可以使用兼容 AWS S3 的 REST 接口替代 Ozone 客户端 API。</p>
<h2 id="创建-ozone-客户端">创建 Ozone 客户端</h2>
<p>ozone 客户端由客户端工厂创建，我们可以通过如下调用获得一个 RPC 客户端对象：</p>
<div class="highlight"><pre style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4"><code class="language-java" data-lang="java">OzoneClient ozClient <span style="color:#f92672">=</span> OzoneClientFactory<span style="color:#f92672">.</span><span style="color:#a6e22e">getRpcClient</span><span style="color:#f92672">();</span></code></pre></div>
<p>如果用户想要创建指定配置的客户端，可以这样调用：</p>
<div class="highlight"><pre style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4"><code class="language-java" data-lang="java">OzoneClient ozClient <span style="color:#f92672">=</span> OzoneClientFactory<span style="color:#f92672">.</span><span style="color:#a6e22e">getClient</span><span style="color:#f92672">();</span></code></pre></div>
<p>这样就会返回一个合适的客户端对象。</p>
<h2 id="使用-ozone-客户端写数据">使用 Ozone 客户端写数据</h2>
<p>ozone 中的数据层次为卷、桶和键。卷是桶的集合，桶是键的集合，如果要向 ozone 写数据，你需要依次获得卷、桶和键。</p>
<h3 id="创建卷">创建卷</h3>
<p>有了客户端对象之后，我们需要获取 ObjectStore 的引用，获取方法为：</p>
<div class="highlight"><pre style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4"><code class="language-java" data-lang="java">ObjectStore objectStore <span style="color:#f92672">=</span> ozClient<span style="color:#f92672">.</span><span style="color:#a6e22e">getObjectStore</span><span style="color:#f92672">();</span></code></pre></div>
<p>ObjectStore 对象表示了客户端连接的集群。</p>
<div class="highlight"><pre style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4"><code class="language-java" data-lang="java"><span style="color:#75715e">// 让我们创建一个卷来存储资产数据
</span><span style="color:#75715e">// 使用默认参数来创建资产卷
</span><span style="color:#75715e"></span>objectStore<span style="color:#f92672">.</span><span style="color:#a6e22e">createVolume</span><span style="color:#f92672">(</span><span style="color:#e6db74">&#34;assets&#34;</span><span style="color:#f92672">);</span>
<span style="color:#75715e">// 验证 assets 卷是否已创建
</span><span style="color:#75715e"></span>OzoneVolume assets <span style="color:#f92672">=</span> objectStore<span style="color:#f92672">.</span><span style="color:#a6e22e">getVolume</span><span style="color:#f92672">(</span><span style="color:#e6db74">&#34;assets&#34;</span><span style="color:#f92672">);</span></code></pre></div>
<p>createVolume 方法也支持传入参数数组来指定卷的创建参数。</p>
<h3 id="创建桶">创建桶</h3>
<p>有了卷之后，你就可以在卷中创建桶。</p>
<div class="highlight"><pre style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4"><code class="language-java" data-lang="java"><span style="color:#75715e">// 创建一个名为 videos 的桶
</span><span style="color:#75715e"></span>assets<span style="color:#f92672">.</span><span style="color:#a6e22e">createBucket</span><span style="color:#f92672">(</span><span style="color:#e6db74">&#34;videos&#34;</span><span style="color:#f92672">);</span>
OzoneBucket video <span style="color:#f92672">=</span> assets<span style="color:#f92672">.</span><span style="color:#a6e22e">getBucket</span><span style="color:#f92672">(</span><span style="color:#e6db74">&#34;videos&#34;</span><span style="color:#f92672">);</span></code></pre></div>
<p>此时我们有了一个可用的卷和一个桶，卷名为 <em>assets</em> ，桶名为 <em>videos</em> 。</p>
<p>接下来我们创建一个键。</p>
<h3 id="键的读写">键的读写</h3>
<p>通过桶对象可以进行键的读写，下面的代码从本地磁盘读取名为 intro.mp4 的视频文件，并把它存储到我们刚刚创建的 <em>video</em> 桶中。</p>
<div class="highlight"><pre style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4"><code class="language-java" data-lang="java"><span style="color:#75715e">// 从文件读取数据，需要由用户提供读取函数
</span><span style="color:#75715e"></span><span style="color:#66d9ef">byte</span> <span style="color:#f92672">[]</span> videoData <span style="color:#f92672">=</span> readFile<span style="color:#f92672">(</span><span style="color:#e6db74">&#34;intro.mp4&#34;</span><span style="color:#f92672">);</span>
<span style="color:#75715e">// 创建一个输出流并写数据
</span><span style="color:#75715e"></span>OzoneOutputStream videoStream <span style="color:#f92672">=</span> video<span style="color:#f92672">.</span><span style="color:#a6e22e">createKey</span><span style="color:#f92672">(</span><span style="color:#e6db74">&#34;intro.mp4&#34;</span><span style="color:#f92672">,</span> 1048576<span style="color:#f92672">);</span>
videoStream<span style="color:#f92672">.</span><span style="color:#a6e22e">write</span><span style="color:#f92672">(</span>videoData<span style="color:#f92672">);</span>
<span style="color:#75715e">// 写操作完成之后关闭输出流
</span><span style="color:#75715e"></span>videoStream<span style="color:#f92672">.</span><span style="color:#a6e22e">close</span><span style="color:#f92672">();</span>
<span style="color:#75715e">// 我们可以使用同一个桶，通过创建输入流来读取刚刚写入的文件
</span><span style="color:#75715e">// 先创建一个用来存储视频的字节数组
</span><span style="color:#75715e"></span><span style="color:#66d9ef">byte</span><span style="color:#f92672">[]</span> data <span style="color:#f92672">=</span> <span style="color:#66d9ef">new</span> <span style="color:#66d9ef">byte</span><span style="color:#f92672">[(</span><span style="color:#66d9ef">int</span><span style="color:#f92672">)</span>1048576<span style="color:#f92672">];</span>
OzoneInputStream introStream <span style="color:#f92672">=</span> video<span style="color:#f92672">.</span><span style="color:#a6e22e">readKey</span><span style="color:#f92672">(</span><span style="color:#e6db74">&#34;intro.mp4&#34;</span><span style="color:#f92672">);</span>
<span style="color:#75715e">// 读取 intro.mp4 到缓冲区中
</span><span style="color:#75715e"></span>introStream<span style="color:#f92672">.</span><span style="color:#a6e22e">read</span><span style="color:#f92672">(</span>data<span style="color:#f92672">);</span>
introStream<span style="color:#f92672">.</span><span style="color:#a6e22e">close</span><span style="color:#f92672">();</span></code></pre></div>
<p>下面是一个完整的代码示例，请注意代码中 close 函数的调用。</p>
<div class="highlight"><pre style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4"><code class="language-java" data-lang="java"><span style="color:#75715e">// 创建客户端对象
</span><span style="color:#75715e"></span>OzoneClient ozClient <span style="color:#f92672">=</span> OzoneClientFactory<span style="color:#f92672">.</span><span style="color:#a6e22e">getClient</span><span style="color:#f92672">();</span>
<span style="color:#75715e">// 通过客户端对象获取 ObjectStore 的引用
</span><span style="color:#75715e"></span>ObjectStore objectStore <span style="color:#f92672">=</span> ozClient<span style="color:#f92672">.</span><span style="color:#a6e22e">getObjectStore</span><span style="color:#f92672">();</span>
<span style="color:#75715e">// 创建用于存储数据的 assets 卷
</span><span style="color:#75715e">// 此处创建的卷采用默认参数
</span><span style="color:#75715e"></span>objectStore<span style="color:#f92672">.</span><span style="color:#a6e22e">createVolume</span><span style="color:#f92672">(</span><span style="color:#e6db74">&#34;assets&#34;</span><span style="color:#f92672">);</span>
<span style="color:#75715e">// 验证卷是否已创建
</span><span style="color:#75715e"></span>OzoneVolume assets <span style="color:#f92672">=</span> objectStore<span style="color:#f92672">.</span><span style="color:#a6e22e">getVolume</span><span style="color:#f92672">(</span><span style="color:#e6db74">&#34;assets&#34;</span><span style="color:#f92672">);</span>
<span style="color:#75715e">// 创建名为 videos 的桶
</span><span style="color:#75715e"></span>assets<span style="color:#f92672">.</span><span style="color:#a6e22e">createBucket</span><span style="color:#f92672">(</span><span style="color:#e6db74">&#34;videos&#34;</span><span style="color:#f92672">);</span>
OzoneBucket video <span style="color:#f92672">=</span> assets<span style="color:#f92672">.</span><span style="color:#a6e22e">getBucket</span><span style="color:#f92672">(</span><span style="color:#e6db74">&#34;videos&#34;</span><span style="color:#f92672">);</span>
<span style="color:#75715e">// 从文件中读取数据，需要用户提供此函数
</span><span style="color:#75715e"></span><span style="color:#66d9ef">byte</span> <span style="color:#f92672">[]</span> videoData <span style="color:#f92672">=</span> readFile<span style="color:#f92672">(</span><span style="color:#e6db74">&#34;intro.mp4&#34;</span><span style="color:#f92672">);</span>
<span style="color:#75715e">// 创建输出流并写数据
</span><span style="color:#75715e"></span>OzoneOutputStream videoStream <span style="color:#f92672">=</span> video<span style="color:#f92672">.</span><span style="color:#a6e22e">createKey</span><span style="color:#f92672">(</span><span style="color:#e6db74">&#34;intro.mp4&#34;</span><span style="color:#f92672">,</span> 1048576<span style="color:#f92672">);</span>
videoStream<span style="color:#f92672">.</span><span style="color:#a6e22e">write</span><span style="color:#f92672">(</span>videoData<span style="color:#f92672">);</span>
<span style="color:#75715e">// 写操作完成之后关闭输出流
</span><span style="color:#75715e"></span>videoStream<span style="color:#f92672">.</span><span style="color:#a6e22e">close</span><span style="color:#f92672">();</span>
<span style="color:#75715e">// 我们可以使用同一个桶，通过创建输入流来读取刚刚写入的文件
</span><span style="color:#75715e">// 先创建一个用来存储视频的字节数组
</span><span style="color:#75715e"></span>
<span style="color:#66d9ef">byte</span><span style="color:#f92672">[]</span> data <span style="color:#f92672">=</span> <span style="color:#66d9ef">new</span> <span style="color:#66d9ef">byte</span><span style="color:#f92672">[(</span><span style="color:#66d9ef">int</span><span style="color:#f92672">)</span>1048576<span style="color:#f92672">];</span>
OzoneInputStream introStream <span style="color:#f92672">=</span> video<span style="color:#f92672">.</span><span style="color:#a6e22e">readKey</span><span style="color:#f92672">(</span><span style="color:#e6db74">&#34;intro.mp4&#34;</span><span style="color:#f92672">);</span>
introStream<span style="color:#f92672">.</span><span style="color:#a6e22e">read</span><span style="color:#f92672">(</span>data<span style="color:#f92672">);</span>
<span style="color:#75715e">// 读操作完成之后关闭输入流
</span><span style="color:#75715e"></span>introStream<span style="color:#f92672">.</span><span style="color:#a6e22e">close</span><span style="color:#f92672">();</span>
<span style="color:#75715e">// 关闭客户端
</span><span style="color:#75715e"></span>ozClient<span style="color:#f92672">.</span><span style="color:#a6e22e">close</span><span style="color:#f92672">();</span></code></pre></div>
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