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<h1><b><a href="https://www.sipmann.com/reading-files-java-readAllBytes-outofmemory.html" title="Permalink to Java - Files.readAllBytes throws OutOfMemory">Java - Files.readAllBytes throws OutOfMemory</a></b></h1>
<h5>
<i class="fa fa-calendar"></i><time class="w3-opacity" datetime="2018-02-17T13:00:00-02:00"> Sat 17 February 2018</time>
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<p><p>When you need to interact with files, there's the possibility to read all bytes from the file with <cite>Files.readAllBytes</cite>. But be aware of the kinds of files your application will deal with because the Java API files have a limit for the buffer that is defined as <cite>Integer.MAX_VALUE</cite> as you can see above or at the OpenJDK sources.</p>
<div class="highlight"><pre><span></span><span class="kd">public</span> <span class="kd">static</span> <span class="kt">byte</span><span class="o">[]</span> <span class="nf">readAllBytes</span><span class="p">(</span><span class="n">Path</span> <span class="n">path</span><span class="p">)</span> <span class="kd">throws</span> <span class="n">IOException</span> <span class="p">{</span>
<span class="k">try</span> <span class="p">(</span><span class="n">FileChannel</span> <span class="n">fc</span> <span class="o">=</span> <span class="n">FileChannel</span><span class="p">.</span><span class="na">open</span><span class="p">(</span><span class="n">path</span><span class="p">))</span> <span class="p">{</span>
<span class="kt">long</span> <span class="n">size</span> <span class="o">=</span> <span class="n">fc</span><span class="p">.</span><span class="na">size</span><span class="p">();</span>
<span class="k">if</span> <span class="p">(</span><span class="n">size</span> <span class="o">></span> <span class="p">(</span><span class="kt">long</span><span class="p">)</span><span class="n">Integer</span><span class="p">.</span><span class="na">MAX_VALUE</span><span class="p">)</span>
<span class="k">throw</span> <span class="k">new</span> <span class="n">OutOfMemoryError</span><span class="p">(</span><span class="s">"Required array size too large"</span><span class="p">);</span>
<span class="kt">byte</span><span class="o">[]</span> <span class="n">arr</span> <span class="o">=</span> <span class="k">new</span> <span class="kt">byte</span><span class="o">[</span><span class="p">(</span><span class="kt">int</span><span class="p">)</span><span class="n">size</span><span class="o">]</span><span class="p">;</span>
<span class="n">ByteBuffer</span> <span class="n">bb</span> <span class="o">=</span> <span class="n">ByteBuffer</span><span class="p">.</span><span class="na">wrap</span><span class="p">(</span><span class="n">arr</span><span class="p">);</span>
<span class="k">while</span> <span class="p">(</span><span class="n">bb</span><span class="p">.</span><span class="na">hasRemaining</span><span class="p">())</span> <span class="p">{</span>
<span class="k">if</span> <span class="p">(</span><span class="n">fc</span><span class="p">.</span><span class="na">read</span><span class="p">(</span><span class="n">bb</span><span class="p">)</span> <span class="o"><</span> <span class="mi">0</span><span class="p">)</span> <span class="p">{</span>
<span class="c1">// truncated</span>
<span class="k">break</span><span class="p">;</span>
<span class="p">}</span>
<span class="p">}</span>
<span class="kt">int</span> <span class="n">nread</span> <span class="o">=</span> <span class="n">bb</span><span class="p">.</span><span class="na">position</span><span class="p">();</span>
<span class="k">return</span> <span class="p">(</span><span class="n">nread</span> <span class="o">==</span> <span class="n">size</span><span class="p">)</span> <span class="o">?</span> <span class="n">arr</span> <span class="p">:</span> <span class="n">Arrays</span><span class="p">.</span><span class="na">copyOf</span><span class="p">(</span><span class="n">arr</span><span class="p">,</span> <span class="n">nread</span><span class="p">);</span>
<span class="p">}</span>
<span class="p">}</span>
</pre></div>
<p>With that in mind, check if isn't better read chunks of bytes e work with that slice in exchange of loading the whole file into the memory ;). Above a simple example of how you can read chunks of bytes from the file.</p>
<div class="highlight"><pre><span></span><span class="kt">byte</span><span class="o">[]</span> <span class="n">buffer</span> <span class="o">=</span> <span class="k">new</span> <span class="kt">byte</span><span class="o">[</span><span class="mi">1024</span><span class="o">]</span><span class="p">;</span>
<span class="n">FileInputStream</span> <span class="n">in</span> <span class="o">=</span> <span class="k">new</span> <span class="n">FileInputStream</span><span class="p">(</span><span class="n">file</span><span class="p">);</span>
<span class="kt">int</span> <span class="n">rc</span> <span class="o">=</span> <span class="n">in</span><span class="p">.</span><span class="na">read</span><span class="p">(</span><span class="n">buffer</span><span class="p">);</span>
<span class="k">while</span> <span class="p">(</span><span class="n">rc</span> <span class="o">!=</span> <span class="o">-</span><span class="mi">1</span><span class="p">)</span>
<span class="p">{</span>
<span class="c1">//crazy stuff here with buffer</span>
<span class="n">rc</span> <span class="o">=</span> <span class="n">in</span><span class="p">.</span><span class="na">read</span><span class="p">(</span><span class="n">buffer</span><span class="p">);</span>
<span class="p">}</span>
</pre></div>
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