Implemented the file identifier functionality for Java.

Also fixed flatc not outputting these identifiers for files
compiled on the command-line.

Bug: 16983987
Change-Id: I8b714cfea3a8e144fa52133f62b2f7eda6eb044a
Tested: on Linux
This commit is contained in:
Wouter van Oortmerssen
2014-09-04 16:31:44 -07:00
parent 96592d5dbb
commit 09a2999c66
16 changed files with 113 additions and 17 deletions

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@@ -64,7 +64,8 @@ $(document).ready(function(){initNavTree('md__compiler.html','');});
<li><code>-b</code> : If data is contained in this file, generate a <code>filename.bin</code> containing the binary flatbuffer.</li>
<li><code>-t</code> : If data is contained in this file, generate a <code>filename.json</code> representing the data in the flatbuffer.</li>
<li><code>-o PATH</code> : Output all generated files to PATH (either absolute, or relative to the current directory). If omitted, PATH will be the current directory. PATH should end in your systems path separator, e.g. <code>/</code> or <code>\</code>.</li>
<li><code>-S</code> : Generate strict JSON (field names are enclosed in quotes). By default, no quotes are generated. </li>
<li><code>-S</code> : Generate strict JSON (field names are enclosed in quotes). By default, no quotes are generated.</li>
<li><code>-P</code> : Don't prefix enum values in generated C++ by their enum type. </li>
</ul>
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@@ -104,6 +104,7 @@ assert(inv-&gt;Get(9) == 9);
<p>if <code>ok</code> is true, the buffer is safe to read.</p>
<p>Besides untrusted data, this function may be useful to call in debug mode, as extra insurance against data being corrupted somewhere along the way.</p>
<p>While verifying a buffer isn't "free", it is typically faster than a full traversal (since any scalar data is not actually touched), and since it may cause the buffer to be brought into cache before reading, the actual overhead may be even lower than expected.</p>
<p>In specialized cases where a denial of service attack is possible, the verifier has two additional constructor arguments that allow you to limit the nesting depth and total amount of tables the verifier may encounter before declaring the buffer malformed.</p>
<h2>Text &amp; schema parsing</h2>
<p>Using binary buffers with the generated header provides a super low overhead use of FlatBuffer data. There are, however, times when you want to use text formats, for example because it interacts better with source control, or you want to give your users easy access to data.</p>
<p>Another reason might be that you already have a lot of data in JSON format, or a tool that generates JSON, and if you can write a schema for it, this will provide you an easy way to use that data directly.</p>

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@@ -63,7 +63,9 @@ Vec3 pos = monster.pos();
<p>Sadly the string accessors currently always create a new string when accessed, since FlatBuffer's UTF-8 strings can't be read in-place by Java.</p>
<p>Vector access is also a bit different from C++: you pass an extra index to the vector field accessor. Then a second method with the same name suffixed by <code>Length</code> let's you know the number of elements you can access: </p><pre class="fragment">for (int i = 0; i &lt; monster.inventoryLength(); i++)
monster.inventory(i); // do something here
</pre><p>You can also construct these buffers in Java using the static methods found in the generated code, and the FlatBufferBuilder class: </p><pre class="fragment">FlatBufferBuilder fbb = new FlatBufferBuilder();
</pre><p>If you specified a file_indentifier in the schema, you can query if the buffer is of the desired type before accessing it using: </p><pre class="fragment">if (Monster.MonsterBufferHasIdentifier(bb, start)) ...
</pre><h2>Buffer construction in Java</h2>
<p>You can also construct these buffers in Java using the static methods found in the generated code, and the FlatBufferBuilder class: </p><pre class="fragment">FlatBufferBuilder fbb = new FlatBufferBuilder();
</pre><p>Create strings: </p><pre class="fragment">int str = fbb.createString("MyMonster");
</pre><p>Create a table with a struct contained therein: </p><pre class="fragment">Monster.startMonster(fbb);
Monster.addPos(fbb, Vec3.createVec3(fbb, 1.0f, 2.0f, 3.0f, 3.0, (byte)4, (short)5, (byte)6));
@@ -83,6 +85,8 @@ for (byte i = 4; i &gt;=0; i--) fbb.addByte(i);
int inv = fbb.endVector();
</pre><p>You can use the generated method <code>startInventoryVector</code> to conveniently call <code>startVector</code> with the right element size. You pass the number of elements you want to write. You write the elements backwards since the buffer is being constructed back to front.</p>
<p>There are <code>add</code> functions for all the scalar types. You use <code>addOffset</code> for any previously constructed objects (such as other tables, strings, vectors). For structs, you use the appropriate <code>create</code> function in-line, as shown above in the <code>Monster</code> example.</p>
<p>To finish the buffer, call: </p><pre class="fragment">Monster.finishMonsterBuffer(fbb, mon);
</pre><p>The buffer is now ready to be transmitted. It is contained in the <code>ByteBuffer</code> which you can obtain from <code>fbb.dataBuffer()</code>. Importantly, the valid data does not start from offset 0 in this buffer, but from <code>fbb.dataStart()</code> (this is because the data was built backwards in memory). It ends at <code>fbb,capacity()</code>.</p>
<h2>Text Parsing</h2>
<p>There currently is no support for parsing text (Schema's and JSON) directly from Java, though you could use the C++ parser through JNI. Please see the C++ documentation for more on text parsing. </p>
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