Added accessor in Java to get vectors as ByteBuffers.

Also cleaned up ByteBuffer usage in general: ByteBuffer.position
now universally indicates the start of a ByteBuffer.

Change-Id: Ic4bfb98f9df9501b8fc82de2c45db7d7311135ac
Tested: on Linux.

docs/html/md__java_usage.html

@@ -60,10 +60,11 @@ Monster monster = Monster.getRootAsMonster(bb);
 Vec3 pos = monster.pos();
 </pre><p>Note that whenever you access a new object like in the <code>pos</code> example above, a new temporary accessor object gets created. If your code is very performance sensitive (you iterate through a lot of objects), there's a second <code>pos()</code> method to which you can pass a <code>Vec3</code> object you've already created. This allows you to reuse it across many calls and reduce the amount of object allocation (and thus garbage collection) your program does.</p>
 <p>Java does not support unsigned scalars. This means that any unsigned types you use in your schema will actually be represented as a signed value. This means all bits are still present, but may represent a negative value when used. For example, to read a <code>byte b</code> as an unsigned number, you can do: <code>(short)(b &amp; 0xFF)</code></p>
-<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>The default string accessor (e.g. <code>monster.name()</code>) currently always create a new Java <code>String</code> when accessed, since FlatBuffer's UTF-8 strings can't be used in-place by <code>String</code>. Alternatively, use <code>monster.nameAsByteBuffer()</code> which returns a <code>ByteBuffer</code> referring to the UTF-8 data in the original <code>ByteBuffer</code>, which is much more efficient. The <code>ByteBuffer</code>'s <code>position</code> points to the first character, and its <code>limit</code> to just after the last.</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>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><p>Alternatively, much like strings, you can use <code>monster.inventoryAsByteBuffer()</code> to get a <code>ByteBuffer</code> referring to the whole vector. Use <code>ByteBuffer</code> methods like <code>asFloatBuffer</code> to get specific views if needed.</p>
+<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)) ...
 </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");
@@ -86,7 +87,7 @@ 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>
+</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.dataBuffer().position()</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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