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Added accessor in Java to get vectors as ByteBuffers.

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

Change-Id: Ic4bfb98f9df9501b8fc82de2c45db7d7311135ac
Tested: on Linux.
This commit is contained in:
Wouter van Oortmerssen
2014-09-10 16:38:37 -07:00
parent 32f2c1c3b9
commit 858e9961e2
7 changed files with 93 additions and 33 deletions
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28
java/flatbuffers/Table.java
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@@ -38,6 +38,10 @@ public class Table {
}
// Create a java String from UTF-8 data stored inside the flatbuffer.
// This allocates a new string and converts to wide chars upon each access,
// which is not very efficient. Instead, each FlatBuffer string also comes with an
// accessor based on __vector_as_bytebuffer below, which is much more efficient,
// assuming your Java program can handle UTF-8 data directly.
protected String __string(int offset) {
offset += bb.getInt(offset);
if (bb.hasArray()) {
@@ -45,10 +49,11 @@ public class Table {
} else {
// We can't access .array(), since the ByteBuffer is read-only.
// We're forced to make an extra copy:
bb.position(offset + SIZEOF_INT);
byte[] copy = new byte[bb.getInt(offset)];
int old_pos = bb.position();
bb.position(offset + SIZEOF_INT);
bb.get(copy);
bb.position(0);
bb.position(old_pos);
return new String(copy, 0, copy.length, Charset.forName("UTF-8"));
}
}
@@ -66,6 +71,21 @@ public class Table {
return offset + bb.getInt(offset) + SIZEOF_INT; // data starts after the length
}
// Get a whole vector as a ByteBuffer. This is efficient, since it only allocates a new
// bytebuffer object, but does not actually copy the data, it still refers to the same
// bytes as the original ByteBuffer.
// Also useful with nested FlatBuffers etc.
protected ByteBuffer __vector_as_bytebuffer(int vector_offset, int elem_size) {
int o = __offset(vector_offset);
if (o == 0) return null;
int old_pos = bb.position();
bb.position(__vector(o));
ByteBuffer nbb = bb.slice();
bb.position(old_pos);
nbb.limit(__vector_len(o) * elem_size);
return nbb;
}
// Initialize any Table-derived type to point to the union at the given offset.
protected Table __union(Table t, int offset) {
offset += bb_pos;
@@ -74,12 +94,12 @@ public class Table {
return t;
}
protected static boolean __has_identifier(ByteBuffer bb, int offset, String ident) {
protected static boolean __has_identifier(ByteBuffer bb, String ident) {
if (ident.length() != FILE_IDENTIFIER_LENGTH)
throw new AssertionError("FlatBuffers: file identifier must be length " +
FILE_IDENTIFIER_LENGTH);
for (int i = 0; i < FILE_IDENTIFIER_LENGTH; i++) {
if (ident.charAt(i) != (char)bb.get(offset + SIZEOF_INT + i)) return false;
if (ident.charAt(i) != (char)bb.get(bb.position() + SIZEOF_INT + i)) return false;
}
return true;
}