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[Java][FlexBuffers] Abstract buffer access from ByteBuffer (#5743)

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To read and build flexbuffers on Java, one needs to wrap the data
using  ByteBuffer. But for the common case of having ByteBuffers
backed by arrays, accessing from a ByteBuffer might be inefficient.

So this change introduces two interfaces: ReadBuf and ReadWriteBuf.
It allows one to read and writes data directly on an array. It also allow
 other buffer implementations to be used with flexbuffers.

Another change is that FlexBuffersBuilder backed by array allows
the buffer to grow with the increase of the message size. Something
that could not be done with ByteBuffer.
This commit is contained in:
Paulo Pinheiro
2020-02-21 20:46:40 +01:00
committed by GitHub
parent 3ec7a53c62
commit cd88e6b2aa
8 changed files with 712 additions and 55 deletions
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73
java/com/google/flatbuffers/FlexBuffers.java
View File

@@ -36,7 +36,7 @@ import java.nio.charset.StandardCharsets;
* <p>
* Example of usage:
* <pre>
* ByteBuffer bb = ... // load message from file or network
* ReadBuf bb = ... // load message from file or network
* FlexBuffers.Reference r = FlexBuffers.getRoot(bb); // Reads the root element
* FlexBuffers.Map map = r.asMap(); // We assumed root object is a map
* System.out.println(map.get("name").asString()); // prints element with key "name"
@@ -100,7 +100,7 @@ public class FlexBuffers {
/** Represent a vector of booleans type */
public static final int FBT_VECTOR_BOOL = 36; // To Allow the same type of conversion of type to vector type
private static final ByteBuffer EMPTY_BB = ByteBuffer.allocate(1).asReadOnlyBuffer();
private static final ReadBuf EMPTY_BB = new ArrayReadWriteBuf(new byte[] {0}, 1);
/**
* Checks where a type is a typed vector
@@ -151,13 +151,13 @@ public class FlexBuffers {
}
// return position of the element that the offset is pointing to
private static int indirect(ByteBuffer bb, int offset, int byteWidth) {
// we assume all offset fits on a int, since ByteBuffer operates with that assumption
private static int indirect(ReadBuf bb, int offset, int byteWidth) {
// we assume all offset fits on a int, since ReadBuf operates with that assumption
return (int) (offset - readUInt(bb, offset, byteWidth));
}
// read unsigned int with size byteWidth and return as a 64-bit integer
private static long readUInt(ByteBuffer buff, int end, int byteWidth) {
private static long readUInt(ReadBuf buff, int end, int byteWidth) {
switch (byteWidth) {
case 1: return byteToUnsignedInt(buff.get(end));
case 2: return shortToUnsignedInt(buff.getShort(end));
@@ -168,12 +168,12 @@ public class FlexBuffers {
}
// read signed int of size byteWidth and return as 32-bit int
private static int readInt(ByteBuffer buff, int end, int byteWidth) {
private static int readInt(ReadBuf buff, int end, int byteWidth) {
return (int) readLong(buff, end, byteWidth);
}
// read signed int of size byteWidth and return as 64-bit int
private static long readLong(ByteBuffer buff, int end, int byteWidth) {
private static long readLong(ReadBuf buff, int end, int byteWidth) {
switch (byteWidth) {
case 1: return buff.get(end);
case 2: return buff.getShort(end);
@@ -183,7 +183,7 @@ public class FlexBuffers {
}
}
private static double readDouble(ByteBuffer buff, int end, int byteWidth) {
private static double readDouble(ReadBuf buff, int end, int byteWidth) {
switch (byteWidth) {
case 4: return buff.getFloat(end);
case 8: return buff.getDouble(end);
@@ -192,12 +192,23 @@ public class FlexBuffers {
}
/**
* Reads a FlexBuffer message in ByteBuffer and returns {@link Reference} to
* Reads a FlexBuffer message in ReadBuf and returns {@link Reference} to
* the root element.
* @param buffer ByteBuffer containing FlexBuffer message
* @param buffer ReadBuf containing FlexBuffer message
* @return {@link Reference} to the root object
*/
@Deprecated
public static Reference getRoot(ByteBuffer buffer) {
return getRoot( buffer.hasArray() ? new ArrayReadWriteBuf(buffer.array(), buffer.limit()) : new ByteBufferReadWriteBuf(buffer));
}
/**
* Reads a FlexBuffer message in ReadBuf and returns {@link Reference} to
* the root element.
* @param buffer ReadBuf containing FlexBuffer message
* @return {@link Reference} to the root object
*/
public static Reference getRoot(ReadBuf buffer) {
// See Finish() below for the serialization counterpart of this.
// The root ends at the end of the buffer, so we parse backwards from there.
int end = buffer.limit();
@@ -213,17 +224,17 @@ public class FlexBuffers {
public static class Reference {
private static final Reference NULL_REFERENCE = new Reference(EMPTY_BB, 0, 1, 0);
private ByteBuffer bb;
private ReadBuf bb;
private int end;
private int parentWidth;
private int byteWidth;
private int type;
Reference(ByteBuffer bb, int end, int parentWidth, int packedType) {
Reference(ReadBuf bb, int end, int parentWidth, int packedType) {
this(bb, end, parentWidth, (1 << (packedType & 3)), packedType >> 2);
}
Reference(ByteBuffer bb, int end, int parentWidth, int byteWidth, int type) {
Reference(ReadBuf bb, int end, int parentWidth, int byteWidth, int type) {
this.bb = bb;
this.end = end;
this.parentWidth = parentWidth;
@@ -484,13 +495,13 @@ public class FlexBuffers {
if (isString()) {
int start = indirect(bb, end, parentWidth);
int size = (int) readUInt(bb, start - byteWidth, byteWidth);
return Utf8.getDefault().decodeUtf8(bb, start, size);
return bb.getString(start, size);
}
else if (isKey()){
int start = indirect(bb, end, byteWidth);
for (int i = start; ; i++) {
if (bb.get(i) == 0) {
return Utf8.getDefault().decodeUtf8(bb, start, i - start);
return bb.getString(start, i - start);
}
}
} else {
@@ -619,11 +630,11 @@ public class FlexBuffers {
* Points into the data buffer and allows access to one type.
*/
private static abstract class Object {
ByteBuffer bb;
ReadBuf bb;
int end;
int byteWidth;
Object(ByteBuffer buff, int end, int byteWidth) {
Object(ReadBuf buff, int end, int byteWidth) {
this.bb = buff;
this.end = end;
this.byteWidth = byteWidth;
@@ -640,9 +651,9 @@ public class FlexBuffers {
// Stores size in `byte_width_` bytes before end position.
private static abstract class Sized extends Object {
private final int size;
protected final int size;
Sized(ByteBuffer buff, int end, int byteWidth) {
Sized(ReadBuf buff, int end, int byteWidth) {
super(buff, end, byteWidth);
size = readInt(bb, end - byteWidth, byteWidth);
}
@@ -655,14 +666,14 @@ public class FlexBuffers {
/**
* Represents a array of bytes element in the buffer
*
* <p>It can be converted to `ByteBuffer` using {@link data()},
* <p>It can be converted to `ReadBuf` using {@link data()},
* copied into a byte[] using {@link getBytes()} or
* have individual bytes accessed individually using {@link get(int)}</p>
*/
public static class Blob extends Sized {
static final Blob EMPTY = new Blob(EMPTY_BB, 1, 1);
Blob(ByteBuffer buff, int end, int byteWidth) {
Blob(ReadBuf buff, int end, int byteWidth) {
super(buff, end, byteWidth);
}
@@ -672,11 +683,11 @@ public class FlexBuffers {
}
/**
* Return {@link Blob} as `ByteBuffer`
* @return blob as `ByteBuffer`
* Return {@link Blob} as `ReadBuf`
* @return blob as `ReadBuf`
*/
public ByteBuffer data() {
ByteBuffer dup = bb.duplicate();
ByteBuffer dup = ByteBuffer.wrap(bb.data());
dup.position(end);
dup.limit(end + size());
return dup.asReadOnlyBuffer().slice();
@@ -709,7 +720,7 @@ public class FlexBuffers {
*/
@Override
public String toString() {
return Utf8.getDefault().decodeUtf8(bb, end, size());
return bb.getString(end, size());
}
/**
@@ -718,7 +729,7 @@ public class FlexBuffers {
@Override
public StringBuilder toString(StringBuilder sb) {
sb.append('"');
sb.append(Utf8.getDefault().decodeUtf8(bb, end, size()));
sb.append(bb.getString(end, size()));
return sb.append('"');
}
}
@@ -731,7 +742,7 @@ public class FlexBuffers {
private static final Key EMPTY = new Key(EMPTY_BB, 0, 0);
Key(ByteBuffer buff, int end, int byteWidth) {
Key(ReadBuf buff, int end, int byteWidth) {
super(buff, end, byteWidth);
}
@@ -760,7 +771,7 @@ public class FlexBuffers {
break;
}
}
return Utf8.getDefault().decodeUtf8(bb, end, size);
return bb.getString(end, size);
}
int compareTo(byte[] other) {
@@ -808,7 +819,7 @@ public class FlexBuffers {
public static class Map extends Vector {
private static final Map EMPTY_MAP = new Map(EMPTY_BB, 1, 1);
Map(ByteBuffer bb, int end, int byteWidth) {
Map(ReadBuf bb, int end, int byteWidth) {
super(bb, end, byteWidth);
}
@@ -913,7 +924,7 @@ public class FlexBuffers {
private static final Vector EMPTY_VECTOR = new Vector(EMPTY_BB, 1, 1);
Vector(ByteBuffer bb, int end, int byteWidth) {
Vector(ReadBuf bb, int end, int byteWidth) {
super(bb, end, byteWidth);
}
@@ -976,7 +987,7 @@ public class FlexBuffers {
private final int elemType;
TypedVector(ByteBuffer bb, int end, int byteWidth, int elemType) {
TypedVector(ReadBuf bb, int end, int byteWidth, int elemType) {
super(bb, end, byteWidth);
this.elemType = elemType;
}