[英]java bytebuffer write read append
我正在尝试使用 ByteBuffer 来解析作为字节数组接收的数据包流,并且可能包含部分或多个数据包。 数据包的长度可变,所以我需要解析前两个字节来获取数据包长度,似乎一旦我翻转()缓冲区来读取数据包,如果数据包不完整,我就无法返回并附加更多数据。
如何将数据写入缓冲区,读取其中的一些数据以验证内容,然后在保留读取数据的同时在必要时向其中附加更多数据?
class Foo {
static final byte[] DATA1 = {0, 13, 2, 65, 88, 80, 55, 51, 52, 84, 82, 43, -111};
static final byte[] DATA2 = {0, 21, 6, 2, 3, 67, 23, 71, -77, 24, -66, -12, -76, 98, 25, 61, 54, -20, 127, -118, 71};
static final byte[] DATA3 = {0, 21, 5, 3, 5, 67};
static final byte[] DATA4 = {23, 72, -50, 24, -66, -9, -31, -86, 25, 61, -95, 75, 71, 47, -102, 0, 13, 2, 84};
static final byte[] DATA5 = {82, 65, 28, 10, 65, 71, 52, 44, 11};
ByteBuffer mByteBuffer = ByteBuffer.allocate(4096);
public void test() {
mByteBuffer.order(ByteOrder.BIG_ENDIAN);
parse(DATA1);
parse(DATA2);
parse(DATA3);
parse(DATA4);
parse(DATA5);
}
public void parse(byte[] bytes) {
short byteCount;
short crc;
mByteBuffer.put(bytes);
mByteBuffer.flip();
while (mByteBuffer.remaining() > 5) {
byteCount = mByteBuffer.getShort();
// check for invalid buffer
if (byteCount < 5) {
mByteBuffer.clear();
return;
}
if (mByteBuffer.remaining() < (byteCount - 2)) {
// TODO: incomplete packet, do something
}
// payload (u8[1 .. 4092])
byte[] payload = new byte[byteCount - 4];
mByteBuffer.get(payload, 0, payload.length);
// crc (u16)
crc = mByteBuffer.getShort();
}
mByteBuffer.clear();
}
}
在getShort()
之后或通常在任何获取或写入序列之后以及下一个read()
之前,调用compact()
read()
。
我在这里做了很多更改,所有这些更改都在注释中进行了说明。
private final ByteBuffer mByteBufferAlloc = ByteBuffer.allocate( 4096 );
private ByteBuffer mByteBuffer = mByteBufferAlloc.duplicate(); // create a duplicate so we can use without affecting the original allocated buffer so we have a blank slate to reset to
public void test()
{
mByteBuffer.order( ByteOrder.BIG_ENDIAN );
parse( DATA1 );
parse( DATA2 );
parse( DATA3 );
parse( DATA4 );
parse( DATA5 );
}
public void parse( byte[] bytes )
{
short byteCount;
short crc;
if( bytes.length > mByteBuffer.remaining() ) // Ran out of room, compact anything not yet processed back to the beginning of the buffer and start back with a copy of the allocated buffer
{
int numBytes = mByteBuffer.position();
if( numBytes > 0 )
{
byte[] toCompact = new byte[numBytes];
((ByteBuffer) mByteBuffer.flip()).get( toCompact );
mByteBuffer = mByteBufferAlloc.duplicate().put( toCompact );
}
else // nothing in the buffer, simply start fresh
mByteBuffer = mByteBufferAlloc.duplicate();
}
mByteBuffer.put( bytes );
mByteBuffer.flip();
while( mByteBuffer.remaining() > 5 )
{
byteCount = mByteBuffer.getShort();
// check for invalid buffer
if( byteCount < 5 )
{
System.err.println( "Invalid data, throwing away buffer." );
mByteBuffer.clear(); // something was invalid, throw away the entire buffer, but we should probably log an error or something
return;
}
if( mByteBuffer.remaining() < (byteCount - 2) )
{
// not enough data, wait for more
break;
}
// payload (u8[1 .. 4092])
byte[] payload = new byte[byteCount - 4];
mByteBuffer.get( payload, 0, payload.length );
// crc (u16)
crc = mByteBuffer.getShort();
int pos = mByteBuffer.position(), limit = mByteBuffer.limit(), capacity = mByteBuffer.capacity();
mByteBuffer = ((ByteBuffer) mByteBuffer.limit( capacity )).slice();
mByteBuffer.limit( limit - pos ); // cut the packet off the beginning so we won't parse it again
// TODO do something with the packet
}
mByteBuffer.position( mByteBuffer.limit() ).limit( mByteBuffer.capacity() ); // reset the position to the end of the added data and the limit to the capacity
// mByteBuffer.clear(); Don't want to do this because we want the next call to append to the buffer so retain state
}
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