I have a Java class
public class MsgLayout{
int field1;
String field2;
long field3;
}
I have to write this object as a byte array in a Socket output stream. The three fields (instance variables) have a layout. i.e. field1
must occupy 1 byte, field2
must occupy 4 bytes and开发者_运维百科 field3
must occupy 8 bytes.
ByteBuffer bbf = ByteBuffer.allocate(TOTAL_SIZE);
bbf.put(Integer.toString(this.getField1()).getBytes(), 0, FIELD1_SIZE);
bbf.position(FIELD2_OFFSET);
bbf.put(Long.toString(this.getField2()).getBytes(), 0, FIELD2_SIZE);
bbf.position(FIELD3_OFFSET);
bbf.put(Long.toString(this.getField3()).getBytes(), 0, FIELD3_SIZE);
byte[] msg = bbf.array();
Using the above code, I am trying to fit each field in the byte array according to its desired size. But I am getting IndexOutOfBoundException
In short, the problem is about how to fit the fields in the layout-defined size. For Example FIELD1_OFFSET = 0, FIELD1_SIZE=1, FIELD2_OFFSET=1, FIELD2_SIZE=4, FIELD3_OFFSET=5, FIELD3_SIZE=8.
Now when I convert field1
into String, it does not fit into 1 byte when converted into byte[]. If I do not convert to String, and use putInt(int) it writes 4 bytes into the resulting byte array.
What your code is currently doing is encoding your numeric fields as strings and then outputting the bytes of those characters.
I would suggest using the DataOutputStream class to wrap your SocketOutput stream and write your binary data as so:
DataOutput output = new DataOutputStream(socketOutputStream);
int field1 = 1;
String field2 = "Hello";
long field3 = 5000000000L;
output.writeByte(field1);
output.writeBytes(field2.substring(0, 3));
output.writeLong(field3);
There are a couple assumptions in this code. First I'm assuming for field 2 you want 4 characters serialized as a single byte each. If you want to do any multibyte encoding using something like UTF-8, then you need to do something a little differently. Second, I'm assuming that field 2 will always have at least 4 characters.
field1
may only have one byte of data, but its string representation will be one or more characters (e.g. "0"
, "63"
, "127"
). Each character in the String is in fact a char
(a two byte value). So I would expect one byte of data to inflate to two to six bytes of data when it goes through a byte->String->byte[] conversion.
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