Re: creating byte[] with subfields
On 1/18/2013 8:33 PM, Arne Vajh?j wrote:
On 1/18/2013 3:35 AM, Roedy Green wrote:
I often have to construct byte arrays with binary fields, or read
them.
I use a ByteArrayOutputStream and a DataOutputStream to compose them.
I wondered if there is a simpler way, one that does not require
computing each byte individually with shifts.
A DataOutputStream on top of a ByteArrayOutputStream is the
old Java way of doing it. And if you do not need to manipulate bits
and you are happy with big endian then you should not to use shifts.
The new Java way is ByteBuffer which support both big and little
endian, so you only need shift for bit manipulation.
Those are both pretty low level. If you need something more
high level, then you will need to look outside of standard
Java API.
PS: I actually have something on the shelf for that.
Data class:
import dk.vajhoej.record.Endian;
import dk.vajhoej.record.FieldType;
import dk.vajhoej.record.Struct;
import dk.vajhoej.record.StructField;
@Struct(endianess=Endian.LITTLE)
public class Data {
@StructField(n=0,type=FieldType.BIT,length=4)
private int bf1;
@StructField(n=1,type=FieldType.BIT,length=4)
private int bf2;
@StructField(n=2,type=FieldType.INT4)
private int iv;
@StructField(n=3,type=FieldType.VARSTR,prefixlength=1,encoding="ISO-8859-1")
private String sv;
public Data() {
this(0, 0, 0, "");
}
public Data(int bf1, int bf2, int iv, String sv) {
this.bf1 = bf1;
this.bf2 = bf2;
this.iv = iv;
this.sv = sv;
}
public int getBf1() {
return bf1;
}
public void setBf1(int bf1) {
this.bf1 = bf1;
}
public int getBf2() {
return bf2;
}
public void setBf2(int bf2) {
this.bf2 = bf2;
}
public int getIv() {
return iv;
}
public void setIv(int iv) {
this.iv = iv;
}
public String getSv() {
return sv;
}
public void setSv(String sv) {
this.sv = sv;
}
}
Test program:
import dk.vajhoej.record.RecordException;
import dk.vajhoej.record.StructReader;
import dk.vajhoej.record.StructWriter;
public class RW {
public static void main(String[] args) throws RecordException {
Data o1 = new Data(1, 2, 3, "ABC");
StructWriter sw = new StructWriter();
sw.write(o1);
byte[] ba = sw.getBytes();
for(byte b1 : ba) {
System.out.printf(" %02X" , b1);
}
System.out.println();
StructReader sr = new StructReader(ba);
Data o2 = sr.read(Data.class);
System.out.println(o2.getBf1() + " " + o2.getBf2() + " " + o2.getIv()
+ " " + o2.getSv());
}
}
Output:
12 03 00 00 00 03 41 42 43
1 2 3 ABC
Arne