Retrieving binary data from SQL table in JAVA with Byte array and BitSet class

Question

Table Structure - Column X(Binary (15),null)

Value in Column X - 000000000000000000000000000000000000000000100000000000000000000000000000000000000000000000000000000000000000000000000000

i.e 15x8=120 bits

SQL query

Select X from tablename;

Java Code part for retrieving value: barray is byte[] and bits is new BitSet().

barray = resultset.getBytes("X");

if(barray != null) {
   for (int i = 0; i < barray.length * 8; i++) {
      if ((barray[barray.length-i/8-1]&(1<<(i%8))) > 0) {
         bits.set(i);
      }
   }
}

Problem: The 2nd if statement is returning false value(not sure y?) thus the bits object is not getting populated. Please suggest a solution.

Java code part:barray= resultSet.getBytes("X"); if(barray!=null){ for (int i=0; i<barray.length*8; i++) { if ((barray[barray.length-i/8-1]&(1<<(i%8))) >= 0) { bits.set(i); } } } — JavaBits
– JavaBits, Commented Mar 22, 2011 at 12:22
What bytes are you getting? Just print them out, to see if you're getting nonzero data out of the DB -- then you can figure out whether the problem is in the DB read or in the BitSet transcoding. — Vance Maverick
– Vance Maverick, Commented Mar 22, 2011 at 12:43
for the next time: you can format your source by putting 4 spaces before it, or using `` to wrap it inline. — Paŭlo Ebermann
– Paŭlo Ebermann, Commented Mar 22, 2011 at 13:01

Paŭlo Ebermann · Accepted Answer · 2011-03-22 14:01:22Z

3

I think your mistake is outside of the code you posted, as I wrapped it in this program, and it works here:

package de.fencing_game.paul.examples;

import java.util.BitSet;

/**
 * Test class for http://stackoverflow.com/questions/5391097/retrieving-binary-data-from-sql-table-in-java-with-byte-array-and-bitset-class.
 */
public class BitSetByteArrayTest {


    public static void main(String[] params) {

        byte[] barray= new byte[]{ 0x01, 0x02, 0x04, 0x08,
                                   0x10, 0x20, 0x40, (byte)0x80,
                                   };
        BitSet bits = new BitSet();

        if(barray!=null){
            for (int i=0; i<barray.length*8; i++) {
                if ((barray[barray.length-i/8-1]&(1<<(i%8))) > 0) {
                    bits.set(i);
                }
            }
        }
        System.out.println(bits);
    }
}

It works also with your input

    byte[] barray = { 0,    0, 0, 0, 0,
                      0x20, 0, 0, 0, 0,
                      0,    0, 0, 0, 0};

instead of the sample array, showing {77} then.

answered Mar 22, 2011 at 14:01

Paŭlo Ebermann

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Paŭlo Ebermann Over a year ago

@JavaBits: What was the reason?

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