redis bitmap数据结构之java对等操作详解

127.0.0.1:6379> setbit bm1 222 1
(integer) 0
127.0.0.1:6379> getbit bm1 222
(integer) 1

 @Test
    public void testJavaBitmap() {
        BitSet bitmap = new BitSet();
        bitmap.set(88);
        // exist = true
        boolean exist = bitmap.get(88);
        BitSet bitmap2 = new BitSet();
        bitmap2.set(99);
        // bitmap中将包含 [88, 99]
        bitmap.or(bitmap2);
    }

 /*
     * BitSets are packed into arrays of "words."  Currently a word is
     * a long, which consists of 64 bits, requiring 6 address bits.
     * The choice of word size is determined purely by performance concerns.
     */
    private final static int ADDRESS_BITS_PER_WORD = 6;
    
    /**
     * Sets the bit at the specified index to {@code true}.
     *
     * @param  bitIndex a bit index
     * @throws IndexOutOfBoundsException if the specified index is negative
     * @since  JDK1.0
     */
    public void set(int bitIndex) {
        if (bitIndex < 0)
            throw new IndexOutOfBoundsException("bitIndex < 0: " + bitIndex);

        int wordIndex = wordIndex(bitIndex);
        expandTo(wordIndex);

        words[wordIndex] |= (1L << bitIndex); // Restores invariants

        checkInvariants();
    }
    /**
     * Given a bit index, return word index containing it.
     */
    private static int wordIndex(int bitIndex) {
        return bitIndex >> ADDRESS_BITS_PER_WORD;
    }

@Test
    public void testSetBitmapData2Redis() {
        //创建一个连接
        Jedis jedis = new Jedis("localhost", 6379);
        // 正向设置redis bitmap
        String testBitmapKey = "mybitmap1";
        jedis.set(testBitmapKey.getBytes(),
                genRedisBitmap(2, 55, 133, 65537, 10_0000));
        Assert.assertEquals("bitmap取值不正确", true,
                jedis.getbit(testBitmapKey, 2L));
        Assert.assertEquals("bitmap取值不正确", true,
                jedis.getbit(testBitmapKey, 133L));
        Assert.assertEquals("bitmap取值不正确", true,
                jedis.getbit(testBitmapKey, 65537L));
        Assert.assertEquals("bitmap取值不正确", true,
                jedis.getbit(testBitmapKey, 10_0000L));
        Assert.assertEquals("bitmap取值不正确", false,
                jedis.getbit(testBitmapKey, 3L));
        //在redis中获取name值
        byte[] redisBitmapData = jedis.get("mybitmap1".getBytes());
        BitSet bitSet = convertRedisBitmapToJava(redisBitmapData);
        Assert.assertTrue("redisBitmap反解不正确", bitSet.get(2));
        Assert.assertTrue("redisBitmap反解不正确", bitSet.get(133));
        Assert.assertTrue("redisBitmap反解不正确", bitSet.get(65537));
        Assert.assertTrue("redisBitmap反解不正确", bitSet.get(10_0000));
        Assert.assertFalse("redisBitmap反解不正确", bitSet.get(332));
        jedis.close();
    }

    // 将redis的bitmap转换为java 的bitset
    private BitSet convertRedisBitmapToJava(byte[] redisBitmapData) {
        int len = redisBitmapData.length;
        BitSet bitSet = new BitSet();
        // 每个 byte 8位, 所以整个bitmap 的长度为 len * 8
        for (int i = 0; i < len * 8; i++) {
            byte currentSegment = redisBitmapData[i / 8];
            if(currentSegment == 0) {
                continue;
            }
            if((currentSegment & (1 << (7 - (i % 8) ) ) ) != 0 ) {
                bitSet.set(i);
            }
        }
        return bitSet;
    }

    // 生成redis的bitmap数据
    private byte[] genRedisBitmap(int... items) {
        BitSet bitSet = new BitSet();
        // 2 55 133
        for (int k : items) {
            bitSet.set(k);
        }
        byte[] targetBitmap = bitSet.toByteArray();
        convertJavaToRedisBitmap(targetBitmap);
        return targetBitmap;
    }

    // 将java中的字节数组转换为redis的bitmap数据形式
    private void convertJavaToRedisBitmap(byte[] bytes) {
        int len = bytes.length;
        for (int i = 0; i < len; i++) {
            byte b1 = bytes[i];
            if(b1 == 0) {
                continue;
            }
            byte transByte = 0;
            for (byte j = 0; j < 8; j++) {
                transByte |= (b1 & (1 << j)) >> j << (7 -j);
            }
            bytes[i] = transByte;
        }
    }