redis bitmap数据结构之java对等操作详解

1. redis基本的bitmap操作命令

2. java中的原生bitmap

3. java和redis的bitmap互操作

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;
}
}