How to use opsForList().range() in redis

Conclusion (please read below for specific test data)

1. If start—end maintains the overall order, there will be no problem

2. Follow the order, even if start N-1 can also query data

3. Special usage: Through stringRedisTemplate.opsForList().range(key, 0, -1), you can query the first index to the last index ( That is, all data)

1. Environment redis

2. Test code:

  @Resource
    private StringRedisTemplate stringRedisTemplate;

    @Test
    void testRedis() {
        String key = "testList";
        String[] data = new String[]{"1_1", "1-2", "2_1", "2_2"};
        Boolean flag = stringRedisTemplate.hasKey(key);
        if (!flag) {
            stringRedisTemplate.opsForList().leftPushAll(key, data);
        }
        List<String> range = stringRedisTemplate.opsForList().range(key, -100, -1);
        System.out.println("range = " + range);
    }

3. Test data (assuming the List length is N)

4. The test starts from the reciprocal index

4.1. stringRedisTemplate.opsForList().range(key, -4, -1)

From the results: the 4th from the last index - the 1st from the last index

4.2, stringRedisTemplate.opsForList().range(key, -3, -1)

From the results: the third from the last index - the first from the last index

4.3, stringRedisTemplate. opsForList().range(key, -3, -2)

From the results: the third from the last index - the second from the last index

4.4, stringRedisTemplate.opsForList().range(key, -2, -3)

From the results: the second from the last index - the third from the last index will not work, from The third from the bottom of the index - the second from the bottom of the index is fine.

Conclusion: Starting from the Nth index, it must be in order (i.e. -N, -(N-1), -(N-2),..., -1). Reverse order is not possible. ’

5. The test starts from the positive index number

5.1. stringRedisTemplate.opsForList().range(key, 0, 3)

From the results: From the first index - the fourth index

##5.2, stringRedisTemplate.opsForList().range(key, 1,2)

From the results: From the second index - the third index

##5.3, stringRedisTemplate.opsForList().range(key, 2,1)

From the results: from the 3rd index - the 2nd index is not possible, from the 2nd index - the 3rd index is OK

Conclusion : Starting from index 0, it must be in order (i.e. 0, 1, 2,..., N-1), reverse order is not possible

6. Test index Countdown——Positive index (positive index, subscript 0 is the first one)

6.1, stringRedisTemplate.opsForList().range(key, -2, 2)

Judging from the results: it is not difficult to understand, from the second to last index (that is, row is 3), to the third index (that is, row is 3)

6.2. stringRedisTemplate.opsForList().range(key, -4, 3)

From the results: it is not difficult to understand, from the fourth to last index (that is, row is 1), to the index 3 (that is, row is 4)

6.3, stringRedisTemplate.opsForList().range(key, -4, 5)

From the results: From the 4th to last index (i.e., row is 1), to the 5th index (i.e., row is 6)

Conclusion: It is no problem to exceed in order

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