How to check null value from REDIS MGET via Jedis client in java

Question

I have some keys in redis. I can do a MGET and fetch the values. But when the key is not present I get a (nil) from redis. But how to check that in java ? I am checking for null but it is not working.

127.0.0.1:6379> MGET key1 key2 key3 key4 1) "Hello" 2) "World" 3) "Hi" 4) "Hi-World" 127.0.0.1:6379> MGET key1 key2 key3 key5 key4 1) "Hello" 2) "World" 3) "Hi" 4) (nil) 5) "Hi-World" 127.0.0.1:6379>

In my java class actually I am mapping the key-list and value-list from MGET in a hash map. And on the value list I am doing some operations. There I need to put a null check. But simple java null is not working.

Which Jedis version are you using? Please add shortest reproducible Java code that you think is not working. — sazzad
– sazzad, Commented Dec 10, 2021 at 18:59

Rafat · Accepted Answer · 2021-12-10 09:58:44Z

2

You can always call exists to check if a key exists in Redis. To check with java, first, create a client and call the appropriate method.

Jedis jedis = new Jedis(host, port); List<String> values = jedis.mget(keys); //get all values for the given keys values.removeAll(Collections.singletonList(null)); //remove all null values if(jedis.exists(key)) { //check if a particular key exists or not System.out.println(key + " exists"); }

edited Dec 10, 2021 at 9:58

answered Dec 10, 2021 at 9:54

Rafat

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6 Comments

Som Over a year ago

This is to check a particular key. Again in that case I need to loop through the entire List. I am using mget and getting the list and returning the list. In somewhere else I am looping through the list and checking if its null. How to do that.

Rafat Over a year ago

I've updated my answer. You can remove all null values before returning the values

Som Over a year ago

This will remove if the value is exactly null. But it is returning (nil) and and not a null . There is my problem. How do I do a null check on that. Please see the output from REDIS in my question.

Som Over a year ago

Actually I am mapping the key-list and value-list in a hash map. And on the value list I am doing some operations. There I need to put a null check.

Rafat Over a year ago

I've just run some codes again on my PC and it returns null in java instead of nil if I try to get some values that don't exist in Redis via mget. It shows nil in the console though.

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Bhushan · Accepted Answer · 2021-12-10 09:32:06Z

If you have object as a map then you can access it like this

System.out.println(redissonClient.getMap("object").get("key")==null);

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