Problem description

When accessing redis using jedis SDK, the following exceptions are thrown sometimes

java.lang.ClassCastException: java.lang.Long cannot be cast to [B
	at redis.clients.jedis.Connection.getBinaryBulkReply(Connection.java:259)
	at redis.clients.jedis.Connection.getBulkReply(Connection.java:248)
	at redis.clients.jedis.Jedis.hget(Jedis.java:674)

Sometimes it may be accompanied by timeout exceptions:

redis.clients.jedis.exceptions.JedisConnectionException: java.net.SocketTimeoutException: Read timed out
	at redis.clients.util.RedisInputStream.ensureFill(RedisInputStream.java:202)
	at redis.clients.util.RedisInputStream.readByte(RedisInputStream.java:40)
	at redis.clients.jedis.Protocol.process(Protocol.java:151)
	at redis.clients.jedis.Protocol.read(Protocol.java:215)
	at redis.clients.jedis.Connection.readProtocolWithCheckingBroken(Connection.java:340)
	at redis.clients.jedis.Connection.getBinaryBulkReply(Connection.java:259)
	at redis.clients.jedis.Connection.getBulkReply(Connection.java:248)
	at redis.clients.jedis.Jedis.hget(Jedis.java:674)

Reason & Solution:

There are three main reasons:

A jedis connection is returned to the connection pool after throwing an exception (such as timeout exception) when it is in use. This connection may run similar exceptions when it is used next time. Specifically, it is related to the last data requested by the Sockt buffer. Refer to link 1.

In this case, you need to close the jedis correctly. Some articles may say that you need to call the returnbrokenresource method, which is an ancient method. At least above 2.9.0, you can close it directly. If an exception is caught, you need to close it in finally.

Multithreading access to jedis objects

According to jedis documentation, jedispool is thread safe and jedis is non thread safe. Check whether the code has multithreaded logic.

Redis cluster resources are heavily loaded and full

This is why I read redis first and then write it. I keep throwing this exception. If the comments are written out, read-only operation is OK. After the comment is read out, the following exceptions are thrown. This kind of load re throwing exception is also mentioned in the issue of link 2.

redis.clients.jedis.exceptions.JedisDataException: ERR 
	at redis.clients.jedis.Protocol.processError(Protocol.java:127)
	at redis.clients.jedis.Protocol.process(Protocol.java:161)
	at redis.clients.jedis.Protocol.read(Protocol.java:215)
	at redis.clients.jedis.Connection.readProtocolWithCheckingBroken(Connection.java:340)
	at redis.clients.jedis.Connection.getOne(Connection.java:322)
	at redis.clients.jedis.ShardedJedisPipeline.sync(ShardedJedisPipeline.java:44)

Finally, I applied to the operation and maintenance department for a new redis, which can be read and written normally. If you maintain your own redis, check the log.