Key should be unique by a host. So it seems item prototype is not correct and creates duplicates what is forbidden.
Please review the prototype.
Not I'm closing this as WON'T FIX.

majun, are you attempting to discover multiple JVMs on the same host by any chance ?

I not attempting to discover multiple JVMs on the same host.
i just want to discovery this jvm different ThreadPool name,
so i create a jvm lld. jmx.discovery[attributes,"*:type=ThreadPool,name=*"]
and create two Item prototypes jmx[{#JMXOBJ},currentThreadCount] and jmx[{#JMXOBJ},maxThreads].
there is no other items in this host.

two Item prototypes data is normal. just jmx discovery appear error "Cannot create item: item with the same key ..."
I can't find out where the problem is.

I not attempting to discover multiple JVMs on the same host.
i just want to discovery this jvm different ThreadPool name,
so i create a jvm lld. jmx.discovery[attributes,"*:type=ThreadPool,name=*"]
and create two Item prototypes jmx[

,maxThreads].
there is no other items in this host.

two Item prototypes data is normal. just jmx discovery appear error "Cannot create item: item with the same key ..."
I can't find out where the problem is.

Please increase log level for java pollers and grab from the output the JSON which is used for jmx.discovery[attributes,"*:type=ThreadPool,name=*"]. I think there are some duplicates.

if we can use zabbix_get to check it , and What is the format of the command。

No zabbix_get not help here. Only parse debug log.

my zabbix_java and zabbix_server is in a host and i not found Increase the log level configuration option in settings.sh.

if edit increase log level for java pollers in zabbix_server.conf files?

majun, you should increase log level of the zabbix_server.

To increase log level in run time mode you can use zabbix_server option -R. For example: zabbix_server -R log_level_increase=java\ poller

thank you. but i not found error in log.
i will attach my log, please check it.

This not fit to initial problem.

 59117:20180403:102003.886 JSON before sending [{"request":"java gateway jmx","jmx_endpoint":"service:jmx:rmi:///jndi/rmi://11.8.44.146:8449/jmxrmi","keys":["jmx.discovery[Catalina,\"*:type=ThreadPool,name=*\"]"]}]
59117:20180403:102003.898 JSON back [{"response":"success","data":[{"error":"invalid discovery mode: Catalina"}]}]

Which error do you have for this rule?

Based on example outputs of jmx.discovery from the documentation I can make a conclusion that {#JMXOBJ} is not necessarily unique. Therefore your discovery rule tries to create multiple items with same keys. I think you should have a single item prototype jmx[{#JMXOBJ},{#JMXATTR}] and leave only {#JMXATTR} equal to currentThreadCount or maxThreads using LLD filters.

ok i will try it.
we can close this case.

Changing resolution to Workaround proposed.