arthas-watch

Watch method return value

$ watch [com.example.MyClass] [myMethod] returnObj

$ watch [com.example.MyClass] [myMethod] '{params, returnObj}'

$ watch [com.example.MyClass] [myMethod] returnObj 'returnObj != null'

$ watch [com.example.MyClass] [myMethod] '{params, throwExp}' -e

watch [-n count] [-b|-e|-s|-f] class-pattern method-pattern express [condition-express]

watch is an Arthas command that observes method arguments, return values, and exceptions in real-time. It uses OGNL expressions to extract and display specific data from method invocations.
This enables debugging production issues without stopping the application or adding logging code.

class-pattern

Class name (supports wildcards)

Method name (supports wildcards)

OGNL expression for what to watch

Watch before method execution

Watch on exception

Watch on success return

Watch on finish (both success and exception)

Stop after count invocations

Filter condition (OGNL)

- params: Method parameters array
- returnObj: Return value
- throwExp: Exception thrown
- target: Object instance

OGNL expressions can be complex; test carefully. Watching hot methods may impact performance.

arthas(1), arthas-trace(1)