3.1 KiB
Currently, visiting http://localhost/user/0 will return a 500 error:
curl http://localhost/user/0
{{execute T3}}
{"timestamp":1550223186170,"status":500,"error":"Internal Server Error","exception":"java.lang.IllegalArgumentException","message":"id < 1","path":"/user/0"}
But what are the specific parameters of the request, what is the exception stack?
View the parameters/exception of UserController
Execute in Arthas:
watch com.example.demo.arthas.user.UserController * '{params, throwExp}'
{{execute T2}}
- The first argument is the class name, which supports wildcards.
- The second argument is the function name, which supports wildcards.
Visit curl http://localhost/user/0
{{execute T3}} , the watch
command will print the parameters and exception
$ watch com.example.demo.arthas.user.UserController * '{params, throwExp}'
Press Q or Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:2) cost in 53 ms.
ts=2019-02-15 01:35:25; [cost=0.996655ms] result=@ArrayList[
@Object[][isEmpty=false;size=1],
@IllegalArgumentException[java.lang.IllegalArgumentException: id < 1],
]
The user can see that the actual thrown exception is IllegalArgumentException
.
The user can exit the watch command by typing Q
{{execute T2}} or Ctrl+C
.
If the user want to expand the result, can use the -x
option:
watch com.example.demo.arthas.user.UserController * '{params, throwExp}' -x 2
{{execute T2}}
The return value expression
In the above example, the third argument is the return value expression
, which is actually an ognl
expression that supports some built-in objects:
- loader
- clazz
- method
- target
- params
- returnObj
- throwExp
- isBefore
- isThrow
- isReturn
You can use these built-in objects in the expressions. For example, return an array:
watch com.example.demo.arthas.user.UserController * '{params[0], target, returnObj}'
{{execute T2}}
More references: https://alibaba.github.io/arthas/en/advice-class.html
The conditional expression
The watch
command supports conditional expressions in the fourth argument, such as:
watch com.example.demo.arthas.user.UserController * returnObj 'params[0] > 100'
{{execute T2}}
When visit https://HOST_SUBDOMAIN-80-KATACODA_HOST.environments.katacoda.com/user/1 , the watch
command print nothing.
When visit https://HOST_SUBDOMAIN-80-KATACODA_HOST.environments.katacoda.com/user/101 , the watch
command will print:
$ watch com.example.demo.arthas.user.UserController * returnObj 'params[0] > 100'
Press Q or Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:2) cost in 47 ms.
ts=2019-02-13 19:42:12; [cost=0.821443ms] result=@User[
id=@Integer[101],
name=@String[name101],
]
Capture when an exception occurs
The watch
command supports the -e
option, which means that only requests that throw an exception are caught:
watch com.example.demo.arthas.user.UserController * "{params[0],throwExp}" -e
{{execute T2}}
Filter by cost
The watch command supports filtering by cost, such as:
watch com.example.demo.arthas.user.UserController * '{params, returnObj}' '#cost>200'
{{execute T2}}