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116 lines
3.8 KiB
Markdown
116 lines
3.8 KiB
Markdown
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Currently, visiting http://localhost/user/0 will return a 500 error:
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`curl http://localhost/user/0`{{execute T3}}
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```
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{"timestamp":1550223186170,"status":500,"error":"Internal Server Error","exception":"java.lang.IllegalArgumentException","message":"id < 1","path":"/user/0"}
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```
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But what are the specific parameters of the request, what is the exception stack?
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### View the parameters/exception of UserController
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Execute in Arthas:
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`watch com.example.demo.arthas.user.UserController * '{params, throwExp}'`{{execute T2}}
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1. The first argument is the class name, which supports wildcards.
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2. The second argument is the function name, which supports wildcards.
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Visit `curl http://localhost/user/0`{{execute T3}} , the `watch` command will print the parameters and exception
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```bash
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$ watch com.example.demo.arthas.user.UserController * '{params, throwExp}'
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Press Q or Ctrl+C to abort.
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Affect(class-cnt:1 , method-cnt:2) cost in 53 ms.
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ts=2019-02-15 01:35:25; [cost=0.996655ms] result=@ArrayList[
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@Object[][isEmpty=false;size=1],
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@IllegalArgumentException[java.lang.IllegalArgumentException: id < 1],
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]
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```
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The user can see that the actual thrown exception is `IllegalArgumentException`.
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The user can exit the watch command by typing `Q`{{execute T2}} or `Ctrl+C`.
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If the user want to expand the result, can use the `-x` option:
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`watch com.example.demo.arthas.user.UserController * '{params, throwExp}' -x 2`{{execute T2}}
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```bash
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$ watch com.example.demo.arthas.user.UserController * '{params, throwExp}' -x 2
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Press Q or Ctrl+C to abort.
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Affect(class count: 1 , method count: 2) cost in 190 ms, listenerId: 1
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ts=2020-08-13 05:22:45; [cost=4.805432ms] result=@ArrayList[
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@Object[][
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@Integer[0],
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],
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java.lang.IllegalArgumentException: id < 1
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at com.example.demo.arthas.user.UserController.findUserById(UserController.java:19)
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at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
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at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
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at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
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...
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,
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]
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```
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### The return value expression
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In the above example, the third argument is the `return value expression`, which is actually an `ognl` expression that supports some built-in objects:
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* loader
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* clazz
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* method
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* target
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* params
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* returnObj
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* throwExp
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* isBefore
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* isThrow
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* isReturn
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You can use these built-in objects in the expressions. For example, return an array:
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`watch com.example.demo.arthas.user.UserController * '{params[0], target, returnObj}'`{{execute T2}}
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More references: https://arthas.aliyun.com/doc/en/advice-class.html
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### The conditional expression
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The `watch` command supports conditional expressions in the fourth argument, such as:
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`watch com.example.demo.arthas.user.UserController * returnObj 'params[0] > 100'`{{execute T2}}
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When visit https://[[HOST_SUBDOMAIN]]-80-[[KATACODA_HOST]].environments.katacoda.com/user/1 , the `watch` command print nothing.
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When visit https://[[HOST_SUBDOMAIN]]-80-[[KATACODA_HOST]].environments.katacoda.com/user/101 , the `watch` command will print:
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```bash
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$ watch com.example.demo.arthas.user.UserController * returnObj 'params[0] > 100'
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Press Q or Ctrl+C to abort.
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Affect(class-cnt:1 , method-cnt:2) cost in 47 ms.
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ts=2019-02-13 19:42:12; [cost=0.821443ms] result=@User[
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id=@Integer[101],
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name=@String[name101],
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]
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```
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### Capture when an exception occurs
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The `watch` command supports the `-e` option, which means that only requests that throw an exception are caught:
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`watch com.example.demo.arthas.user.UserController * "{params[0],throwExp}" -e`{{execute T2}}
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### Filter by cost
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The watch command supports filtering by cost, such as:
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`watch com.example.demo.arthas.user.UserController * '{params, returnObj}' '#cost>200'`{{execute T2}} |