A few days ago when automation interface to do an electricity supplier, has been very good with regular expression extractor sudden failure, the interface is always to get any value. 
Then when extracting token represents no problem, but in the follow-up to extract some customer id, order id, id when they fail to pay up.
The final reason is because the returned data is json format, not all being fully applicable. jmeter kind to provide users extract json plugin version low jmeter may need to manually install the package architecture, high version comes with the plugin. 
Add a json extractor inside the post processor, the fixed format is as follows: 
fixed format expression is: should contain illegal character, as shown 
in the tree view the results which can be the first P in the JSON A T H E X P R & lt E S S I O n-input box to input expression, whether the click test test value can be acquired, if the value can be acquired, then the expression inside the extractor filled into JSON. It can completely replace regular.
Emphasize writing expressions, are a few examples:
1, the expression in the figure below is: should contain illegal characters as 
2 expression in the figure below is: should contain illegal characters as 
3, if they have in the case of an array, any array, is [field: value], there are brackets, for example, is written as:.. $ data [0] .cwVouchId
Well, that's it.