Regex consists of set of symbols. Following are the common matching symbols used for regex purpose.
Symbol
|
Description
|
.
|
Any character
|
^ $
|
Regex matches beginning of the line and end of the line
|
[abc][pq]
|
Matches a/b/c followed by p/q
|
[^abc]
|
Negates the matching pattern
|
[p-z4-9]
|
Matches characters between p and z or 4 to 9.
|
p|q
|
Equivalent to [pq]
|
pq
|
q immediately follows p
|
These matching symbols are further defined by quantifiers which will be defining number of occurrences of regex pattern.
Regex
|
Description
|
{p,q}
|
Occurs between p to q times
|
{p}
|
Occurs p times
|
*
|
{0,}
|
+
|
{1,}
|
?
|
{0,1}
|
There are certain meta characters that can be used to simplify defining symbols.
Symbol
|
Description
|
\s
|
Equivalent of [ \t\n\x0b\r\f]
|
\S
|
[ ^\t\n\x0b\r\f]
|
\w
|
[A-Za-Z0-9_]
|
\W
|
[^\w]
|
\d
|
[0-9]
|
\D
|
[^0-9]
|
\b
|
\w
|
Note: Grouping of regex elements can be done using ( ) operators.
p(?!q) denotes regex matches iff p is not followed by q.
Eventually we can consider following example, where I wanted to identify following string
{
"@nil":"true"
}
and replace this string with empty("") String.
Input String;
{
"Opportunities":{
"Opportunity":[
{
"Name":"Firzhan",
"Age":"30 years",
"EPF_Start_Date__c":{
"@nil":"true"
},
"EPF-Id":"006E000000",
"EPF_End_Date__c":{
"@nil":"true"
},
"EPF_Closed_Date__c":{
"@nil":"true"
},
"CreatedDate":"2016-12-12+05:30",
"Location":"Dehiwala"
},
{
"Name":"Firzhan2",
"Age":"31 years",
"Puppies":{
"@nil":"true"
},
"EPF-Id":"006E000000",
"EPF_Start_Date__c":"2017-03-25+05:30",
"EPF_End_Date__c":"2017-03-02T00:00:00.000+05:30",
"EPF_Closed_Date__c":"2017-07-17T12:26:46.000+05:30",
"CreatedDate":"2013-12-12+05:30",
"Location":"Dehiwala"
}
]
}
}
Pattern pattern = Pattern.compile(Utils.JSON_REGEX_CONSTANT); //Matcher matcher = pattern.matcher(opportunityJson.replaceAll("^\\s|\n\\s|\\s$", "''"));Matcher matcher = pattern.matcher(jsonResponse); jsonResponse = matcher.replaceAll("\"\"");
Here JSON_REGEX_CONSTANT is equal to
([\{]{1}[\s|\n]*(\"@nil\"){1}(\s*|\n*[:]+\s*|\n*)(\"true\"){1}[\s|\n]*[\}]{1})
