I have a method which reads through a CSV file and if any of the columns match my keyset prepares them in an sObject, with my test files which contained 1,000 records but only 4 columns this worked fine, however increasing the number of columns now (22 columns) returns "Regex too complicated" despite only having around 100 rows.

How can I get around this issue? I have googled and found articles like this but they are missing key parts of the code which renders this unusable.

2 Answers 2


The regex too complicated error occurs when you reach 1,000,000 input sequences, which can occur even on incredibly small strings. For example, accord to the knowledge article:

Pattern pat = Pattern.compile('(A)?(B)?(C)?(D)?(E)?(F)?(G)?(H)?(I)?(J)?(K)?(L)?(M)?(N)?(O)?(P)?(Q)?(R)?(S)?(T)?(U)?(V)?(W)?(X)?(Y)?(Z)?(AA)?(AB)?(AC)?(AD)?(AE)?(AF)?(AG)?(AH)?(AI)?(AJ)?(AK)?(AL)?(AM)?(AN)?(AO)?(AP)?(AQ)?(AR)?(AS)?(AT)?(AU)?(AV)?(AW)?(AX)?(AY)?(AZ)?$');
Matcher mat = pat.matcher('asdfasdfasdfasdfasdfasdf');

This code would fail because of the complexity of the pattern. Realistically, any Apex code that tries to parse a CSV is doomed to fail if it uses any regex matching on any reasonable sized file. Your best bet is to implement a finite state parser to parse your CSV file (note: link goes to a Java-based finite state CSV parser, not written by me).

Because of the overhead of Apex, I wouldn't necessarily try to directly duplicate the Java-based version above, but hopefully it will get you started in a direction that will allow you to process larger CSV files more efficiently.

Your processing input loop can make use of a switch to implement a state engine efficiently:

Integer index = 0;
while(index < input.size()) {
  String charAtX = input.substring(index, index+1);
  switch on currentState {
    when BEGIN_FIELD {
    when FOUND_QUOTE {
  • 1
    N.B. I can recall solving this using a custom iterator/iterable and a batch class - works if each row can be considered independent of each other
    – cropredy
    Commented Sep 17, 2018 at 22:42
  • @cropredy Yes, that's also viable. You just can't put a full csv through a single pattern.
    – sfdcfox
    Commented Sep 17, 2018 at 23:25

Not sure if this is the best approach but what I have done is a custom iterator with a batch class and split each line for processing (mentioned in my initial question).

This has allowed me to bypass the regex errors.

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