How to serialize a java.util.regex.Pattern using protobuf?

Question

I have an object that I want to serialize using Protocol Buffers and store in redis. The object contains a java.util.regex.Pattern that is complied when the object is instantiated.

public class SerializableEntity {
    private Pattern pattern;
    private List<String> options;
}

This pattern is used to validate inputs to a certain api. Since compiling the pattern each time is expensive , I'm compiling the pattern once during instantiation and then reusing the same pattern instance each time the api is invoked. How do I serialize this compile Pattern field in the following schema so I when I de-serialize the object, I can use it without compiling the pattern again?

 message SerializableEntityProto {
     repeated string option = 1;
     // compiled pattern
 }

Thanks.

Answer 1

java.util.regex.Pattern does not have encode and decode proto functions implemented in itself. However, you can implement that yourself pretty easy (as Andy Turner suggests). Something like this:

Proto

syntax = "proto2";

package termin4t0r;
option java_package = "com.example.termin4t0r";

// Proto for java.util.regex.Pattern
message RegexPatternProto {
  // See Pattern.pattern()
  optional string pattern = 1;
  // See Pattern.flags()
  optional int64 flags = 2;
}

Java encode and decode functions

class RegexpPatternProtos {
  public static RegexPatternProto encode(java.util.regex.Pattern pattern) {
    return RegexPatternProto.newBuilder()
        .setPattern(pattern.pattern())
        .setFlags(pattern.flags())
        .build();
  }

  public static java.util.regex.Pattern decode(RegexPatternProto patternProto) {
    return new RegexPatternProto(
      patternProto.getPattern(), patternProto.getFlags());
  }
}

I leave the unittests as an exercise :) I even find serializing this way preferable as protocol buffers have forward and backward compatibility, whereas java serialization has problems with that.

Answer 2

I think this is a case of square peg and round hole, protobuf and serialization is not meant to be used that way.

Anyway it seems like you initialize a regex with every API call. I don't know how your app decides which Regex to use for a particular API, but you must start out with a Regex string to compile. Instead of trying to serializing the pattern, store it in memory in a HashMap<String,Pattern> ( Regex string as a key and the compiled pattern as value). And then get the pattern when you need it.