Strategy Pattern in Java 8

Marco CastigliegoJune 30th, 2015Last Updated: June 28th, 2015

3 45 1 minute read

These are two examples on how to implement a Strategy pattern design using Java 8 functional style together with Cyclops pattern matching and Hamcrest libraries.

PrintDependingOnInput method is a strategy that will System.println some message based on the log passed.

AddPrefix is another strategy that will add a prefix to a message based on the message content.

package com.marco.patternmatching; 

 

import static org.hamcrest.Matchers.containsString;
import static org.hamcrest.Matchers.not;
import static org.hamcrest.Matchers.startsWith;
import static org.hamcrest.core.AllOf.allOf;
import java.util.ArrayList;
import java.util.List;
import com.aol.cyclops.matcher.builders.Matching; 

 

public class FunctionalStrategy {

  public static void main(String[] args) {
     List<String> toTest = new ArrayList<>();
     toTest.add("INFO everything is fine");
     toTest.add("WARN something weird happened");
     toTest.add("ERROR NullPointerException");
     toTest.add("ERROR IOException");
     
     toTest.stream().forEach(FunctionalStrategy::printDependingOnInput);

     System.out.println("--------------------");

     List<String> messages = new ArrayList<>();
     messages.add("everything is fine");
     messages.add("something weird happened");
     messages.add("NullPointerException");
     messages.add("IOException");

     messages.stream().map(FunctionalStrategy::addPrefix).forEach(System.out::println);
  }

        
  public static void printDependingOnInput(String log) {

     Matching
        .when().isMatch(startsWith("INFO"))
                   .thenConsume(System.out::println)
        .when().isMatch(startsWith("WARN"))
                   .thenConsume(message -> System.out.println("Found one warning : " + message))
        .when().isMatch(allOf(startsWith("ERROR"), containsString("NullPointerException")))
                   .thenConsume(message -> System.err.println(message))
        .when().isMatch(allOf(startsWith("ERROR"), containsString("IOException")))
                   .thenConsume(message -> System.err.println(message + " Retrying a couple of times"))
        .match(log);

   }

   public static String addPrefix(String log) {

     return Matching
        .when().isMatch(allOf(not(containsString("Exception")), not(containsString("weird"))))
                    .thenApply(message -> "INFO " + message)
        .when().isMatch(containsString("weird"))
                    .thenApply(message -> "WARN " + message)
        .when().isMatch(containsString("Exception"))
                    .thenApply(message -> "ERROR " + message)
        .match(log).get();

  }
}

Nice and clean ;)

Reference:

Strategy Pattern in Java 8 from our JCG partner Marco Castigliego at the Remove duplication and fix bad names blog.