Create decorator using lambda expression (#37)

Author: mperor

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/structural/decorator/TextProcessor.java

@@ -0,0 +1,25 @@
+package pl.mperor.lab.java.design.pattern.structural.decorator;
+
+import java.util.Arrays;
+import java.util.function.UnaryOperator;
+
+@FunctionalInterface
+public interface TextProcessor extends UnaryOperator<String> {
+
+    default TextProcessor chain(TextProcessor after) {
+        return input -> after.apply(this.apply(input));
+    }
+
+    static TextProcessor identity() {
+        return s -> s;
+    }
+
+    static TextProcessor of(TextProcessor processor) {
+        return processor;
+    }
+
+    static TextProcessor of(TextProcessor... processors) {
+        return Arrays.stream(processors)
+                .reduce(TextProcessor.identity(), TextProcessor::chain);
+    }
+}

DesignPatterns/src/test/java/pl/mperor/lab/java/design/pattern/structural/decorator/TextProcessorTest.java

@@ -0,0 +1,26 @@
+package pl.mperor.lab.java.design.pattern.structural.decorator;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class TextProcessorTest {
+
+    @Test
+    public void shouldAllowToCreateTextProcessorAsChainOfFunctions() {
+        Assertions.assertEquals("prefix@Hello World@suffix",
+                TextProcessor.of(String::strip)
+                        .chain(s -> "prefix" + s)
+                        .chain(s -> s + "suffix")
+                        .apply("  @Hello World@")
+        );
+
+        Assertions.assertEquals("HEX",
+                TextProcessor.of(
+                        String::toUpperCase,
+                        s -> s.replace("L", "X"),
+                        s -> s.substring(0, 3)
+                ).apply("Hello World")
+        );
+    }
+
+}