#160 let's get rid of List.add() - Part 3

src/main/java/org/takes/misc/Transform.java

@@ -0,0 +1,109 @@
+/**
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2015 Yegor Bugayenko
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included
+ * in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+package org.takes.misc;
+
+import java.util.Iterator;
+
+/**
+ * Transform elements in an iterable (in type T) into others (in type K).
+ *
+ * @author Jason Wong ([email protected])
+ * @version $Id$
+ * @since 0.15.2
+ */
+public class Transform<T, K> implements Iterable<K> {
+
+    /**
+     * Internal storage.
+     */
+    private final transient Iterable<T> list;
+
+    /**
+     * The action to transform the elements in the iterator.
+     */
+    private final transient TransformAction<T, K> action;
+
+    /**
+     * Ctor.
+     * @param itb Iterable to be transformed
+     * @param act The actual transformation implementation
+     */
+    public Transform(final Iterable<T> itb,
+        final TransformAction<T, K> act) {
+        this.list = itb;
+        this.action = act;
+    }
+
+    @Override
+    public final Iterator<K> iterator() {
+        return new TransformIterator<T, K>(this.list.iterator(), this.action);
+    }
+
+    /**
+     * The iterator to iterator through the original type B and return the
+     * transformed element in type A.
+     *
+     * <p>This class is NOT thread-safe.
+     */
+    private static class TransformIterator<B, A> implements Iterator<A> {
+
+        /**
+         * The iterator to reflect the traverse state.
+         */
+        private final transient Iterator<B> iterator;
+
+        /**
+         * The action to transform the elements in the iterator.
+         */
+        private final transient TransformAction<B, A> action;
+
+        /**
+         * Ctor. ConcatIterator traverses the element.
+         * @param itr Iterator of the original iterable
+         * @param act Action to transform elements
+         */
+        public TransformIterator(final Iterator<B> itr,
+            final TransformAction<B, A> act) {
+            this.action = act;
+            this.iterator = itr;
+        }
+
+        @Override
+        public boolean hasNext() {
+            return this.iterator.hasNext();
+        }
+
+        @Override
+        public A next() {
+            return this.action.transform(this.iterator.next());
+        }
+
+        @Override
+        public void remove() {
+            throw new UnsupportedOperationException(
+                "This iterable is immutable and cannot remove anything"
+            );
+        }
+    }
+}

src/main/java/org/takes/misc/TransformAction.java

@@ -0,0 +1,63 @@
+/**
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2015 Yegor Bugayenko
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included
+ * in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+package org.takes.misc;
+
+/**
+ * Action for {@link Transform} to perform actual transformation.
+ *
+ * @author Jason Wong ([email protected])
+ * @version $Id$
+ * @since 0.15.2
+ */
+public interface TransformAction<T, K> {
+    /**
+     * The transform action of the element of type T to K.
+     * @param element Element of the iterable
+     * @return Transformed element
+     */
+    K transform(T element);
+
+    /**
+     * Trimming action used with {@link Transform}.
+     */
+    class Trim implements TransformAction<String, String> {
+
+        @Override
+        public String transform(final String element) {
+            return element.trim();
+        }
+    }
+
+    /**
+     * Convert CharSequence into String.
+     */
+    class ToString implements TransformAction<CharSequence, String> {
+
+        @Override
+        public String transform(final CharSequence element) {
+            return element.toString();
+        }
+
+    }
+}

src/main/java/org/takes/rs/RsWithHeaders.java

@@ -54,6 +54,12 @@ public RsWithHeaders(final Response res, final CharSequence... headers) {
 
     /**
      * Ctor.
+     * @todo #160:DEV To implement the concatenation and
+     *  transformation with conjunction of Concat class
+     *  and Transform class to get rid of the use of List.add()
+     *  in the anonymous Response class head() method. That is,
+     *  we are going to do something like this:
+     *  return new Concat(res.head(), new Transform(headers, new Trim()))
      * @param res Original response
      * @param headers Headers
      */

src/test/java/org/takes/misc/TransformTest.java

@@ -0,0 +1,62 @@
+/**
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2015 Yegor Bugayenko
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included
+ * in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+package org.takes.misc;
+
+import com.google.common.base.Joiner;
+import java.util.Arrays;
+import org.hamcrest.MatcherAssert;
+import org.hamcrest.Matchers;
+import org.junit.Test;
+
+/**
+ * Test case for {@link Transform}.
+ *
+ * @author Jason Wong ([email protected])
+ * @version $Id$
+ * @since 0.15.2
+ */
+public final class TransformTest {
+
+    /**
+     * Transform can transform list.
+     */
+    @Test
+    public void transformsList() {
+        MatcherAssert.assertThat(
+            Joiner.on(" ").join(
+                new Transform<String, String>(
+                    Arrays.asList("one", "two", "three"),
+                    new TransformAction<String, String>() {
+                        @Override
+                        public String transform(final String element) {
+                            return element.concat("t");
+                        }
+                    }
+                )
+            ),
+            Matchers.equalTo("onet twot threet")
+        );
+    }
+
+}