DATACMNS-635 - Slice and Page can now be mapped using a Converter.

Introduced a map(Converter converter) method on Slice and Page to be able to easily transform the elements and create a new Slice or Page of the transformation result.

On Java 8 this allows code like this:

Page<String> strings = …;
Page<Integer> ints = strings.map(String::length);

src/main/java/org/springframework/data/domain/Chunk.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2014 the original author or authors.
+ * Copyright 2014-2015 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -21,6 +21,7 @@ import java.util.Collections;
 import java.util.Iterator;
 import java.util.List;
 
+import org.springframework.core.convert.converter.Converter;
 import org.springframework.util.Assert;
 
 /**
@@ -151,6 +152,25 @@ abstract class Chunk<T> implements Slice<T>, Serializable {
 		return content.iterator();
 	}
 
+	/**
+	 * Applies the given {@link Converter} to the content of the {@link Chunk}.
+	 * 
+	 * @param converter must not be {@literal null}.
+	 * @return
+	 */
+	protected <S> List<S> getConvertedContent(Converter<? super T, ? extends S> converter) {
+
+		Assert.notNull(converter, "Converter must not be null!");
+
+		List<S> result = new ArrayList<S>(content.size());
+
+		for (T element : this) {
+			result.add(converter.convert(element));
+		}
+
+		return result;
+	}
+
 	/*
 	 * (non-Javadoc)
 	 * @see java.lang.Object#equals(java.lang.Object)

src/main/java/org/springframework/data/domain/Page.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2008-2014 the original author or authors.
+ * Copyright 2008-2015 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -15,6 +15,8 @@
  */
 package org.springframework.data.domain;
 
+import org.springframework.core.convert.converter.Converter;
+
 /**
  * A page is a sublist of a list of objects. It allows gain information about the position of it in the containing
  * entire list.
@@ -37,4 +39,13 @@ public interface Page<T> extends Slice<T> {
 	 * @return the total amount of elements
 	 */
 	long getTotalElements();
+
+	/**
+	 * Returns a new {@link Page} with the content of the current one mapped by the given {@link Converter}.
+	 * 
+	 * @param converter must not be {@literal null}.
+	 * @return a new {@link Page} with the content of the current one mapped by the given {@link Converter}.
+	 * @since 1.10
+	 */
+	<S> Page<S> map(Converter<? super T, ? extends S> converter);
 }

src/main/java/org/springframework/data/domain/PageImpl.java

@@ -17,6 +17,7 @@ package org.springframework.data.domain;
 
 import java.util.List;
 
+import org.springframework.core.convert.converter.Converter;
 import org.springframework.util.Assert;
 
 /**
@@ -30,6 +31,7 @@ public class PageImpl<T> extends Chunk<T> implements Page<T> {
 	private static final long serialVersionUID = 867755909294344406L;
 
 	private final long total;
+	private final Pageable pageable;
 
 	/**
 	 * Constructor of {@code PageImpl}.
@@ -45,6 +47,7 @@ public class PageImpl<T> extends Chunk<T> implements Page<T> {
 		Assert.isTrue(total >= content.size(), "Total must not be less than the number of elements given!");
 
 		this.total = total;
+		this.pageable = pageable;
 	}
 
 	/**
@@ -93,6 +96,15 @@ public class PageImpl<T> extends Chunk<T> implements Page<T> {
 		return !hasNext();
 	}
 
+	/* 
+	 * (non-Javadoc)
+	 * @see org.springframework.data.domain.Slice#transform(org.springframework.core.convert.converter.Converter)
+	 */
+	@Override
+	public <S> Page<S> map(Converter<? super T, ? extends S> converter) {
+		return new PageImpl<S>(getConvertedContent(converter), pageable, total);
+	}
+
 	/*
 	 * (non-Javadoc)
 	 * @see java.lang.Object#toString()

src/main/java/org/springframework/data/domain/Slice.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2014 the original author or authors.
+ * Copyright 2014-2015 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -17,6 +17,8 @@ package org.springframework.data.domain;
 
 import java.util.List;
 
+import org.springframework.core.convert.converter.Converter;
+
 /**
  * A slice of data that indicates whether there's a next or previous slice available. Allows to obtain a
  * {@link Pageable} to request a previous or next {@link Slice}.
@@ -113,4 +115,13 @@ public interface Slice<T> extends Iterable<T> {
 	 * @return
 	 */
 	Pageable previousPageable();
+
+	/**
+	 * Returns a new {@link Slice} with the content of the current one mapped by the given {@link Converter}.
+	 * 
+	 * @param converter must not be {@literal null}.
+	 * @return a new {@link Slice} with the content of the current one mapped by the given {@link Converter}.
+	 * @since 1.10
+	 */
+	<S> Slice<S> map(Converter<? super T, ? extends S> converter);
 }

src/main/java/org/springframework/data/domain/SliceImpl.java

@@ -17,6 +17,8 @@ package org.springframework.data.domain;
 
 import java.util.List;
 
+import org.springframework.core.convert.converter.Converter;
+
 /**
  * Default implementation of {@link Slice}.
  * 
@@ -28,6 +30,7 @@ public class SliceImpl<T> extends Chunk<T> {
 	private static final long serialVersionUID = 867755909294344406L;
 
 	private final boolean hasNext;
+	private final Pageable pageable;
 
 	/**
 	 * Creates a new {@link Slice} with the given content and {@link Pageable}.
@@ -40,6 +43,7 @@ public class SliceImpl<T> extends Chunk<T> {
 
 		super(content, pageable);
 		this.hasNext = hasNext;
+		this.pageable = pageable;
 	}
 
 	/**
@@ -60,6 +64,15 @@ public class SliceImpl<T> extends Chunk<T> {
 		return hasNext;
 	}
 
+	/* 
+	 * (non-Javadoc)
+	 * @see org.springframework.data.domain.Slice#transform(org.springframework.core.convert.converter.Converter)
+	 */
+	@Override
+	public <S> Slice<S> map(Converter<? super T, ? extends S> converter) {
+		return new SliceImpl<S>(getConvertedContent(converter), pageable, hasNext);
+	}
+
 	/*
 	 * (non-Javadoc)
 	 * @see java.lang.Object#toString()

src/test/java/org/springframework/data/domain/PageImplUnitTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2008-2014 the original author or authors.
+ * Copyright 2008-2015 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -15,7 +15,7 @@
  */
 package org.springframework.data.domain;
 
-import static org.hamcrest.CoreMatchers.*;
+import static org.hamcrest.Matchers.*;
 import static org.junit.Assert.*;
 import static org.springframework.data.domain.UnitTestUtils.*;
 
@@ -24,6 +24,7 @@ import java.util.Collections;
 import java.util.List;
 
 import org.junit.Test;
+import org.springframework.core.convert.converter.Converter;
 
 /**
  * Unit test for {@link PageImpl}.
@@ -134,4 +135,22 @@ public class PageImplUnitTests {
 	public void rejectsTotalLessThanContentLength() {
 		new PageImpl<String>(Arrays.asList("foo", "bar"), new PageRequest(0, 10), 1);
 	}
+
+	/**
+	 * @see DATACMNS-635
+	 */
+	@Test
+	public void transformsPageCorrectly() {
+
+		Page<Integer> transformed = new PageImpl<String>(Arrays.asList("foo", "bar"), new PageRequest(0, 2), 10)
+				.map(new Converter<String, Integer>() {
+					@Override
+					public Integer convert(String source) {
+						return source.length();
+					}
+				});
+
+		assertThat(transformed.getContent(), hasSize(2));
+		assertThat(transformed.getContent(), contains(3, 3));
+	}
 }