Polishing.

See #4139
Original pull request: #4182.

Author: christophstrobl

Diff for: spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/AbstractAggregationExpression.java

@@ -23,9 +23,9 @@
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
-import java.util.stream.Collectors;
 
 import org.bson.Document;
+
 import org.springframework.data.domain.Sort;
 import org.springframework.data.domain.Sort.Order;
 import org.springframework.data.mongodb.core.aggregation.ExposedFields.FieldReference;
@@ -78,7 +78,14 @@ private Object unpack(Object value, AggregationOperationContext context) {
 		}
 
 		if (value instanceof Fields fields) {
-			return fields.asList().stream().map(it -> unpack(it, context)).collect(Collectors.toList());
+
+			List<Object> mapped = new ArrayList<>(fields.size());
+
+			for (Field field : fields) {
+				mapped.add(unpack(field, context));
+			}
+
+			return mapped;
 		}
 
 		if (value instanceof Sort sort) {
@@ -98,7 +105,9 @@ private Object unpack(Object value, AggregationOperationContext context) {
 			List<Object> sourceList = (List<Object>) value;
 			List<Object> mappedList = new ArrayList<>(sourceList.size());
 
-			sourceList.stream().map((item) -> unpack(item, context)).forEach(mappedList::add);
+			for (Object o : sourceList) {
+				mappedList.add(unpack(o, context));
+			}
 
 			return mappedList;
 		}
@@ -150,7 +159,7 @@ protected List<Object> append(Object value) {
 		return append(value, Expand.EXPAND_VALUES);
 	}
 
-	@SuppressWarnings({ "unchecked", "rawtypes" })
+	@SuppressWarnings({ "unchecked" })
 	protected Map<String, Object> append(String key, Object value) {
 
 		Assert.isInstanceOf(Map.class, this.value, "Value must be a type of Map");
@@ -165,6 +174,7 @@ private Map<String, Object> append(Map<String, Object> existing, String key, Obj
 		return clone;
 	}
 
+	@SuppressWarnings("rawtypes")
 	protected Map<String, Object> appendTo(String key, Object value) {
 
 		Assert.isInstanceOf(Map.class, this.value, "Value must be a type of Map");

Diff for: spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/DateOperators.java

@@ -826,7 +826,7 @@ public DateFromString fromString() {
 		 */
 		public TsIncrement tsIncrement() {
 
-			if(timezone != null && !Timezone.none().equals(timezone)) {
+			if (timezone != null && !Timezone.none().equals(timezone)) {
 				throw new IllegalArgumentException("$tsIncrement does not support timezones");
 			}
 
@@ -841,7 +841,7 @@ public TsIncrement tsIncrement() {
 		 */
 		public TsSecond tsSecond() {
 
-			if(timezone != null && !Timezone.none().equals(timezone)) {
+			if (timezone != null && !Timezone.none().equals(timezone)) {
 				throw new IllegalArgumentException("$tsSecond does not support timezones");
 			}
 

Diff for: spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/DensifyOperation.java

@@ -190,7 +190,7 @@ public DensifyRange incrementBy(Number step, DensifyUnit unit) {
 
 		/**
 		 * Set the {@link DensifyUnit unit} for the step field.
-		 * 
+		 *
 		 * @param unit
 		 * @return this.
 		 */
@@ -354,6 +354,8 @@ public DensifyOperationBuilder range(Range range) {
 		 */
 		public DensifyOperationBuilder fullRange(Consumer<DensifyRange> consumer) {
 
+			Assert.notNull(consumer, "Consumer must not be null");
+
 			DensifyRange range = Range.full();
 			consumer.accept(range);
 
@@ -374,7 +376,7 @@ public DensifyOperationBuilder partitionRange(Consumer<DensifyRange> consumer) {
 			return range(range);
 		}
 
-		DensifyOperation build() {
+		public DensifyOperation build() {
 			return new DensifyOperation(target.field, target.partitionBy, target.range);
 		}
 	}

Diff for: spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/ObjectOperators.java

@@ -18,10 +18,8 @@
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
-import java.util.Set;
 
 import org.bson.Document;
-import org.springframework.data.mongodb.core.aggregation.Aggregation.SystemVariable;
 import org.springframework.util.Assert;
 
 /**
@@ -135,7 +133,7 @@ public ObjectToArray toArray() {
 		 * @since 4.0
 		 */
 		public GetField getField(String fieldName) {
-			return GetField.getField(fieldName).from(value);
+			return GetField.getField(fieldName).of(value);
 		}
 
 		/**
@@ -145,7 +143,7 @@ public GetField getField(String fieldName) {
 		 * @since 4.0
 		 */
 		public SetField setField(String fieldName) {
-			return SetField.setField(fieldName).of(value);
+			return SetField.field(fieldName).input(value);
 		}
 
 		/**
@@ -155,7 +153,7 @@ public SetField setField(String fieldName) {
 		 * @since 4.0
 		 */
 		public AggregationExpression removeField(String fieldName) {
-			return SetField.setField(fieldName).of(value).toValue(SystemVariable.REMOVE);
+			return SetField.field(fieldName).input(value).toValue(SystemVariable.REMOVE);
 		}
 	}
 
@@ -329,23 +327,49 @@ protected GetField(Object value) {
 			super(value);
 		}
 
+		/**
+		 * Creates new {@link GetField aggregation expression} that takes the value pointed to by given {@code fieldName}.
+		 *
+		 * @param fieldName must not be {@literal null}.
+		 * @return new instance of {@link GetField}.
+		 */
 		public static GetField getField(String fieldName) {
 			return new GetField(Collections.singletonMap("field", fieldName));
 		}
 
+		/**
+		 * Creates new {@link GetField aggregation expression} that takes the value pointed to by given {@link Field}.
+		 *
+		 * @param field must not be {@literal null}.
+		 * @return new instance of {@link GetField}.
+		 */
 		public static GetField getField(Field field) {
 			return getField(field.getTarget());
 		}
 
-		public GetField from(String fieldRef) {
-			return from(Fields.field(fieldRef));
+		/**
+		 * Creates new {@link GetField aggregation expression} that takes the value pointed to by given
+		 * {@code field reference}.
+		 *
+		 * @param fieldRef must not be {@literal null}.
+		 * @return new instance of {@link GetField}.
+		 */
+		public GetField of(String fieldRef) {
+			return of(Fields.field(fieldRef));
 		}
 
-		public GetField from(AggregationExpression expression) {
-			return from((Object) expression);
+		/**
+		 * Creates new {@link GetField aggregation expression} that takes the value pointed to by given
+		 * {@link AggregationExpression}.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link GetField}.
+		 */
+		public GetField of(AggregationExpression expression) {
+			return of((Object) expression);
 		}
 
-		private GetField from(Object fieldRef) {
+		private GetField of(Object fieldRef) {
 			return new GetField(append("input", fieldRef));
 		}
 
@@ -367,34 +391,87 @@ protected SetField(Object value) {
 			super(value);
 		}
 
-		public static SetField setField(String fieldName) {
+		/**
+		 * Creates new {@link SetField aggregation expression} that takes the value pointed to by given input
+		 * {@code fieldName}.
+		 *
+		 * @param fieldName must not be {@literal null}.
+		 * @return new instance of {@link SetField}.
+		 */
+		public static SetField field(String fieldName) {
 			return new SetField(Collections.singletonMap("field", fieldName));
 		}
 
-		public static SetField setField(Field field) {
-			return setField(field.getTarget());
+		/**
+		 * Creates new {@link SetField aggregation expression} that takes the value pointed to by given input {@link Field}.
+		 *
+		 * @param field must not be {@literal null}.
+		 * @return new instance of {@link SetField}.
+		 */
+		public static SetField field(Field field) {
+			return field(field.getTarget());
 		}
 
-		public SetField of(String fieldRef) {
-			return of(Fields.field(fieldRef));
+		/**
+		 * Creates new {@link GetField aggregation expression} that takes the value pointed to by given input
+		 * {@code field reference}.
+		 *
+		 * @param fieldRef must not be {@literal null}.
+		 * @return new instance of {@link GetField}.
+		 */
+		public SetField input(String fieldRef) {
+			return input(Fields.field(fieldRef));
 		}
 
-		public SetField of(AggregationExpression expression) {
-			return of((Object) expression);
+		/**
+		 * Creates new {@link SetField aggregation expression} that takes the value pointed to by given input
+		 * {@link AggregationExpression}.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link SetField}.
+		 */
+		public SetField input(AggregationExpression expression) {
+			return input((Object) expression);
 		}
 
-		private SetField of(Object fieldRef) {
+		/**
+		 * Creates new {@link SetField aggregation expression} that takes the value pointed to by given input
+		 * {@code field reference}.
+		 *
+		 * @param fieldRef must not be {@literal null}.
+		 * @return new instance of {@link SetField}.
+		 */
+		private SetField input(Object fieldRef) {
 			return new SetField(append("input", fieldRef));
 		}
 
+		/**
+		 * Creates new {@link SetField aggregation expression} providing the {@code value} using {@literal fieldReference}.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @return new instance of {@link SetField}.
+		 */
 		public SetField toValueOf(String fieldReference) {
 			return toValue(Fields.field(fieldReference));
 		}
 
+		/**
+		 * Creates new {@link SetField aggregation expression} providing the {@code value} using
+		 * {@link AggregationExpression}.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link SetField}.
+		 */
 		public SetField toValueOf(AggregationExpression expression) {
 			return toValue(expression);
 		}
 
+		/**
+		 * Creates new {@link SetField aggregation expression} providing the {@code value}.
+		 *
+		 * @param value
+		 * @return new instance of {@link SetField}.
+		 */
 		public SetField toValue(Object value) {
 			return new SetField(append("value", value));
 		}

Diff for: spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/SelectionOperators.java

@@ -261,7 +261,7 @@ public static First first(int numberOfResults) {
 		 * Limits the number of returned elements to the given value.
 		 *
 		 * @param numberOfResults
-		 * @return new instance of {@link Bottom}.
+		 * @return new instance of {@link First}.
 		 */
 		public First limit(int numberOfResults) {
 			return limit((Object) numberOfResults);
@@ -272,7 +272,7 @@ public First limit(int numberOfResults) {
 		 * expression}.
 		 *
 		 * @param expression must not be {@literal null}.
-		 * @return new instance of {@link Bottom}.
+		 * @return new instance of {@link First}.
 		 */
 		public First limit(AggregationExpression expression) {
 			return limit((Object) expression);
@@ -286,7 +286,7 @@ private First limit(Object value) {
 		 * Define the field to serve as source.
 		 *
 		 * @param fieldName must not be {@literal null}.
-		 * @return new instance of {@link Bottom}.
+		 * @return new instance of {@link First}.
 		 */
 		public First of(String fieldName) {
 			return input(fieldName);
@@ -296,7 +296,7 @@ public First of(String fieldName) {
 		 * Define the expression building the value to serve as source.
 		 *
 		 * @param expression must not be {@literal null}.
-		 * @return new instance of {@link Bottom}.
+		 * @return new instance of {@link First}.
 		 */
 		public First of(AggregationExpression expression) {
 			return input(expression);
@@ -306,7 +306,7 @@ public First of(AggregationExpression expression) {
 		 * Define the field to serve as source.
 		 *
 		 * @param fieldName must not be {@literal null}.
-		 * @return new instance of {@link Bottom}.
+		 * @return new instance of {@link First}.
 		 */
 		public First input(String fieldName) {
 			return new First(append("input", Fields.field(fieldName)));
@@ -316,7 +316,7 @@ public First input(String fieldName) {
 		 * Define the expression building the value to serve as source.
 		 *
 		 * @param expression must not be {@literal null}.
-		 * @return new instance of {@link Bottom}.
+		 * @return new instance of {@link First}.
 		 */
 		public First input(AggregationExpression expression) {
 			return new First(append("input", expression));
@@ -355,7 +355,7 @@ public static Last last(int numberOfResults) {
 		 * Limits the number of returned elements to the given value.
 		 *
 		 * @param numberOfResults
-		 * @return new instance of {@link Bottom}.
+		 * @return new instance of {@link Last}.
 		 */
 		public Last limit(int numberOfResults) {
 			return limit((Object) numberOfResults);
@@ -366,7 +366,7 @@ public Last limit(int numberOfResults) {
 		 * expression}.
 		 *
 		 * @param expression must not be {@literal null}.
-		 * @return new instance of {@link Bottom}.
+		 * @return new instance of {@link Last}.
 		 */
 		public Last limit(AggregationExpression expression) {
 			return limit((Object) expression);
@@ -380,7 +380,7 @@ private Last limit(Object value) {
 		 * Define the field to serve as source.
 		 *
 		 * @param fieldName must not be {@literal null}.
-		 * @return new instance of {@link Bottom}.
+		 * @return new instance of {@link Last}.
 		 */
 		public Last of(String fieldName) {
 			return input(fieldName);
@@ -390,7 +390,7 @@ public Last of(String fieldName) {
 		 * Define the expression building the value to serve as source.
 		 *
 		 * @param expression must not be {@literal null}.
-		 * @return new instance of {@link Bottom}.
+		 * @return new instance of {@link Last}.
 		 */
 		public Last of(AggregationExpression expression) {
 			return input(expression);
@@ -400,7 +400,7 @@ public Last of(AggregationExpression expression) {
 		 * Define the field to serve as source.
 		 *
 		 * @param fieldName must not be {@literal null}.
-		 * @return new instance of {@link Bottom}.
+		 * @return new instance of {@link Last}.
 		 */
 		public Last input(String fieldName) {
 			return new Last(append("input", Fields.field(fieldName)));
@@ -410,7 +410,7 @@ public Last input(String fieldName) {
 		 * Define the expression building the value to serve as source.
 		 *
 		 * @param expression must not be {@literal null}.
-		 * @return new instance of {@link Bottom}.
+		 * @return new instance of {@link Last}.
 		 */
 		public Last input(AggregationExpression expression) {
 			return new Last(append("input", expression));