#1798 - Optimization around constructing UriTemplate when supplying TemplateVariables of same type

Reduce the repeated merge routines on ExpandGroups.

Before:
Benchmark                          Mode  Cnt     Score     Error  Units
TemplateVariableBenchmark.concat  thrpt    3  3150,261 ± 263,525  ops/s

After:
Benchmark                          Mode  Cnt      Score      Error  Units
TemplateVariableBenchmark.concat  thrpt    3  55275,436 ± 3778,690  ops/s

src/main/java/org/springframework/hateoas/TemplateVariable.java

@@ -21,7 +21,7 @@ import java.io.Serializable;
 import java.nio.charset.StandardCharsets;
 import java.util.Arrays;
 import java.util.Collection;
-import java.util.List;
+import java.util.EnumSet;
 import java.util.Map;
 import java.util.Objects;
 import java.util.stream.Collectors;
@@ -499,7 +499,7 @@ public final class TemplateVariable implements Serializable, UriTemplate.Expanda
 		 */
 		COMPOSITE_PARAM("*", "", true);
 
-		private static final List<VariableType> COMBINABLE_TYPES = Arrays.asList(REQUEST_PARAM, REQUEST_PARAM_CONTINUED);
+		private static final EnumSet<VariableType> COMBINABLE_TYPES = EnumSet.of(REQUEST_PARAM, REQUEST_PARAM_CONTINUED);
 		static final String DEFAULT_SEPARATOR = ",";
 
 		private final String key, combiner;

src/main/java/org/springframework/hateoas/TemplateVariables.java

@@ -68,11 +68,12 @@ public final class TemplateVariables implements Iterable<TemplateVariable>, Seri
 
 		for (TemplateVariable variable : variables) {
 
-			processed.add(variable.isRequestParameterVariable() && requestParameterFound
+			boolean isRequestParameter = variable.isRequestParameterVariable();
+			processed.add(isRequestParameter && requestParameterFound
 					? variable.withType(REQUEST_PARAM_CONTINUED)
 					: variable);
 
-			if (variable.isRequestParameterVariable()) {
+			if (isRequestParameter) {
 				requestParameterFound = true;
 			}
 		}
@@ -100,12 +101,11 @@ public final class TemplateVariables implements Iterable<TemplateVariable>, Seri
 
 		List<TemplateVariable> result = new ArrayList<>(this.variables.size() + variables.size());
 		result.addAll(this.variables);
-
-		List<TemplateVariable> filtered = variables.stream() //
-				.filter(variable -> !containsEquivalentFor(variable)).collect(Collectors.toList());
-
-		result.addAll(filtered);
-
+		for (TemplateVariable otherVariable : variables) {
+			if (!containsEquivalentFor(otherVariable)) {
+				result.add(otherVariable);
+			}
+		}
 		return new TemplateVariables(result);
 	}
 
@@ -133,9 +133,12 @@ public final class TemplateVariables implements Iterable<TemplateVariable>, Seri
 	}
 
 	private boolean containsEquivalentFor(TemplateVariable candidate) {
-
-		return this.variables.stream() //
-				.anyMatch(variable -> variable.isEquivalent(candidate));
+		for (TemplateVariable variable : variables) {
+			if (variable.isEquivalent(candidate)) {
+				return true;
+			}
+		}
+		return false;
 	}
 
 	/*

src/main/java/org/springframework/hateoas/UriTemplate.java

@@ -18,13 +18,7 @@ package org.springframework.hateoas;
 import java.io.Serializable;
 import java.net.URI;
 import java.nio.charset.StandardCharsets;
-import java.util.ArrayList;
-import java.util.Arrays;
-import java.util.Collections;
-import java.util.HashMap;
-import java.util.Iterator;
-import java.util.List;
-import java.util.Map;
+import java.util.*;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 import java.util.stream.Collectors;
@@ -172,13 +166,10 @@ public class UriTemplate implements Iterable<TemplateVariable>, Serializable {
 		}
 
 		UriComponents components = UriComponentsBuilder.fromUriString(baseUri).build();
+		MultiValueMap<String, String> parameters = components.getQueryParams();
 		List<TemplateVariable> result = new ArrayList<>();
-		String newOriginal = template;
-		ExpandGroups groups = this.groups;
 
 		for (TemplateVariable variable : variables) {
-
-			MultiValueMap<String, String> parameters = components.getQueryParams();
 			boolean isRequestParam = variable.isRequestParameterVariable();
 			boolean alreadyPresent = parameters.containsKey(variable.getName());
 
@@ -195,9 +186,20 @@ public class UriTemplate implements Iterable<TemplateVariable>, Serializable {
 				variable = variable.withType(VariableType.REQUEST_PARAM_CONTINUED);
 			}
 
-			ExpandGroup existing = groups.findLastExpandGroupOfType(variable.getType());
-			ExpandGroup group = new ExpandGroup(Collections.singletonList(variable));
+			result.add(variable);
+		}
 
+
+		String newOriginal = template;
+		ExpandGroups groups = this.groups;
+		LinkedHashMap<VariableType, List<TemplateVariable>> groupedByVariableType = result.stream()
+				.collect(
+						Collectors.groupingBy(TemplateVariable::getType, LinkedHashMap::new, Collectors.toList()));
+
+
+		for (Map.Entry<VariableType, List<TemplateVariable>> entry : groupedByVariableType.entrySet()) {
+			ExpandGroup existing = groups.findLastExpandGroupOfType(entry.getKey());
+			ExpandGroup group = new ExpandGroup(entry.getValue());
 			if (existing != null) {
 				group = existing.merge(group);
 				newOriginal = newOriginal.replace(existing.asString(), group.asString());
@@ -206,7 +208,6 @@ public class UriTemplate implements Iterable<TemplateVariable>, Serializable {
 			}
 
 			groups = groups.addOrAugment(group);
-			result.add(variable);
 		}
 
 		return new UriTemplate(baseUri, newOriginal, this.variables.concat(result), groups);