From 3dfab2ec0397f554b591fb9856340c983f093a6f Mon Sep 17 00:00:00 2001
From: Oliver Drotbohm <odrotbohm@vmware.com>
Date: Wed, 1 Jun 2022 17:38:30 +0200
Subject: [PATCH] #1775 - Polishing.
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Avoid grouping of template variables via stream.

Before:

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

After:

Benchmark                          Mode  Cnt      Score     Error  Units
TemplateVariableBenchmark.concat  thrpt    3  64587,790 ± 735,705  ops/s
---
 .../hateoas/TemplateVariables.java            |  2 +-
 .../springframework/hateoas/UriTemplate.java  | 22 ++++++++++++++-----
 2 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/src/main/java/org/springframework/hateoas/TemplateVariables.java b/src/main/java/org/springframework/hateoas/TemplateVariables.java
index beef80ae..d54c8e64 100644
--- a/src/main/java/org/springframework/hateoas/TemplateVariables.java
+++ b/src/main/java/org/springframework/hateoas/TemplateVariables.java
@@ -25,7 +25,6 @@ import java.util.Collections;
 import java.util.Iterator;
 import java.util.List;
 import java.util.Objects;
-import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
 import org.springframework.hateoas.TemplateVariable.VariableType;
@@ -69,6 +68,7 @@ public final class TemplateVariables implements Iterable<TemplateVariable>, Seri
 		for (TemplateVariable variable : variables) {
 
 			boolean isRequestParameter = variable.isRequestParameterVariable();
+
 			processed.add(isRequestParameter && requestParameterFound
 					? variable.withType(REQUEST_PARAM_CONTINUED)
 					: variable);
diff --git a/src/main/java/org/springframework/hateoas/UriTemplate.java b/src/main/java/org/springframework/hateoas/UriTemplate.java
index dfac120d..3af0f30c 100644
--- a/src/main/java/org/springframework/hateoas/UriTemplate.java
+++ b/src/main/java/org/springframework/hateoas/UriTemplate.java
@@ -18,7 +18,13 @@ package org.springframework.hateoas;
 import java.io.Serializable;
 import java.net.URI;
 import java.nio.charset.StandardCharsets;
-import java.util.*;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 import java.util.stream.Collectors;
@@ -26,6 +32,7 @@ import java.util.stream.Collectors;
 import org.springframework.hateoas.TemplateVariable.VariableType;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
+import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
 import org.springframework.util.StringUtils;
 import org.springframework.web.util.UriBuilderFactory;
@@ -189,17 +196,20 @@ public class UriTemplate implements Iterable<TemplateVariable>, Serializable {
 			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()));
 
+		MultiValueMap<VariableType, TemplateVariable> groupedByVariableType = new LinkedMultiValueMap<>();
+
+		for (TemplateVariable templateVariable : result) {
+			groupedByVariableType.add(templateVariable.getType(), templateVariable);
+		}
+
+		for (Entry<VariableType, List<TemplateVariable>> entry : groupedByVariableType.entrySet()) {
 
-		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());