#1583 - Full support for level 4 URI templates.

Significant rewrite of UriTemplate to bring it up to level for template variables. We now additionally support:

* Composite values correctly
* Prefix values
* Multi-value template variables
* Path-style parameters
* Label expansion with dot-prefix
* Reserved expansion

Unit tests have been enriched with all examples given in the corresponding RFC [0]. Template variable types have been aligned with the terminology used in the RFC. Currently differently named types have been deprecated in favor of the new ones.

The commit slightly changes the behavior in two different aspects:

1. Query parameter values are now encoded as described in the RFC. Previously, special characters like comma (,) have not been percent encoded but now are. To create comma-separated values, expand an array of values instead of a prepared String. I.e. instead of expanding {?sort} with "foo,asc", expand it with [ "foo", "asc" ].

2. The aspect of variable optionality has been deprecated as it doesn't actually exist for template variables. This causes expansions that were previously rejected (e.g. ones using {foo} in paths) are now not rejected anymore. This is due to the way that the expansions are defined in the RFC.

[0] https://datatracker.ietf.org/doc/html/rfc6570

Author: odrotbohm

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

@@ -26,6 +26,7 @@
 import java.util.List;
 import java.util.Objects;
 import java.util.stream.Collectors;
+import java.util.stream.Stream;
 
 import org.springframework.hateoas.TemplateVariable.VariableType;
 import org.springframework.util.Assert;
@@ -61,7 +62,21 @@ public TemplateVariables(List<TemplateVariable> variables) {
 		Assert.notNull(variables, "Template variables must not be null!");
 		Assert.noNullElements(variables.toArray(), "Variables must not contain null values!");
 
-		this.variables = Collections.unmodifiableList(variables);
+		boolean requestParameterFound = false;
+		List<TemplateVariable> processed = new ArrayList<>(variables.size());
+
+		for (TemplateVariable variable : variables) {
+
+			processed.add(variable.isRequestParameterVariable() && requestParameterFound
+					? variable.withType(REQUEST_PARAM_CONTINUED)
+					: variable);
+
+			if (variable.isRequestParameterVariable()) {
+				requestParameterFound = true;
+			}
+		}
+
+		this.variables = Collections.unmodifiableList(processed);
 	}
 
 	/**
@@ -112,6 +127,10 @@ public List<TemplateVariable> asList() {
 		return this.variables;
 	}
 
+	public Stream<TemplateVariable> stream() {
+		return this.variables.stream();
+	}
+
 	private boolean containsEquivalentFor(TemplateVariable candidate) {
 
 		return this.variables.stream() //
@@ -165,7 +184,7 @@ String toString(boolean appended) {
 			}
 
 			previous = variable;
-			builder.append(variable.getName());
+			builder.append(variable.essence());
 		}
 
 		return builder.append("}").toString();
@@ -174,10 +193,12 @@ String toString(boolean appended) {
 	@Override
 	public boolean equals(Object o) {
 
-		if (this == o)
+		if (this == o) {
 			return true;
-		if (o == null || getClass() != o.getClass())
+		}
+		if (o == null || getClass() != o.getClass()) {
 			return false;
+		}
 		TemplateVariables that = (TemplateVariables) o;
 		return Objects.equals(this.variables, that.variables);
 	}