Replace NAMES_PATTERN in UriTemplate

The URI template is now manually parsed vs using a regex to extract
URI variable names and to create a pattern for matching to actual URLs.
This provides more control to deal with nested curly braces.

Issue: SPR-13627

spring-web/src/main/java/org/springframework/web/util/UriTemplate.java

@@ -18,9 +18,9 @@ package org.springframework.web.util;
 
 import java.io.Serializable;
 import java.net.URI;
+import java.util.ArrayList;
 import java.util.Collections;
 import java.util.LinkedHashMap;
-import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
 import java.util.regex.Matcher;
@@ -37,19 +37,13 @@ import org.springframework.util.Assert;
  *
  * @author Arjen Poutsma
  * @author Juergen Hoeller
+ * @author Rossen Stoyanchev
  * @since 3.0
  * @see <a href="http://bitworking.org/projects/URI-Templates/">URI Templates</a>
  */
 @SuppressWarnings("serial")
 public class UriTemplate implements Serializable {
 
-	/** Captures URI template variable names. */
-	private static final Pattern NAMES_PATTERN = Pattern.compile("\\{([^/]+?)\\}");
-
-	/** Replaces template variables in the URI template. */
-	private static final String DEFAULT_VARIABLE_PATTERN = "(.*)";
-
-
 	private final UriComponents uriComponents;
 
 	private final List<String> variableNames;
@@ -64,11 +58,13 @@ public class UriTemplate implements Serializable {
 	 * @param uriTemplate the URI template string
 	 */
 	public UriTemplate(String uriTemplate) {
-		Parser parser = new Parser(uriTemplate);
+		Assert.hasText(uriTemplate, "'uriTemplate' must not be null");
 		this.uriTemplate = uriTemplate;
-		this.variableNames = parser.getVariableNames();
-		this.matchPattern = parser.getMatchPattern();
 		this.uriComponents = UriComponentsBuilder.fromUriString(uriTemplate).build();
+
+		TemplateInfo info = TemplateInfo.parse(uriTemplate);
+		this.variableNames = Collections.unmodifiableList(info.getVariableNames());
+		this.matchPattern = info.getMatchPattern();
 	}
 
 
@@ -169,60 +165,81 @@ public class UriTemplate implements Serializable {
 
 
 	/**
-	 * Static inner class to parse URI template strings into a matching regular expression.
+	 * Helper to extract variable names and regex for matching to actual URLs.
 	 */
-	private static class Parser {
+	private static class TemplateInfo {
 
-		private final List<String> variableNames = new LinkedList<String>();
+		private final List<String> variableNames;
 
-		private final StringBuilder patternBuilder = new StringBuilder();
+		private final Pattern pattern;
 
-		private Parser(String uriTemplate) {
-			Assert.hasText(uriTemplate, "'uriTemplate' must not be null");
-			Matcher matcher = NAMES_PATTERN.matcher(uriTemplate);
-			int end = 0;
-			while (matcher.find()) {
-				this.patternBuilder.append(quote(uriTemplate, end, matcher.start()));
-				String match = matcher.group(1);
-				int colonIdx = match.indexOf(':');
-				if (colonIdx == -1) {
-					this.patternBuilder.append(DEFAULT_VARIABLE_PATTERN);
-					this.variableNames.add(match);
-				}
-				else {
-					if (colonIdx + 1 == match.length()) {
-						throw new IllegalArgumentException(
-								"No custom regular expression specified after ':' in \"" + match + "\"");
+
+		private TemplateInfo(List<String> vars, Pattern pattern) {
+			this.variableNames = vars;
+			this.pattern = pattern;
+		}
+
+		public List<String> getVariableNames() {
+			return this.variableNames;
+		}
+
+		public Pattern getMatchPattern() {
+			return this.pattern;
+		}
+
+		private static TemplateInfo parse(String uriTemplate) {
+			int level = 0;
+			List<String> variableNames = new ArrayList<String>();
+			StringBuilder pattern = new StringBuilder();
+			StringBuilder builder = new StringBuilder();
+			for (int i = 0 ; i < uriTemplate.length(); i++) {
+				char c = uriTemplate.charAt(i);
+				if (c == '{') {
+					level++;
+					if (level == 1) {
+						pattern.append(quote(builder));
+						builder = new StringBuilder();
+						continue;
 					}
-					String variablePattern = match.substring(colonIdx + 1, match.length());
-					this.patternBuilder.append('(');
-					this.patternBuilder.append(variablePattern);
-					this.patternBuilder.append(')');
-					String variableName = match.substring(0, colonIdx);
-					this.variableNames.add(variableName);
 				}
-				end = matcher.end();
-			}
-			this.patternBuilder.append(quote(uriTemplate, end, uriTemplate.length()));
-			int lastIdx = this.patternBuilder.length() - 1;
-			if (lastIdx >= 0 && this.patternBuilder.charAt(lastIdx) == '/') {
-				this.patternBuilder.deleteCharAt(lastIdx);
+				else if (c == '}') {
+					level--;
+					if (level == 0) {
+						String variable = builder.toString();
+						int idx = variable.indexOf(':');
+						if (idx == -1) {
+							pattern.append("(.*)");
+							variableNames.add(variable);
+						}
+						else {
+							if (idx + 1 == variable.length()) {
+								throw new IllegalArgumentException(
+										"No custom regular expression specified after ':' " +
+												"in \"" + variable + "\"");
+							}
+							String regex = variable.substring(idx + 1, variable.length());
+							pattern.append('(');
+							pattern.append(regex);
+							pattern.append(')');
+							variableNames.add(variable.substring(0, idx));
+						}
+						builder = new StringBuilder();
+						continue;
+					}
+				}
+				if (i + 1 == uriTemplate.length()) {
+					if (c != '/') {
+						builder.append(c);
+					}
+					pattern.append(quote(builder));
+				}
+				builder.append(c);
 			}
+			return new TemplateInfo(variableNames, Pattern.compile(pattern.toString()));
 		}
 
-		private String quote(String fullPath, int start, int end) {
-			if (start == end) {
-				return "";
-			}
-			return Pattern.quote(fullPath.substring(start, end));
-		}
-
-		private List<String> getVariableNames() {
-			return Collections.unmodifiableList(this.variableNames);
-		}
-
-		private Pattern getMatchPattern() {
-			return Pattern.compile(this.patternBuilder.toString());
+		private static String quote(StringBuilder builder) {
+			return builder.length() != 0 ? Pattern.quote(builder.toString()) : "";
 		}
 	}