UriComponentsBuilder supports query without value

Fix UriComponentsBuilder to support query parameters that do not
include a value without losing '='. The following styles are now
supported:

    http://example.com/foo?bar=baz
    http://example.com/foo?bar=
    http://example.com/foo?bar

Issue: SPR-10215

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

 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2013 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -53,7 +53,7 @@ import org.springframework.util.StringUtils;
  */
 public class UriComponentsBuilder {
 
-	private static final Pattern QUERY_PARAM_PATTERN = Pattern.compile("([^&=]+)=?([^&]+)?");
+	private static final Pattern QUERY_PARAM_PATTERN = Pattern.compile("([^&=]+)(=?)([^&]+)?");
 
 	private static final String SCHEME_PATTERN = "([^:/?#]+):";
 
@@ -496,8 +496,10 @@ public class UriComponentsBuilder {
 			Matcher m = QUERY_PARAM_PATTERN.matcher(query);
 			while (m.find()) {
 				String name = m.group(1);
-				String value = m.group(2);
-				queryParam(name, value);
+				String eq = m.group(2);
+				String value = m.group(3);
+				queryParam(name, (value != null ? value :
+					(StringUtils.hasLength(eq) ? "" : null)));
 			}
 		}
 		else {

spring-web/src/test/java/org/springframework/web/util/UriComponentsBuilderTests.java

 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2013 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -27,10 +27,12 @@ import org.junit.Test;
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
 
+import static org.hamcrest.Matchers.equalTo;
 import static org.junit.Assert.*;
 
 /**
  * @author Arjen Poutsma
+ * @author Phillip Webb
  */
 public class UriComponentsBuilderTests {
 
@@ -312,4 +314,22 @@ public class UriComponentsBuilderTests {
 		assertEquals("mailto:foo@example.com", result.toUriString());
 	}
 
+	@Test
+	public void queryParamWithValueWithEquals() throws Exception {
+		UriComponents uriComponents = UriComponentsBuilder.fromUriString("http://example.com/foo?bar=baz").build();
+		assertThat(uriComponents.toUriString(), equalTo("http://example.com/foo?bar=baz"));
+	}
+
+	@Test
+	public void queryParamWithoutValueWithEquals() throws Exception {
+		UriComponents uriComponents = UriComponentsBuilder.fromUriString("http://example.com/foo?bar=").build();
+		assertThat(uriComponents.toUriString(), equalTo("http://example.com/foo?bar="));
+	}
+
+	@Test
+	public void queryParamWithoutValueWithoutEquals() throws Exception {
+		UriComponents uriComponents = UriComponentsBuilder.fromUriString("http://example.com/foo?bar").build();
+		assertThat(uriComponents.toUriString(), equalTo("http://example.com/foo?bar"));
+	}
+
 }