UriComponentsBuilder method to configure URI variables

See Javadoc on UriComponentsBuilder#uriVariables for details.

This helps to prepare for SPR-17027 where the MvcUriComponentsBuilder
already does a partial expand but was forced to build UriComonents
and then create a new UriComponentsBuilder from it to continue. This
change makes it possible to stay with the same builder instance.

Issue: SPR-17027

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

@@ -20,6 +20,7 @@ import java.net.URI;
 import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
@@ -35,6 +36,7 @@ import org.springframework.util.MultiValueMap;
 import org.springframework.util.ObjectUtils;
 import org.springframework.util.StringUtils;
 import org.springframework.web.util.HierarchicalUriComponents.PathComponent;
+import org.springframework.web.util.UriComponents.UriTemplateVariables;
 
 /**
  * Builder for {@link UriComponents}.
@@ -121,6 +123,8 @@ public class UriComponentsBuilder implements UriBuilder, Cloneable {
 	@Nullable
 	private String fragment;
 
+	private final Map<String, Object> uriVariables = new HashMap<>(4);
+
 	private boolean encodeTemplate;
 
 	private Charset charset = StandardCharsets.UTF_8;
@@ -381,15 +385,20 @@ public class UriComponentsBuilder implements UriBuilder, Cloneable {
 	 * @return the URI components
 	 */
 	public UriComponents build(boolean encoded) {
+		UriComponents result;
 		if (this.ssp != null) {
-			return new OpaqueUriComponents(this.scheme, this.ssp, this.fragment);
+			result = new OpaqueUriComponents(this.scheme, this.ssp, this.fragment);
 		}
 		else {
-			HierarchicalUriComponents uriComponents =
-					new HierarchicalUriComponents(this.scheme, this.fragment, this.userInfo,
-							this.host, this.port, this.pathBuilder.build(), this.queryParams, encoded);
-			return (this.encodeTemplate ? uriComponents.encodeTemplate(this.charset) : uriComponents);
+			HierarchicalUriComponents uric = new HierarchicalUriComponents(this.scheme, this.fragment,
+					this.userInfo, this.host, this.port, this.pathBuilder.build(), this.queryParams, encoded);
+
+			result = this.encodeTemplate ? uric.encodeTemplate(this.charset) : uric;
+		}
+		if (!this.uriVariables.isEmpty()) {
+			result = result.expand(name -> this.uriVariables.getOrDefault(name, UriTemplateVariables.SKIP_VALUE));
 		}
+		return result;
 	}
 
 	/**
@@ -433,7 +442,7 @@ public class UriComponentsBuilder implements UriBuilder, Cloneable {
 	 * @see UriComponents#toUriString()
 	 */
 	public String toUriString() {
-		return build().encode().toUriString();
+		return encode().build().toUriString();
 	}
 
 
@@ -752,6 +761,25 @@ public class UriComponentsBuilder implements UriBuilder, Cloneable {
 		return this;
 	}
 
+	/**
+	 * Configure URI variables to be expanded at build time.
+	 * <p>The provided variables may be a subset of all required ones. At build
+	 * time, the available ones are expanded, while unresolved URI placeholders
+	 * are left in place and can still be expanded later.
+	 * <p>In contrast to {@link UriComponents#expand(Map)} or
+	 * {@link #buildAndExpand(Map)}, this method is useful when you need to
+	 * supply URI variables without building the {@link UriComponents} instance
+	 * just yet, or perhaps pre-expand some shared default values such as host
+	 * and port.
+	 * @param uriVariables the URI variables to use
+	 * @return this UriComponentsBuilder
+	 * @since 5.0.8
+	 */
+	public UriComponentsBuilder uriVariables(Map<String, Object> uriVariables) {
+		this.uriVariables.putAll(uriVariables);
+		return this;
+	}
+
 	/**
 	 * Adapt this builder's scheme+host+port from the given headers, specifically
 	 * "Forwarded" (<a href="http://tools.ietf.org/html/rfc7239">RFC 7239</a>,

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

@@ -70,19 +70,12 @@ public class UriComponentsTests {
 	@Test
 	public void encodeAndExpandPartially() {
 
-		Map<String, Object> uriVars = new HashMap<>();
-		uriVars.put("city", "Z\u00fcrich");
-
 		UriComponents uri = UriComponentsBuilder
-				.fromPath("/hotel list/{city} specials").queryParam("q", "{value}").encode().build()
-				.expand(name -> uriVars.getOrDefault(name, UriTemplateVariables.SKIP_VALUE));
-
-		assertEquals("/hotel%20list/Z%C3%BCrich%20specials?q={value}", uri.toString());
+				.fromPath("/hotel list/{city} specials").queryParam("q", "{value}").encode()
+				.uriVariables(Collections.singletonMap("city", "Z\u00fcrich"))
+				.build();
 
-		uriVars.put("value", "a+b");
-		uri = uri.expand(uriVars);
-
-		assertEquals("/hotel%20list/Z%C3%BCrich%20specials?q=a%2Bb", uri.toString());
+		assertEquals("/hotel%20list/Z%C3%BCrich%20specials?q=a%2Bb", uri.expand("a+b").toString());
 	}
 
 	@Test

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/MvcUriComponentsBuilder.java

@@ -63,7 +63,6 @@ import org.springframework.web.method.support.CompositeUriComponentsContributor;
 import org.springframework.web.servlet.DispatcherServlet;
 import org.springframework.web.servlet.mvc.method.RequestMappingInfoHandlerMapping;
 import org.springframework.web.servlet.support.ServletUriComponentsBuilder;
-import org.springframework.web.util.UriComponents;
 import org.springframework.web.util.UriComponentsBuilder;
 
 /**
@@ -547,8 +546,7 @@ public class MvcUriComponentsBuilder {
 		String path = pathMatcher.combine(typePath, methodPath);
 		builder.path(path);
 
-		UriComponents uriComponents = applyContributors(builder, method, args);
-		return UriComponentsBuilder.newInstance().uriComponents(uriComponents);
+		return applyContributors(builder, method, args);
 	}
 
 	private static UriComponentsBuilder getBaseUrlToUse(@Nullable UriComponentsBuilder baseUrl) {
@@ -626,7 +624,7 @@ public class MvcUriComponentsBuilder {
 		}
 	}
 
-	private static UriComponents applyContributors(UriComponentsBuilder builder, Method method, Object... args) {
+	private static UriComponentsBuilder applyContributors(UriComponentsBuilder builder, Method method, Object... args) {
 		CompositeUriComponentsContributor contributor = getUriComponentsContributor();
 
 		int paramCount = method.getParameterCount();
@@ -643,9 +641,8 @@ public class MvcUriComponentsBuilder {
 			contributor.contributeMethodArgument(param, args[i], builder, uriVars);
 		}
 
-		// We may not have all URI var values, expand only what we have
-		return builder.build().expand(name ->
-				uriVars.getOrDefault(name, UriComponents.UriTemplateVariables.SKIP_VALUE));
+		// This may not be all the URI variables, supply what we have so far..
+		return builder.uriVariables(uriVars);
 	}
 
 	private static CompositeUriComponentsContributor getUriComponentsContributor() {
@@ -851,7 +848,7 @@ public class MvcUriComponentsBuilder {
 		public MethodArgumentBuilder(@Nullable UriComponentsBuilder baseUrl, Class<?> controllerType, Method method) {
 			Assert.notNull(controllerType, "'controllerType' is required");
 			Assert.notNull(method, "'method' is required");
-			this.baseUrl = (baseUrl != null ? baseUrl : initBaseUrl());
+			this.baseUrl = baseUrl != null ? baseUrl : UriComponentsBuilder.fromPath(getPath());
 			this.controllerType = controllerType;
 			this.method = method;
 			this.argumentValues = new Object[method.getParameterCount()];
@@ -860,10 +857,10 @@ public class MvcUriComponentsBuilder {
 			}
 		}
 
-		private static UriComponentsBuilder initBaseUrl() {
+		private static String getPath() {
 			UriComponentsBuilder builder = ServletUriComponentsBuilder.fromCurrentServletMapping();
 			String path = builder.build().getPath();
-			return (path != null ? UriComponentsBuilder.fromPath(path) : UriComponentsBuilder.newInstance());
+			return path != null ? path : "";
 		}
 
 		public MethodArgumentBuilder arg(int index, Object value) {
@@ -872,13 +869,13 @@ public class MvcUriComponentsBuilder {
 		}
 
 		public String build() {
-			return fromMethodInternal(this.baseUrl, this.controllerType, this.method,
-					this.argumentValues).build(false).encode().toUriString();
+			return fromMethodInternal(this.baseUrl, this.controllerType, this.method, this.argumentValues)
+					.build(false).encode().toUriString();
 		}
 
 		public String buildAndExpand(Object... uriVars) {
-			return fromMethodInternal(this.baseUrl, this.controllerType, this.method,
-					this.argumentValues).build(false).expand(uriVars).encode().toString();
+			return fromMethodInternal(this.baseUrl, this.controllerType, this.method, this.argumentValues)
+					.build(false).expand(uriVars).encode().toString();
 		}
 	}