Added check for expanding already encoded UriComponents object

org.springframework.web/src/main/java/org/springframework/web/util/UriComponents.java

@@ -336,6 +336,8 @@ public final class UriComponents {
 	}
 
 	private UriComponents expandInternal(UriTemplateVariables uriVariables) {
+		Assert.state(!encoded, "Cannot expand an already encoded UriComponents object");
+		
 		String expandedScheme = expandUriComponent(this.scheme, uriVariables);
 		String expandedUserInfo = expandUriComponent(this.userInfo, uriVariables);
 		String expandedHost = expandUriComponent(this.host, uriVariables);

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

@@ -54,4 +54,9 @@ public class UriComponentsTests {
 		assertEquals("http://example.com/1 2 3 4", uriComponents.toUriString());
 	}
 
+	@Test(expected = IllegalStateException.class)
+	public void expandEncoded() {
+		UriComponentsBuilder.fromPath("/{foo}").build().encode().expand("bar");
+	}
+
 }