Support ordered interceptors in RestTemplate

This commit sorts `ClientHttpRequestInterceptor`s when those are set in
`InterceptingHttpAccessor` (which `RestTemplate` extends from).

Interceptors can now be annotated with `@Order` or implements `Ordered`
to reflect their order of execution for each request.

Issue: SPR-13971

spring-web/src/test/java/org/springframework/http/client/support/InterceptingHttpAccessorTests.java

@@ -0,0 +1,91 @@
+/*
+ * Copyright 2002-2016 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.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.http.client.support;
+
+import static org.junit.Assert.*;
+
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.List;
+
+import org.hamcrest.Matchers;
+import org.junit.Test;
+
+import org.springframework.core.Ordered;
+import org.springframework.core.annotation.Order;
+import org.springframework.http.HttpRequest;
+import org.springframework.http.client.ClientHttpRequestExecution;
+import org.springframework.http.client.ClientHttpRequestInterceptor;
+import org.springframework.http.client.ClientHttpResponse;
+
+/**
+ * Tests for {@link InterceptingHttpAccessor}.
+ *
+ * @author Brian Clozel
+ */
+public class InterceptingHttpAccessorTests {
+
+	@Test
+	public void getInterceptors() throws Exception {
+		TestInterceptingHttpAccessor accessor = new TestInterceptingHttpAccessor();
+		List<ClientHttpRequestInterceptor> interceptors = Arrays.asList(
+				new SecondClientHttpRequestInterceptor(),
+				new ThirdClientHttpRequestInterceptor(),
+				new FirstClientHttpRequestInterceptor()
+
+		);
+		accessor.setInterceptors(interceptors);
+
+		assertThat(accessor.getInterceptors().get(0), Matchers.instanceOf(FirstClientHttpRequestInterceptor.class));
+		assertThat(accessor.getInterceptors().get(1), Matchers.instanceOf(SecondClientHttpRequestInterceptor.class));
+		assertThat(accessor.getInterceptors().get(2), Matchers.instanceOf(ThirdClientHttpRequestInterceptor.class));
+	}
+
+	private class TestInterceptingHttpAccessor extends InterceptingHttpAccessor {
+	}
+
+	@Order(1)
+	private class FirstClientHttpRequestInterceptor implements ClientHttpRequestInterceptor {
+		@Override
+		public ClientHttpResponse intercept(HttpRequest request, byte[] body,
+				ClientHttpRequestExecution execution) throws IOException {
+			return null;
+		}
+	}
+
+	private class SecondClientHttpRequestInterceptor implements ClientHttpRequestInterceptor, Ordered {
+		@Override
+		public ClientHttpResponse intercept(HttpRequest request, byte[] body,
+				ClientHttpRequestExecution execution) throws IOException {
+			return null;
+		}
+
+		@Override
+		public int getOrder() {
+			return 2;
+		}
+	}
+
+	private class ThirdClientHttpRequestInterceptor implements ClientHttpRequestInterceptor {
+		@Override
+		public ClientHttpResponse intercept(HttpRequest request, byte[] body,
+				ClientHttpRequestExecution execution) throws IOException {
+			return null;
+		}
+	}
+
+}