Support for @Order at the bean declaration level

This commit introduces OrderProvider and OrderProviderComparator, two
interfaces designed to externalize how a collection of element is sorted
according to their order value.

FactoryAwareOrderProvider is an OrderProvider implementation that knows
about the objects to order and the corresponding BeanFactory instance.
This allows to retrieve additional metadata about the actual instances
to sort, such as its factory method.

A @Bean method can now holds an additional @Order to define the order
value that this bean should have when injected as part of a collection
or array.

Issue: SPR-11310

spring-core/src/test/java/org/springframework/core/annotation/DefaultOrderProviderComparatorTests.java

@@ -0,0 +1,193 @@
+/*
+ * Copyright 2002-2014 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.core.annotation;
+
+import static org.junit.Assert.*;
+
+import java.util.Arrays;
+import java.util.List;
+
+import org.junit.Test;
+
+import org.springframework.core.Ordered;
+
+/**
+ *
+ * @author Stephane Nicoll
+ */
+public class DefaultOrderProviderComparatorTests {
+
+	private final DefaultOrderProviderComparator comparator = new DefaultOrderProviderComparator();
+
+	@Test
+	public void listNoFactoryMethod() {
+		A a = new A();
+		C c = new C(-50);
+		B b = new B();
+
+		List<?> items = Arrays.asList(a, c, b);
+		comparator.sortList(items, new OrderProvider() {
+			@Override
+			public Integer getOrder(Object obj) {
+				return null;
+			}
+		});
+		assertOrder(items, c, a, b);
+	}
+
+	@Test
+	public void listFactoryMethod() {
+		A a = new A();
+		C c = new C(3);
+		B b = new B();
+
+		List<?> items = Arrays.asList(a, c, b);
+		comparator.sortList(items, new OrderProvider() {
+			@Override
+			public Integer getOrder(Object obj) {
+				if (obj == a) {
+					return 4;
+				}
+				if (obj == b) {
+					return 2;
+				}
+				return null;
+			}
+		});
+		assertOrder(items, b, c, a);
+	}
+
+	@Test
+	public void listFactoryMethodOverridesStaticOrder() {
+		A a = new A();
+		C c = new C(5);
+		C c2 = new C(-5);
+
+
+		List<?> items = Arrays.asList(a, c, c2);
+		comparator.sortList(items, new OrderProvider() {
+			@Override
+			public Integer getOrder(Object obj) {
+				if (obj == a) {
+					return 4;
+				}
+				if (obj == c2) {
+					return 2;
+				}
+				return null;
+			}
+		});
+		assertOrder(items, c2, a, c);
+	}
+
+	@Test
+	public void arrayNoFactoryMethod() {
+		A a = new A();
+		C c = new C(-50);
+		B b = new B();
+
+		Object[] items = new Object[] {a, c, b};
+		comparator.sortArray(items, new OrderProvider() {
+			@Override
+			public Integer getOrder(Object obj) {
+				return null;
+			}
+		});
+		assertOrder(items, c, a, b);
+	}
+
+	@Test
+	public void arrayFactoryMethod() {
+		A a = new A();
+		C c = new C(3);
+		B b = new B();
+
+		Object[] items = new Object[] {a, c, b};
+		comparator.sortArray(items, new OrderProvider() {
+			@Override
+			public Integer getOrder(Object obj) {
+				if (obj == a) {
+					return 4;
+				}
+				if (obj == b) {
+					return 2;
+				}
+				return null;
+			}
+		});
+		assertOrder(items, b, c, a);
+	}
+
+	@Test
+	public void arrayFactoryMethodOverridesStaticOrder() {
+		A a = new A();
+		C c = new C(5);
+		C c2 = new C(-5);
+
+		Object[] items = new Object[] {a, c, c2};
+		comparator.sortArray(items, new OrderProvider() {
+			@Override
+			public Integer getOrder(Object obj) {
+				if (obj == a) {
+					return 4;
+				}
+				if (obj == c2) {
+					return 2;
+				}
+				return null;
+			}
+		});
+		assertOrder(items, c2, a, c);
+	}
+
+	private void assertOrder(List<?> actual, Object... expected) {
+		for (int i = 0; i < actual.size(); i++) {
+			assertSame("Wrong instance at index '" + i + "'", expected[i], actual.get(i));
+		}
+		assertEquals("Wrong number of items", expected.length, actual.size());
+	}
+
+	private void assertOrder(Object[] actual, Object... expected) {
+		for (int i = 0; i < actual.length; i++) {
+			assertSame("Wrong instance at index '" + i + "'", expected[i], actual[i]);
+		}
+		assertEquals("Wrong number of items", expected.length, expected.length);
+	}
+
+
+	@Order(1)
+	private static class A {
+	}
+
+	@Order(2)
+	private static class B {
+	}
+
+	private static class C implements Ordered {
+		private final int order;
+
+		private C(int order) {
+			this.order = order;
+		}
+
+		@Override
+		public int getOrder() {
+			return order;
+		}
+	}
+
+}