Treat the only one default candidate as effectively primary

Close spring-projectsGH-34432

Signed-off-by: Yanming Zhou <zhouyanming@gmail.com>

Author: quaff

spring-beans/src/main/java/org/springframework/beans/factory/support/DefaultListableBeanFactory.java

@@ -118,6 +118,7 @@
  * @author Phillip Webb
  * @author Stephane Nicoll
  * @author Sebastien Deleuze
+ * @author Yanming Zhou
  * @since 16 April 2001
  * @see #registerBeanDefinition
  * @see #addBeanPostProcessor
@@ -1479,6 +1480,9 @@ else if (candidateNames.length > 1) {
 			if (candidateName == null) {
 				candidateName = determineHighestPriorityCandidate(candidates, requiredType.toClass());
 			}
+			if (candidateName == null) {
+				candidateName = determineEffectivelyPrimaryCandidate(candidates, requiredType.toClass());
+			}
 			if (candidateName != null) {
 				Object beanInstance = candidates.get(candidateName);
 				if (beanInstance == null) {
@@ -2046,6 +2050,34 @@ else if (candidatePriority < highestPriority) {
 		return highestPriorityBeanName;
 	}
 
+	/**
+	 * Determine the candidate which is the only one default candidate in the given set of beans.
+	 * @param candidates a Map of candidate names and candidate instances
+	 * (or candidate classes if not created yet) that match the required type
+	 * @param requiredType the target dependency type to match against
+	 * @return the name of the only one default candidate,
+	 * or {@code null} if none found
+	 */
+	@Nullable
+	protected String determineEffectivelyPrimaryCandidate(Map<String, Object> candidates, Class<?> requiredType) {
+		String candidateBeanName = null;
+		for (Map.Entry<String, Object> entry : candidates.entrySet()) {
+			String transformedBeanName = transformedBeanName(entry.getKey());
+			if (containsBeanDefinition(transformedBeanName)) {
+				RootBeanDefinition bd = getMergedLocalBeanDefinition(transformedBeanName);
+				if (bd.isAutowireCandidate() && bd.isDefaultCandidate()) {
+					if (candidateBeanName == null) {
+						candidateBeanName = entry.getKey();
+					}
+					else {
+						return null;
+					}
+				}
+			}
+		}
+		return candidateBeanName;
+	}
+
 	/**
 	 * Return whether the bean definition for the given bean name has been
 	 * marked as a primary bean.

spring-beans/src/test/java/org/springframework/beans/factory/DefaultListableBeanFactoryTests.java

@@ -113,6 +113,7 @@
  * @author Chris Beams
  * @author Phillip Webb
  * @author Stephane Nicoll
+ * @author Yanming Zhou
  */
 class DefaultListableBeanFactoryTests {
 
@@ -1664,6 +1665,18 @@ void getBeanByTypeWithPrimary() {
 		assertThat(lbf.containsSingleton("bd1")).isFalse();
 	}
 
+	@Test
+	void getBeanByTypeWithEffectivelyPrimary() {
+		RootBeanDefinition bd1 = new RootBeanDefinition(TestBean.class);
+		bd1.setDefaultCandidate(false);
+		RootBeanDefinition bd2 = new RootBeanDefinition(TestBean.class);
+		lbf.registerBeanDefinition("bd1", bd1);
+		lbf.registerBeanDefinition("bd2", bd2);
+
+		TestBean bean = lbf.getBean(TestBean.class);
+		assertThat(bean.getBeanName()).isEqualTo("bd2");
+	}
+
 	@Test
 	@SuppressWarnings("rawtypes")
 	void getFactoryBeanByTypeWithPrimary() {