@lazy falls back to empty map/list/set for non-required collection dependency

Issue: SPR-15858

Author: jhoeller

spring-context/src/main/java/org/springframework/context/annotation/ContextAnnotationAutowireCandidateResolver.java

@@ -18,6 +18,11 @@
 
 import java.lang.annotation.Annotation;
 import java.lang.reflect.Method;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
 
 import org.springframework.aop.TargetSource;
 import org.springframework.aop.framework.ProxyFactory;
@@ -83,6 +88,16 @@ public boolean isStatic() {
 			public Object getTarget() {
 				Object target = beanFactory.doResolveDependency(descriptor, beanName, null, null);
 				if (target == null) {
+					Class<?> type = getTargetClass();
+					if (Map.class == type) {
+						return Collections.EMPTY_MAP;
+					}
+					else if (List.class == type) {
+						return Collections.EMPTY_LIST;
+					}
+					else if (Set.class == type || Collection.class == type) {
+						return Collections.EMPTY_SET;
+					}
 					throw new NoSuchBeanDefinitionException(descriptor.getResolvableType(),
 							"Optional dependency not present for lazy injection point");
 				}

spring-context/src/test/java/org/springframework/context/annotation/LazyAutowiredAnnotationBeanPostProcessorTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 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.
@@ -18,6 +18,7 @@
 
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
+import java.util.List;
 
 import org.junit.Test;
 
@@ -59,6 +60,24 @@ private void doTestLazyResourceInjection(Class<? extends TestBeanHolder> annotat
 	@Test
 	public void testLazyResourceInjectionWithField() {
 		doTestLazyResourceInjection(FieldResourceInjectionBean.class);
+
+		AnnotationConfigApplicationContext ac = new AnnotationConfigApplicationContext();
+		RootBeanDefinition abd = new RootBeanDefinition(FieldResourceInjectionBean.class);
+		abd.setScope(RootBeanDefinition.SCOPE_PROTOTYPE);
+		ac.registerBeanDefinition("annotatedBean", abd);
+		RootBeanDefinition tbd = new RootBeanDefinition(TestBean.class);
+		tbd.setLazyInit(true);
+		ac.registerBeanDefinition("testBean", tbd);
+		ac.refresh();
+
+		FieldResourceInjectionBean bean = ac.getBean("annotatedBean", FieldResourceInjectionBean.class);
+		assertFalse(ac.getBeanFactory().containsSingleton("testBean"));
+		assertFalse(bean.getTestBeans().isEmpty());
+		assertNull(bean.getTestBeans().get(0).getName());
+		assertTrue(ac.getBeanFactory().containsSingleton("testBean"));
+		TestBean tb = (TestBean) ac.getBean("testBean");
+		tb.setName("tb");
+		assertSame("tb", bean.getTestBean().getName());
 	}
 
 	@Test
@@ -114,7 +133,7 @@ public void testLazyResourceInjectionWithNonExistingTarget() {
 			fail("Should have thrown NoSuchBeanDefinitionException");
 		}
 		catch (NoSuchBeanDefinitionException ex) {
-			// expected;
+			// expected
 		}
 	}
 
@@ -131,12 +150,14 @@ public void testLazyOptionalResourceInjectionWithNonExistingTarget() {
 
 		OptionalFieldResourceInjectionBean bean = (OptionalFieldResourceInjectionBean) bf.getBean("annotatedBean");
 		assertNotNull(bean.getTestBean());
+		assertNotNull(bean.getTestBeans());
+		assertTrue(bean.getTestBeans().isEmpty());
 		try {
 			bean.getTestBean().getName();
 			fail("Should have thrown NoSuchBeanDefinitionException");
 		}
 		catch (NoSuchBeanDefinitionException ex) {
-			// expected;
+			// expected
 		}
 	}
 
@@ -152,9 +173,16 @@ public static class FieldResourceInjectionBean implements TestBeanHolder {
 		@Autowired @Lazy
 		private TestBean testBean;
 
+		@Autowired @Lazy
+		private List<TestBean> testBeans;
+
 		public TestBean getTestBean() {
 			return this.testBean;
 		}
+
+		public List<TestBean> getTestBeans() {
+			return testBeans;
+		}
 	}
 
 
@@ -163,9 +191,16 @@ public static class OptionalFieldResourceInjectionBean implements TestBeanHolder
 		@Autowired(required = false) @Lazy
 		private TestBean testBean;
 
+		@Autowired(required = false) @Lazy
+		private List<TestBean> testBeans;
+
 		public TestBean getTestBean() {
 			return this.testBean;
 		}
+
+		public List<TestBean> getTestBeans() {
+			return this.testBeans;
+		}
 	}