Restrict scalars in MapBinder to java.lang

Fixes gh-9209

spring-boot/src/main/java/org/springframework/boot/context/properties/bind/MapBinder.java

@@ -16,7 +16,6 @@
 
 package org.springframework.boot.context.properties.bind;
 
-import java.util.Collection;
 import java.util.Map;
 import java.util.Properties;
 
@@ -28,6 +27,7 @@ import org.springframework.boot.context.properties.source.ConfigurationPropertyS
 import org.springframework.boot.context.properties.source.IterableConfigurationPropertySource;
 import org.springframework.core.CollectionFactory;
 import org.springframework.core.ResolvableType;
+import org.springframework.util.ClassUtils;
 
 /**
  * {@link AggregateBinder} for Maps.
@@ -130,9 +130,9 @@ class MapBinder extends AggregateBinder<Map<Object, Object>> {
 
 		private boolean isScalarValue(ConfigurationPropertySource source,
 				ConfigurationPropertyName name) {
-			if (Map.class.isAssignableFrom(this.valueType.resolve())
-					|| Collection.class.isAssignableFrom(this.valueType.resolve())
-					|| this.valueType.isArray()) {
+			Class<?> resolved = this.valueType.resolve();
+			String packageName = ClassUtils.getPackageName(resolved);
+			if (!packageName.startsWith("java.lang") && !resolved.isEnum()) {
 				return false;
 			}
 			ConfigurationProperty property = source.getConfigurationProperty(name);

spring-boot/src/test/java/org/springframework/boot/context/properties/bind/MapBinderTests.java

@@ -388,4 +388,39 @@ public class MapBinderTests {
 				eq(target), any(), isA(Properties.class));
 	}
 
+	@Test
+	public void bindToMapShouldNotTreatClassWithStringConstructorAsScalar() throws Exception {
+		this.sources
+				.add(new MockConfigurationPropertySource("foo.bar.pattern", "1", "line1"));
+		BindHandler handler = mock(BindHandler.class,
+				withSettings().defaultAnswer(Answers.CALLS_REAL_METHODS));
+		Bindable<Map<String, Foo>> target = Bindable.of(ResolvableType.forClassWithGenerics(Map.class, String.class, Foo.class));
+		this.binder.bind("foo", target, handler);
+		InOrder inOrder = inOrder(handler);
+		inOrder.verify(handler).onSuccess(eq(ConfigurationPropertyName.of("foo.bar.pattern")),
+				eq(Bindable.of(String.class)), any(), eq("1"));
+		inOrder.verify(handler).onSuccess(eq(ConfigurationPropertyName.of("foo")),
+				eq(target), any(), isA(Map.class));
+	}
+
+	public static class Foo {
+		private String pattern;
+
+		public Foo() {
+		}
+
+		public Foo(String pattern) {
+			this.pattern = pattern;
+		}
+
+		public String getPattern() {
+			return this.pattern;
+		}
+
+		public void setPattern(String pattern) {
+			this.pattern = pattern;
+		}
+
+	}
+
 }