Add support for binding to Properties in @ConfigurationProperties

Fixes gh-4250

spring-boot/src/main/java/org/springframework/boot/bind/RelaxedDataBinder.java

@@ -25,6 +25,7 @@ import java.util.LinkedHashMap;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
+import java.util.Properties;
 import java.util.Set;
 
 import org.springframework.beans.BeanWrapper;
@@ -311,6 +312,10 @@ public class RelaxedDataBinder extends DataBinder {
 		if (descriptor == null || descriptor.getMapValueTypeDescriptor() == null) {
 			return false;
 		}
+		if (Properties.class.isAssignableFrom(descriptor.getObjectType())) {
+			// Properties is declared as Map<Object,Object> but we know it's really Map<String,String>
+			return true;
+		}
 		Class<?> valueType = descriptor.getMapValueTypeDescriptor().getObjectType();
 		return (valueType != null && CharSequence.class.isAssignableFrom(valueType));
 	}

spring-boot/src/test/java/org/springframework/boot/bind/RelaxedDataBinderTests.java

@@ -16,6 +16,14 @@
 
 package org.springframework.boot.bind;
 
+import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.nullValue;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertThat;
+
 import java.lang.annotation.Documented;
 import java.lang.annotation.ElementType;
 import java.lang.annotation.Retention;
@@ -40,7 +48,6 @@ import javax.validation.constraints.NotNull;
 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.rules.ExpectedException;
-
 import org.springframework.beans.MutablePropertyValues;
 import org.springframework.beans.NotWritablePropertyException;
 import org.springframework.context.support.StaticMessageSource;
@@ -53,14 +60,6 @@ import org.springframework.validation.DataBinder;
 import org.springframework.validation.FieldError;
 import org.springframework.validation.beanvalidation.LocalValidatorFactoryBean;
 
-import static org.hamcrest.Matchers.equalTo;
-import static org.hamcrest.Matchers.nullValue;
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertFalse;
-import static org.junit.Assert.assertNotNull;
-import static org.junit.Assert.assertNull;
-import static org.junit.Assert.assertThat;
-
 /**
  * Tests for {@link RelaxedDataBinder}.
  *
@@ -371,6 +370,14 @@ public class RelaxedDataBinderTests {
 		assertEquals("123", target.getNested().get("value.foo"));
 	}
 
+	@Test
+	public void testBindNestedProperties() throws Exception {
+		TargetWithNestedProperties target = new TargetWithNestedProperties();
+		bind(target, "nested.foo: bar\n" + "nested.value.foo: 123");
+		assertEquals("bar", target.getNested().get("foo"));
+		assertEquals("123", target.getNested().get("value.foo"));
+	}
+
 	@Test
 	public void testBindNestedMapOfEnum() throws Exception {
 		this.conversionService = new DefaultConversionService();
@@ -780,6 +787,20 @@ public class RelaxedDataBinderTests {
 
 	}
 
+	public static class TargetWithNestedProperties {
+
+		private Properties nested;
+
+		public Properties getNested() {
+			return this.nested;
+		}
+
+		public void setNested(Properties nested) {
+			this.nested = nested;
+		}
+
+	}
+
 	public static class TargetWithNestedMapOfString {
 
 		private Map<String, String> nested;