Support binding with multiple constructors

Update `DefaultBindConstructorProvider` so that binding to objects with
multiple constructors is allowed, as long as there is only one
non-public candidate.

Closes gh-23117

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

@@ -17,6 +17,7 @@
 package org.springframework.boot.context.properties.bind;
 
 import java.lang.reflect.Constructor;
+import java.lang.reflect.Modifier;
 
 import org.springframework.beans.BeanUtils;
 import org.springframework.core.KotlinDetector;
@@ -42,6 +43,18 @@ class DefaultBindConstructorProvider implements BindConstructorProvider {
 		if (constructors.length == 1 && constructors[0].getParameterCount() > 0) {
 			return constructors[0];
 		}
+		Constructor<?> constructor = null;
+		for (Constructor<?> candidate : constructors) {
+			if (!Modifier.isPrivate(candidate.getModifiers())) {
+				if (constructor != null) {
+					return null;
+				}
+				constructor = candidate;
+			}
+		}
+		if (constructor != null && constructor.getParameterCount() > 0) {
+			return constructor;
+		}
 		return null;
 	}
 

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

@@ -123,6 +123,18 @@ class ValueObjectBinderTests {
 		assertThat(bound).isFalse();
 	}
 
+	@Test
+	void bindToClassWithMultipleConstructorsWhenOnlyOneIsNotPrivateShouldBind() {
+		MockConfigurationPropertySource source = new MockConfigurationPropertySource();
+		source.put("foo.int-value", "12");
+		this.sources.add(source);
+		MultipleConstructorsOnlyOneNotPrivateBean bean = this.binder
+				.bind("foo", Bindable.of(MultipleConstructorsOnlyOneNotPrivateBean.class)).get();
+		bean = bean.withString("test");
+		assertThat(bean.getIntValue()).isEqualTo(12);
+		assertThat(bean.getStringValue()).isEqualTo("test");
+	}
+
 	@Test
 	void bindToClassShouldBindNested() {
 		MockConfigurationPropertySource source = new MockConfigurationPropertySource();
@@ -341,7 +353,6 @@ class ValueObjectBinderTests {
 		Bindable<NamedParameter> target = Bindable.of(NamedParameter.class);
 		NamedParameter bound = this.binder.bindOrCreate("test", target);
 		assertThat(bound.getImportName()).isEqualTo("test");
-
 	}
 
 	private void noConfigurationProperty(BindException ex) {
@@ -417,6 +428,35 @@ class ValueObjectBinderTests {
 
 	}
 
+	static class MultipleConstructorsOnlyOneNotPrivateBean {
+
+		private final int intValue;
+
+		private final String stringValue;
+
+		MultipleConstructorsOnlyOneNotPrivateBean(int intValue) {
+			this(intValue, 23L, "hello");
+		}
+
+		private MultipleConstructorsOnlyOneNotPrivateBean(int intValue, long longValue, String stringValue) {
+			this.intValue = intValue;
+			this.stringValue = stringValue;
+		}
+
+		int getIntValue() {
+			return this.intValue;
+		}
+
+		String getStringValue() {
+			return this.stringValue;
+		}
+
+		MultipleConstructorsOnlyOneNotPrivateBean withString(String stringValue) {
+			return new MultipleConstructorsOnlyOneNotPrivateBean(this.intValue, 0, stringValue);
+		}
+
+	}
+
 	abstract static class ExampleAbstractBean {
 
 		private final String name;