Resolve property placeholders in constructor binding default values

Resolve each annotated default using the binder placeholder resolver
before conversion.

Signed-off-by: Wan bin yu <3431359639@qq.com>

See gh-51661

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

@@ -33,11 +33,12 @@ import java.lang.annotation.Target;
  * the default value for the property will not be used even if the property value is
  * empty.
  * <p>
- * NOTE: This annotation does not support property placeholder resolution and the value
+ * Property placeholders in the default value are resolved using the {@link Binder}'s
- * must be constant.
+ * {@link PlaceholdersResolver} before the value is converted to the property's type.
  *
  * @author Madhura Bhave
  * @author Pavel Anisimov
+ * @author Wan bin yu
  * @since 2.2.0
  */
 @Retention(RetentionPolicy.RUNTIME)

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

@@ -62,6 +62,7 @@ import org.springframework.util.Assert;
  * @author Phillip Webb
  * @author Scott Frederick
  * @author Ondřej Světlík
+ * @author Wan bin yu
  */
 class ValueObjectBinder implements DataObjectBinder {
 
@@ -135,12 +136,22 @@ class ValueObjectBinder implements DataObjectBinder {
 				if (defaultValue.length == 0) {
 					return getNewDefaultValueInstanceIfPossible(context, type);
 				}
-				return convertDefaultValue(context.getConverter(), defaultValue, type, annotations);
+				return convertDefaultValue(context.getConverter(),
+						resolveDefaultValue(context.getPlaceholdersResolver(), defaultValue), type, annotations);
 			}
 		}
 		return context.getConverter().convert(null, type);
 	}
 
+	private String[] resolveDefaultValue(PlaceholdersResolver resolver, String[] defaultValue) {
+		String[] resolved = new String[defaultValue.length];
+		for (int i = 0; i < defaultValue.length; i++) {
+			Object value = resolver.resolvePlaceholders(defaultValue[i]);
+			resolved[i] = String.valueOf(value);
+		}
+		return resolved;
+	}
+
 	private <T> @Nullable T convertDefaultValue(BindConverter converter, String[] defaultValue, ResolvableType type,
 			Annotation[] annotations) {
 		try {

core/spring-boot/src/test/java/org/springframework/boot/context/properties/ConfigurationPropertiesTests.java

@@ -132,6 +132,7 @@ import static org.mockito.Mockito.mock;
  * @author Stephane Nicoll
  * @author Madhura Bhave
  * @author Vladislav Kisel
+ * @author Wan bin yu
  */
 @ExtendWith(OutputCaptureExtension.class)
 class ConfigurationPropertiesTests {
@@ -1016,6 +1017,38 @@ class ConfigurationPropertiesTests {
 		assertThat(bean.getOptional()).isEmpty();
 	}
 
+	@Test
+	void loadWhenDefaultValuesContainPlaceholdersShouldResolveAndConvert() {
+		load(PlaceholderDefaultsConfiguration.class, "defaults.name=resolved", "defaults.duration=3d",
+				"defaults.count=7");
+		PlaceholderDefaultsProperties bean = this.context.getBean(PlaceholderDefaultsProperties.class);
+		assertThat(bean.name).isEqualTo("resolved/suffix");
+		assertThat(bean.duration).isEqualTo(Duration.ofDays(3));
+		assertThat(bean.counts).containsExactly(7, 2);
+		assertThat(bean.names).containsExactly("resolved", "fallback");
+	}
+
+	@Test
+	void loadWhenDefaultValuesContainPlaceholdersShouldUsePlaceholderDefaults() {
+		load(PlaceholderDefaultsConfiguration.class);
+		PlaceholderDefaultsProperties bean = this.context.getBean(PlaceholderDefaultsProperties.class);
+		assertThat(bean.name).isEqualTo("default/suffix");
+		assertThat(bean.duration).isEqualTo(Duration.ofDays(1));
+		assertThat(bean.counts).containsExactly(1, 2);
+		assertThat(bean.names).containsExactly("default", "fallback");
+	}
+
+	@Test
+	void loadWhenExplicitValuesOverridePlaceholderDefaultsShouldUseExplicitValues() {
+		load(PlaceholderDefaultsConfiguration.class, "test.name=explicit", "test.duration=5d", "test.counts=8,9",
+				"test.names=one,two");
+		PlaceholderDefaultsProperties bean = this.context.getBean(PlaceholderDefaultsProperties.class);
+		assertThat(bean.name).isEqualTo("explicit");
+		assertThat(bean.duration).isEqualTo(Duration.ofDays(5));
+		assertThat(bean.counts).containsExactly(8, 9);
+		assertThat(bean.names).containsExactly("one", "two");
+	}
+
 	@Test
 	void loadWhenBindingToConstructorParametersWithDefaultDataUnitShouldBind() {
 		load(ConstructorParameterWithUnitConfiguration.class);
@@ -2467,6 +2500,35 @@ class ConfigurationPropertiesTests {
 
 	}
 
+	@Configuration(proxyBeanMethods = false)
+	@EnableConfigurationProperties(PlaceholderDefaultsProperties.class)
+	static class PlaceholderDefaultsConfiguration {
+
+	}
+
+	@ConfigurationProperties("test")
+	static class PlaceholderDefaultsProperties {
+
+		private final String name;
+
+		private final Duration duration;
+
+		private final int[] counts;
+
+		private final List<String> names;
+
+		PlaceholderDefaultsProperties(@DefaultValue("${defaults.name:default}/suffix") String name,
+				@DefaultValue("${defaults.duration:1d}") Duration duration,
+				@DefaultValue({ "${defaults.count:1}", "2" }) int[] counts,
+				@DefaultValue({ "${defaults.name:default}", "${defaults.other:fallback}" }) List<String> names) {
+			this.name = name;
+			this.duration = duration;
+			this.counts = counts;
+			this.names = names;
+		}
+
+	}
+
 	@ConfigurationProperties("test")
 	static class ConstructorParameterEmptyDefaultValueProperties {
 

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

@@ -21,6 +21,7 @@ import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.time.LocalDate;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.EnumMap;
 import java.util.List;
 import java.util.Map;
@@ -52,6 +53,7 @@ import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
  * @author Pavel Anisimov
  * @author Yanming Zhou
  * @author Ondřej Světlík
+ * @author Wan bin yu
  */
 class ValueObjectBinderTests {
 
@@ -307,6 +309,26 @@ class ValueObjectBinderTests {
 		assertThat(bean.getDate()).hasToString("2019-05-10");
 	}
 
+	@Test
+	void createWithDefaultValuePlaceholderAndNoResolverShouldRetainPlaceholder() {
+		PlaceholderDefaultValue bean = this.binder.bindOrCreate("foo", PlaceholderDefaultValue.class);
+		assertThat(bean.value()).isEqualTo("${value}");
+	}
+
+	@Test
+	void createWithUnresolvedDefaultValuePlaceholderShouldRetainPlaceholder() {
+		Binder binder = new Binder(this.sources, new PropertySourcesPlaceholdersResolver(Collections.emptyList()));
+		PlaceholderDefaultValue bean = binder.bindOrCreate("foo", PlaceholderDefaultValue.class);
+		assertThat(bean.value()).isEqualTo("${value}");
+	}
+
+	@Test
+	void createWithDefaultValuePlaceholderResolvingToNonStringShouldConvert() {
+		Binder binder = new Binder(this.sources, (value) -> 42);
+		PlaceholderDefaultValue bean = binder.bindOrCreate("foo", PlaceholderDefaultValue.class);
+		assertThat(bean.value()).isEqualTo("42");
+	}
+
 	@Test
 	void bindWhenAllPropertiesBoundShouldClearConfigurationProperty() { // gh-18704
 		MockConfigurationPropertySource source = new MockConfigurationPropertySource();
@@ -639,6 +661,10 @@ class ValueObjectBinderTests {
 
 	}
 
+	record PlaceholderDefaultValue(@DefaultValue("${value}") String value) {
+
+	}
+
 	static class ExampleDefaultValueBean {
 
 		private final int intValue;