Add ability to ignore configuration properties

Properties which should be ignored can be specified in the
additional-spring-configuration-metadata.json file. The ignored
properties section is copied into the final
spring-configuration-metadata.json file, and the ignored properties are
removed from the properties element in the final file.

Closes gh-2421

spring-boot-project/spring-boot-tools/spring-boot-configuration-processor/src/main/java/org/springframework/boot/configurationprocessor/ConfigurationMetadataAnnotationProcessor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -48,6 +48,7 @@ import javax.tools.Diagnostic.Kind;
 import org.springframework.boot.configurationprocessor.metadata.ConfigurationMetadata;
 import org.springframework.boot.configurationprocessor.metadata.InvalidConfigurationMetadataException;
 import org.springframework.boot.configurationprocessor.metadata.ItemDeprecation;
+import org.springframework.boot.configurationprocessor.metadata.ItemIgnore;
 import org.springframework.boot.configurationprocessor.metadata.ItemMetadata;
 
 /**
@@ -372,6 +373,7 @@ public class ConfigurationMetadataAnnotationProcessor extends AbstractProcessor
 	protected ConfigurationMetadata writeMetadata() throws Exception {
 		ConfigurationMetadata metadata = this.metadataCollector.getMetadata();
 		metadata = mergeAdditionalMetadata(metadata);
+		removeIgnored(metadata);
 		if (!metadata.getItems().isEmpty()) {
 			this.metadataStore.writeMetadata(metadata);
 			return metadata;
@@ -379,6 +381,12 @@ public class ConfigurationMetadataAnnotationProcessor extends AbstractProcessor
 		return null;
 	}
 
+	private void removeIgnored(ConfigurationMetadata metadata) {
+		for (ItemIgnore itemIgnore : metadata.getIgnored()) {
+			metadata.removeMetadata(itemIgnore.getType(), itemIgnore.getName());
+		}
+	}
+
 	private ConfigurationMetadata mergeAdditionalMetadata(ConfigurationMetadata metadata) {
 		try {
 			ConfigurationMetadata merged = new ConfigurationMetadata(metadata);

spring-boot-project/spring-boot-tools/spring-boot-configuration-processor/src/main/java/org/springframework/boot/configurationprocessor/metadata/ConfigurationMetadata.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -22,6 +22,7 @@ import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 
+import org.springframework.boot.configurationprocessor.metadata.ItemMetadata.ItemType;
 import org.springframework.boot.configurationprocessor.support.ConventionUtils;
 
 /**
@@ -29,6 +30,7 @@ import org.springframework.boot.configurationprocessor.support.ConventionUtils;
  *
  * @author Stephane Nicoll
  * @author Phillip Webb
+ * @author Moritz Halbritter
  * @since 1.2.0
  * @see ItemMetadata
  */
@@ -38,14 +40,18 @@ public class ConfigurationMetadata {
 
 	private final Map<String, List<ItemHint>> hints;
 
+	private final Map<String, List<ItemIgnore>> ignored;
+
 	public ConfigurationMetadata() {
 		this.items = new LinkedHashMap<>();
 		this.hints = new LinkedHashMap<>();
+		this.ignored = new LinkedHashMap<>();
 	}
 
 	public ConfigurationMetadata(ConfigurationMetadata metadata) {
 		this.items = new LinkedHashMap<>(metadata.items);
 		this.hints = new LinkedHashMap<>(metadata.hints);
+		this.ignored = new LinkedHashMap<>(metadata.ignored);
 	}
 
 	/**
@@ -73,6 +79,32 @@ public class ConfigurationMetadata {
 		add(this.hints, itemHint.getName(), itemHint, false);
 	}
 
+	/**
+	 * Add item ignore.
+	 * @param itemIgnore the item ignore to add
+	 * @since 3.5.0
+	 */
+	public void add(ItemIgnore itemIgnore) {
+		add(this.ignored, itemIgnore.getName(), itemIgnore, false);
+	}
+
+	/**
+	 * Remove item meta-data for the given item type and name.
+	 * @param itemType the item type
+	 * @param name the name
+	 * @since 3.5.0
+	 */
+	public void removeMetadata(ItemType itemType, String name) {
+		List<ItemMetadata> metadata = this.items.get(name);
+		if (metadata == null) {
+			return;
+		}
+		metadata.removeIf((item) -> item.isOfItemType(itemType));
+		if (metadata.isEmpty()) {
+			this.items.remove(name);
+		}
+	}
+
 	/**
 	 * Merge the content from another {@link ConfigurationMetadata}.
 	 * @param metadata the {@link ConfigurationMetadata} instance to merge
@@ -84,6 +116,9 @@ public class ConfigurationMetadata {
 		for (ItemHint itemHint : metadata.getHints()) {
 			add(itemHint);
 		}
+		for (ItemIgnore itemIgnore : metadata.getIgnored()) {
+			add(itemIgnore);
+		}
 	}
 
 	/**
@@ -102,6 +137,14 @@ public class ConfigurationMetadata {
 		return flattenValues(this.hints);
 	}
 
+	/**
+	 * Return ignore meta-data.
+	 * @return the ignores
+	 */
+	public List<ItemIgnore> getIgnored() {
+		return flattenValues(this.ignored);
+	}
+
 	protected void mergeItemMetadata(ItemMetadata metadata) {
 		ItemMetadata matching = findMatchingItemMetadata(metadata);
 		if (matching != null) {

spring-boot-project/spring-boot-tools/spring-boot-configuration-processor/src/main/java/org/springframework/boot/configurationprocessor/metadata/ItemIgnore.java

@@ -0,0 +1,87 @@
+/*
+ * Copyright 2012-2025 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.configurationprocessor.metadata;
+
+import java.util.Objects;
+
+import org.springframework.boot.configurationprocessor.metadata.ItemMetadata.ItemType;
+
+/**
+ * Ignored item.
+ *
+ * @author Moritz Halbritter
+ * @since 3.5.0
+ */
+public final class ItemIgnore implements Comparable<ItemIgnore> {
+
+	private final ItemType type;
+
+	private final String name;
+
+	private ItemIgnore(ItemType type, String name) {
+		if (name == null) {
+			throw new IllegalArgumentException("'name' must not be null");
+		}
+		if (type == null) {
+			throw new IllegalArgumentException("'type' must not be null");
+		}
+		this.type = type;
+		this.name = name;
+	}
+
+	public String getName() {
+		return this.name;
+	}
+
+	public ItemType getType() {
+		return this.type;
+	}
+
+	@Override
+	public int compareTo(ItemIgnore other) {
+		return getName().compareTo(other.getName());
+	}
+
+	/**
+	 * Create an ignore for a property with the given name.
+	 * @param name the name
+	 * @return the item ignore
+	 */
+	public static ItemIgnore forProperty(String name) {
+		return new ItemIgnore(ItemType.PROPERTY, name);
+	}
+
+	@Override
+	public boolean equals(Object o) {
+		if (o == null || getClass() != o.getClass()) {
+			return false;
+		}
+		ItemIgnore that = (ItemIgnore) o;
+		return this.type == that.type && Objects.equals(this.name, that.name);
+	}
+
+	@Override
+	public int hashCode() {
+		return Objects.hash(this.type, this.name);
+	}
+
+	@Override
+	public String toString() {
+		return "ItemIgnore{" + "type=" + this.type + ", name='" + this.name + '\'' + '}';
+	}
+
+}

spring-boot-project/spring-boot-tools/spring-boot-configuration-processor/src/main/java/org/springframework/boot/configurationprocessor/metadata/JsonConverter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -31,6 +31,7 @@ import org.springframework.boot.configurationprocessor.metadata.ItemMetadata.Ite
  *
  * @author Stephane Nicoll
  * @author Phillip Webb
+ * @author Moritz Halbritter
  */
 class JsonConverter {
 
@@ -59,6 +60,21 @@ class JsonConverter {
 		return jsonArray;
 	}
 
+	JSONObject toJsonObject(Collection<ItemIgnore> ignored) throws Exception {
+		JSONObject result = new JSONObject();
+		result.put("properties", ignoreToJsonArray(
+				ignored.stream().filter((itemIgnore) -> itemIgnore.getType() == ItemType.PROPERTY).toList()));
+		return result;
+	}
+
+	private JSONArray ignoreToJsonArray(Collection<ItemIgnore> ignored) throws Exception {
+		JSONArray result = new JSONArray();
+		for (ItemIgnore itemIgnore : ignored) {
+			result.put(toJsonObject(itemIgnore));
+		}
+		return result;
+	}
+
 	JSONObject toJsonObject(ItemMetadata item) throws Exception {
 		JSONObject jsonObject = new JSONObject();
 		jsonObject.put("name", item.getName());
@@ -103,6 +119,12 @@ class JsonConverter {
 		return jsonObject;
 	}
 
+	private JSONObject toJsonObject(ItemIgnore ignore) throws Exception {
+		JSONObject jsonObject = new JSONObject();
+		jsonObject.put("name", ignore.getName());
+		return jsonObject;
+	}
+
 	private JSONArray getItemHintValues(ItemHint hint) throws Exception {
 		JSONArray values = new JSONArray();
 		for (ItemHint.ValueHint value : hint.getValues()) {

spring-boot-project/spring-boot-tools/spring-boot-configuration-processor/src/main/java/org/springframework/boot/configurationprocessor/metadata/JsonMarshaller.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -30,6 +30,7 @@ import java.util.Set;
 import java.util.TreeSet;
 
 import org.springframework.boot.configurationprocessor.json.JSONArray;
+import org.springframework.boot.configurationprocessor.json.JSONException;
 import org.springframework.boot.configurationprocessor.json.JSONObject;
 import org.springframework.boot.configurationprocessor.metadata.ItemMetadata.ItemType;
 
@@ -50,6 +51,7 @@ public class JsonMarshaller {
 			object.put("groups", converter.toJsonArray(metadata, ItemType.GROUP));
 			object.put("properties", converter.toJsonArray(metadata, ItemType.PROPERTY));
 			object.put("hints", converter.toJsonArray(metadata.getHints()));
+			object.put("ignored", converter.toJsonObject(metadata.getIgnored()));
 			outputStream.write(object.toString(2).getBytes(StandardCharsets.UTF_8));
 		}
 		catch (Exception ex) {
@@ -67,7 +69,7 @@ public class JsonMarshaller {
 		ConfigurationMetadata metadata = new ConfigurationMetadata();
 		JSONObject object = new JSONObject(toString(inputStream));
 		JsonPath path = JsonPath.root();
-		checkAllowedKeys(object, path, "groups", "properties", "hints");
+		checkAllowedKeys(object, path, "groups", "properties", "hints", "ignored");
 		JSONArray groups = object.optJSONArray("groups");
 		if (groups != null) {
 			for (int i = 0; i < groups.length(); i++) {
@@ -88,9 +90,27 @@ public class JsonMarshaller {
 				metadata.add(toItemHint((JSONObject) hints.get(i), path.resolve("hints").index(i)));
 			}
 		}
+		JSONObject ignored = object.optJSONObject("ignored");
+		if (ignored != null) {
+			checkAllowedKeys(ignored, path.resolve("ignored"), "properties");
+			addIgnoredProperties(metadata, ignored, path.resolve("ignored"));
+		}
 		return metadata;
 	}
 
+	private void addIgnoredProperties(ConfigurationMetadata metadata, JSONObject ignored, JsonPath path)
+			throws JSONException {
+		JSONArray properties = ignored.optJSONArray("properties");
+		if (properties == null) {
+			return;
+		}
+		for (int i = 0; i < properties.length(); i++) {
+			JSONObject jsonObject = properties.getJSONObject(i);
+			checkAllowedKeys(jsonObject, path.resolve("properties").index(i), "name");
+			metadata.add(ItemIgnore.forProperty(jsonObject.getString("name")));
+		}
+	}
+
 	private ItemMetadata toItemMetadata(JSONObject object, JsonPath path, ItemType itemType) throws Exception {
 		switch (itemType) {
 			case GROUP -> checkAllowedKeys(object, path, "name", "type", "description", "sourceType", "sourceMethod");

spring-boot-project/spring-boot-tools/spring-boot-configuration-processor/src/test/java/org/springframework/boot/configurationprocessor/ConfigurationMetadataAnnotationProcessorTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -22,6 +22,7 @@ import java.time.temporal.ChronoUnit;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.boot.configurationprocessor.metadata.ConfigurationMetadata;
+import org.springframework.boot.configurationprocessor.metadata.ItemIgnore;
 import org.springframework.boot.configurationprocessor.metadata.ItemMetadata;
 import org.springframework.boot.configurationprocessor.metadata.Metadata;
 import org.springframework.boot.configurationsample.deprecation.Dbcp2Configuration;
@@ -38,6 +39,7 @@ import org.springframework.boot.configurationsample.simple.DescriptionProperties
 import org.springframework.boot.configurationsample.simple.HierarchicalProperties;
 import org.springframework.boot.configurationsample.simple.HierarchicalPropertiesGrandparent;
 import org.springframework.boot.configurationsample.simple.HierarchicalPropertiesParent;
+import org.springframework.boot.configurationsample.simple.IgnoredProperties;
 import org.springframework.boot.configurationsample.simple.InnerClassWithPrivateConstructor;
 import org.springframework.boot.configurationsample.simple.NotAnnotated;
 import org.springframework.boot.configurationsample.simple.SimpleArrayProperties;
@@ -570,4 +572,24 @@ class ConfigurationMetadataAnnotationProcessorTests extends AbstractMetadataGene
 			.withDescription("last description in Javadoc"));
 	}
 
+	@Test
+	void shouldIgnoreProperties() {
+		String additionalMetadata = """
+				{
+					"ignored": {
+						"properties": [
+							{
+								"name": "ignored.prop3"
+							}
+						]
+					}
+				}
+				""";
+		ConfigurationMetadata metadata = compile(additionalMetadata, IgnoredProperties.class);
+		assertThat(metadata).has(Metadata.withProperty("ignored.prop1", String.class));
+		assertThat(metadata).has(Metadata.withProperty("ignored.prop2", String.class));
+		assertThat(metadata).doesNotHave(Metadata.withProperty("ignored.prop3", String.class));
+		assertThat(metadata.getIgnored()).containsExactly(ItemIgnore.forProperty("ignored.prop3"));
+	}
+
 }

spring-boot-project/spring-boot-tools/spring-boot-configuration-processor/src/test/java/org/springframework/boot/configurationprocessor/metadata/JsonMarshallerTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -34,6 +34,7 @@ import static org.assertj.core.api.Assertions.assertThatException;
  *
  * @author Phillip Webb
  * @author Stephane Nicoll
+ * @author Moritz Halbritter
  */
 class JsonMarshallerTests {
 
@@ -174,14 +175,36 @@ class JsonMarshallerTests {
 				"\"java.lang.Boolean\"", "\"com.example.bravo.aaa\"", "\"java.lang.Integer\"", "\"com.example.Bar");
 	}
 
+	@Test
+	void shouldReadIgnoredProperties() throws Exception {
+		String json = """
+				{
+					"ignored": {
+						"properties": [
+							{
+								"name": "prop1"
+							},
+							{
+								"name": "prop2"
+							}
+						]
+					}
+				}
+				""";
+		ConfigurationMetadata metadata = read(json);
+		assertThat(metadata.getIgnored()).containsExactly(ItemIgnore.forProperty("prop1"),
+				ItemIgnore.forProperty("prop2"));
+	}
+
 	@Test
 	void shouldCheckRootFields() {
 		String json = """
 				{
-					"groups": [], "properties": [], "hints": [], "dummy": []
+					"groups": [], "properties": [], "hints": [], "ignored": {}, "dummy": []
 				}""";
 		assertThatException().isThrownBy(() -> read(json))
-			.withMessage("Expected only keys [groups, hints, properties], but found additional keys [dummy]. Path: .");
+			.withMessage(
+					"Expected only keys [groups, hints, ignored, properties], but found additional keys [dummy]. Path: .");
 	}
 
 	@Test
@@ -324,9 +347,41 @@ class JsonMarshallerTests {
 					"Expected only keys [name, parameters], but found additional keys [dummy]. Path: .hints.[0].providers.[0]");
 	}
 
-	private void read(String json) throws Exception {
+	@Test
+	void shouldCheckIgnoreFields() {
+		String json = """
+				{
+					"ignored": {
+						"properties": [],
+						"dummy": {}
+					}
+				}
+				""";
+		assertThatException().isThrownBy(() -> read(json))
+			.withMessage("Expected only keys [properties], but found additional keys [dummy]. Path: .ignored");
+	}
+
+	@Test
+	void shouldCheckIgnorePropertiesFields() {
+		String json = """
+				{
+					"ignored": {
+						"properties": [
+							{
+								"name": "prop1",
+								"dummy": true
+							}
+						]
+					}
+				}
+				""";
+		assertThatException().isThrownBy(() -> read(json))
+			.withMessage("Expected only keys [name], but found additional keys [dummy]. Path: .ignored.properties.[0]");
+	}
+
+	private ConfigurationMetadata read(String json) throws Exception {
 		JsonMarshaller marshaller = new JsonMarshaller();
-		marshaller.read(new ByteArrayInputStream(json.getBytes(StandardCharsets.UTF_8)));
+		return marshaller.read(new ByteArrayInputStream(json.getBytes(StandardCharsets.UTF_8)));
 	}
 
 }

spring-boot-project/spring-boot-tools/spring-boot-configuration-processor/src/test/java/org/springframework/boot/configurationsample/simple/IgnoredProperties.java

@@ -0,0 +1,59 @@
+/*
+ * Copyright 2012-2025 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.configurationsample.simple;
+
+import org.springframework.boot.configurationsample.ConfigurationProperties;
+
+/**
+ * Configuration properties where some of them are being ignored.
+ *
+ * @author Moritz Halbritter
+ */
+@ConfigurationProperties("ignored")
+public class IgnoredProperties {
+
+	private String prop1;
+
+	private String prop2;
+
+	private String prop3;
+
+	public String getProp1() {
+		return this.prop1;
+	}
+
+	public void setProp1(String prop1) {
+		this.prop1 = prop1;
+	}
+
+	public String getProp2() {
+		return this.prop2;
+	}
+
+	public void setProp2(String prop2) {
+		this.prop2 = prop2;
+	}
+
+	public String getProp3() {
+		return this.prop3;
+	}
+
+	public void setProp3(String prop3) {
+		this.prop3 = prop3;
+	}
+
+}