Support DocumentPostProcessors in RAG Advisor

spring-ai-docs/src/main/antora/modules/ROOT/pages/api/retrieval-augmented-generation.adoc

@@ -119,7 +119,7 @@ PromptTemplate customPromptTemplate = PromptTemplate.builder()
 
 NOTE: The `QuestionAnswerAdvisor.Builder.userTextAdvise()` method is deprecated in favor of using `.promptTemplate()` for more flexible customization.
 
-=== RetrievalAugmentationAdvisor (Incubating)
+=== RetrievalAugmentationAdvisor
 
 Spring AI includes a xref:api/retrieval-augmented-generation.adoc#modules[library of RAG modules] that you can use to build your own RAG flows.
 The `RetrievalAugmentationAdvisor` is an `Advisor` providing an out-of-the-box implementation for the most common RAG flows,
@@ -211,6 +211,8 @@ String answer = chatClient.prompt()
         .content();
 ----
 
+You can also use the `DocumentPostProcessor` API to post-process the retrieved documents before passing them to the model. For example, you can use such an interface to perform re-ranking of the retrieved documents based on their relevance to the query, remove irrelevant or redundant documents, or compress the content of each document to reduce noise and redundancy.
+
 [[modules]]
 == Modules
 

spring-ai-integration-tests/src/test/java/org/springframework/ai/integration/tests/client/advisor/RetrievalAugmentationAdvisorIT.java

@@ -261,6 +261,32 @@ void ragWithMultiQuery() {
 		evaluateRelevancy(question, chatResponse);
 	}
 
+	@Test
+	void ragWithDocumentPostProcessor() {
+		String question = "Where does the adventure of Anacletus and Birba take place?";
+
+		RetrievalAugmentationAdvisor ragAdvisor = RetrievalAugmentationAdvisor.builder()
+			.documentRetriever(VectorStoreDocumentRetriever.builder().vectorStore(this.pgVectorStore).build())
+			.documentPostProcessors((query, documents) -> List
+				.of(Document.builder().text("The adventure of Anacletus and Birba takes place in Molise").build()))
+			.build();
+
+		ChatResponse chatResponse = ChatClient.builder(this.openAiChatModel)
+			.build()
+			.prompt(question)
+			.advisors(ragAdvisor)
+			.call()
+			.chatResponse();
+
+		assertThat(chatResponse).isNotNull();
+
+		String response = chatResponse.getResult().getOutput().getText();
+		System.out.println(response);
+		assertThat(response).containsIgnoringCase("Molise");
+
+		evaluateRelevancy(question, chatResponse);
+	}
+
 	private void evaluateRelevancy(String question, ChatResponse chatResponse) {
 		EvaluationRequest evaluationRequest = new EvaluationRequest(question,
 				chatResponse.getMetadata().get(RetrievalAugmentationAdvisor.DOCUMENT_CONTEXT),

spring-ai-rag/src/main/java/org/springframework/ai/rag/advisor/RetrievalAugmentationAdvisor.java

@@ -34,6 +34,7 @@
 import org.springframework.ai.rag.Query;
 import org.springframework.ai.rag.generation.augmentation.ContextualQueryAugmenter;
 import org.springframework.ai.rag.generation.augmentation.QueryAugmenter;
+import org.springframework.ai.rag.postretrieval.document.DocumentPostProcessor;
 import org.springframework.ai.rag.preretrieval.query.expansion.QueryExpander;
 import org.springframework.ai.rag.preretrieval.query.transformation.QueryTransformer;
 import org.springframework.ai.rag.retrieval.join.ConcatenationDocumentJoiner;
@@ -70,6 +71,8 @@ public final class RetrievalAugmentationAdvisor implements BaseAdvisor {
 
 	private final DocumentJoiner documentJoiner;
 
+	private final List<DocumentPostProcessor> documentPostProcessors;
+
 	private final QueryAugmenter queryAugmenter;
 
 	private final TaskExecutor taskExecutor;
@@ -80,14 +83,16 @@ public final class RetrievalAugmentationAdvisor implements BaseAdvisor {
 
 	private RetrievalAugmentationAdvisor(@Nullable List<QueryTransformer> queryTransformers,
 			@Nullable QueryExpander queryExpander, DocumentRetriever documentRetriever,
-			@Nullable DocumentJoiner documentJoiner, @Nullable QueryAugmenter queryAugmenter,
-			@Nullable TaskExecutor taskExecutor, @Nullable Scheduler scheduler, @Nullable Integer order) {
+			@Nullable DocumentJoiner documentJoiner, @Nullable List<DocumentPostProcessor> documentPostProcessors,
+			@Nullable QueryAugmenter queryAugmenter, @Nullable TaskExecutor taskExecutor, @Nullable Scheduler scheduler,
+			@Nullable Integer order) {
 		Assert.notNull(documentRetriever, "documentRetriever cannot be null");
 		Assert.noNullElements(queryTransformers, "queryTransformers cannot contain null elements");
 		this.queryTransformers = queryTransformers != null ? queryTransformers : List.of();
 		this.queryExpander = queryExpander;
 		this.documentRetriever = documentRetriever;
 		this.documentJoiner = documentJoiner != null ? documentJoiner : new ConcatenationDocumentJoiner();
+		this.documentPostProcessors = documentPostProcessors != null ? documentPostProcessors : List.of();
 		this.queryAugmenter = queryAugmenter != null ? queryAugmenter : ContextualQueryAugmenter.builder().build();
 		this.taskExecutor = taskExecutor != null ? taskExecutor : buildDefaultTaskExecutor();
 		this.scheduler = scheduler != null ? scheduler : BaseAdvisor.DEFAULT_SCHEDULER;
@@ -130,6 +135,11 @@ public ChatClientRequest before(ChatClientRequest chatClientRequest, @Nullable A
 		// 4. Combine documents retrieved based on multiple queries and from multiple data
 		// sources.
 		List<Document> documents = this.documentJoiner.join(documentsForQuery);
+
+		// 5. Post-process the documents.
+		for (var documentPostProcessor : this.documentPostProcessors) {
+			documents = documentPostProcessor.process(originalQuery, documents);
+		}
 		context.put(DOCUMENT_CONTEXT, documents);
 
 		// 5. Augment user query with the document contextual data.
@@ -197,6 +207,8 @@ public static final class Builder {
 
 		private DocumentJoiner documentJoiner;
 
+		private List<DocumentPostProcessor> documentPostProcessors;
+
 		private QueryAugmenter queryAugmenter;
 
 		private TaskExecutor taskExecutor;
@@ -209,11 +221,14 @@ private Builder() {
 		}
 
 		public Builder queryTransformers(List<QueryTransformer> queryTransformers) {
+			Assert.noNullElements(queryTransformers, "queryTransformers cannot contain null elements");
 			this.queryTransformers = queryTransformers;
 			return this;
 		}
 
 		public Builder queryTransformers(QueryTransformer... queryTransformers) {
+			Assert.notNull(queryTransformers, "queryTransformers cannot be null");
+			Assert.noNullElements(queryTransformers, "queryTransformers cannot contain null elements");
 			this.queryTransformers = Arrays.asList(queryTransformers);
 			return this;
 		}
@@ -233,6 +248,19 @@ public Builder documentJoiner(DocumentJoiner documentJoiner) {
 			return this;
 		}
 
+		public Builder documentPostProcessors(List<DocumentPostProcessor> documentPostProcessors) {
+			Assert.noNullElements(documentPostProcessors, "documentPostProcessors cannot contain null elements");
+			this.documentPostProcessors = documentPostProcessors;
+			return this;
+		}
+
+		public Builder documentPostProcessors(DocumentPostProcessor... documentPostProcessors) {
+			Assert.notNull(documentPostProcessors, "documentPostProcessors cannot be null");
+			Assert.noNullElements(documentPostProcessors, "documentPostProcessors cannot contain null elements");
+			this.documentPostProcessors = Arrays.asList(documentPostProcessors);
+			return this;
+		}
+
 		public Builder queryAugmenter(QueryAugmenter queryAugmenter) {
 			this.queryAugmenter = queryAugmenter;
 			return this;
@@ -255,7 +283,8 @@ public Builder order(Integer order) {
 
 		public RetrievalAugmentationAdvisor build() {
 			return new RetrievalAugmentationAdvisor(this.queryTransformers, this.queryExpander, this.documentRetriever,
-					this.documentJoiner, this.queryAugmenter, this.taskExecutor, this.scheduler, this.order);
+					this.documentJoiner, this.documentPostProcessors, this.queryAugmenter, this.taskExecutor,
+					this.scheduler, this.order);
 		}
 
 	}