Improve TokenTextSplitter for punctuations handling

Make punctuations configurable and support Chinese punctuations.

Signed-off-by: Harold Li <power0721@gmail.com>

Author: power721

spring-ai-commons/src/main/java/org/springframework/ai/transformer/splitter/TokenTextSplitter.java

@@ -17,6 +17,8 @@
 package org.springframework.ai.transformer.splitter;
 
 import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
 import java.util.List;
 
 import com.knuddels.jtokkit.Encodings;
@@ -46,6 +48,8 @@ public class TokenTextSplitter extends TextSplitter {
 
 	private static final boolean KEEP_SEPARATOR = true;
 
+	private static final List<Character> DEFAULT_PUNCTUATIONS = List.of('.', '?', '!', '。', '？', '！', '\n');
+
 	private final EncodingRegistry registry = Encodings.newLazyEncodingRegistry();
 
 	private final Encoding encoding = this.registry.getEncoding(EncodingType.CL100K_BASE);
@@ -64,21 +68,24 @@ public class TokenTextSplitter extends TextSplitter {
 
 	private final boolean keepSeparator;
 
+	private final List<Character> punctuations;
+
 	public TokenTextSplitter() {
-		this(DEFAULT_CHUNK_SIZE, MIN_CHUNK_SIZE_CHARS, MIN_CHUNK_LENGTH_TO_EMBED, MAX_NUM_CHUNKS, KEEP_SEPARATOR);
+		this(DEFAULT_CHUNK_SIZE, MIN_CHUNK_SIZE_CHARS, MIN_CHUNK_LENGTH_TO_EMBED, MAX_NUM_CHUNKS, KEEP_SEPARATOR, DEFAULT_PUNCTUATIONS);
 	}
 
 	public TokenTextSplitter(boolean keepSeparator) {
-		this(DEFAULT_CHUNK_SIZE, MIN_CHUNK_SIZE_CHARS, MIN_CHUNK_LENGTH_TO_EMBED, MAX_NUM_CHUNKS, keepSeparator);
+		this(DEFAULT_CHUNK_SIZE, MIN_CHUNK_SIZE_CHARS, MIN_CHUNK_LENGTH_TO_EMBED, MAX_NUM_CHUNKS, keepSeparator, DEFAULT_PUNCTUATIONS);
 	}
 
 	public TokenTextSplitter(int chunkSize, int minChunkSizeChars, int minChunkLengthToEmbed, int maxNumChunks,
-			boolean keepSeparator) {
+			boolean keepSeparator, List<Character> punctuations) {
 		this.chunkSize = chunkSize;
 		this.minChunkSizeChars = minChunkSizeChars;
 		this.minChunkLengthToEmbed = minChunkLengthToEmbed;
 		this.maxNumChunks = maxNumChunks;
 		this.keepSeparator = keepSeparator;
+		this.punctuations = punctuations;
 	}
 
 	public static Builder builder() {
@@ -124,8 +131,10 @@ protected List<String> doSplit(String text, int chunkSize) {
 			// This prevents unnecessary splitting of small texts
 			if (tokens.size() > chunkSize) {
 				// Find the last period or punctuation mark in the chunk
-				int lastPunctuation = Math.max(chunkText.lastIndexOf('.'), Math.max(chunkText.lastIndexOf('?'),
-						Math.max(chunkText.lastIndexOf('!'), chunkText.lastIndexOf('\n'))));
+				int lastPunctuation = -1;
+				for (char punctuation : punctuations) {
+					lastPunctuation = Math.max(lastPunctuation, chunkText.lastIndexOf(punctuation));
+				}
 
 				if (lastPunctuation != -1 && lastPunctuation > this.minChunkSizeChars) {
 					// Truncate the chunk text at the punctuation mark
@@ -180,6 +189,8 @@ public static final class Builder {
 
 		private boolean keepSeparator = KEEP_SEPARATOR;
 
+		private List<Character> punctuations = DEFAULT_PUNCTUATIONS;
+
 		private Builder() {
 		}
 
@@ -208,9 +219,18 @@ public Builder withKeepSeparator(boolean keepSeparator) {
 			return this;
 		}
 
+		public Builder withPunctuations(char... punctuations) {
+			List<Character> list = new ArrayList<>();
+			for (char punctuation : punctuations) {
+				list.add(punctuation);
+			}
+			this.punctuations = Collections.unmodifiableList(list);
+			return this;
+		}
+
 		public TokenTextSplitter build() {
 			return new TokenTextSplitter(this.chunkSize, this.minChunkSizeChars, this.minChunkLengthToEmbed,
-					this.maxNumChunks, this.keepSeparator);
+					this.maxNumChunks, this.keepSeparator, this.punctuations);
 		}
 
 	}

spring-ai-commons/src/test/java/org/springframework/ai/transformer/splitter/TokenTextSplitterTest.java

@@ -165,4 +165,26 @@ public void testLargeTextStillSplitsAtPunctuation() {
 		assertThat(splitted.get(0).getText()).endsWith(".");
 	}
 
+	@Test
+	public void testLargeTextStillSplitsAtChinesePunctuation() {
+		// Verify that punctuation-based splitting still works when text exceeds chunk
+		// size
+		TokenTextSplitter splitter = TokenTextSplitter.builder()
+			.withKeepSeparator(true)
+			.withChunkSize(15)
+			.withMinChunkSizeChars(10)
+			.build();
+
+		// This text has multiple sentences and will exceed 15 tokens
+		Document testDoc = new Document(
+				"This is the first sentence with enough words。 This is the second sentence。 And this is the third sentence。");
+		List<Document> splitted = splitter.split(testDoc);
+
+		// Should split into multiple chunks at punctuation marks
+		assertThat(splitted.size()).isGreaterThan(1);
+
+		// Verify first chunk ends with punctuation
+		assertThat(splitted.get(0).getText()).endsWith("。");
+	}
+
 }