[BUG] Introduce parser supplier support in FileSystemDocumentLoader (#…

…1031)

## Issue
#1026


## General checklist
<!-- Please double-check the following points and mark them like this:
[X] -->
- [X] There are no breaking changes
- [X] I have added unit and integration tests for my change
- [X] I have manually run all the unit and integration tests in the
module I have added/changed, and they are all green
- [X] I have manually run all the unit and integration tests in the
[core](https://github.com/langchain4j/langchain4j/tree/main/langchain4j-core)
and
[main](https://github.com/langchain4j/langchain4j/tree/main/langchain4j)
modules, and they are all green
- [X] I have added/updated the
[documentation](https://github.com/langchain4j/langchain4j/tree/main/docs/docs)
- [ ] I have added an example in the [examples
repo](https://github.com/langchain4j/langchain4j-examples) (only for
"big" features)

document-parsers/langchain4j-document-parser-apache-tika/src/main/java/dev/langchain4j/data/document/parser/apache/tika/ApacheTikaDocumentParser.java

@@ -1,7 +1,7 @@
 package dev.langchain4j.data.document.parser.apache.tika;
 
-import dev.langchain4j.data.document.Document;
 import dev.langchain4j.data.document.BlankDocumentException;
+import dev.langchain4j.data.document.Document;
 import dev.langchain4j.data.document.DocumentParser;
 import org.apache.tika.exception.ZeroByteFileException;
 import org.apache.tika.metadata.Metadata;
@@ -12,6 +12,7 @@
 import org.xml.sax.ContentHandler;
 
 import java.io.InputStream;
+import java.util.function.Supplier;
 
 import static dev.langchain4j.internal.Utils.getOrDefault;
 import static dev.langchain4j.internal.Utils.isNullOrBlank;
@@ -25,19 +26,23 @@
 public class ApacheTikaDocumentParser implements DocumentParser {
 
     private static final int NO_WRITE_LIMIT = -1;
+    public static final Supplier<Parser> DEFAULT_PARSER_SUPPLIER = AutoDetectParser::new;
+    public static final Supplier<Metadata> DEFAULT_METADATA_SUPPLIER = Metadata::new;
+    public static final Supplier<ParseContext> DEFAULT_PARSE_CONTEXT_SUPPLIER = ParseContext::new;
+    public static final Supplier<ContentHandler> DEFAULT_CONTENT_HANDLER_SUPPLIER = () -> new BodyContentHandler(NO_WRITE_LIMIT);
 
-    private final Parser parser;
-    private final ContentHandler contentHandler;
-    private final Metadata metadata;
-    private final ParseContext parseContext;
+    private final Supplier<Parser> parserSupplier;
+    private final Supplier<ContentHandler> contentHandlerSupplier;
+    private final Supplier<Metadata> metadataSupplier;
+    private final Supplier<ParseContext> parseContextSupplier;
 
     /**
      * Creates an instance of an {@code ApacheTikaDocumentParser} with the default Tika components.
      * It uses {@link AutoDetectParser}, {@link BodyContentHandler} without write limit,
      * empty {@link Metadata} and empty {@link ParseContext}.
      */
     public ApacheTikaDocumentParser() {
-        this(null, null, null, null);
+        this((Supplier<Parser>) null, null, null, null);
     }
 
     /**
@@ -48,22 +53,50 @@ public ApacheTikaDocumentParser() {
      * @param contentHandler Tika content handler. Default: {@link BodyContentHandler} without write limit
      * @param metadata       Tika metadata. Default: empty {@link Metadata}
      * @param parseContext   Tika parse context. Default: empty {@link ParseContext}
+     * @deprecated Use the constructor with suppliers for Tika components if you intend to use this parser for multiple files.
      */
+    @Deprecated
     public ApacheTikaDocumentParser(Parser parser,
                                     ContentHandler contentHandler,
                                     Metadata metadata,
                                     ParseContext parseContext) {
-        this.parser = getOrDefault(parser, AutoDetectParser::new);
-        this.contentHandler = getOrDefault(contentHandler, () -> new BodyContentHandler(NO_WRITE_LIMIT));
-        this.metadata = getOrDefault(metadata, Metadata::new);
-        this.parseContext = getOrDefault(parseContext, ParseContext::new);
+        this(
+                () -> getOrDefault(parser, DEFAULT_PARSER_SUPPLIER),
+                () -> getOrDefault(contentHandler, DEFAULT_CONTENT_HANDLER_SUPPLIER),
+                () -> getOrDefault(metadata, DEFAULT_METADATA_SUPPLIER),
+                () -> getOrDefault(parseContext, DEFAULT_PARSE_CONTEXT_SUPPLIER)
+        );
+    }
+
+    /**
+     * Creates an instance of an {@code ApacheTikaDocumentParser} with the provided suppliers for Tika components.
+     * If some of the suppliers are not provided ({@code null}), the defaults will be used.
+     *
+     * @param parserSupplier         Supplier for Tika parser to use. Default: {@link AutoDetectParser}
+     * @param contentHandlerSupplier Supplier for Tika content handler. Default: {@link BodyContentHandler} without write limit
+     * @param metadataSupplier       Supplier for Tika metadata. Default: empty {@link Metadata}
+     * @param parseContextSupplier   Supplier for Tika parse context. Default: empty {@link ParseContext}
+     */
+    public ApacheTikaDocumentParser(Supplier<Parser> parserSupplier,
+                                    Supplier<ContentHandler> contentHandlerSupplier,
+                                    Supplier<Metadata> metadataSupplier,
+                                    Supplier<ParseContext> parseContextSupplier) {
+        this.parserSupplier = getOrDefault(parserSupplier, () -> DEFAULT_PARSER_SUPPLIER);
+        this.contentHandlerSupplier = getOrDefault(contentHandlerSupplier, () -> DEFAULT_CONTENT_HANDLER_SUPPLIER);
+        this.metadataSupplier = getOrDefault(metadataSupplier, () -> DEFAULT_METADATA_SUPPLIER);
+        this.parseContextSupplier = getOrDefault(parseContextSupplier, () -> DEFAULT_PARSE_CONTEXT_SUPPLIER);
     }
 
     // TODO allow automatically extract metadata (e.g. creator, last-author, created/modified timestamp, etc)
 
     @Override
     public Document parse(InputStream inputStream) {
         try {
+            Parser parser = parserSupplier.get();
+            ContentHandler contentHandler = contentHandlerSupplier.get();
+            Metadata metadata = metadataSupplier.get();
+            ParseContext parseContext = parseContextSupplier.get();
+
             parser.parse(inputStream, contentHandler, metadata, parseContext);
             String text = contentHandler.toString();
 

document-parsers/langchain4j-document-parser-apache-tika/src/test/java/dev/langchain4j/data/document/parser/apache/tika/ApacheTikaDocumentParserTest.java

@@ -1,9 +1,10 @@
 package dev.langchain4j.data.document.parser.apache.tika;
 
-import dev.langchain4j.data.document.Document;
 import dev.langchain4j.data.document.BlankDocumentException;
+import dev.langchain4j.data.document.Document;
 import dev.langchain4j.data.document.DocumentParser;
 import org.apache.tika.parser.AutoDetectParser;
+import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.ValueSource;
 
@@ -40,7 +41,7 @@ void should_parse_doc_ppt_and_pdf_files(String fileName) {
     })
     void should_parse_xls_files(String fileName) {
 
-        DocumentParser parser = new ApacheTikaDocumentParser(new AutoDetectParser(), null, null, null);
+        DocumentParser parser = new ApacheTikaDocumentParser(AutoDetectParser::new, null, null, null);
         InputStream inputStream = getClass().getClassLoader().getResourceAsStream(fileName);
 
         Document document = parser.parse(inputStream);
@@ -50,6 +51,24 @@ void should_parse_xls_files(String fileName) {
         assertThat(document.metadata().asMap()).isEmpty();
     }
 
+    @Test
+    void should_parse_files_stateless() {
+
+        DocumentParser parser = new ApacheTikaDocumentParser();
+        InputStream inputStream1 = getClass().getClassLoader().getResourceAsStream("test-file.xls");
+        InputStream inputStream2 = getClass().getClassLoader().getResourceAsStream("test-file.xls");
+
+        Document document1 = parser.parse(inputStream1);
+        Document document2 = parser.parse(inputStream2);
+
+        assertThat(document1.text())
+                .isEqualToIgnoringWhitespace("Sheet1\ntest content\nSheet2\ntest content");
+        assertThat(document2.text())
+                .isEqualToIgnoringWhitespace("Sheet1\ntest content\nSheet2\ntest content");
+        assertThat(document1.metadata().asMap()).isEmpty();
+        assertThat(document2.metadata().asMap()).isEmpty();
+    }
+
     @ParameterizedTest
     @ValueSource(strings = {
             "empty-file.txt",