Add streaming ItemReader for legacy .xls files

Signed-off-by: Kebba Manneh <kebbaman@gmail.com>

Author: kebbaman

spring-batch-excel/src/main/java/org/springframework/batch/extensions/excel/streaming/StreamingXlsItemReader.java

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+/*
+ * Copyright 2006-2026 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.batch.extensions.excel.streaming;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import org.apache.poi.hssf.record.BoundSheetRecord;
+import org.apache.poi.hssf.record.EOFRecord;
+import org.apache.poi.hssf.record.ExtendedFormatRecord;
+import org.apache.poi.hssf.record.FormatRecord;
+import org.apache.poi.hssf.record.Record;
+import org.apache.poi.hssf.record.RecordFactoryInputStream;
+import org.apache.poi.hssf.record.SSTRecord;
+import org.apache.poi.poifs.filesystem.DocumentInputStream;
+import org.apache.poi.poifs.filesystem.POIFSFileSystem;
+
+import org.springframework.batch.extensions.excel.AbstractExcelItemReader;
+import org.springframework.batch.extensions.excel.Sheet;
+import org.springframework.core.io.Resource;
+
+/**
+ * Low-memory streaming {@code ItemReader} for legacy binary {@code .xls} (BIFF8 / HSSF)
+ * workbooks. It mirrors {@link StreamingXlsxItemReader} but reads the OLE2
+ * {@code "Workbook"} stream record-by-record using Apache POI's pull primitive
+ * {@link RecordFactoryInputStream}, so rows are produced lazily with a bounded memory
+ * footprint instead of materialising the whole workbook object graph like the
+ * {@code PoiItemReader}.
+ * <p>
+ * The shared, immutable workbook globals (the {@link SSTRecord shared-string table} and
+ * the number/date format table) are read once when the file is opened and handed,
+ * read-only, to every {@link XlsSheet}. Each sheet then opens its own stream positioned
+ * at its {@code BOF} offset, matching the way {@code StreamingXlsxItemReader} gives every
+ * sheet its own {@code InputStream}.
+ * <p>
+ * Encrypted {@code .xls} files are not supported by this reader (consistent with
+ * {@code StreamingXlsxItemReader}); a configured password is ignored.
+ *
+ * @param <T> the type
+ * @author Kebba Manneh
+ * @since 0.3.0
+ */
+public class StreamingXlsItemReader<T> extends AbstractExcelItemReader<T> {
+
+	/**
+	 * Candidate names of the workbook stream inside the OLE2 container, newest first.
+	 */
+	private static final String[] WORKBOOK_ENTRY_NAMES = {"Workbook", "Book", "WORKBOOK", "BOOK", "workbook", "book"};
+
+	private final List<XlsSheet> sheets = new ArrayList<>();
+
+	private POIFSFileSystem poifs;
+
+	@Override
+	protected Sheet getSheet(int sheet) {
+		return this.sheets.get(sheet);
+	}
+
+	@Override
+	protected int getNumberOfSheets() {
+		return this.sheets.size();
+	}
+
+	@Override
+	protected void openExcelFile(Resource resource, String password) throws Exception {
+		this.poifs = resource.isFile() ? new POIFSFileSystem(resource.getFile())
+				: new POIFSFileSystem(resource.getInputStream());
+		String workbookEntry = resolveWorkbookEntry(this.poifs);
+		initSheets(workbookEntry);
+	}
+
+	// Read the globals substream once to capture the shared, immutable state (shared
+	// strings + format table + the bound sheets), then create one lazy XlsSheet per
+	// worksheet sharing that state.
+	private void initSheets(String workbookEntry) throws IOException {
+		SSTRecord sst = null;
+		List<ExtendedFormatRecord> extendedFormats = new ArrayList<>();
+		Map<Integer, String> formats = new HashMap<>();
+		List<BoundSheetRecord> boundSheets = new ArrayList<>();
+
+		try (DocumentInputStream dis = this.poifs.createDocumentInputStream(workbookEntry)) {
+			RecordFactoryInputStream rfis = new RecordFactoryInputStream(dis, false);
+			Record record;
+			while ((record = rfis.nextRecord()) != null) {
+				if (record instanceof EOFRecord) {
+					// End of the globals substream, everything shared has been read.
+					break;
+				}
+				else if (record instanceof SSTRecord sstRecord) {
+					sst = sstRecord;
+				}
+				else if (record instanceof ExtendedFormatRecord extendedFormat) {
+					extendedFormats.add(extendedFormat);
+				}
+				else if (record instanceof FormatRecord format) {
+					formats.put(format.getIndexCode(), format.getFormatString());
+				}
+				else if (record instanceof BoundSheetRecord boundSheet) {
+					boundSheets.add(boundSheet);
+				}
+			}
+		}
+
+		for (BoundSheetRecord boundSheet : BoundSheetRecord.orderByBofPosition(boundSheets)) {
+			this.sheets.add(new XlsSheet(boundSheet.getSheetname(), this.poifs, workbookEntry,
+					boundSheet.getPositionOfBof(), sst, extendedFormats, formats, getDataFormatter()));
+		}
+
+		if (this.logger.isTraceEnabled()) {
+			this.logger.trace("Prepared " + this.sheets.size() + " sheets.");
+		}
+	}
+
+	private static String resolveWorkbookEntry(POIFSFileSystem poifs) {
+		for (String name : WORKBOOK_ENTRY_NAMES) {
+			if (poifs.getRoot().hasEntry(name)) {
+				return name;
+			}
+		}
+		throw new IllegalStateException("Unable to locate a workbook stream in the OLE2 container.");
+	}
+
+	@Override
+	protected void doClose() throws Exception {
+		for (XlsSheet sheet : this.sheets) {
+			sheet.close();
+		}
+		this.sheets.clear();
+
+		if (this.poifs != null) {
+			this.poifs.close();
+			this.poifs = null;
+		}
+		super.doClose();
+	}
+
+}