add DeferredGeneration sample

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1879493 13f79535-47bb-0310-9956-ffa450edef68

src/examples/src/org/apache/poi/xssf/streaming/examples/DeferredGeneration.java

@@ -0,0 +1,63 @@
+/*
+ *  ====================================================================
+ *    Licensed to the Apache Software Foundation (ASF) under one or more
+ *    contributor license agreements.  See the NOTICE file distributed with
+ *    this work for additional information regarding copyright ownership.
+ *    The ASF licenses this file to You 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
+ *
+ *        http://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.apache.poi.xssf.streaming.examples;
+
+import org.apache.poi.xssf.streaming.DeferredSXSSFSheet;
+import org.apache.poi.xssf.streaming.DeferredSXSSFWorkbook;
+import org.apache.poi.xssf.streaming.SXSSFCell;
+import org.apache.poi.xssf.streaming.SXSSFRow;
+
+import java.io.FileOutputStream;
+
+/**
+ * An example that outputs a simple generated workbook that uses deferred creation of the rows in the sheets.
+ * When the workbook is written to an output stream, the output data is streamed immediately.
+ * There is no collation of the data in temp files prior to writing the overall file.
+ * This depends on how efficient the row generating functions are.
+ */
+public final class DeferredGeneration {
+
+    private DeferredGeneration() {}
+
+    public static void main(String[] args) throws Exception {
+        String filename;
+        if(args.length == 0) {
+            filename = "deferred-generation.xlsx";
+        } else {
+            filename = args[0];
+        }
+        try (DeferredSXSSFWorkbook wb = new DeferredSXSSFWorkbook()){
+            for(int i = 0; i < 10; i++) {
+                DeferredSXSSFSheet sheet = wb.createSheet("Sheet" + i);
+                sheet.setRowGenerator((sh) -> {
+                    for (int r = 0; r < 1000; r++) {
+                        SXSSFRow row = sheet.createRow(r);
+                        for (int c = 0; c < 100; c++) {
+                            SXSSFCell cell = row.createCell(c);
+                            cell.setCellValue("abcd");
+                        }
+                    }
+                });
+            }
+            wb.write(new FileOutputStream(filename));
+            System.out.println("wrote " + filename);
+        }
+    }
+}