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this work for additional information regarding copyright ownership.
The ASF licenses this file to You under the Apache License, Version 2.0
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package org.apache.poi.xssf.usermodel.examples;

import java.io.FileOutputStream;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import org.apache.poi.ss.usermodel.*;
import org.apache.poi.xssf.usermodel.*;
import org.openxmlformats.schemas.spreadsheetml.x2006.main.impl.CTRowImpl;

/**
 * Shows how various alignment options work.
 *
 * Modified by Cristian Petrula, Romania on May 26, 2010
 * New method was added centerAcrossSelection to center a column content over 
 * one selection using ALIGN_CENTER_SELECTION
 * To create this method example was change for XSSF only and the previous
 * AligningCells.java example has been moved into the SS examples folder.
 */
public class AligningCells {

    public static void main(String[] args) throws IOException {
        XSSFWorkbook wb = new XSSFWorkbook();

        XSSFSheet sheet = wb.createSheet();
        XSSFRow row = sheet.createRow((short) 2);
        row.setHeightInPoints(30);
        for (int i = 0; i < 8; i++) {
            //column width is set in units of 1/256th of a character width
            sheet.setColumnWidth(i, 256 * 15);
        }

        createCell(wb, row, (short) 0, XSSFCellStyle.ALIGN_CENTER, XSSFCellStyle.VERTICAL_BOTTOM);
        createCell(wb, row, (short) 1, XSSFCellStyle.ALIGN_CENTER_SELECTION, XSSFCellStyle.VERTICAL_BOTTOM);
        createCell(wb, row, (short) 2, XSSFCellStyle.ALIGN_FILL, XSSFCellStyle.VERTICAL_CENTER);
        createCell(wb, row, (short) 3, XSSFCellStyle.ALIGN_GENERAL, XSSFCellStyle.VERTICAL_CENTER);
        createCell(wb, row, (short) 4, XSSFCellStyle.ALIGN_JUSTIFY, XSSFCellStyle.VERTICAL_JUSTIFY);
        createCell(wb, row, (short) 5, XSSFCellStyle.ALIGN_LEFT, XSSFCellStyle.VERTICAL_TOP);
        createCell(wb, row, (short) 6, XSSFCellStyle.ALIGN_RIGHT, XSSFCellStyle.VERTICAL_TOP);

        //center text over B4, C4, D4
        row = sheet.createRow((short) 3);
        centerAcrossSelection(wb, row, (short) 1, (short) 3, XSSFCellStyle.VERTICAL_CENTER);

        // Write the output to a file
        FileOutputStream fileOut = new FileOutputStream("xssf-align.xlsx");
        wb.write(fileOut);
        fileOut.close();
    }

    /**
     * Creates a cell and aligns it a certain way.
     *
     * @param wb     the workbook
     * @param row    the row to create the cell in
     * @param column the column number to create the cell in
     * @param halign the horizontal alignment for the cell.
     */
    private static void createCell(XSSFWorkbook wb, XSSFRow row, short column,
            short halign, short valign) {
        XSSFCell cell = row.createCell(column);
        cell.setCellValue(new XSSFRichTextString("Align It"));
        CellStyle cellStyle = wb.createCellStyle();
        cellStyle.setAlignment(halign);
        cellStyle.setVerticalAlignment(valign);
        cell.setCellStyle(cellStyle);
    }

    /**
     * Center a text over multiple columns using ALIGN_CENTER_SELECTION
     *
     * @param wb the workbook
     * @param row the row to create the cell in
     * @param start_column  the column number to create the cell in and where the selection starts
     * @param end_column    the column number where the selection ends
     * @param valign the horizontal alignment for the cell.
     *
     * @author Cristian Petrula, Romania
     */
    private static void centerAcrossSelection(XSSFWorkbook wb, XSSFRow row,
            short start_column, short end_column, short valign) {

        // Create cell style with ALIGN_CENTER_SELECTION
        XSSFCellStyle cellStyle = wb.createCellStyle();
        cellStyle.setAlignment(XSSFCellStyle.ALIGN_CENTER_SELECTION);
        cellStyle.setVerticalAlignment(valign);

        // Create cells over the selected area
        for (int i = start_column; i <= end_column; i++) {
            XSSFCell cell = row.createCell(i);
            cell.setCellStyle(cellStyle);
        }

        // Set value to the first cell
        XSSFCell cell = row.getCell(start_column);
        cell.setCellValue(new XSSFRichTextString("Align It"));

        // Make the selection
        CTRowImpl ctRow = (CTRowImpl) row.getCTRow();

        // Add object with format start_coll:end_coll. For example 1:3 will span from
        // cell 1 to cell 3, where the column index starts with 0
        //
        // You can add multiple spans for one row
        Object span = start_column + ":" + end_column;

        List<Object> spanList = new ArrayList<Object>();
        spanList.add(span);

        //add spns to the row
        ctRow.setSpans(spanList);
    }
}
