poi/src/ooxml/java/org/apache/poi/xssf/model/SharedStringsTable.java

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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.model;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.apache.xmlbeans.XmlException;
import org.apache.xmlbeans.XmlOptions;
import org.apache.poi.POIXMLDocumentPart;
import org.openxmlformats.schemas.spreadsheetml.x2006.main.CTRst;
import org.openxmlformats.schemas.spreadsheetml.x2006.main.CTSst;
import org.openxmlformats.schemas.spreadsheetml.x2006.main.SstDocument;
import org.apache.poi.openxml4j.opc.PackagePart;
import org.apache.poi.openxml4j.opc.PackageRelationship;


/**
 * Table of strings shared across all sheets in a workbook.
 * <p>
 * A workbook may contain thousands of cells containing string (non-numeric) data. Furthermore this data is very
 * likely to be repeated across many rows or columns. The goal of implementing a single string table that is shared
 * across the workbook is to improve performance in opening and saving the file by only reading and writing the
 * repetitive information once.
 * </p>
 * <p>
 * Consider for example a workbook summarizing information for cities within various countries. There may be a
 * column for the name of the country, a column for the name of each city in that country, and a column
 * containing the data for each city. In this case the country name is repetitive, being duplicated in many cells.
 * In many cases the repetition is extensive, and a tremendous savings is realized by making use of a shared string
 * table when saving the workbook. When displaying text in the spreadsheet, the cell table will just contain an
 * index into the string table as the value of a cell, instead of the full string.
 * </p>
 * <p>
 * The shared string table contains all the necessary information for displaying the string: the text, formatting
 * properties, and phonetic properties (for East Asian languages).
 * </p>
 *
 * @author Nick Birch
 * @author Yegor Kozlov
 */
public class SharedStringsTable extends POIXMLDocumentPart {

    /**
     *  Array of individual string items in the Shared String table.
     */
    private final List<CTRst> strings = new ArrayList<CTRst>();

    /**
     *  Maps strings and their indexes in the <code>strings</code> arrays
     */
    private final Map<String, Integer> stmap = new HashMap<String, Integer>();

    /**
     * An integer representing the total count of strings in the workbook. This count does not
     * include any numbers, it counts only the total of text strings in the workbook.
     */
    private int count;

    /**
     * An integer representing the total count of unique strings in the Shared String Table.
     * A string is unique even if it is a copy of another string, but has different formatting applied
     * at the character level.
     */
    private int uniqueCount;

    public SstDocument _sstDoc;

    public SharedStringsTable() {
        super();
        _sstDoc = SstDocument.Factory.newInstance();
        _sstDoc.addNewSst();
    }

    public SharedStringsTable(PackagePart part, PackageRelationship rel) throws IOException {
        super(part, rel);
        readFrom(part.getInputStream());
    }

    /**
     * Read this shared strings table from an XML file.
     * 
     * @param is The input stream containing the XML document.
     * @throws IOException if an error occurs while reading.
     */
    public void readFrom(InputStream is) throws IOException {
        try {
            int cnt = 0;
            _sstDoc = SstDocument.Factory.parse(is);
            CTSst sst = _sstDoc.getSst();
            count = (int)sst.getCount();
            uniqueCount = (int)sst.getUniqueCount();
            for (CTRst st : sst.getSiArray()) {
                stmap.put(st.toString(), cnt);
                strings.add(st);
                cnt++;
            }
        } catch (XmlException e) {
            throw new IOException(e.getLocalizedMessage());
        }
    }

    /**
     * Return a string item by index
     *
     * @param idx index of item to return.
     * @return the item at the specified position in this Shared String table.
     */
    public CTRst getEntryAt(int idx) {
        return strings.get(idx);
    }

    /**
     * Return an integer representing the total count of strings in the workbook. This count does not
     * include any numbers, it counts only the total of text strings in the workbook.
     *
     * @return the total count of strings in the workbook
     */
    public int getCount(){
        return count;
    }

    /**
     * Returns an integer representing the total count of unique strings in the Shared String Table.
     * A string is unique even if it is a copy of another string, but has different formatting applied
     * at the character level.
     *
     * @return the total count of unique strings in the workbook
     */
    public int getUniqueCount(){
        return uniqueCount;
    }

    /**
     * Add an entry to this Shared String table (a new value is appened to the end).
     *
     * <p>
     * If the Shared String table already contains this <code>CTRst</code> bean, its index is returned.
     * Otherwise a new entry is aded.
     * </p>
     *
     * @param st the entry to add
     * @return index the index of added entry
     */
    public int addEntry(CTRst st) {
        String s = st.toString();
        count++;
        if (stmap.containsKey(s)) {
            return stmap.get(s);
        }

        uniqueCount++;
        //create a CTRst bean attached to this SstDocument and copy the argument CTRst into it
        CTRst newSt = _sstDoc.getSst().addNewSi();
        newSt.set(st);
        int idx = strings.size();
        stmap.put(s, idx);
        strings.add(newSt);
        return idx;
    }
    /**
     * Provide low-level access to the underlying array of CTRst beans
     *
     * @return array of CTRst beans
     */
    public List<CTRst> getItems() {
        return strings;
    }

    /**
     * Write this table out as XML.
     * 
     * @param out The stream to write to.
     * @throws IOException if an error occurs while writing.
     */
    public void writeTo(OutputStream out) throws IOException {
        XmlOptions options = new XmlOptions(DEFAULT_XML_OPTIONS);
        // the following two lines turn off writing CDATA
        // see Bugzilla 48936
        options.setSaveCDataLengthThreshold(1000000);
        options.setSaveCDataEntityCountThreshold(-1);

        //re-create the sst table every time saving a workbook
        CTSst sst = _sstDoc.getSst();
        sst.setCount(count);
        sst.setUniqueCount(uniqueCount);

        _sstDoc.save(out, options);
    }

    @Override
    protected void commit() throws IOException {
        PackagePart part = getPackagePart();
        OutputStream out = part.getOutputStream();
        writeTo(out);
        out.close();
    }
}