http://poi.apache.org/: Apache POI - Java API To Access Microsoft Format Files (Apache Software Foundation) 
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package org.apache.poi.xssf.model;

import static org.apache.poi.ooxml.POIXMLTypeLoader.DEFAULT_XML_OPTIONS;
import static org.apache.poi.xssf.usermodel.XSSFRelation.NS_SPREADSHEETML;

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

import org.apache.poi.ooxml.POIXMLDocumentPart;
import org.apache.poi.openxml4j.opc.PackagePart;
import org.apache.poi.ss.usermodel.RichTextString;
import org.apache.poi.util.Removal;
import org.apache.poi.xssf.usermodel.XSSFRichTextString;
import org.apache.xmlbeans.XmlException;
import org.apache.xmlbeans.XmlOptions;
import org.openxmlformats.schemas.spreadsheetml.x2006.main.CTRst;
import org.openxmlformats.schemas.spreadsheetml.x2006.main.CTSst;
import org.openxmlformats.schemas.spreadsheetml.x2006.main.SstDocument;


Table of strings shared across all sheets in a workbook.


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.




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.




The shared string table contains all the necessary information for displaying the string: the text, formatting
properties, and phonetic properties (for East Asian languages).



/**
 * 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>
 */
public class SharedStringsTable extends POIXMLDocumentPart implements SharedStrings, Closeable {

    
 Array of individual string items in the Shared String table.

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

    
 Maps strings and their indexes in the strings arrays

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

    
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.

/**
     * 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.
     */
    protected 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.

/**
     * 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.
     */
    protected int uniqueCount;

    private SstDocument _sstDoc;

    private static final XmlOptions options = new XmlOptions();
    static {
        options.put( XmlOptions.SAVE_INNER );
        options.put( XmlOptions.SAVE_AGGRESSIVE_NAMESPACES );
        options.put( XmlOptions.SAVE_USE_DEFAULT_NAMESPACE );
        options.setSaveImplicitNamespaces(Collections.singletonMap("", NS_SPREADSHEETML));
    }

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

    
Since:POI 3.14-Beta1
/**
     * @since POI 3.14-Beta1
     */
    public SharedStringsTable(PackagePart part) throws IOException {
        super(part);
        readFrom(part.getInputStream());
    }

    
Read this shared strings table from an XML file.

Params:
  • is – The input stream containing the XML document.
Throws:
/**
     * 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, DEFAULT_XML_OPTIONS);
            CTSst sst = _sstDoc.getSst();
            count = (int)sst.getCount();
            uniqueCount = (int)sst.getUniqueCount();
            //noinspection deprecation
            for (CTRst st : sst.getSiArray()) {
                stmap.put(xmlText(st), cnt);
                strings.add(st);
                cnt++;
            }
        } catch (XmlException e) {
            throw new IOException("unable to parse shared strings table", e);
        }
    }

    protected String xmlText(CTRst st) {
        return st.xmlText(options);
    }

    
Return a string item by index

Params:
  • idx – index of item to return.
Returns:the item at the specified position in this Shared String table.
Deprecated:use getItemAt(int idx) instead
/**
     * 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.
     * @deprecated use <code>getItemAt(int idx)</code> instead
     */
    @Removal(version = "4.2")
    public CTRst getEntryAt(int idx) {
        return strings.get(idx);
    }

    
Return a string item by index

Params:
  • idx – index of item to return.
Returns:the item at the specified position in this Shared String table.
/**
     * 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.
     */
    @Override
    public RichTextString getItemAt(int idx) {
        return new XSSFRichTextString(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.

Returns:the total count of strings in the workbook
/**
     * 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
     */
    @Override
    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.

Returns:the total count of unique strings in the workbook
/**
     * 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
     */
    @Override
    public int getUniqueCount(){
        return uniqueCount;
    }

    
Add an entry to this Shared String table (a new value is appended to the end).


If the Shared String table already contains this CTRst bean, its index is returned.
Otherwise a new entry is aded.



Params:
  • st – the entry to add
Returns:index the index of added entry
Deprecated:use addSharedStringItem(RichTextString string) instead
/**
     * Add an entry to this Shared String table (a new value is appended 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
     * @deprecated use <code>addSharedStringItem(RichTextString string)</code> instead
     */
    @Removal(version = "4.2") //make private in 4.2
    public int addEntry(CTRst st) {
        String s = xmlText(st);
        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;
    }

    
Add an entry to this Shared String table (a new value is appended to the end).


If the Shared String table already contains this string entry, its index is returned.
Otherwise a new entry is added.



Params:
  • string – the entry to add
Since:POI 4.0.0
Returns:index the index of added entry
/**
     * Add an entry to this Shared String table (a new value is appended to the end).
     *
     * <p>
     * If the Shared String table already contains this string entry, its index is returned.
     * Otherwise a new entry is added.
     * </p>
     *
     * @param string the entry to add
     * @since POI 4.0.0
     * @return index the index of added entry
     */
    public int addSharedStringItem(RichTextString string) {
        if(!(string instanceof XSSFRichTextString)){
            throw new IllegalArgumentException("Only XSSFRichTextString argument is supported");
        }
        return addEntry(((XSSFRichTextString) string).getCTRst());
    }

    
Provide low-level access to the underlying array of CTRst beans

Returns:array of CTRst beans
Deprecated:use getSharedStringItems instead
/**
     * Provide low-level access to the underlying array of CTRst beans
     *
     * @return array of CTRst beans
     * @deprecated use <code>getSharedStringItems</code> instead
     */
    @Removal(version = "4.2")
    public List<CTRst> getItems() {
        return Collections.unmodifiableList(strings);
    }

    
Provide access to the strings in the SharedStringsTable

Returns:list of shared string instances
/**
     * Provide access to the strings in the SharedStringsTable
     *
     * @return list of shared string instances
     */
    public List<RichTextString> getSharedStringItems() {
        ArrayList<RichTextString> items = new ArrayList<>();
        for (CTRst rst : strings) {
            items.add(new XSSFRichTextString(rst));
        }
        return Collections.unmodifiableList(items);
    }

    
Write this table out as XML.

Params:
  • out – The stream to write to.
Throws:
/**
     * 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 xmlOptions = new XmlOptions(DEFAULT_XML_OPTIONS);
        // the following two lines turn off writing CDATA
        // see Bugzilla 48936
        xmlOptions.setSaveCDataLengthThreshold(1000000);
        xmlOptions.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, xmlOptions);
    }

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

    
Close any open resources, like temp files. This method is called by XSSFWorkbook#close().


    This implementation is empty but subclasses may need to implement some logic.



Throws:
Since:4.0.0
/**
     * Close any open resources, like temp files. This method is called by <code>XSSFWorkbook#close()</code>.
     * <p>
     *     This implementation is empty but subclasses may need to implement some logic.
     * </p>
     *
     * @since 4.0.0
     * @throws IOException if an error occurs while closing.
     */
    @Override
    public void close() throws IOException {}
}