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java poi 操作excel实例教程
2018-04-16 10:37:45      个评论    来源:崔世勋CSDN博客  
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HSSF是POI对Excel-97(-2007)文件操作的纯Java实现。XSSF是POI对Excel 2007 OOXML(.xlsx)文件操作的纯Java实现。从POI 3.8版本开始,提供了一种基于XSSF的低内存占用的API(SXSSF)。

POI提供两种读写API模型:事件模型和用户模型。事件模型是基于流的方式实现,使用sax(simple api for XML)模型进行内容解析,对CPU和内存的消耗小,但无法进行写操作。用户模型基于内存树的方式实现,使用DOM进行excel的解析,对CPU和内存的消耗大,但能够以面向对象的方式进行操作,可读可写。

Event API (HSSF Only)

它可以以比较小的内存来读一个xls文件,为了使用这个API,你需要:

(1)创建一个org.apache.poi.hssf.eventmodel.HSSFRequest的实例

(2)实现org.apache.poi.hssf.eventmodel.HSSFListener接口的类。

(3)HSSFRequest.addListener(yourlistener,recordid)注册(2)中实现的类,recordid应该是org.apache.poi.hssf.record的属性。或者也可认使用HSSFRequest.addListerForAllRecords(yourlistener)。

(4)创建一个org.apache.poi.poifs.filesystem.FileSystem实例, 并把XLS文件通过输入流方式输入。

(5)可以把(4)中创建的实例通过HSSFEventFactory.processWorkbookEvents(request,Filesystem)方法或HSSFEventFactory.processEvents(request,inputstream)与绑定。

(6)这样listener就会调用processRecord(Record)方法,直到整个文件读完。

/**
 * This example shows how to use the event API for reading a file.
 */
public class EventExample
        implements HSSFListener
{
    private SSTRecord sstrec;

    /**
     * This method listens for incoming records and handles them as required.
     * @param record    The record that was found while reading.
     */
    public void processRecord(Record record)
    {
        switch (record.getSid())
        {
            // the BOFRecord can represent either the beginning of a sheet or the workbook
            case BOFRecord.sid:
                BOFRecord bof = (BOFRecord) record;
                if (bof.getType() == bof.TYPE_WORKBOOK)
                {
                    System.out.println("Encountered workbook");
                    // assigned to the class level member
                } else if (bof.getType() == bof.TYPE_WORKSHEET)
                {
                    System.out.println("Encountered sheet reference");
                }
                break;
            case BoundSheetRecord.sid:
                BoundSheetRecord bsr = (BoundSheetRecord) record;
                System.out.println("New sheet named: " + bsr.getSheetname());
                break;
            case RowRecord.sid:
                RowRecord rowrec = (RowRecord) record;
                System.out.println("Row found, first column at "
                        + rowrec.getFirstCol() + " last column at " + rowrec.getLastCol());
                break;
            case NumberRecord.sid:
                NumberRecord numrec = (NumberRecord) record;
                System.out.println("Cell found with value " + numrec.getValue()
                        + " at row " + numrec.getRow() + " and column " + numrec.getColumn());
                break;
                // SSTRecords store a array of unique strings used in Excel.
            case SSTRecord.sid:
                sstrec = (SSTRecord) record;
                for (int k = 0; k < sstrec.getNumUniqueStrings(); k++)
                {
                    System.out.println("String table value " + k + " = " + sstrec.getString(k));
                }
                break;
            case LabelSSTRecord.sid:
                LabelSSTRecord lrec = (LabelSSTRecord) record;
                System.out.println("String cell found with value "
                        + sstrec.getString(lrec.getSSTIndex()));
                break;
        }
    }

    /**
     * Read an excel file and spit out what we find.
     *
     * @param args      Expect one argument that is the file to read.
     * @throws IOException  When there is an error processing the file.
     */
    public static void main(String[] args) throws IOException
    {
        // create a new file input stream with the input file specified
        // at the command line
        FileInputStream fin = new FileInputStream(args[0]);
        // create a new org.apache.poi.poifs.filesystem.Filesystem
        POIFSFileSystem poifs = new POIFSFileSystem(fin);
        // get the Workbook (excel part) stream in a InputStream
        InputStream din = poifs.createDocumentInputStream("Workbook");
        // construct out HSSFRequest object
        HSSFRequest req = new HSSFRequest();
        // lazy listen for ALL records with the listener shown above
        req.addListenerForAllRecords(new EventExample());
        // create our event factory
        HSSFEventFactory factory = new HSSFEventFactory();
        // process our events based on the document input stream
        factory.processEvents(req, din);
        // once all the events are processed close our file input stream
        fin.close();
        // and our document input stream (don't want to leak these!)
        din.close();
        System.out.println("done.");
    }
}

Event API(XSSF和SAX)

使用较少的内存读取XLSX文件。

import java.io.InputStream;
import java.util.Iterator;

import org.apache.poi.xssf.eventusermodel.XSSFReader;
import org.apache.poi.xssf.model.SharedStringsTable;
import org.apache.poi.openxml4j.opc.OPCPackage;
import org.xml.sax.Attributes;
import org.xml.sax.ContentHandler;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import org.xml.sax.XMLReader;
import org.xml.sax.helpers.DefaultHandler;
import org.xml.sax.helpers.XMLReaderFactory;

public class ExampleEventUserModel {
	public void processOneSheet(String filename) throws Exception {
		OPCPackage pkg = OPCPackage.open(filename);
		XSSFReader r = new XSSFReader( pkg );
		SharedStringsTable sst = r.getSharedStringsTable();

		XMLReader parser = fetchSheetParser(sst);

		// To look up the Sheet Name / Sheet Order / rID,
		//  you need to process the core Workbook stream.
		// Normally it's of the form rId# or rSheet#
		InputStream sheet2 = r.getSheet("rId2");
		InputSource sheetSource = new InputSource(sheet2);
		parser.parse(sheetSource);
		sheet2.close();
	}

	public void processAllSheets(String filename) throws Exception {
		OPCPackage pkg = OPCPackage.open(filename);
		XSSFReader r = new XSSFReader( pkg );
		SharedStringsTable sst = r.getSharedStringsTable();
		
		XMLReader parser = fetchSheetParser(sst);

		Iterator sheets = r.getSheetsData();
		while(sheets.hasNext()) {
			System.out.println("Processing new sheet:\n");
			InputStream sheet = sheets.next();
			InputSource sheetSource = new InputSource(sheet);
			parser.parse(sheetSource);
			sheet.close();
			System.out.println("");
		}
	}

	public XMLReader fetchSheetParser(SharedStringsTable sst) throws SAXException {
		XMLReader parser =
			XMLReaderFactory.createXMLReader(
					"org.apache.xerces.parsers.SAXParser"
			);
		ContentHandler handler = new SheetHandler(sst);
		parser.setContentHandler(handler);
		return parser;
	}

	/** 
	 * See org.xml.sax.helpers.DefaultHandler javadocs 
	 */
	private static class SheetHandler extends DefaultHandler {
		private SharedStringsTable sst;
		private String lastContents;
		private boolean nextIsString;
		
		private SheetHandler(SharedStringsTable sst) {
			this.sst = sst;
		}
		
		public void startElement(String uri, String localName, String name,
				Attributes attributes) throws SAXException {
			// c => cell
			if(name.equals("c")) {
				// Print the cell reference
				System.out.print(attributes.getValue("r") + " - ");
				// Figure out if the value is an index in the SST
				String cellType = attributes.getValue("t");
				if(cellType != null && cellType.equals("s")) {
					nextIsString = true;
				} else {
					nextIsString = false;
				}
			}
			// Clear contents cache
			lastContents = "";
		}
		
		public void endElement(String uri, String localName, String name)
				throws SAXException {
			// Process the last contents as required.
			// Do now, as characters() may be called more than once
			if(nextIsString) {
				int idx = Integer.parseInt(lastContents);
				lastContents = new XSSFRichTextString(sst.getEntryAt(idx)).toString();
				nextIsString = false;
			}

			// v => contents of a cell
			// Output after we've seen the string contents
			if(name.equals("v")) {
				System.out.println(lastContents);
			}
		}

		public void characters(char[] ch, int start, int length)
				throws SAXException {
			lastContents += new String(ch, start, length);
		}
	}
	
	public static void main(String[] args) throws Exception {
		ExampleEventUserModel example = new ExampleEventUserModel();
		example.processOneSheet(args[0]);
		example.processAllSheets(args[0]);
	}
}

SXSSF

SXSSF位于org.apache.poi.xssf.streaming包下,用于spreadsheets比较大时,api和XSSF兼容。SXSSF通过一个滑动窗口来限制访问Row的数量从而达到低内存占用,不在窗口的rows不可再访问。

可以在创建SXSSFWorkbook(int windowSize)指定窗口大小,或者针对sheet设置窗口大小

SXSSFSheet#setRandomAccessWindowSize(int windowSize)

当通过createRow()创建一个新Row时,窗口中的行数已经超过了固定的大小,索引最小的会被flush。

默认的窗口大小是100,当窗口大小是-1时,表示窗口无限大。SXSSF会生成临时文件,所以必须通过dispose方法进行删除。

SXSSFWorkbook 默认使用inline strings而不是一个共享的string table,这样就不用在内存中保存数据,但这样可能会使产生的文档与客户端不兼容。如果开启String table可能会占用大量内存,这种权衡需要用户决定。

另外是否会消耗内存取决于你要使用的特性,比如:merged region , hyperlinks, comments等。

import junit.framework.Assert;
import org.apache.poi.ss.usermodel.Cell;
import org.apache.poi.ss.usermodel.Row;
import org.apache.poi.ss.usermodel.Sheet;
import org.apache.poi.ss.usermodel.Workbook;
import org.apache.poi.ss.util.CellReference;
import org.apache.poi.xssf.streaming.SXSSFWorkbook;

    public static void main(String[] args) throws Throwable {
        SXSSFWorkbook wb = new SXSSFWorkbook(100); // keep 100 rows in memory, exceeding rows will be flushed to disk
        Sheet sh = wb.createSheet();
        for(int rownum = 0; rownum < 1000; rownum++){
            Row row = sh.createRow(rownum);
            for(int cellnum = 0; cellnum < 10; cellnum++){
                Cell cell = row.createCell(cellnum);
                String address = new CellReference(cell).formatAsString();
                cell.setCellValue(address);
            }

        }

        // Rows with rownum < 900 are flushed and not accessible
        for(int rownum = 0; rownum < 900; rownum++){
          Assert.assertNull(sh.getRow(rownum));
        }

        // ther last 100 rows are still in memory
        for(int rownum = 900; rownum < 1000; rownum++){
            Assert.assertNotNull(sh.getRow(rownum));
        }
        
        FileOutputStream out = new FileOutputStream("/temp/sxssf.xlsx");
        wb.write(out);
        out.close();

        // dispose of temporary files backing this workbook on disk
        wb.dispose();
    }

SXSSF会把sheet数据放在临时(一个sheet一个临时文件),所以临时文件可能很大,例如一个20MB的csv数据,xml临时文件可能多在1G,所以如果临时文件的大小是一个问题,可以使SXSSF使用gzip压缩。

SXSSFWorkbook wb = new SXSSFWorkbook(); 
  wb.setCompressTempFiles(true); // temp files will be gzipped
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