关于Poi读取Excel引发内存溢出问题的解决方法

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前言

最近生产环境有个老项目一直内存报警，不时的还出现内存泄漏，导致需要重启服务器，已经严重影响正常服务了。

分析

1.dump内存文件

liunx使用如下命令：

./jmap -dump:format=b,file=heap.hprof pid

2.使用Eclipse Memory Analysis进行分析

异常如下：

at org.apache.poi.xssf.usermodel.XSSFRow.<init>(Lorg/openxmlformats/schemas/spreadsheetml/x2006/main/CTRow;Lorg/apache/poi/xssf/usermodel/XSSFSheet;)V (XSSFRow.java:68)
at org.apache.poi.xssf.usermodel.XSSFSheet.initRows(Lorg/openxmlformats/schemas/spreadsheetml/x2006/main/CTWorksheet;)V (XSSFSheet.java:157)
at org.apache.poi.xssf.usermodel.XSSFSheet.read(Ljava/io/InputStream;)V (XSSFSheet.java:132)
at org.apache.poi.xssf.usermodel.XSSFSheet.onDocumentRead()V (XSSFSheet.java:119)
at org.apache.poi.xssf.usermodel.XSSFWorkbook.onDocumentRead()V (XSSFWorkbook.java:222)
at org.apache.poi.POIXMLDocument.load(Lorg/apache/poi/POIXMLFactory;)V (POIXMLDocument.java:200)
at org.apache.poi.xssf.usermodel.XSSFWorkbook.<init>(Ljava/io/InputStream;)V (XSSFWorkbook.java:179)

POI在加载Excel引发了内存泄漏，中间创建了大量的对象，占用了大量的内存

3.查看上传的Excel大小

经查看发现很多Excel大小在9M的文件

4.查看代码POI读取Excel的方式

发现使用的是用户模式，这样会占用大量的内存；POI提供了2中读取Excel的模式，分别是：

用户模式：也就是poi下的usermodel有关包，它对用户友好，有统一的接口在ss包下，但是它是把整个文件读取到内存中的，
对于大量数据很容易内存溢出，所以只能用来处理相对较小量的数据；
事件模式：在poi下的eventusermodel包下，相对来说实现比较复杂，但是它处理速度快，占用内存少，可以用来处理海量的Excel数据。

经上面分析基本可以确定问题出在使用POI的用户模式去读取Excel大文件，导致内存泄漏。

本地重现

下面模拟一个600kb大小的Excel（test.xlsx），分别用两种模式读取，然后观察内存波动；

1.需要引入的库maven：

<dependencies>
 <dependency>
  <groupId>org.apache.poi</groupId>
  <artifactId>poi-ooxml</artifactId>
  <version>3.6</version>
 </dependency>
 <dependency>
  <groupId>com.syncthemall</groupId>
  <artifactId>boilerpipe</artifactId>
  <version>1.2.1</version>
 </dependency>
</dependencies>

2.用户模式代码如下：

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
 
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.xssf.usermodel.XSSFWorkbook;
 
public class UserModel {
 
 public static void main(String[] args) throws InterruptedException {
  try {
   Thread.sleep(5000);
   System.out.println("start read");
   for (int i = 0; i < 100; i++) {
    try {
     Workbook wb = null;
     File file = new File("D:/test.xlsx");
     InputStream fis = new FileInputStream(file);
     wb = new XSSFWorkbook(fis);
     Sheet sheet = wb.getSheetAt(0);
     for (Row row : sheet) {
      for (Cell cell : row) {
       System.out.println("row:" + row.getRowNum() + ",cell:" + cell.toString());
      }
     }
    } catch (IOException e) {
     e.printStackTrace();
    }
   }
   Thread.sleep(1000);
  } catch (Exception e) {
   e.printStackTrace();
  }
 }
}

3.事件模式代码如下：

import java.io.InputStream;
 
import org.apache.poi.openxml4j.opc.OPCPackage;
import org.apache.poi.xssf.eventusermodel.XSSFReader;
import org.apache.poi.xssf.model.SharedStringsTable;
import org.apache.poi.xssf.usermodel.XSSFRichTextString;
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 EventModel {
 
 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);
  InputStream sheet2 = r.getSheet("rId1");
  InputSource sheetSource = new InputSource(sheet2);
  parser.parse(sheetSource);
  sheet2.close();
 }
 
 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;
 }
 
 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 {
   if (name.equals("c")) {
    System.out.print(attributes.getValue("r") + " - ");
    String cellType = attributes.getValue("t");
    if (cellType != null && cellType.equals("s")) {
     nextIsString = true;
    } else {
     nextIsString = false;
    }
   }
   lastContents = "";
  }
 
  public void endElement(String uri, String localName, String name) throws SAXException {
   if (nextIsString) {
    int idx = Integer.parseInt(lastContents);
    lastContents = new XSSFRichTextString(sst.getEntryAt(idx)).toString();
    nextIsString = false;
   }
 
   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 {
  Thread.sleep(5000);
  System.out.println("start read");
  for (int i = 0; i < 100; i++) {
   EventModel example = new EventModel();
   example.processOneSheet("D:/test.xlsx");
   Thread.sleep(1000);
  }
 }
}

具体代码来源：http://poi.apache.org/spreadsheet/how-to.html#xssf_sax_api

4.设置VM arguments：-Xms100m -Xmx100m

UserModel运行结果直接报OutOfMemoryError，如下所示：

Exception in thread "main" java.lang.OutOfMemoryError: GC overhead limit exceeded
 at java.lang.String.substring(String.java:1877)
 at org.apache.poi.ss.util.CellReference.separateRefParts(CellReference.java:353)
 at org.apache.poi.ss.util.CellReference.<init>(CellReference.java:87)
 at org.apache.poi.xssf.usermodel.XSSFCell.<init>(XSSFCell.java:105)
 at org.apache.poi.xssf.usermodel.XSSFRow.<init>(XSSFRow.java:68)
 at org.apache.poi.xssf.usermodel.XSSFSheet.initRows(XSSFSheet.java:157)
 at org.apache.poi.xssf.usermodel.XSSFSheet.read(XSSFSheet.java:132)
 at org.apache.poi.xssf.usermodel.XSSFSheet.onDocumentRead(XSSFSheet.java:119)
 at org.apache.poi.xssf.usermodel.XSSFWorkbook.onDocumentRead(XSSFWorkbook.java:222)
 at org.apache.poi.POIXMLDocument.load(POIXMLDocument.java:200)
 at org.apache.poi.xssf.usermodel.XSSFWorkbook.<init>(XSSFWorkbook.java:179)
 at zh.excelTest.UserModel.main(UserModel.java:23)

EventModel可以正常运行，使用Java VisualVM监控结果如下：