Java通过导出超大Excel文件解决内存溢出问题

前言

将业务数据导出到Excel表中，导出任务数据量较大时，导出的项目就会内存溢出，本文通过Java操作Poi的SXSSFWorkbook类进行导出，解决内存溢出问题。

1.采用Poi中的SXSSFWorkbook

在实现excel导出时，在数据量过大的情况下，总是容易发生内存溢出的情况。可以使用POI提供的 SXSSFWorkbook 类来避免内存溢出。

2.maven中引入Poi

		<!-- poi start -->
		<dependency>
			<groupId>org.apache.poi</groupId>
			<artifactId>poi</artifactId>
			<version>4.1.2</version>
		</dependency>
		<dependency>
			<groupId>org.apache.poi</groupId>
			<artifactId>poi-ooxml</artifactId>
			<version>4.1.2</version>
		</dependency>
		<dependency>
			<groupId>org.apache.poi</groupId>
			<artifactId>poi-ooxml-schemas</artifactId>
			<version>4.1.2</version>
		</dependency>
		<!-- poi end -->

3.测试过程

先使用普通的写法测试(XSSFWorkbook)，编写writeNormalExcelTest测试方法，写入的行数太多时，会报内存溢出（在设置-server -Xmx64m -Xms64m -Xmn32m的情况下）。

接着编写SXSSFWorkbook操作excel的测试，测试方法writeHugeExcelTest（同样在设置-server -Xmx64m -Xms64m -Xmn32m的情况下），结果证明无内存溢出，能完好的导出1000000行测试数据，整个Java类代码如下:

4.单元测试Java代码

package cn.gzsendi.exceltest;

import java.io.FileOutputStream;
import java.io.IOException;

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.streaming.SXSSFWorkbook;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;
import org.junit.Test;

public class HugeExcelExportTest {
	
	private int totalRowNumber = 1000000; //写入的excel数据行数
	private int totalCellNumber = 40; //excel每行共40列
	
	//普通的写入excel的方法，会消耗内存，写入的行数太大时，会报内存溢出
	@Test
	public void writeNormalExcelTest(){
	
	   Workbook wb = null;
	   FileOutputStream out = null;
		
	   try {

		   long startTime = System.currentTimeMillis();
	        
	       wb = new XSSFWorkbook();
	       Sheet sheet = wb.createSheet("Sheet 1");
	        
	       //定义Row和Cell变量, Rows从0开始.
	       Row row;
	       Cell cell;
	        
	       for (int rowNumber = 0; rowNumber < totalRowNumber; rowNumber++) {
	    	   row = sheet.createRow(rowNumber);
	           for (int cellNumber = 0; cellNumber < totalCellNumber; cellNumber++) {
	        	   cell = row.createCell(cellNumber);
	               cell.setCellValue(Math.random()); //写入一个随机数
	           }
	            
	           //打印测试，
	           if(rowNumber % 10000 ==0) {
	        	   System.out.println(rowNumber);
	           }
	       }
	
	       //Write excel to a file
	       out = new FileOutputStream("d:\\temp\\normalExcel_" + totalRowNumber + ".xlsx");
	       wb.write(out);
	       long endTime = System.currentTimeMillis();
	        
	       System.out.println("process " + totalRowNumber + " spent time:" + (endTime - startTime) + " ms.");
	
	    } catch (Exception e) {
	    	
	       e.printStackTrace();
	        
	    } finally {
	    	
	    	
	    	try {
				if(out != null) out.close();
			} catch (IOException e) {
				e.printStackTrace();
			}
	    	
		    try {
		    	if(wb != null) wb.close();
			} catch (IOException e) {
				e.printStackTrace();
			}
	    	
	    }
		
	}
	
	//结合临时文件压缩等写入excel，默认超过100行就写到临时文件，不会报内存溢出
	@Test
	public void writeHugeExcelTest(){

      SXSSFWorkbook wb = null;
      FileOutputStream out = null;
      
      try {
      	
      	long startTime = System.currentTimeMillis();
      	
          wb = new SXSSFWorkbook();//默认100行，超100行将写入临时文件
          wb.setCompressTempFiles(false); //是否压缩临时文件，否则写入速度更快，但更占磁盘，但程序最后是会将临时文件删掉的
          Sheet sheet = wb.createSheet("Sheet 1");
          
          //定义Row和Cell变量, Rows从0开始.
	        Row row;
	        Cell cell;
	        
	        for (int rowNumber = 0; rowNumber < totalRowNumber; rowNumber++) {
	        	
	        	row = sheet.createRow(rowNumber);
	        	for (int cellNumber = 0; cellNumber < totalCellNumber; cellNumber++) {
	                cell = row.createCell(cellNumber);
	                cell.setCellValue(Math.random()); //写入一个随机数
	            }
	        	
	        	
	        	//打印测试，
	            if(rowNumber % 10000 ==0) {
	            	System.out.println(rowNumber);
	            }
	        	
	        }
          
	        //Write excel to a file
	        out = new FileOutputStream("d:\\temp\\hugeExcel_" + totalRowNumber + ".xlsx");
	        wb.write(out);

	        long endTime = System.currentTimeMillis();
	        
	        System.out.println("process " + totalRowNumber + " spent time:" + (endTime - startTime) + " ms.");
          
      } catch (Exception ex) {
      	
          ex.printStackTrace();
          
      } finally {
      	
          if (wb != null) {
          	wb.dispose();// 删除临时文件，很重要，否则磁盘可能会被写满
          }
          
          try {
				if(out != null) out.close();
			} catch (IOException e) {
				e.printStackTrace();
			}
	    	
		    try {
		    	if(wb != null) wb.close();
			} catch (IOException e) {
				e.printStackTrace();
			}
		    
      }
		
	}

}