说明：我的电脑 2.0CPU 2G内存 能够十秒钟导出 20W 条数据 ,12.8M的excel内容压缩后2.68M
我们知道在POI导出Excel时，数据量大了，很容易导致内存溢出。由于Excel 一个sheet允许的最大行数是65536这时我们想到分sheet进行导出；但是这种情况也不能解决内存溢出的问题。毕竟数据还是一次性在内存中进行保存的。这时我们想是不是可以导出多个excel呢？下面我就尝试着按照导出多个excel
首先：我们要确定数据量有多大，然后确定一个excel导出多少条数据，这样就可以确定导出的Excel的数量，于是我们就可以循环的导出excel并保存在任意的临时目录中。去这样如果内存不够的话虚拟机就会去进行回收已经保存的excel在内存中的空间。
假设我们我们已经成功的生成了多个excel，这时我们怎么把这N个excel文档传到客户端呢？其实一个一个的传也未尝不可，但是考虑那样对用户来说体验不够好，再次多个文件在网络上传输也比较慢。我们可以考虑对生成的几个文件进行压缩，然后传到客户端。
总结一下第一、分批次生成excel第二、压缩后到客户端
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下面我把我的一个小实例贴上供大家参考
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第一、Person.java 普通javabean
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package bean; /** * * @author QQ:三二8二4七6七六 * */ public class Person { private Integer id; private String name; private String address; private String tel; private Double money=0.0; public Double getMoney() { return money; } public void setMoney(Double money) { this.money = money; } public Person(Integer id, String name, String address, String tel,Double money) { super(); this.id = id; this.name = name; this.address = address; this.tel = tel; this.money=money; } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getAddress() { return address; } public void setAddress(String address) { this.address = address; } public String getTel() { return tel; } public void setTel(String tel) { this.tel = tel; } }
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第二、PersonService模拟业务逻辑循环生成100023个Person对象
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package service;
import java.util.ArrayList;
import java.util.List;
import bean.Person;
/**
*
* @author QQ:三二8二4七6七六
*
*/
public class PersonService {
public static List getPerson(){
List<Person> list =new ArrayList<Person>();
for(int i=0;i<100320;i++){
list.add(new Person(i,"zhangsan"+i,"北京"+i,"13214587632",123123.12+i));
}
return list;
}
}
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?第三、业务处理Servlet
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package servlet;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.poi.hssf.usermodel.HSSFWorkbook;
import org.apache.poi.hssf.util.CellRangeAddress;
import org.apache.poi.ss.usermodel.Cell;
import org.apache.poi.ss.usermodel.CellStyle;
import org.apache.poi.ss.usermodel.Row;
import org.apache.poi.ss.usermodel.Sheet;
import org.apache.poi.ss.usermodel.Workbook;
import bean.Person;
import service.PersonService;
/**
*
* @author QQ:三二8二4七6七六
*
*/
public class PersonServlet extends HttpServlet {
private String fileName;
public PersonServlet() {
super();
}
public void destroy() {
super.destroy(); // Just puts "destroy" string in log
// Put your code here
}
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// 文件名获取
Date date = new Date();
SimpleDateFormat format = new SimpleDateFormat("yyyyMMddHHmmss");
String f = "Person-" + format.format(date);
this.fileName = f;
setResponseHeader(response);
OutputStream out = null;
try {
out = response.getOutputStream();
List<Person> list = PersonService.getPerson();
toExcel(list,request,10000,f,out);
} catch (IOException e1) {
e1.printStackTrace();
} finally {
try {
out.flush();
out.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
/** 设置响应头 */
public void setResponseHeader(HttpServletResponse response) {
try {
response.setContentType("application/octet-stream;charset=UTF-8");
response.setHeader("Content-Disposition", "attachment;filename="
+ java.net.URLEncoder.encode(this.fileName, "UTF-8")
+ ".zip");
response.addHeader("Pargam", "no-cache");
response.addHeader("Cache-Control", "no-cache");
} catch (Exception ex) {
ex.printStackTrace();
}
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
public void init() throws ServletException {
// Put your code here
}
public void toExcel(List<Person> list, HttpServletRequest request,
int length, String f, OutputStream out) throws IOException {
List<String> fileNames = new ArrayList();// 用于存放生成的文件名称s
File zip = new File(request.getRealPath("/files") + "/" + f + ".zip");// 压缩文件
// 生成excel
for (int j = 0, n = list.size() / length + 1; j < n; j++) {
Workbook book = new HSSFWorkbook();
Sheet sheet = book.createSheet("person");
double d = 0;// 用来统计
String file = request.getRealPath("/files") + "/" + f + "-" + j
+ ".xls";
fileNames.add(file);
FileOutputStream o = null;
try {
o = new FileOutputStream(file);
// sheet.addMergedRegion(new
// CellRangeAddress(list.size()+1,0,list.size()+5,6));
Row row = sheet.createRow(0);
row.createCell(0).setCellValue("ID");
row.createCell(1).setCellValue("NAME");
row.createCell(2).setCellValue("ADDRESS");
row.createCell(3).setCellValue("TEL");
row.createCell(4).setCellValue("Money");
int m = 1;
for (int i = 1, min = (list.size() - j * length + 1) > (length + 1) ? (length + 1)
: (list.size() - j * length + 1); i < min; i++) {
m++;
Person user = list.get(length * (j) + i - 1);
Double dd = user.getMoney();
if (dd == null) {
dd = 0.0;
}
d += dd;
row = sheet.createRow(i);
row.createCell(0).setCellValue(user.getId());
row.createCell(1).setCellValue(user.getName());
row.createCell(2).setCellValue(user.getAddress());
row.createCell(3).setCellValue(user.getTel());
row.createCell(4).setCellValue(dd);
}
CellStyle cellStyle2 = book.createCellStyle();
cellStyle2.setAlignment(CellStyle.ALIGN_CENTER);
row = sheet.createRow(m);
Cell cell0 = row.createCell(0);
cell0.setCellValue("Total");
cell0.setCellStyle(cellStyle2);
Cell cell4 = row.createCell(4);
cell4.setCellValue(d);
cell4.setCellStyle(cellStyle2);
sheet.addMergedRegion(new CellRangeAddress(m, m, 0, 3));
} catch (Exception e) {
e.printStackTrace();
}
try {
book.write(o);
} catch (Exception ex) {
ex.printStackTrace();
} finally {
o.flush();
o.close();
}
}
File srcfile[] = new File[fileNames.size()];
for (int i = 0, n = fileNames.size(); i < n; i++) {
srcfile[i] = new File(fileNames.get(i));
}
util.FileZip.ZipFiles(srcfile, zip);
FileInputStream inStream = new FileInputStream(zip);
byte[] buf = new byte[4096];
int readLength;
while (((readLength = inStream.read(buf)) != -1)) {
out.write(buf, 0, readLength);
}
inStream.close();
}
}
最后还有个工具类package util;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.zip.ZipEntry;
import java.util.zip.ZipOutputStream;
/**
*
* @author QQ:三二8二4七6七六
*
*/
public class FileZip {
/**
*
* @param srcfile 文件名数组
* @param zipfile 压缩后文件
*/
public static void ZipFiles(java.io.File[] srcfile, java.io.File zipfile) {
byte[] buf = new byte[1024];
try {
ZipOutputStream out = new ZipOutputStream(new FileOutputStream(
zipfile));
for (int i = 0; i < srcfile.length; i++) {
FileInputStream in = new FileInputStream(srcfile[i]);
out.putNextEntry(new ZipEntry(srcfile[i].getName()));
int len;
while ((len = in.read(buf)) > 0) {
out.write(buf, 0, len);
}
out.closeEntry();
in.close();
}
out.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
OK全部内容完成
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12.8M的excel内容压缩后2.68M，给力吧
以后记得代码加注释
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