使用Apache POI API读写Excel

原文地址:http://www.journaldev.com/2562/java-readwrite-excel-file-using-apache-poi-api.

有时候我们需要从Excel文件中读取数据,或者我们为了商务或者财政的目的生成Excel格式的报表.Java没有对操作Excel文件提供内在的支持,所以我们需要寻找开源的APIs.当我开始寻找操作Excel的APIs时候,大部分人建议使用JExcel或者Apache POI.

在深入研究后,我发现由于以下主要原因Apache POI是正确的选择.还有些关于高级特性的原因,但是我们不深入太多细节.

1)Apache基金的支持.

2)JExcel不支持xlsx格式而POI既支持xls格式又支持xlsx格式.

3)Apache POI是基于流的处理,因此更适合大文件和要求更少的内存.

Apache POI对处理Excel文件提供了强大的支持,并且能处理xls和xlsx格式的电子表格.

关于Apache POI一些重要的地方:

1)Apache POI包含适合Excel97-2007(.xls文件)的HSSF实现.

2)Apache POI XSSF实现用来处理Excel2007文件(.xlsx).

3)Apache POI HSSF和XSSF提供了读/写/修改Excel表格的机制.

4)Apache POI提供了XSSF的一个扩展SXSSF用来处理非常大的Excel工作单元.SXSSF API需要更少的内存,因此当处理非常大的电子表格同时堆内存又有限时,很合适使用.

5)有两种模式可供选择--事件模式和用户模式.事件模式要求更少的内存,因为用tokens来读取Excel并处理.用户模式更加面向对象并且容易使用,因此在我们的示例中使用用户 模式.

6)Apache POI为额外的Excel特性提供了强大支持,例如处理公式,创建单元格样式--颜色,边框,字体,头部,脚部,数据验证,图像,超链接等.

Apache POI的Maven依赖

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<span style="font-size:14px;"><dependency>

<groupId>org.apache.poi</groupId>

<artifactId>poi</artifactId>

<version>3.10-FINAL</version>

</dependency>

<dependency>

<groupId>org.apache.poi</groupId>

<artifactId>poi-ooxml</artifactId>

<version>3.10-FINAL</version>

</dependency></span>

Apache POI的当前版本是3.10-FINAL.如果你使用单独的java应用,添加jars根据下面的图片.

读取Excel文件

假设我们有一个叫Sample.xlsx的Excel文件,里面有两个sheet并且下面图片中的数据.我们想要读取这个Excel文件并且创建Countries list.sheet1有些额外的数据,当我们解析时会忽略它.





我们的国家(Country)java bean如下:

Country.java

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package com.journaldev.excel.read;

public class Country {

private String name;

private String shortCode;

public Country(String n, String c){

this.name=n;

this.shortCode=c;

}

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

public String getShortCode() {

return shortCode;

}

public void setShortCode(String shortCode) {

this.shortCode = shortCode;

}

@Override

public String toString(){

return name + "::" + shortCode;

}

}

读取Excel文件并创建Countries list代码如下:

ReadExcelFileToList.java

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package com.journaldev.excel.read;

import java.io.FileInputStream;

import java.io.IOException;

import java.util.ArrayList;

import java.util.Iterator;

import java.util.List;

import org.apache.poi.hssf.usermodel.HSSFWorkbook;

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 ReadExcelFileToList {

public static List<Country> readExcelData(String fileName) {

List<Country> countriesList = new ArrayList<Country>();

try {

//Create the input stream from the xlsx/xls file

FileInputStream fis = new FileInputStream(fileName);

//Create Workbook instance for xlsx/xls file input stream

Workbook workbook = null;

if(fileName.toLowerCase().endsWith("xlsx")){

workbook = new XSSFWorkbook(fis);

}else if(fileName.toLowerCase().endsWith("xls")){

workbook = new HSSFWorkbook(fis);

}

//Get the number of sheets in the xlsx file

int numberOfSheets = workbook.getNumberOfSheets();

//loop through each of the sheets

for(int i=0; i < numberOfSheets; i++){

//Get the nth sheet from the workbook

Sheet sheet = workbook.getSheetAt(i);

//every sheet has rows, iterate over them

Iterator<Row> rowIterator = sheet.iterator();

while (rowIterator.hasNext())

{

String name = "";

String shortCode = "";

//Get the row object

Row row = rowIterator.next();

//Every row has columns, get the column iterator and iterate over them

Iterator<Cell> cellIterator = row.cellIterator();

while (cellIterator.hasNext())

{

//Get the Cell object

Cell cell = cellIterator.next();

//check the cell type and process accordingly

switch(cell.getCellType()){

case Cell.CELL_TYPE_STRING:

if(shortCode.equalsIgnoreCase("")){

shortCode = cell.getStringCellValue().trim();

}else if(name.equalsIgnoreCase("")){

//2nd column

name = cell.getStringCellValue().trim();

}else{

//random data, leave it

System.out.println("Random data::"+cell.getStringCellValue());

}

break;

case Cell.CELL_TYPE_NUMERIC:

System.out.println("Random data::"+cell.getNumericCellValue());

}

} //end of cell iterator

Country c = new Country(name, shortCode);

countriesList.add(c);

} //end of rows iterator

} //end of sheets for loop

//close file input stream

fis.close();

} catch (IOException e) {

e.printStackTrace();

}

return countriesList;

}

public static void main(String args[]){

List<Country> list = readExcelData("Sample.xlsx");

System.out.println("Country List\n"+list);

}

}

这个程序很容易明白,主要步骤如下:

1)根据文件类型(.xls与.xlsx)创建Workbook实例,xlsx用XSSFWorkbook,xls用HSSFWorkbook.我们可以基于文件名字使用工 厂模式创建一个包装类来创建Workbook实例.

2)使用Workbook
getNumberOfSheets()来获取sheet的数量,然后循环解析每一个sheet.使用getSheetAt(int i)方法获取 Sheet实例.

3)获取Row和Cell迭代器来获取每一个Cell对象.Apache
POI在这里使用了迭代器模式.

4)使用switch-case根据Cell的类型来处理它.

现在我们运行上面的程序,在控制台产生如下的输出:

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Random data::1.0

Random data::2.0

Random data::3.0

Random data::4.0

Country List

[India::IND, Afghanistan::AFG, United States of America::USA, Anguilla::AIA,

Denmark ::DNK, Dominican Republic ::DOM, Algeria ::DZA, Ecuador ::ECU]

写入Excel文件

除了我们首先创建Workbook,然后设置sheets,rows,cells的值并且使用FileOutputStream把Workbook写入文件外,与读取Excel的操作相似.我们把从上面的方法读取countries
list写入到另一个文件作一个例子:

WriteListToExcelFile.java

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package com.journaldev.excel.read;

import java.io.FileOutputStream;

import java.util.Iterator;

import java.util.List;

import org.apache.poi.hssf.usermodel.HSSFWorkbook;

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 WriteListToExcelFile {

public static void writeCountryListToFile(String fileName, List<Country> countryList) throws Exception{

Workbook workbook = null;

if(fileName.endsWith("xlsx")){

workbook = new XSSFWorkbook();

}else if(fileName.endsWith("xls")){

workbook = new HSSFWorkbook();

}else{

throw new Exception("invalid file name, should be xls or xlsx");

}

Sheet sheet = workbook.createSheet("Countries");

Iterator<Country> iterator = countryList.iterator();

int rowIndex = 0;

while(iterator.hasNext()){

Country country = iterator.next();

Row row = sheet.createRow(rowIndex++);

Cell cell0 = row.createCell(0);

cell0.setCellValue(country.getName());

Cell cell1 = row.createCell(1);

cell1.setCellValue(country.getShortCode());

}

//lets write the excel data to file now

FileOutputStream fos = new FileOutputStream(fileName);

workbook.write(fos);

fos.close();

System.out.println(fileName + " written successfully");

}

public static void main(String args[]) throws Exception{

List<Country> list = ReadExcelFileToList.readExcelData("Sample.xlsx");

WriteListToExcelFile.writeCountryListToFile("Countries.xls", list);

}

}

当我们执行上面的程序后,这个Excel文件被创建了,如下图:

读取Excel公式

有时候我们需要出来带有公司的复杂Excel文件.让我们来看一个关于读取一个有值的cell中的公式的例子:

ReadExcelFormula.java

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package com.journaldev.excel.read;

import java.io.FileInputStream;

import java.io.IOException;

import java.util.Iterator;

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 ReadExcelFormula {

public static void readExcelFormula(String fileName) throws IOException{

FileInputStream fis = new FileInputStream(fileName);

//assuming xlsx file

Workbook workbook = new XSSFWorkbook(fis);

Sheet sheet = workbook.getSheetAt(0);

Iterator<Row> rowIterator = sheet.iterator();

while (rowIterator.hasNext())

{

Row row = rowIterator.next();

Iterator<Cell> cellIterator = row.cellIterator();

while (cellIterator.hasNext())

{

Cell cell = cellIterator.next();

switch(cell.getCellType()){

case Cell.CELL_TYPE_NUMERIC:

System.out.println(cell.getNumericCellValue());

break;

case Cell.CELL_TYPE_FORMULA:

System.out.println("Cell Formula="+cell.getCellFormula());

System.out.println("Cell Formula Result Type="+cell.getCachedFormulaResultType());

if(cell.getCachedFormulaResultType() == Cell.CELL_TYPE_NUMERIC){

System.out.println("Formula Value="+cell.getNumericCellValue());

}

}

}

}

}

public static void main(String args[]) throws IOException {

readExcelFormula("FormulaMultiply.xlsx");

}

}

当我们执行上面的程序后,我们得到下面的输出:

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1.0

2.0

3.0

4.0

Cell Formula=A1*A2*A3*A4

Cell Formula Result Type=0

Formula Value=24.0

写入Excel公式

有时候,我们需要做一些计算然后把值写入cell.我们可以使用Excel公司来做这些计算,这样会更加精确,因为这些值会随着计算的值改变而改变.让我们来看一个关于写入一个带有公式的Excel的例子:

WriteExcelWithFormula.java

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package com.journaldev.excel.read;

import java.io.FileOutputStream;

import java.io.IOException;

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 WriteExcelWithFormula {

public static void writeExcelWithFormula(String fileName) throws IOException{

Workbook workbook = new XSSFWorkbook();

Sheet sheet = workbook.createSheet("Numbers");

Row row = sheet.createRow(0);

row.createCell(0).setCellValue(10);

row.createCell(1).setCellValue(20);

row.createCell(2).setCellValue(30);

//set formula cell

row.createCell(3).setCellFormula("A1*B1*C1");

//lets write to file

FileOutputStream fos = new FileOutputStream(fileName);

workbook.write(fos);

fos.close();

System.out.println(fileName + " written successfully");

}

public static void main(String[] args) throws IOException {

writeExcelWithFormula("Formulas.xlsx");

}

}

当我们执行上面的程序后,Excel被创建了,如下图:



这就是所有Apache POI处理Excel文件的内容.查看POI源代码可以学习它的更多特性.