使用Apache POI API读写Excel

目录(?)[-]

1. 读取Excel文件
2. 写入Excel文件
3. 读取Excel公式
4. 写入Excel公式

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

 "font-size:14px;">
     org.apache.poi
     poi
     3.10-FINAL


     org.apache.poi
     poi-ooxml
     3.10-FINAL

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

 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

 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 readExcelData(String fileName) {
         List countriesList = new ArrayList();

         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 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 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 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:

 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

 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 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 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 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

 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 rowIterator = sheet.iterator();
         while (rowIterator.hasNext())
         {
             Row row = rowIterator.next();
             Iterator 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:

 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

 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.