Apache POI 操作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

<dependency>
    <groupId>org.apache.poigroupId>
    <artifactId>poiartifactId>
    <version>3.10-FINALversion>
dependency>
<dependency>
    <groupId>org.apache.poigroupId>
    <artifactId>poi-ooxmlartifactId>
    <version>3.10-FINALversion>
dependency>

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:

• 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.
• 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.
• 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.
• 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:

[java] view plaincopy在CODE上查看代码片派生到我的代码片 
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.