Here is a java code that reads the excel file using Apache POI api.

 import java.io.*;
 import java.util.*;
 import org.apache.poi.hssf.usermodel.HSSFSheet;
 import org.apache.poi.hssf.usermodel.HSSFWorkbook;
 import org.apache.poi.hssf.usermodel.HSSFRow;
 import org.apache.poi.hssf.usermodel.HSSFCell;

    public class ReadExcel{
        public static void main(String[]args){
    short a=0;  
    short b=1;  
     int i=0;   
    ArrayList list1=new ArrayList();
    ArrayList list2=new ArrayList();
        String   value1="", value2="";  
       String filename ="C:/data.xls";     
        if(filename != null && !filename.equals("")){
        try{    
        FileInputStream fs =new FileInputStream(filename);    
        HSSFWorkbook wb = new HSSFWorkbook(fs);   
        for(int k = 0; k < wb.getNumberOfSheets(); k++){    
         int j=i+1;    
         HSSFSheet sheet = wb.getSheetAt(k);    
         int rows  = sheet.getPhysicalNumberOfRows();    
         for(int r =     1; r < rows; r++){    
         HSSFRow row   = sheet.getRow(r);    
         int cells = row.getPhysicalNumberOfCells();    
            HSSFCell cell1  = row.getCell(a);      
            value1 = cell1.getStringCellValue();   
            HSSFCell cell2  = row.getCell(b);     
            value2 = cell2.getStringCellValue();    

            list1.add(value1);
            list2.add(value2);   
          }       
          i++;   
        }    
}catch(Exception e){  

 }

 }
 for(int j=0;j<list1.size();j++){
     System.out.println(list1.get(j).toString()+"\t"+list2.get(j).toString());
 }


        }
    }

For more information, visit the following link:

http://www.roseindia.net/tutorial/java/poi/readExcelFile.html

Now to create an excel file or to add data to excel file, here is a code.

import  java.io.*;  
import  org.apache.poi.hssf.usermodel.HSSFSheet;  
import  org.apache.poi.hssf.usermodel.HSSFWorkbook; 
import  org.apache.poi.hssf.usermodel.HSSFRow;
import  org.apache.poi.hssf.usermodel.HSSFCell;  

public class CreateExcelFile{
    public static void main(String[]args){
try{
String filename="c:/hello.xls" ;
HSSFWorkbook hwb=new HSSFWorkbook();
HSSFSheet sheet =  hwb.createSheet("new sheet");

HSSFRow rowhead=   sheet.createRow((short)0);
rowhead.createCell((short) 0).setCellValue("SNo");
rowhead.createCell((short) 1).setCellValue("First Name");
rowhead.createCell((short) 2).setCellValue("Last Name");
rowhead.createCell((short) 3).setCellValue("Username");
rowhead.createCell((short) 4).setCellValue("E-mail");
rowhead.createCell((short) 5).setCellValue("Country");

HSSFRow row=   sheet.createRow((short)1);
row.createCell((short) 0).setCellValue("1");
row.createCell((short) 1).setCellValue("Rose");
row.createCell((short) 2).setCellValue("India");
row.createCell((short) 3).setCellValue("roseindia");
row.createCell((short) 4).setCellValue("[email protected]");
row.createCell((short) 5).setCellValue("India");

FileOutputStream fileOut =  new FileOutputStream(filename);
hwb.write(fileOut);
fileOut.close();
System.out.println("Your excel file has been generated!");

} catch ( Exception ex ) {
    System.out.println(ex);

}
}
}