<apex:page sidebar="false" controller="UploadOpportunityScheduleLineItem123">
    <apex:form >
        <apex:sectionHeader title="Upload data from CSV file"/>
          <apex:pagemessages />  
            <center>
                <apex:inputFile value="{!contentFile}" filename="{!nameFile}" />
                <apex:commandButton action="{!ReadFile}" value="Upload File" id="theButton" style="width:70px;"/>
                <br/> <br/>
            </center>  
   </apex:form>   
</apex:page>

public with sharing class UploadOpportunityScheduleLineItem123{

    // Global variables
    public string nameFile{get;set;}


    Public Id parentId{get;set;}

    public Blob contentFile{get;set;}


    List<account> lstScheduleToUpdate = new List<account>();

    public account objSchedule{get;set;}
    //String array for taking csv data by line.
    String[] filelines = new String[]{};


    //set for storing all id's from csv.
    set<String> opptoupload{get;set;}



       //Main constructor
    public UploadOpportunityScheduleLineItem123()
    {
        //Initalizing required objects.
        objSchedule = new account();
        opptoupload = new set<String>();

    }
    //Method to read file content and check extension and file format.
    public Pagereference ReadFile()
    {

        parentId=Apexpages.currentPage().getParameters().get('ParentId');
        //If without selecting csv file you clicked on upload it will give error message.
      if(nameFile == null)
        {
            ApexPages.Message errormsg = new ApexPages.Message(ApexPages.severity.ERROR,'You should select csv file to upload');
            ApexPages.addMessage(errormsg);
            return null;
        }
        //Taking file extension.
        String extension = nameFile.substring(nameFile.lastIndexOf('.')+1);
        //Checking if file extension is .csv.
        if(extension == 'csv' ||extension == 'CSV')
        { 
            nameFile =blobToString( contentFile,'ISO-8859-1');
            //Spliting by new line

            filelines = nameFile.split('\n');
            //Spliting values by (,) for checking coloumn size

                for (Integer i=1;i<filelines.size();i++){               
                String[] inputconvalues = new String[]{};
                inputconvalues = filelines[i].split(',');
                account b = new account();
                b.name= inputconvalues[0];
                b.billingcountry = inputconvalues[1];
                b.billingcity = inputconvalues[2];
                lstScheduleToUpdate.add(b);                
                }
                //Checking if list is not empty then updating.
                if(lstScheduleToUpdate.Size()>0)
                {
                    insert lstScheduleToUpdate;
                }
                ApexPages.Message errormsg = new ApexPages.Message(ApexPages.severity.info,'Batches File uploaded successfully');
                ApexPages.addMessage(errormsg);
            return null;
        }
        //If file is not csv type then it will give error message.
        else
        {
            ApexPages.Message errormsg = new ApexPages.Message(ApexPages.severity.ERROR,'File type should be csv type');
            ApexPages.addMessage(errormsg);
            return null;
        }
    }
    public static String blobToString(Blob input, String inCharset){
        String hex = EncodingUtil.convertToHex(input);
        System.assertEquals(0, hex.length() & 1);
        final Integer bytesCount = hex.length() >> 1;
        String[] bytes = new String[bytesCount];
        for(Integer i = 0; i < bytesCount; ++i)
        bytes[i] =  hex.mid(i << 1, 2);
        return EncodingUtil.urlDecode('%' + String.join(bytes, '%'), inCharset);
    }    
}

@IsTest(SeeAllData=true)

    private class testexceltoaccount
    {
          static testmethod void testLoadData() {
                   StaticResource testdoc = [Select Id,Body from StaticResource where name ='testMethodCSVUpload1'];
             UploadOpportunityScheduleLineItem123 testUpload = new UploadOpportunityScheduleLineItem123();
             testUpload.contentFile= testdoc.Body;
             testUpload.ReadFile();
              }

    }

String extension = nameFile.substring(nameFile.lastIndexOf('.')+1);
        //Checking if file extension is .csv.
        if(extension == 'csv' ||extension == 'CSV')
        {