How to generate and download file(text) in visualforce page

Question

I have a visualforce page in which there is a button called download.
If I click that button then it will download all the account records as text file. For this use case how can I implement.
Do not redirect to another visualforce page
Can someone suggest some ideas to implement?

My vfp code:

<apex:page standardController="Account" extensions="AccountDownload" recordSetVar="accounts" sidebar="false">    
    <apex:form >    
        <apex:pageBlock title="Archiver For Account">   
        <apex:pageBlockSection >                
            <apex:commandButton action="{!Download}" value="download" id="theButton" /><br/>    
             <apex:outputPanel id="panel1" rendered="{!ren}">   
                 <apex:pageBlockTable value="{!accounts}" var="ac">    
                     <apex:column value="{!ac.Name}"/>   
                     <apex:column value="{!ac.AccountNumber}"/>  
                     <apex:column value="{!ac.AnnualRevenue}"/>   
                     <apex:column value="{!ac.Phone}"/>   
                     <apex:column value="{!ac.Type}"/>       
                 </apex:pageBlockTable>                  
             </apex:outputPanel>   
        </apex:pageBlockSection>   
        </apex:pageBlock>           
    </apex:form>     
</apex:page>    

Controller:

   public class AccountDownload {    
    public boolean ren{get;set;}
    public AccountDownload(ApexPages.StandardSetController controller) {
        ren=false;
    }
    public PageReference Download(){
        ren=true;
        return null;

    }
}

Answer 1

You would need to create another VF page with contentType="text/csv#filename.csv".

On clicking the download button, from the method you can return a page reference to this new page.

<apex:page controller="AccountDownload" contentType="text/csv#filename.csv" >

<apex:repeat value="{!accounts}" var="acc">

{!acc.Name},{!acc.AccountNumber},{!acc.AnnualRevenue},{!acc.Phone}, {!acc.Type},

</apex:repeat>
</apex:page>

Answer 2

You may use the renderAs property of page to set it as "PDF" sothat your page will be rendered as a PDF. another way is to define the contenttype of your page as MS word. so after clicking on "Download" button, the page content will be downloaded as word file.

Answer 3

I resolved this problem,I am using the javaScript download function in two ways

Visualforce page:

<apex:page controller="VFPageDownloaderController" action="{!downloadAutomatic}">
    <apex:outputText value="{!msg}" escape="false"></apex:outputText>
    
    <script>
  function download(s,filename,ext)
  {
    console.log(s+'Function call');
      const link = document.createElement('a');
  // create a blobURI pointing to our Blob
  link.href = 'data:application/'+ext+';base64,'+s;
  link.download = filename+'.'+ext;
  // some browser needs the anchor to be in the doc
  document.body.append(link);
  link.click();
  link.remove();
  // in case the Blob uses a lot of memory
       setTimeout(() => URL.revokeObjectURL(link.href), 20000);
  }

  </script>
 <apex:outputText value="{!downloadJS}" escape="false"></apex:outputText>
</apex:page>

Visualforce controller:

public class VFPageDownloaderController {
    
    public String msg {get;set;}
    public String downloadJS {get;set;}
    
    //created a function to make the API request
    public void downloadAutomatic(){
        
        String base64String = '';
        
        // download file as a blob from url request
       /* 
        Http http = new Http();
        HttpRequest request = new HttpRequest();
        request.setMethod('GET');
        request.setHeader('Content-Type', 'application/json');
        request.setEndpoint('request url');
       HttpResponse response = http.send(request);
        System.debug(response.getBodyAsBlob());
        Blob b = response.getBodyAsBlob();
        base64String = EncodingUtil.base64Encode(b); */
        
        // download file from ContentVersion
        ContentVersion c = [SELECT Id, VersionData, FileExtension, Title FROM ContentVersion limit 1];
        base64String = EncodingUtil.base64Encode(c.VersionData);
        String fileName = 'abc'; 
        if (base64String == '') {
            msg = 'file Not Found';
        }else {
              downloadJS ='<script> download("'+base64String+'","'+fileName+'","'+c.FileExtension+'"); </script>';
        }     
   } 
}