In a VF page I have a SelctList and an OutputLink with a field value as part of the definition of the URL using the select list variable "listDocsSQL"

      <apex:pageBlock>
        <apex:selectList id="documentsList" value="{!listDocsSQL}" multiselect="false" style="width:300px" size="5">
            <apex:selectOptions value="{!DocListOptions}" />
        </apex:selectList>
      </apex:pageBlock>

      <apex:pageBlock>
         <apex:outputLink id="docLink" value="https://c.cs10.content.force.com/servlet/servlet.FileDownload?file={!listDocsSQL}" >
          Doc Link
	  <apex:commandButton value="Open Doc" action="{!openSelection}" />
        </apex:outputLink>
      <apex:pageBlock>

I put a button in to set the "listDocsSQL" variable to the selected "id" value and open the URL but, found, using a debug statement, that the variable is set as it should be when the option is selected using the set method for "listDocsSQL" that part seems to work...

snippet ..

public class DocumentSearchController{
    public String listDocsSQL {get; set;} 
    public String filterResources{get; set;}
    String filterRes;
    String filterResID;

    /**
	This method filters the list depending on the user text input
     **/
    public List<Document> getlistDocsSQLOptions() {
        System.debug('getListDocs filterRes: '+ filterRes);
        filterResources = '%'+ filterResources +'%';
        return 
            (List<Document>)
              [select id, Name, url, Type, FolderId, BodyLength
              from Document
               	where (Type = 'pdf') AND (Name LIKE :filterResources )
             ];
    }

    public List<SelectOption> getDocListOptions(){
        List<SelectOption> options1 = new List<SelectOption>();
        List<Document> docListSelectOption = getlistDocsSQLOptions() ;
        for(Document doc : docListSelectOption) {
            System.debug('getDocListOptions name: '+ doc.name +' filterRes: '+ filterRes +', id: '+ doc.id);
            options1.add(new SelectOption(doc.id, doc.name));
        }
        return options1;
    }


    public PageReference openSelection() {
        System.debug('openSelection listDocsSQL: '+ listDocsSQL );
        // https://c.cs10.content.force.com/servlet/servlet.FileDownload?file=015J000000058sW
        
		return null;        
    }
        

It does not work as expected when I try to open the URL after selecting the item in the select list, the URL link will open the selected document only when I first push the button.  This is not expected.

I do not want to have the button on the page.  Is there a way I can select the item from the list, then open the URL without having to push the button first?

Thanks.