dynamically Calling apex from java script custom button based on pick list value

Javascript :
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{!REQUIRESCRIPT("/soap/ajax/30.0/connection.js")}
{!REQUIRESCRIPT("/soap/ajax/24.0/apex.js")}
var ReferraAccepted = sforce.connection.query("SELECT id from {!Account.Routing_Rule__c} where AccountId ='{!Account.Id}'");
records = ReferraAccepted.getArray("records");
alert(records);
if (!records.length > 0) {
alert("There were no child records been assigned !!")
}
else {
window.open('/apex/RoutingRuleLogic?Id={!Account.Id}&objectName={!Account.Routing_Rule__c}', '_blank', 'height=600,width=600,resizable=yes,scrollbars=yes,toolbar=n‌​o,menubar=no');
}

Visualforce Page :
--------------------

<apex:page controller="RoutingRuleLogic_CLS" sidebar="false" showHeader="false">
    <apex:form >
        <apex:pageBlock >
            <apex:pageBlockTable value="{!objectDetails}" var="a">
                <apex:column value="{!a.id}"/>
                <apex:column headerValue="Name">
                <apex:outputText value="{!a['name']}"/>
                </apex:column>
                <apex:column headerValue="Email">
                <apex:outputText value="{!a['email']}"/>
                </apex:column>
                <apex:column headerValue="Phone">
                <apex:outputText value="{!a['phone']}"/>
                </apex:column>
                <apex:column headerValue="Account Id">
                <apex:outputText value="{!a['Accountid']}"/>
                </apex:column>
            </apex:pageBlockTable>
        </apex:pageBlock>
    </apex:form>
</apex:page>

Apex Logic :
---------------
public with sharing class RoutingRuleLogic_CLS {
    public string objectName {get;set;}
    public String query {get;set;}  
    public RoutingRuleLogic_CLS(){
        objectName = apexpages.currentpage().getparameters().get('objectName');
        if(objectName != '' && objectName != NULL){
            getRecordsBasedOnObjectName(objectName);
        }              
    }
    public list<sObject> objectDetails {get;set;}
    public Map<String,Schema.SObjectType> schemaGlobalDescription ;
    public Schema.sObjectType objType ;
    public Map<String,Schema.SObjectField> mapFieldList;
    public void getRecordsBasedOnObjectName(string objectName){
        query = 'Select ';
        schemaGlobalDescription  = Schema.getGlobalDescribe();
        objType = schemaGlobalDescription.get(objectName);
        Schema.DescribeSObjectResult objDescribeSObjectResult = objType.getDescribe();
        mapFieldList = objDescribeSObjectResult.fields.getMap();      
        for(Schema.SObjectField field : mapFieldList.values()){
            Schema.DescribeFieldResult fieldResult = field.getDescribe();
            if(fieldResult.getName() == 'Id'){          
            }else{
                query += fieldResult.getName()+ ',';
            }
        }
        query += ' Id from '+objectName+' limit 100';      
        objectDetails = new list<sObject>();
        if(String.isNotBlank(query)){
            objectDetails = database.query(query);
        }            
    }
}