In this article I will explain with an example, how to create a Generic HTTP Handler in ASP.Net that returns JSON data.
The Generic HTTP Handler will pull records from database and return the records in JSON format to the client.
I have made use of the following table Customers with the schema as follows.
JSON Generic HTTP Handler example in ASP.Net
I have already inserted few records in the table.
JSON Generic HTTP Handler example in ASP.Net
Note: You can download the database table SQL by clicking the download link below.
          Download SQL file
Adding Generic Handler
You will need to add a new Generic Handler (ASHX) file using Add New Item Dialog of Visual Studio as shown below.
JSON Generic HTTP Handler example in ASP.Net
Building a JSON Generic HTTP Handler
The following JSON Generic HTTP Handler gets the records from the Customers table and returns it in JSON format.
There JSON Generic HTTP Handler accepts two optional QueryString parameters.
1. customerId – If a valid ID is passed, it will return the record only for the specific Customer.
2. callback – This parameter holds the value of the Callback function which will be executed by the client side script when the response is received.
The callback feature is generally used when calling the JSON Generic HTTP Handler using JavaScript or jQuery.
<%@ WebHandler Language="C#" Class="Handler" %>
using System;
using System.Web;
using System.Data;
using System.Configuration;
using System.Data.SqlClient;
using System.Collections.Generic;
using System.Web.Script.Serialization;
public class Handler : IHttpHandler
    public void ProcessRequest(HttpContext context)
        string callback = context.Request.QueryString["callback"];
        int customerId = 0;
        int.TryParse(context.Request.QueryString["customerId"], out customerId);
        string json = this.GetCustomersJSON(customerId);
        if (!string.IsNullOrEmpty(callback))
            json = string.Format("{0}({1});", callback, json);
        context.Response.ContentType = "text/json";
    private string GetCustomersJSON(int customerId)
        List<object> customers = new List<object>();
        using (SqlConnection conn = new SqlConnection())
            conn.ConnectionString = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
            using (SqlCommand cmd = new SqlCommand())
                cmd.CommandText = "SELECT * FROM Customers WHERE CustomerId = @CustomerId OR @CustomerId = 0";
                cmd.Parameters.AddWithValue("@CustomerId", customerId);
                cmd.Connection = conn;
                using (SqlDataReader sdr = cmd.ExecuteReader())
                    while (sdr.Read())
                            CustomerId = sdr["CustomerId"],
                            Name = sdr["Name"],
                            Country = sdr["Country"]
            return (new JavaScriptSerializer().Serialize(customers));
    public bool IsReusable
            return false;
<%@ WebHandler Language="VB" Class=" Handler" %>
Imports System
Imports System.Web
Imports System.Data
Imports System.Configuration
Imports System.Data.SqlClient
Imports System.Collections.Generic
Imports System.Web.Script.Serialization
Public Class Handler : Implements IHttpHandler
    Public Sub ProcessRequest(ByVal context As HttpContext) Implements IHttpHandler.ProcessRequest
        Dim callback As String = context.Request.QueryString("callback")
        Dim customerId As Integer = 0
        Integer.TryParse(context.Request.QueryString("customerId"), customerId)
        Dim json As String = Me.GetCustomersJSON(customerId)
        If Not String.IsNullOrEmpty(callback) Then
            json = String.Format("{0}({1});", callback, json)
        End If
        context.Response.ContentType = "text/json"
    End Sub
    Private Function GetCustomersJSON(customerId As Integer) As String
        Dim customers As New List(Of Object)()
        Using conn As New SqlConnection()
            conn.ConnectionString = ConfigurationManager.ConnectionStrings("constr").ConnectionString
            Using cmd As New SqlCommand()
                cmd.CommandText = "SELECT * FROM Customers WHERE CustomerId = @CustomerId OR @CustomerId = 0"
                cmd.Parameters.AddWithValue("@CustomerId", customerId)
                cmd.Connection = conn
                Using sdr As SqlDataReader = cmd.ExecuteReader()
                    While sdr.Read()
                        customers.Add(New With { _
                          .CustomerId = sdr("CustomerId"), _
                          .Name = sdr("Name"), _
                          .Country = sdr("Country") _
                    End While
                End Using
            End Using
            Return (New JavaScriptSerializer().Serialize(customers))
        End Using
    End Function
    Public ReadOnly Property IsReusable() As Boolean Implements IHttpHandler.IsReusable
            Return False
        End Get
    End Property
End Class
JSON Generic HTTP Handler returning all Customer records
JSON Generic HTTP Handler example in ASP.Net
JSON Generic HTTP Handler record for specific Customer
JSON Generic HTTP Handler example in ASP.Net
JSON Generic HTTP Handler with Callback parameter
JSON Generic HTTP Handler example in ASP.Net