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MCSD Web Applications: File System and leveraging Web services

5/15/2015 04:20:00 pm , , ,

Index

  • Intro
  • File System
  • Modify files
  • What are web services
  • REST Services
  • Asynchronous programming

Intro

I want to talk today about how to work with the file system and why we need it, so let's talk about the different scenarios where you'll be using the System.IO .Net library.


Besides we'll be scratching the surface of a couple of web services called "SOAP" and "REST", which you could be already familiar with. Finally, asynchronous programming will come over.

File System

Benefits of read and write from the file system:

  • Show existing data to user
  • Integrate user-provided data
  • Serialize objects out of memory
  • Persist data across sessions
  • Determine environment configuration

How to write:

  • This is simplified with Framework methods; 
    • open / shut (File.WriteAllText / File.ReadAllText) (see example below)
  • Open for reading to keep open and keep writing.
  • Open as stream for large payloads and real-time processing: let's say you want to see a movie through Netflix, you don't download the entire movie file into your PC and then you start watching. You download just a small peace of that huge file depending on where you are in the movie.
See an example of how write/read a file using .Net


var dir = System.IO.Directory.GetCurrentDirectory();
var file = System.IO.Path.Combine(dir, "File.txt");
var content = "how now brown cow?";

// write
System.IO.File.WriteAllText(file, content);

// read
var read = System.IO.File.ReadAllText(file);
Trace.Assert(read.Equals(content));


How do we find files?

  • Get Windows folder with Environment Special Folder
  • Get the Current folder with File.IO.GetCurrentDirectory()
  • Use Isolated Storage dedicated to the current application: 
    • dedicated application storage not used very often by developers.
  • Anything Else.Caveat: Windows Store App development

// special folders
var docs = Environment.SpecialFolder.MyDocuments;
var app = Environment.SpecialFolder.CommonApplicationData;
var prog = Environment.SpecialFolder.ProgramFiles;
var desk = Environment.SpecialFolder.Desktop;

// application folder
var dir = System.IO.Directory.GetCurrentDirectory();

// isolated storage folder(s)
var iso = IsolatedStorageFile
    .GetStore(IsolatedStorageScope.Assembly, "Demo")
    .GetDirectoryNames("*");

// manual path
var temp = new System.IO.DirectoryInfo("c:\temp");

In the previous example you can see how to reach the typical windows directories, your app and your isolated storage folder in .Net. Finally directoryInfo provides you useful info about certain directory like size, rights, etc. You are not allowed to do whatever you want in your PC, at some folder you probably need some rights in order to read, write or... delete!

Modify files

Please see here a small piece of code to show you how to edit files, following these steps:

  • Iterate through files using GetFiles()
  • Rename / Move with System.IO methods
  • Get File Info with System.UI.FileInfo

// files
foreach (var item in System.IO.Directory.GetFiles(dir))
    Console.WriteLine(System.IO.Path.GetFileName(item));

// rename / move
var path1 = "c:\temp\file1.txt";
var path2 = "c:\temp\file2.txt";
System.IO.File.Move(path1, path2);

// file info
var info = new System.IO.FileInfo(path1);
Console.WriteLine("{0}kb", info.Length / 1000);


See how we get all the files defined in the "dir" variable (let say "C:\temp") using GetFiles. Then we print all those files placed in the "dir" directory using GetFileName. Then moving a file to the same folder which purely it's a renaming operation. Finally, we'll get some meta data using the FileInfo method and we use the result of that method to print on the console the length of that file.

What are web services

See some web services (WS) features:

  • Web services encapsulate implementation: this means we don't know how a third party service is implemented. You can be using Facebook web services but you don't know how their WS are implemented.
  • WS expose to disparate system.
  • WS allow client systems to communicate servers: which is great because allow you to separate the different parts when you're building a new application.
    • Web protocols (HTTP, GET, POST, etc)
  • WS are important to Service Oriented Architecture
    • With and without metadata
    • Loose coupling: when a system has different moving parts depending on others and add something new means add a lot of extra changes.

What is SOAP? Easy, it's a type of web service. See some features:


  • SOAP is a standard for returning structured data from a Web Service as XML
    • Envelope (Header / Body / ...)
  • SOAP handling is a built-in feature of Visual Studio
The idea is to serialize the information provided by our application into our web service to send that information to our clients. Then our clients will de serialize that information in order to be able to read it.

The downside of this is the de/serialization process is heavy. At first, save 400 bytes it's not a big deal, but in case of companies like Facebook which could face millions of requests per day means a lot. There is a few emerging new technologies to bypass this problem...

REST Services

REST (Representative State Transfer)

  • ...is becoming a common, industry standard
  • ...does not require XML parsing
  • ...does not require message header
  • ...is generally human-readable
  • ...uses less band-with than SOAP
  • ...services typically return XML or JSON
  • ...JSON is JavaScript Object notation
    • JSON is becoming a common industry standard
    • JSON is generally a lighter payload than XML (or SOAP)

See how to implement a basic JSON reader using the .Net framework:

using System;
using System.Collections.Generic;
using System.Net;
using System.Web.Script.Serialization;

namespace ConsoleApplication1
{
    public class Program
    {
        public static void Main()
        {
            var url = new Uri("http://footballpool.dataaccess.eu/data/info.wso/TopGoalScorers/JSON/debug?iTopN=10");
            var client = new WebClient();
            var json = client.DownloadString(url);

            // deserialize JSON into objects
            var serializer = new JavaScriptSerializer();
            var data = serializer.Deserialize>(json);

            // use the objects
            foreach (var item in data)
                Console.WriteLine("Player: {0,16}, Goals: {1}", item.sName, item.iGoals);

            Console.Read();

            // Output
            // Player:  James Rodríguez, Goals: 6
            // Player:   Thomas Mueller, Goals: 5
            // Player:            Messi, Goals: 4
            // Player:           Neymar, Goals: 4
            // Player:       van Persie, Goals: 4
            // Player:   Andre Schurrle, Goals: 3
            // Player:          Benzema, Goals: 3
            // Player:   Enner Valencia, Goals: 3
            // Player:    Islam Slimani, Goals: 3
            // Player:           Robben, Goals: 3
        }
    }

    public class ObjectReturnedByTheWebService
    {
        public string sName { get; set; }
        public int iGoals { get; set; }

    }
}

If you want to try this solution, you could create a new console application and then add a new reference to System.Web.Extensions in order to get the JavaScriptSerializer class working. The URL I'm using it's a free web service with free football stats called: http://footballpool.dataaccess.eu/. I'm passing the value 10 when building the URL, but you can change that in order to get top3, top5...

I use the WebClient class to call the service and then I de-serialize the message because it comes as a JSON message. Try to go to that URL to see how it looks. There is a small class called ObjectReturnedByTheWebService which is used to convert that json message from plain text into a proper .Net class using a auto mapper.


As an example of how using REST services, please see how to implement an image recognition system in one of my first posts for this blog.

Asynchronous programming

Asynchronous maximizes resources on multi core systems, by allowing units of work to be separated and completed. Asynchronous programming frees up the calling system, especially a user interface, as to not wait for long operations. Don't using this approach will constrain your resources. It improves the user experience using your application by freezing the screen giving a feel like your app is hanging in a long running task.

References



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