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• IT 311 Mobile Application Development 2

Learning Objectives

• Familiarize yourself with JSON
• Understand JSON syntax
• Understand HTTP requests and responses

What is JSON?

• JSON stands for JavaScript Object Notation
• JSON is a lightweight data interchange format used for storing and transporting data
• JSON is often used when data is sent from a server to a webpage
• JSON is a language-independent text format that uses conventions familiar to C family languages
• Languages include C, C++, C#, Java, JavaScript, and Python
• JSON is easy for humans to read and write, and for machines to parse and generate

What is JSON used for?

• JSON is a standard, text-based format for representing structured data, based on JavaScript object syntax
• JSON is commonly used for transmitting data in web applications
• For example, it is used for sending data from a server to a client, or vice versa, for display on a webpage

Is JSON a programming language?

• JSON is not a programming language, but a data interchange format
• Its primary use is for structured data representation
• JSON allows for encoding data in an easily readable format for both machines and humans to parse and generate
• JSON serves as a standard to represent structured data in a simple and human-readable form
• Different programming languages can easily consume the data

JSON Syntax Rules

• JSON represents data as key-value pairs
• The keys are strings
• Values can be strings, numbers, boolean values, arrays, objects, or null
• Data is in name/value pairs
• Data pairs are separated by commas
• Curly braces hold objects
• Square brackets hold arrays

JSON Data

• String example: “Hello”, “Jeffrey Cervantes”, “I”
• Number examples: 10, 50.2, -52
• Boolean examples: true or false
• Null: null
• Array examples: [1,2,3], ["Hello", "Jeff"]
• Object examples: {"key":"value"} {"name":"Jeff"}

Sample of JSON

• key1 has a string value shown as "key1": "value1"
• key2 has a numeric value shown as "key2": 42
• key3 has a boolean value shown as "key3": true
• key4 has an array value shown as "key4": ["item1", "item2", "item3"]
• key5 has an object value shown as "key5": { "nestedKey": "nestedValue" }
• key6 has a null value shown as "key6": null

JSON vs XML - Similarities

• Both JSON and XML are self-describing (human readable)
• Both are hierarchical (values within values)
• Both can be parsed and used by lots of programming languages
• Both can be fetched with an XMLHttpRequest

JSON vs XML - Unsimilarities

• JSON doesn't use end tag
• JSON is shorter
• JSON is quicker to read and write
• JSON can use arrays
• XML must be parsed with an XML parser
• JSON can be parsed by a standard JavaScript function

JSON Example

• {"employees":[ { "firstName":"John", "lastName":"Doe" }, { "firstName":"Anna", "lastName":"Smith" }, { "firstName":"Peter", "lastName":"Jones" } ]}

XML Example

Advantages of JSON

• JSON has a human-readable format with a clear and simple syntax, making it easy to understand and work with
• JSON provides language independence, allowing use with various programming languages and seamless data exchange
• JSON is lightweight, not adding much overhead to data, which makes transmitting across networks and storing configurations efficient
• Most programming languages have libraries or built-in functions for parsing JSON, which makes it convenient for developers
• JSON supports complex data structures including nested objects and arrays; flexibility represents a wide range of data types
• JSON is widely adopted and supported across various programming languages, making it the standard choice for data interchange
• JSON is schema-less, which allows easy modification and extension of data without extensive changes to the data format
• JSON is used for data serialization, converting complex data structures in programming languages into an easy-to-store format
• JSON is native to JavaScript, which makes it easy to work with in web development
• JavaScript provides built-in functions, JSON.parse() and JSON.stringify(), for encoding and decoding JSON
• JSON is supported natively in web browsers, which allows for seamless integration with client-side scripting in web applications

Disadvantages of JSON

• JSON does not support comments within the data itself, which can be inconvenient for developers
• JSON does not define a standard format for date representation
• JSON supports a limited set of data types: strings, numbers, booleans, arrays, objects, and null
• JSON does not provide a native way to represent binary data
• JSON does not enforce a predefined structure for data
• JSON can be relatively verbose, which can lead to larger data payloads
• JSON does not provide built-in support for metadata
• If JSON data is received from an untrusted source and directly executed using JavaScript's eval() function, it can lead to security risks
• An object contains a reference to itself or forms a circular reference chain, causing issues during serialization

HTTP Request

• The Hypertext Transfer Protocol (HTTP) allows communication between clients and servers
• HTTP works as a request-response protocol between a client and server
• An example is a client (browser) sends an HTTP request to the server
• The server returns a response to the client
• The client contains the requested content and status information

HTTP Request Methods

• GET
• POST
• PUT
• HEAD
• DELETE
• PATCH
• OPTIONS

GET methods

• GET is used to request data from a specified resource
• GET is one of the most common HTTP methods
• The query (name/value pairs) is sent in the URL of a GET request
• GET requests can be cached
• GET requests remain in the browser history
• GET requests can be bookmarked
• GET requests should never be used when dealing with sensitive data
• GET requests have length restrictions
• GET requests are only used to request data (not modify)

POST methods

• POST is for sending data to a server to create/update a resource
• The data sent with POST is stored in the request body of the HTTP request
• POST is one of the most common HTTP methods
• POST requests are never cached
• POST requests do not remain in the browser history
• POST requests cannot be bookmarked
• POST requests have no restrictions on data length

PUT methods

• PUT is used to send data to a server to create/update a resource
• PUT requests are idempotent
• Calling the same PUT request multiple times will always produce the same result
• Calling a POST request repeatedly have side effects of creating the same resource multiple times

HEAD methods

• HEAD is almost identical to a GET request but without the response body
• If GET /users returns a list of users, then HEAD /users will make the same request but will not return the list of users
• HEAD requests are useful for checking what a GET request will return before actually making a GET request

DELETE methods

• The DELETE method deletes the specified resource

OPTION methods

• The OPTIONS method describes the communication options for the target resource

HTTP Responses

• When a browser requests a service from a web server, an error might occur, and the server might return an error code like "404 Not Found"
• It is common to name these errors HTTP error messages
• Such messages are called HTTP Status messages; the server always returns a message for every request
• The most common message is 200 OK
• HTTP codes starting with 1 indicate Informational responses
• HTTP codes starting with 2 indicate Successful responses
• HTTP codes starting with 3 indicate Redirection messages
• HTTP codes starting with 4 indicate Client Errors
• HTTP codes starting with 5 indicate Server Errors