What is a callout in salesforce - triggers

I am reading about callout, and it is something I don't understand.
https://trailhead.salesforce.com/en/force_com_dev_beginner/apex_triggers/apex_triggers_intro
Is it a simple asynchronous call?, Is it a callback? What is the meaning?

An Apex callout enables you to tightly integrate your Apex with an external service by making a call to an external Web service or sending a HTTP request from Apex code and then receiving the response. Apex provides integration with Web services that utilize SOAP and WSDL, or HTTP services (RESTful services).
Callouts enable Apex to invoke external web or HTTP services. Apex Web services allow an external application to invoke Apex methods through Web services.

Related

How to make a REST API call from SOAP

I would like to know the best practices of calling a REST API from SOAP.
Requirement:
We have a SOAP-based web service that is already consuming by many applications. we would like to rewrite the SOAP API with Rest(basically a Spring boot application), but we want to call the rest from SOAP to support the existing applications.
The one way I know is we can call the Rest Api from the SOAP server implementation class
EX: Consider EmployeeService;java is a SOAP implementation class
EmployeeService.java
getEmployee(){
Calling new Rest Api
}
Existing app1 ---->SOAP --> REST API
Existing app2 ---->SOAP --> REST API
new app1 --> REST API.
Please let me know is there any best way\alternate way to handle it.
You can use boomerang soap client.
Detail here

SalesForce to integrate with external RESTful service

Being new to SalesForce Integration, I am trying to understand the capability of SalesForce to integrate with external RESTful service (WADL file) and execute to extract data to use in SalesForce UI functionality.
I understand that SalesForce is able to execute SOAP over HTTP (WSDL file) service to integrate but I see there is no solid documents online to explore whether SalesForce can also execute external WADL file.
Please advice me.
There's no built in feature to consume a WADL. You can however, just write your own Apex code to make restful callouts.
Apex Restful Callouts Trailhead
Invoking HTTP Callouts

Can a SOAP web service be called a web API

Is it possible to call a SOAP web service a web api? or is a web api a synonym for a REST Api only ?
It certainly is a web API, so yes. The term API gets used in a lot of different ways, but using it for a SOAP webservice is not unprecedented: SalesForce used to call their SOAP webservice their 'webservice API' but have since renamed it to 'SOAP API'.

What is the benefit of RESTful Web Service Vs Using Just a simple Servlet?

Regardless of whether I create a RESTful Web service to be consumed by Ajax in my own pages, or by any user, I can provide the same functionality (data) to the application or user using a simple servlet.
I mean the user or application don't see any different between response provided by a simple servlet or respone provided by a RESTful web service. So, I'm guessing that the benefit is on the server side and to the developers. Can someone please tell me what are the benefits of using RESTful web services.
I appreciate any respone
By definition a webservice is intended to be consumed by any client granted access. If the client you are developing is the only application that you will ever need or want to access the resource then there is little benefit to creating a webservice. However, if you want to make the resource available as a service endpoint for more than just this application in a way that is implementation agnostic then a Restful webservice is a great way of doing it.

web services,web application

what are web services(Rmi,ejb,soap)? what is the difference between web services and web application? Is it possible to implement web services in web application?
A web service is a way to transmit/expose information in such a way that a Web Service client, which can created in a server script or from a stand-alone program, can call the service for what it wants using methods and functions defined by the service.
One of the benefits of a web service is that it abstracts these methods and functions (and variable types) in such a way that any language that "speaks" web services can use it's own syntax to interface with the service (thus making it cross-language).
Another benefit is that it uses the HTTP protocol (usually transmitting via XML or JSON, but not necessarily either), so it's also cross-platform.
A huge benefit is that an application that typically requires very specific knowledge and software can "expose" information via a web-service. So if you're corporate mainframe has tons of top-secret data that typically requires a terminal client, etc, to get data, certain data can be accessed via a Web Service so that you can have your HR department download and upload timesheet changes from a web site.
A web app can certainly include a web service, but they are not the same thing. You can make a web service using PHP or .NET, and then have a web app written in either language interface with that service, but a web app tends to be an interface for the site you're on, while a web service is about getting info to and from other apps (web or not).
web app is user interface, access by humans, user can browse data , can submit and retrieve data. All user interactivity (the GUI) is done through web pages, but all data is stored and manipulated on the server.
Web service server-based application and meant for interaction with other programs.
A web service is a way to expose some business logic you have over the internet. Say you got a module that connects to the database and does something. You can let other applications on the internet use this module of yours via web services. Web services uses SOAP over HTTP to invoke the request and retrieve the response in XML.
Web application - Person-to-server with HTTP, HTML
Web service - Server-to-server with HTTP, SOAP, XML