Diference between @future (callout= true / false)

Question

I don't understand the difference between:

@future (callout= true)

and

@future (callout= false)

I have read the documentation, but I don't understand where to use one or the other.

Answer 1

If you want to call third party system or any http call outside of salesforce system you need to set callout=true in the future method. If you set it to false it means the method is not making any http callout.

By default its false to there is no need to mention callout= false

Answer 2

The document you linked and the annotation itself both seem quite clear:

To allow callouts in a future method, specify (callout=true). The default is (callout=false), which prevents a method from making callouts.

The following snippet shows how to specify that a method executes a callout:

@future (callout=true)
public static void doCalloutFromFuture() {
    //Add code to perform callout
}

That's just how the language was designed. By default future methods cannot make callouts. It's pretty similar to other asynchronous jobs in forcing you to specify when they interact with external systems.

Using Callouts in Batch Apex

To use a callout in batch Apex, specify Database.AllowsCallouts in the class definition. For example:

global class SearchAndReplace implements Database.Batchable<sObject>,
   Database.AllowsCallouts{
}

Callouts include HTTP requests and methods defined with the webService keyword.

As a consequence of the above, you can determine at compile time (just based on the SymbolTable, for example) which asynchronous methods are strictly internal, versus those that can interact with other systems.

Answer 3

Its quite simple, where you want to callout third party when resources available, annotate the future method as 'callout= true'. If you want perform some other asynch operations/other future method operations like mixed DML then no need to annotate callout as by default its false