Workaround for the 10 web service callout limit in apex?

What are the workarounds for the 10 web service callout limit in apex. If you need to make, say 50 callouts, how do you batch them so that you can execute them all asynchronously? Is there a good design pattern for it?

I’m frequently in this situation and there are different solutions for it that I’m aware of, but I thought it would be good to get this documented on the stackexchange, because it can be tricky and the documentation elsewhere is not great.

Note: The limit was raised to 100 callouts in the Winter ’15 release, so this question is somewhat outdated now: http://docs.releasenotes.salesforce.com/en-us/winter15/release-notes/rn_apex_limits_callout_future.htm

Answer

(community wiki)

@future (valid for triggers and visualforce)

From trigger or VF context you can have up to 10 calls to @future & each of them has a separate context that allows 10 callouts. So you can get up to 100 callouts from a trigger (that itself you’re guaranteed will not contain more than 200 records if it’s saved with API > 20.0, capped at 100 otherwise) or 10+100 in VF. Not bad. Before you decide to abuse it – consider the fact that there’s a 24 hour rolling limit on @future invocations and that multiple callouts to same endpoint might also throw an error. From governor limits page:

A callout request is limited to a maximum of 20 simultaneous requests
to URLs with the same host. The host is defined by the unique
subdomain for the URL, for example, www.mysite.com and
extra.mysite.com are two different hosts. This limit is calculated
across all organizations that access the same host. If this limit is
exceeded, a CalloutException will be thrown.

Batch Jobs

Batch jobs let you process many records (up to 50 M) with whatever granularity you wish (if you don’t specify it, granularity will be 200). Essentially you decide which records you want to work on, you get a fresh context & governor limits for each chunk of data you’re processing and then at the end of the batch job you can send an email, kick-off another batch etc. They’re great for background processing tasks.

In batch jobs you can specify an optional scope parameter. If you really need this, the batch job may even be instructed to process 1 record at a time (and again – each execute() will let you make 10 callouts). That is – if you’ll make sure that the batch class implements Database.AllowsCallouts 😉 Read more about Database.executeBatch if you want to take this path.

Essentially:

public class MyBatchableClass implements Database.Batchable<sObject>, Database.AllowsCallouts{
// definitions of start(), execute() and finish() as in any batch
}

// and then in code that fires it (scheduled class? something that happens 
// after user clicks a button? you use 
Database.executeBatch(new MyBatchableClass(), 1);

// instead of 
// Database.executeBatch(new MyBatchableClass());

Javascript-related solutions

You can jump back and forth in the context. Build a Visualforce page that would process N records at a time, return to the browser, issue a next call that processes another N…

You know your data best – N can be a fixed number or maybe you’ll just want to compare output of Limits methods:

if(Limits.getCallouts() == Limits.getLimitCallouts()){
    return 'I\'m not done yet';
} 

This is best suited in environment where user expects some kind of progress report like “X out of Y records processed”. If you’re after a fully automated background solution that can’t be interrupted by user closing the tab for example – go for one of previous two.

“The call” can be Javascript that hits Apex code in form of webservice call (in ajax toolkit – for example a button on list view that processes selected records), @RemoteAction , actionFunction etc.

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Source : Link , Question Author : paul , Answer Author :
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