How to run a batch class for list of string

Question

I have a requirement where I need to process a list of string having hundreds of records in it . For each string I need to have an http callout so I cant run in a normal apex method. For this I am trying to pass the list to a batch apex class and then execute each callout in the execute method so that I wont hit the callout limit. Here is my problem the start method can return only Database.querylocator or Database.iterable. How to pass a list string from the start method with a specified batch size? below is the code explaining the same

 global  class DF_BatchToExcessFields implements Database.Batchable<sObject>{
global list<String> batchlist = new list<String>();

global DF_BatchToExcessFields(list<String> lstObjectAsString)
    {
        batchlist.addAll(lstObjectAsString);
    }

    global Iterable<sObject> start(Database.BatchableContext info){ 

            //Current code
           //str='select id from account';  // just a query for start method
           // return  Database.getQueryLocator(str);

           // My requiremnt is to pass part of list batchlist  to execute method
    }     
    global void execute(Database.BatchableContext info, List<account> scope){
              //I want to process the string ie http callout here

    }     
    global void finish(Database.BatchableContext info){     
    } 
}

Answer 1

All lists are iterables. Create a constructor to take the list, and change the interface of your class:

global class DF_BatchToExcessFields implements Database.Batchable<String> {...

Then return the list in the Start method. Here's a great article by AFawcett to help you get the idea:

http://andyinthecloud.com/2013/08/11/batch-worker-getting-more-done-with-less-work/

Iterable<String> i = new List<String> { 'A', 'B', 'C' };

public with sharing class SimpleBatchApex implements Database.Batchable<String> {
    public Iterable<String> start(Database.BatchableContext BC) {
        return new List<String> { 'Do something', 'Do something else', 'And something more' };
    }

    public void execute(Database.BatchableContext info, List<String> strings) {
        // Do something really expensive with the string!
        String myString = strings[0];
    }

    public void finish(Database.BatchableContext info) {}
}

then try it out in Developer Console

//Process the String's one by one each with its own governor context
Id jobId = Database.executeBatch(new SimpleBatchApex(), 1);