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Problem in Rescheduling already scheduled apex class
Hi ,
I have a requirement where in i need to reschedule already scheduled apex classes. I have used System.Schedule method to achieve the same. Since System.Schedule only works with the class names(Need to give classname as a third parameter) and since that would become static , i tried using "Reflection concept of java" so that i can pass the instance of an object as a parameter and thus make it work for more than one class. (I have more than once class to schedule in my organisation).
I get an error which states "Attempt to de-reference a null object"
The following is my Controller code.
global with sharing class GetAllApexClasses {
public PageReference shedulerClicked() {
return null;
}
public void scheduleClicked () {
return ;
}
public String asyncapexjob { get; set; }
public string className { get; set; }
public String schedule { get; set; }
public List<AsyncApexJob> apexclassList{get; set;}
public List<ApexClass> classList{get;set;}
public List<CronTrigger> CronList{get;set;}
public GetAllApexClasses(){
apexclassList = new List<AsyncApexJob>();
apexclassList = [SELECT ApexClassID, CompletedDate,Status,CreatedDate,TotalJobItems,CreatedBy.Name from AsyncApexJob ];
}
public void sheduleClicked ()
{
{
System.debug('Class Name : ' +className);
Type t = Type.forName(className);
String sch = '0 10 * * * ?';
Id m=system.schedule('one', sch,(Schedulable)t.newInstance());
}
}
}The following is my Visual force page
<apex:page controller="GetAllApexClasses">
<apex:form >
<apex:pageBlock >
<apex:pageBlockTable value="{!apexclassList}" var="apexclass">
<apex:column headerValue="Class Name" >
<apex:outputField value="{!apexclass.ApexClassID}"/>
</apex:column>
<apex:column headerValue="Completed Date" >
<apex:outputField value="{!apexclass.CompletedDate}"/>
</apex:column>
<apex:column headerValue="Status" >
<apex:outputField value="{!apexclass.Status}"/>
</apex:column>
<apex:column headerValue="Created By" >
<apex:OutputField value="{!apexclass.CreatedBy.Name}"/>
</apex:column>
<apex:column headerValue="CreatedDate" >
<apex:outputField value="{!apexclass.CreatedDate }"/>
</apex:column>
<apex:column headerValue="TotalJobItems">
<apex:outputField value="{!apexclass.TotalJobItems}"/>
</apex:column>
<apex:column headerValue="Schedule ">
<apex:commandButton id="cb1" action="{!sheduleClicked}" value="schedule" rerender="hiddenBlock">
<apex:param name="className" value="{!apexclass.ApexClassID}" assignTo="{!className}"/>
</apex:commandButton>
</apex:column>
</apex:pageBlockTable>
</apex:pageBlock>
<apex:pageBlock id="hiddenBlock" rendered="false"></apex:pageBlock>
</apex:form>
</apex:page>
I am not able to reschedule my class and get the following error when i click on Schedule Command button
System.NullPointerException: Attempt to de-reference a null object
Class.GetAllApexClasses.sheduleClicked: line 88, column 1
Pls help me as it is urgent. Any help would be greatly appreciated.
Thanks in advance
Hello Navneeth,
In following code:
public void scheduleClicked () {
return ;
}
You are not returning anything, write it like:
public void scheduleClicked () {
return null;
}
No , i tried to change the code but it still gives the same error..
A Cron Job "Helper" Object might help. Create one with a Custom field called "CronTriggerID."
When you schedule your job, also create a helper record
new CronHelper__c (Name = 'Your Scheduled Job Name', CronTriggerID__c = the ID returned from System.Schedule());
When rescheduling an already scheduled apex class, revise your process so:
1) Prior to scheduling, query CronHelper__c for jobs with a matching name
2) Using the CronTriggerID__c field in the results of #1, query the CronTrigger object to see if the job is still scheduled
3) Here you can decide on issuing a system.abortJob() on the ID to remove the job or stop you attempt in scheduling a new one
4) If you do use system.abortJob(), schedule your job, retaining the ID returned from System.Schedule();
5) Remove the CronHelper__c record that helped you identify the CronTrigger in #2
6) Create a new CronHelper__c record for your new job in #4
Hope that helps!