How do I save a value into a custom field in JIRA programmatically?

Question

I\'ve spent days trying to find out how to save or update a value into a CustomField programmatically and finally found out how it\'s done. So I\'ll make this a question an

Answer 1

Here a solution that works for me in JIRA 6.4.7 to update a custom field value. Actually Im updating a single select field, therefore I have to get the Option for it:

MutableIssue issue = issueManager.getIssueByCurrentKey(issueKey); 
FieldConfig relevantConfig = customField.getRelevantConfig(issue);
// if you use a text field use String. or double for numeric
Option optionForValue = optionsManager.getOptions(relevantConfig).getOptionForValue(option, null);
issue.setCustomFieldValue(customField,optionForValue);
Map modifiedFields = issue.getModifiedFields();
FieldLayoutItem fieldLayoutItem =
fieldLayoutManager.getFieldLayout(issue).getFieldLayoutItem(customField);
DefaultIssueChangeHolder issueChangeHolder = new DefaultIssueChangeHolder();
final ModifiedValue modifiedValue = modifiedFields.get(customField.getId());
customField.updateValue(fieldLayoutItem, issue, modifiedValue, issueChangeHolder);