import com.atlassian.jira.component.ComponentAccessor;
import com.atlassian.jira.issue.link.DefaultIssueLinkManager;
import com.atlassian.jira.issue.Issue
def defaultIssueLinkManager = ComponentAccessor.getComponent(DefaultIssueLinkManager);
def issue = ComponentAccessor.getIssueManager().getIssueObject("PROJECT-1");
def sysUser = ComponentAccessor.getUserManager().getUserByName("admin");
//get all linked issues
def allLinkIssues = defaultIssueLinkManager.getLinkCollection(issue, sysUser).getAllIssues()
allLinkIssues instanceof ArrayList<Issue>
//get linked issues from linkedType and inward links
def issuesIn = defaultIssueLinkManager.getLinkCollection(issue, sysUser).getInwardIssues("LinkName")
issuesIn instanceof ArrayList<Issue>
//get linked issues from linkedType and outward links
def issuesOut = defaultIssueLinkManager.getLinkCollection(issue, sysUser).getOutwardIssues("LinkName")
issuesOut instanceof ArrayList<Issue>