How to programme the prerequisites in plugin.xml?

	<?xml version="1.0" encoding="UTF-8"?>
	<?eclipse version="3.4"?>
	<plugin>
	   <extension
	         point="com.ibm.team.process.service.operationAdvisors">
	      <operationAdvisor
	            class="helloworldadvisor.WorkItemSave"
	            id="HelloWorldAdvisor.prohibitSave"
	            name="Prohibit Save (Hello World Advisor)"
	            operationId="com.ibm.team.workitem.operation.workItemSave">
	      </operationAdvisor>
	   </extension>
	
	</plugin>

WorkItemSave.java

package helloworldadvisor;

import java.sql.Timestamp;

import org.eclipse.core.runtime.IProgressMonitor;
import com.ibm.team.repository.service.AbstractService;
import com.ibm.team.process.common.IProcessConfigurationElement;
import com.ibm.team.process.common.advice.AdvisableOperation;
import com.ibm.team.process.common.advice.IAdvisorInfo;
import com.ibm.team.process.common.advice.IAdvisorInfoCollector;
import com.ibm.team.process.common.advice.runtime.IOperationAdvisor;
import com.ibm.team.repository.common.IAuditable;
import com.ibm.team.repository.common.TeamRepositoryException;
import com.ibm.team.repository.common.UUID;
import com.ibm.team.workitem.common.IAuditableCommon;
import com.ibm.team.workitem.common.ISaveParameter;
import com.ibm.team.workitem.common.IWorkItemCommon;
import com.ibm.team.workitem.common.model.IAttribute;
import com.ibm.team.workitem.common.model.IWorkItem;
import com.ibm.team.workitem.common.model.IWorkItemType;
import com.ibm.team.workitem.common.model.Identifier;

public class WorkItemSave extends AbstractService implements IOperationAdvisor {
	public static final String PROBLEM_TYPE = " HelloWorldAdvisor.prohibitSave";

	public void run(AdvisableOperation operation,
			IProcessConfigurationElement advisorConfiguration,
			IAdvisorInfoCollector collector, IProgressMonitor monitor)
			throws TeamRepositoryException {
		System.out.println("--->AbstractService");
		Object data = operation.getOperationData();
		
		if (!(data instanceof ISaveParameter))
			return;

		ISaveParameter saveParameter = (ISaveParameter) data;
		IAuditableCommon auditableCommon= (IAuditableCommon) getService(IAuditableCommon.class);
		
		if (!(saveParameter.getNewState() instanceof IWorkItem))
			return;
		
		IWorkItem newState= (IWorkItem) saveParameter.getNewState();
		String strWorkItemType = newState.getWorkItemType();
		System.out.println("strWorkItemType--->" + strWorkItemType + "---");
		if (!"task".equals(strWorkItemType.trim())) {
			System.out.println("--->return");
			return;
		}
		
		System.out.println("--->next step001");
	    Identifier newStateId = newState.getState2();
	    String state = newStateId.getStringIdentifier(); 
		if (null != state) {
			System.out.println("uuidStateId--->" + state);
		}
		
		System.out.println("--->next step002");
		//set currentUser to owner
		newState.setOwner(auditableCommon.getUser());
		
		IWorkItemCommon workItemCommon= this.getService(IWorkItemCommon.class);
		//set currentUser to approveaaa
		IAttribute target= workItemCommon.findAttribute(newState.getProjectArea(), "approveaaa", monitor);
		newState.setValue(target, auditableCommon.getUser());
		
		System.out.println("--->next step003");
		//set now to date
		long now= System.currentTimeMillis();
		IAttribute targetdate= workItemCommon.findAttribute(newState.getProjectArea(), "updatedate", monitor);
		newState.setValue(targetdate, new Timestamp(now));
		System.out.println("--->next step004");
		IAuditable auditable = saveParameter.getNewState();


	}
}