敲了几个小时后得到了解决方案,发布了整个代码,可能对其他人有帮助
//Connect to PE
//Query the queue with wobnum and get the workobject
queryIndex = "F_WobNum";
queryMin[0] = wob;
queryMax[0] = wob;
queryFlag = VWQueue.QUERY_MIN_VALUES_INCLUSIVE + VWQueue.QUERY_MAX_VALUES_INCLUSIVE;
queryType = VWFetchType.FETCH_TYPE_WORKOBJECT;
queryTypeStepElement = VWFetchType.FETCH_TYPE_STEP_ELEMENT;
queue = session.getQueue("Queue_Name");
query = queue.createQuery(queryIndex, queryMin, queryMax, queryFlag, null, null, queryType);
System.out.println("count " + query.fetchCount());
workObject = (VWWorkObject) query.next();
//get the stepelement
stepElement = workObject.fetchStepElement();
parameters = stepElement.getParameters(VWFieldType.ALL_FIELD_TYPES, VWStepElement.FIELD_USER_AND_SYSTEM_DEFINED);
//get the existing attachment value
tempAttA= (VWAttachment[]) stepElement.getParameterValue("attachment_field_name");
//attachment is VWAttachment array
attachment=tempAttA;
//lock the item for working
stepElement.doLock(true);
//set the new values for the new attachment to be added
tempAtt=new VWAttachment();
tempAtt.setAttachmentName("Attachment_name");
tempAtt.setAttachmentDescription("Added by code");
tempAtt.setType(VWAttachmentType.ATTACHMENT_TYPE_DOCUMENT);
tempAtt.setLibraryType(VWLibraryType.LIBRARY_TYPE_CONTENT_ENGINE);
tempAtt.setLibraryName("TOS");
//vs id of the existing CE document , note that adding attachment means refering a CE object , so the document u want to attach should be stored in CE before.
tempAtt.setId(doc.getVersionSeries().getId());
attachment=tempAttA;
//law is a arraylist of VWAttachment type , so u dont override any existing attachments
law.add(attachment[0]);
law.add(tempAtt);
//set the attchment field with new values
stepElement.setParameterValue("attachment_name", law.toArray(), true);