private Object getAttribute(ObjectName objName, String attrName)
throws MBeanException, InstanceNotFoundException, AttributeNotFoundException,
ReflectionException, IOException {
final NameValueMap values = getCachedAttributes(objName, Collections.singleton(attrName));
Object value = values.get(attrName);
if (value != null || values.containsKey(attrName)) {
return value;
}
// Not in cache, presumably because it was omitted from the
// getAttributes result because of an exception. Following
// call will probably provoke the same exception.
return conn.getAttribute(objName, attrName);
}
private synchronized NameValueMap getCachedAttributes(ObjectName objName, Set<String> attrNames)
throws InstanceNotFoundException, ReflectionException, IOException {
NameValueMap values = cachedValues.get(objName);
if (values != null && values.keySet().containsAll(attrNames)) {
return values;
}
attrNames = new TreeSet<String>(attrNames);
Set<String> oldNames = cachedNames.get(objName);
if (oldNames != null) {
attrNames.addAll(oldNames);
}
values = new NameValueMap();
final AttributeList attrs =
conn.getAttributes(objName, attrNames.toArray(new String[attrNames.size()]));
for (Attribute attr : attrs.asList()) {
values.put(attr.getName(), attr.getValue());
}
cachedValues.put(objName, values);
cachedNames.put(objName, attrNames);
return values;
}