The Basics of Configiration System -- ConfigNamespace and ConfigOption

The configuration system is divided to two type, ConfigNamespace and ConfigOption. When the class GraphDatabaseConfiguration is loaded, the class static member consists a configure tree rooted by ROOT_NS.

The Confignamespace does not contain the configure name and value, it only contains the part of the name before the last dot. Take STORAGE_NS for example, it is a sub namespace of ROOT_NS.

public static ConfigNamespace ROOT_NS = new ConfigNamespace(null,"root","Root Configuration Namespace for the HugeGraph Graph Database");

public static final ConfigNamespace STORAGE_NS = new ConfigNamespace(ROOT_NS,"storage","Configuration options for the storage backend.  Some options are applicable only for certain backends.");

public ConfigNamespace(ConfigNamespace parent, String name, String description) {
this(parent,name,description,false);
}

public ConfigNamespace(ConfigNamespace parent, String name, String description, boolean isUmbrella) {
super(parent,name,description);
this.isUmbrella=isUmbrella;
}

The definition of isUmbrella.

/**
* Wether this namespace is an umbrella namespace, that is, is expects immediate sub-namespaces which are user defined.
* @return
*/
public boolean isUmbrella() {
return isUmbrella;
}

That means, if a namespace is umbrella, then user can define subnamespace. You can define a subnamespace in REGISTRATION_NS, but you can not define a namespace in ROOT_NS.

public static final ConfigNamespace REGISTRATION_NS = new ConfigNamespace(ROOT_NS,"system-registration",
"This is used internally to keep track of open instances.",true);

super(parent,name,description) calls the constructor method of ConfigElement.

public ConfigElement(ConfigNamespace namespace, String name, String description) {
this.namespace = namespace;
this.name = name;
this.description = description;
if (namespace!=null) namespace.registerChild(this);
}

Method isRoot in class ConfigElement.

public boolean isRoot() {
return namespace ==null;
}

ConfigOption

public static final ConfigOption<Integer> GRAPHITE_PORT = new ConfigOption<Integer>(METRICS_GRAPHITE_NS,"port",
"The port to which Graphite data are sent",
ConfigOption.Type.MASKABLE, 2003);

public static final<O> Predicate<O> disallowEmpty(Class<O> clazz) {
return new Predicate<O>() {
@Override
public boolean apply(@Nullable O o) {
if (o==null) return false;
if (o instanceof String) return StringUtils.isNotBlank((String)o);
if (o.getClass().isArray() && (Array.getLength(o)==0 || Array.get(o,0)==null)) return false;
if (o instanceof Collection && (((Collection)o).isEmpty() || ((Collection)o).iterator().next()==null)) return false;
return true;
}
};
}

public ConfigOption(ConfigNamespace parent, String name, String description, Type type, Class<O> datatype, O defaultValue, Predicate<O> verificationFct, ConfigOption<?> supersededBy) {
super(parent, name, description);
Preconditions.checkNotNull(type);
Preconditions.checkNotNull(datatype);
Preconditions.checkNotNull(verificationFct);
this.type = type;
this.datatype = datatype;
this.defaultValue = defaultValue;
this.verificationFct = verificationFct;
this.supersededBy = supersededBy;
// This constructor tends to get called by static initializers, so log before throwing the IAE
if (!ACCEPTED_DATATYPES.contains(datatype)) {
String msg = String.format("Datatype %s is not one of %s", datatype, ACCEPTED_DATATYPES_STRING);
log.error(msg);
throw new IllegalArgumentException(msg);
}
}

Enumeration Type in ConfigOption.

public enum Type {
/**
* Once the database has been opened, these configuration options cannot
* be changed for the entire life of the database
*/
FIXED,
/**
* These options can only be changed for the entire database cluster at
* once when all instances are shut down
*/
GLOBAL_OFFLINE,
/**
* These options can only be changed globally across the entire database
* cluster
*/
GLOBAL,
/**
* These options are global but can be overwritten by a local
* configuration file
*/
MASKABLE,
/**
* These options can ONLY be provided through a local configuration file
*/
LOCAL;
}

The definition of managedTypes.

private static final EnumSet<Type> managedTypes = EnumSet.of(Type.FIXED, Type.GLOBAL_OFFLINE, Type.GLOBAL);

ACCEPTED_DATATYPES = ImmutableSet.of(
ConflictAvoidanceMode.class,
Duration.class,
TimestampProviders.class,
Instant.class,
Boolean.class,
Short.class,
Integer.class,
Byte.class,
Long.class,
Float.class,
Double.class,
String.class,
String[].class
);