This provides services for reading, writing, and querying global attributes. The AttributeService is used to get and set global, arbitrary attributes. Attributes typically have a key and a value, where the key consists of three segments (known as a key set) and a value. Attributes are stored in the database so they persist over server restarts.
An example of use is for persisting system-wide JMX configuration properties in Alfresco Content Services. The AttributeService class provides a Java interface for creating and managing attributes, including methods such as:
- Serializable getAttribute(Serializable ... keys) - get an attribute using a list of unique keys
- getAttributes(AttributeQueryCallback callback, Serializable ... keys) - Getting a collection of attributes
- Serializable getAttribute(Serializable ... keys) - Getting a single attribute
- setAttribute(Serializable value, Serializable ... keys) - Set attribute or create attribute if doesn’t exist
- removeAttribute(Serializable ... keys) - Removing an attribute
- removeAttributes(Serializable ... keys) - Removing a collection of attributes
Collections of Attributes can be processed on retrieval by implementing a callback handler object. The callback handler object’s handleAttribute method is invoked for each attribute retrieved.
The following example shows how you could map a unique document identifier to an Alfresco node reference independently of nodes:
public class DocId2NodeRefMapper {
/**
* The Alfresco Service Registry that gives access to all public content services in Alfresco.
*/
private ServiceRegistry serviceRegistry;
public void setServiceRegistry(ServiceRegistry serviceRegistry) {
this.serviceRegistry = serviceRegistry;
}
public static final String ROOT_ATTR_PATH = "docId2NodeRefMappings";
public static final String DOC_ID_ATTR_NAME = "documentId";
public void mapDocId2NodeRef(String doc_id, NodeRef nodeRef) {
// Check if mapping to node ref is already set up
if (this.serviceRegistry.getAttributeService().exists(ROOT_ATTR_PATH, DOC_ID_ATTR_NAME, doc_id)) {
// Check to see if this node has already been registered
if (!this.serviceRegistry.getAttributeService().getAttribute(ROOT_ATTR_PATH, DOC_ID_ATTR_NAME, doc_id).equals(nodeRef)) {
throw new RuntimeException("Duplicate entry id:" + doc_id);
}
}
// Register node reference under document identifier
this.serviceRegistry.getAttributeService().setAttribute(nodeRef, ROOT_ATTR_PATH, DOC_ID_ATTR_NAME, doc_id);
}
}
Notice how when you set the attribute value the value is the first parameter of the setAttribute method.