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/*-
* ============LICENSE_START=======================================================
* util
* ================================================================================
* Copyright (C) 2020 AT&T Intellectual Property. All rights reserved.
* ================================================================================
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
* ============LICENSE_END=========================================================
*/
package org.onap.policy.util;
import java.io.ObjectStreamException;
import java.io.Serializable;
import java.util.HashMap;
import org.onap.policy.drools.core.PolicySession;
/**
* This class provides a way to serialize/deserialize objects by locating
* an already existing object on the remote end, and using that instead. It
* is useful for objects that may be shared by multiple transactions.
*/
public class DroolsSessionCommonSerializable implements Serializable {
private static final long serialVersionUID = 1L;
// identifies an object within a Drools session
private String name;
// the object is serialized, but is only used if the corresponding object
// on the remote end can't be located for some reason
private Object object;
/**
* Constructor - initialize instance, and also store a reference to
* the object in a 'PolicySession' adjunct.
*
* @param name identifies the object within the Drools session
* @param object the shared object
*/
public DroolsSessionCommonSerializable(String name, Object object) {
this.name = name;
this.object = object;
// store a reference to the object within the adjunct
// (only works if we can locate the Drools session)
Adjunct adjunct = getAdjunct();
if (adjunct != null) {
adjunct.put(name, object);
}
}
/**
* Return this object as a String.
*
* {@inheritDoc}
*/
@Override
public String toString() {
return "DroolsSessionCommonSerializable[" + name + "]";
}
/**
* This method runs as part of deserialization. If we are able to locate
* the 'PolicySession' and adjunct, and fetch the replacement object from
* the adjunct, that is used. Otherwise, the deserialized object is used
* (which is likely a duplicate).
*
* @return the local named object (if available), or the deserialized
* object
*/
private Object readResolve() throws ObjectStreamException {
Adjunct adjunct = getAdjunct();
Object replacementObject;
if (adjunct != null && (replacementObject = adjunct.get(name)) != null) {
// we found the adjunct, as well as the replacement object -- use
// the replacement object
return replacementObject;
}
// either we couldn't find the adjunct, or couldn't locate the object
// within the adjunct
return object;
}
/**
* This method will:
* 1) Locate the 'PolicySession' (only works from within the Drools thread),
* 2) Find or create the adjunct.
*
* @return the adjunct, or 'null' if we aren't running within a
* Drools session
*/
private Adjunct getAdjunct() {
// PolicySession - this only works from within the Drools thread
PolicySession session = PolicySession.getCurrentSession();
Adjunct adjunct = null;
if (session != null) {
// we found the 'PolicySession' -- now, look for the adjunct
Object adj = session.getAdjunct(Adjunct.class);
if (!(adj instanceof Adjunct)) {
// adjunct does not exist, or has the wrong type -- create it
adjunct = new Adjunct();
session.setAdjunct(Adjunct.class, adjunct);
} else {
// found the adjunct -- return it
adjunct = (Adjunct) adj;
}
}
return adjunct;
}
/* ============================================================ */
/**
* While 'HashMap<String, Object>' could be used directly instead of defining
* a subclass, you can't do run-time type checking of a parameterized type.
* As a result, the 'getAdjunct' method (above) would get compile-time
* warnings.
*/
private static class Adjunct extends HashMap<String, Object> {
private static final long serialVersionUID = 1L;
}
}
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