Recoverable applications - Software Development Case Studies in Java - page 485

private Trackable target # null ;
// a copy of a recoverable object
private String targetRef;
// the label identifying a recoverable object
private String methodName; // the name of a method
private String when;
// a label assuming values "before" and "after"
public Entry(Trackable target, String methodName,
String when) {
this .target # target.cloneTarget();
this .targetRef # Tracker.getObjectRef(target);
this .methodName # methodName;
this .when # when;
}
public Trackable getTarget() { return target; }
public String getTargetRef() { return targetRef; }
public String toString() {
return targetRef ! "." ! methodName ! "() - " ! when;
}
}
Class Tracker is the service component that implements the function-
alities for managing application recovery. It uses two distinct files to save
stable states and state changes. The first is opened when a stable state is
saved, the second when method startTracking() is invoked, i.e. when the
application is started and when a new stable state is saved.
Member variable recording assumes the value true when Tracker is record-
ing state changes and false when Tracker is redoing operations. Member vari-
able objectList is a hash table that records the references to all the trackable
objects that have been registered with method bind() along with their unique
string identifiers. Member variable entrytList records the list of Entity objects
loaded from the log file when the application is restarted or its operations are
undone or redone.
public final class Tracker {
private static int currentEntry # 0;
private static FileOutputStream outputFile # null ;
private static ObjectOutputStream outputObject # null ;
private static Hashtable objectList # new Hashtable();
private static ArrayList entryList # new ArrayList();
public static final String BEFORE # "before";
public static final String AFTER # "after";
public static void startTracking() {
try {
outputFile # new FileOutputStream
("trackerPhysical.log");