--- /dev/null
+/*******************************************************************************
+ * Copyright (c) 2010, 2011 Sonatype, Inc.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ *
+ * Contributors:
+ * Sonatype, Inc. - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.aether;
+
+/**
+ * A trace of nested requests that are performed by the repository system. This trace information can be used to
+ * correlate repository events with higher level operations in the application code that eventually caused the events. A
+ * single trace can carry an arbitrary object as data which is meant to describe a request/operation that is currently
+ * executed. For call hierarchies within the repository system itself, this data will usually be the {@code *Request}
+ * object that is currently processed. When invoking methods on the repository system, client code may provide a request
+ * trace that has been prepopulated with whatever data is useful for the application to indicate its state for later
+ * evaluation when processing the repository events.
+ *
+ * @see RepositoryEvent#getTrace()
+ */
+public class RequestTrace
+{
+
+ private final RequestTrace parent;
+
+ private final Object data;
+
+ /**
+ * Creates a child of the specified request trace. This method is basically a convenience that will invoke
+ * {@link RequestTrace#newChild(Object) parent.newChild()} when the specified parent trace is not {@code null} or
+ * otherwise instantiante a new root trace.
+ *
+ * @param parent The parent request trace, may be {@code null}.
+ * @param data The data to associate with the child trace, may be {@code null}.
+ * @return The child trace, never {@code null}.
+ */
+ public static RequestTrace newChild( RequestTrace parent, Object data )
+ {
+ if ( parent == null )
+ {
+ return new RequestTrace( data );
+ }
+ return parent.newChild( data );
+ }
+
+ /**
+ * Creates a new root trace with the specified data.
+ *
+ * @param data The data to associate with the trace, may be {@code null}.
+ */
+ public RequestTrace( Object data )
+ {
+ this( null, data );
+ }
+
+ /**
+ * Creates a new trace with the specified data and parent
+ *
+ * @param parent The parent trace, may be {@code null} for a root trace.
+ * @param data The data to associate with the trace, may be {@code null}.
+ */
+ protected RequestTrace( RequestTrace parent, Object data )
+ {
+ this.parent = parent;
+ this.data = data;
+ }
+
+ /**
+ * Gets the data associated with this trace.
+ *
+ * @return The data associated with this trace or {@code null} if none.
+ */
+ public final Object getData()
+ {
+ return data;
+ }
+
+ /**
+ * Gets the parent of this trace.
+ *
+ * @return The parent of this trace or {@code null} if this is the root of the trace stack.
+ */
+ public final RequestTrace getParent()
+ {
+ return parent;
+ }
+
+ /**
+ * Creates a new child of this trace.
+ *
+ * @param data The data to associate with the child, may be {@code null}.
+ * @return The child trace, never {@code null}.
+ */
+ public RequestTrace newChild( Object data )
+ {
+ return new RequestTrace( this, data );
+ }
+
+ @Override
+ public String toString()
+ {
+ return String.valueOf( getData() );
+ }
+
+}