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diff --git a/src/main/javassist/tools/Callback.java b/src/main/javassist/tools/Callback.java
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+/*
+ * Javassist, a Java-bytecode translator toolkit.
+ * Copyright (C) 1999- Shigeru Chiba. All Rights Reserved.
+ *
+ * The contents of this file are subject to the Mozilla Public License Version
+ * 1.1 (the "License"); you may not use this file except in compliance with
+ * the License.  Alternatively, the contents of this file may be used under
+ * the terms of the GNU Lesser General Public License Version 2.1 or later,
+ * or the Apache License Version 2.0.
+ *
+ * Software distributed under the License is distributed on an "AS IS" basis,
+ * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
+ * for the specific language governing rights and limitations under the
+ * License.
+ */
+
+package javassist.tools;
+
+import javassist.CannotCompileException;
+import javassist.CtBehavior;
+
+import java.util.HashMap;
+import java.util.UUID;
+
+/**
+ * Creates bytecode that when executed calls back to the instance's result method.
+ *
+ * Example of how to create and insert a callback:
+ * <pre>{@code
+ * ctMethod.insertAfter(new Callback("Thread.currentThread()") {
+ *     @literal@Override
+ *     public void result(Object... objects) {
+ *         Thread thread = (Thread) objects[0];
+ *         // do something with thread...
+ *     }
+ * }.sourceCode());
+ * }</pre>
+ * Contains utility methods for inserts callbacks in <code>CtBehaviour</code>, example:
+ * <pre>{@code
+ * insertAfter(ctBehaviour, new Callback("Thread.currentThread(), dummyString") {
+ *     @literal@Override
+ *     public void result(Object... objects) {
+ *         Thread thread = (Thread) objects[0];
+ *         // do something with thread...
+ *     }
+ * });
+ * }</pre>
+ *
+ * @author Marten Hedborg
+ */
+public abstract class Callback {
+
+    public static HashMap<String, Callback> callbacks = new HashMap<String, Callback>();
+
+    private final String sourceCode;
+
+    /**
+     * Constructs a new <code>Callback</code> object.
+     *
+     * @param src       The source code representing the inserted callback bytecode.
+     *                  Can be one or many single statements each returning one object.
+     *                  If many single statements are used they must be comma separated.
+     */
+    public Callback(String src){
+        String uuid = UUID.randomUUID().toString();
+        callbacks.put(uuid, this);
+        sourceCode = "((javassist.tools.Callback) javassist.tools.Callback.callbacks.get(\""+uuid+"\")).result(new Object[]{"+src+"});";
+    }
+
+    /**
+     * Gets called when bytecode is executed
+     *
+     * @param objects   Objects that the bytecode in callback returns
+     */
+    public abstract void result(Object... objects);
+
+    @Override
+    public String toString(){
+        return sourceCode();
+    }
+
+    public String sourceCode(){
+        return sourceCode;
+    }
+
+    /**
+     * Utility method to insert callback at the beginning of the body.
+     *
+     * @param callback  The callback
+     *
+     * @see CtBehavior#insertBefore(String)
+     */
+    public static void insertBefore(CtBehavior behavior, Callback callback)
+            throws CannotCompileException
+    {
+        behavior.insertBefore(callback.toString());
+    }
+
+    /**
+     * Utility method to inserts callback at the end of the body.
+     * The callback is inserted just before every return instruction.
+     * It is not executed when an exception is thrown.
+     *
+     * @param behavior  The behaviour to insert callback in
+     * @param callback  The callback
+     *
+     * @see CtBehavior#insertAfter(String, boolean)
+     */
+    public static void insertAfter(CtBehavior behavior,Callback callback)
+            throws CannotCompileException
+    {
+        behavior.insertAfter(callback.toString(), false);
+    }
+
+    /**
+     * Utility method to inserts callback at the end of the body.
+     * The callback is inserted just before every return instruction.
+     * It is not executed when an exception is thrown.
+     *
+     * @param behavior  The behaviour to insert callback in
+     * @param callback  The callback representing the inserted.
+     * @param asFinally True if the inserted is executed
+     *                  Not only when the control normally returns
+     *                  but also when an exception is thrown.
+     *                  If this parameter is true, the inserted code cannot
+     *                  access local variables.
+     *
+     * @see CtBehavior#insertAfter(String, boolean)
+     */
+    public static void insertAfter(CtBehavior behavior, Callback callback, boolean asFinally)
+            throws CannotCompileException
+    {
+        behavior.insertAfter(callback.toString(), asFinally);
+    }
+
+    /**
+     * Utility method to inserts callback at the specified line in the body.
+     *
+     * @param behavior  The behaviour to insert callback in
+     * @param callback  The callback representing.
+     * @param lineNum   The line number.  The callback is inserted at the
+     *                  beginning of the code at the line specified by this
+     *                  line number.
+     *
+     * @return      The line number at which the callback has been inserted.
+     *
+     * @see CtBehavior#insertAt(int, String)
+     */
+    public static int insertAt(CtBehavior behavior, Callback callback, int lineNum)
+            throws CannotCompileException
+    {
+        return behavior.insertAt(lineNum, callback.toString());
+    }
+}