1 files changed, 90 insertions, 0 deletions
diff --git a/sample/evolve/VersionManager.java b/sample/evolve/VersionManager.java
new file mode 100644
index 00000000..d95268b8
--- /dev/null
+++ b/sample/evolve/VersionManager.java
@@ -0,0 +1,90 @@
+package sample.evolve;
+
+import java.util.Hashtable;
+import java.lang.reflect.*;
+import javassist.CtClass;
+
+/**
+ * Runtime system for class evolution
+ */
+public class VersionManager {
+    private static Hashtable versionNo = new Hashtable();
+    public final static String latestVersionField = "_version";
+
+    /**
+     * For updating the definition of class my.X, say:
+     *
+     * VersionManager.update("my.X");
+     */
+    public static void update(String qualifiedClassname)
+	throws CannotUpdateException
+    {
+	try {
+	    Class c = getUpdatedClass(qualifiedClassname);
+	    Field f = c.getField(latestVersionField);
+	    f.set(null, c);
+	}
+	catch (ClassNotFoundException e) {
+	    throw new CannotUpdateException("cannot update class: "
+					    + qualifiedClassname);
+	}
+	catch (Exception e) {
+	    throw new CannotUpdateException(e);
+	}
+    }
+
+    private static Class getUpdatedClass(String qualifiedClassname)
+	throws ClassNotFoundException
+    {
+	int version;
+	Object found = versionNo.get(qualifiedClassname);
+	if (found == null)
+	    version = 0;
+	else
+	    version = ((Integer)found).intValue() + 1;
+
+	Class c = Class.forName(qualifiedClassname + '$' + version);
+	versionNo.put(qualifiedClassname, new Integer(version));
+	return c;
+    }
+
+    /* initiaVersion() is used to initialize the _version field of
+     * the updatable classes.
+     */
+    public static Class initialVersion(String[] params) {
+	try {
+	    return getUpdatedClass(params[0]);
+	}
+	catch (ClassNotFoundException e) {
+	    throw new RuntimeException("cannot initialize " + params[0]);
+	}
+    }
+
+    /** make() performs the object creation of the updatable classes.
+     * The expression "new <updatable class>" is replaced with a call
+     * to this method.
+     */
+    public static Object make(Class clazz, Object[] args) {
+	Constructor[] constructors = clazz.getConstructors();
+	int n = constructors.length;
+	for (int i = 0; i < n; ++i) {
+	    try {
+		return constructors[i].newInstance(args);
+	    }
+	    catch (IllegalArgumentException e) {
+		// try again
+	    }
+	    catch (InstantiationException e) {
+		throw new CannotCreateException(e);
+	    }
+	    catch (IllegalAccessException e) {
+		throw new CannotCreateException(e);
+	    }
+	    catch (InvocationTargetException e) {
+		throw new CannotCreateException(e);
+	    }
+	}
+
+	throw new CannotCreateException("no constructor matches");
+    }
+}