UnresolvedClassAgent.java

/*
 * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

import java.io.DataInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.lang.instrument.ClassDefinition;
import java.lang.instrument.Instrumentation;

/*
 * This class is present during compilation, but will be deleted before execution.
 */
class MyUnresolvedClass {
    static void bar() {
    }
}

class MyRedefinedClass {
    static void foo() {
        MyUnresolvedClass.bar();
    }
}

public class UnresolvedClassAgent {
    public static void main(String... args) {
    }

    public static void premain(String args, Instrumentation inst) throws Exception {
        try {
            MyRedefinedClass.foo();
        } catch(NoClassDefFoundError err) {
            System.out.println("NoClassDefFoundError (expected)");
        }

        File f = new File(System.getProperty("test.classes"), "MyRedefinedClass.class");
        byte[] buf = new byte[(int)f.length()];
        try (DataInputStream dis = new DataInputStream(new FileInputStream(f))) {
            dis.readFully(buf);
        }
        ClassDefinition cd = new ClassDefinition(MyRedefinedClass.class, buf);
        inst.redefineClasses(new ClassDefinition[] {cd});

        try {
            MyRedefinedClass.foo();
        } catch(NoClassDefFoundError err) {
            System.out.println("NoClassDefFoundError (expected again)");
        }
    }
}