lib/classloader/GeneratingClassLoader.java

/*
 * Copyright (c) 2015, 2018, 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.
 */
package jdk.test.lib.classloader;

import java.io.*;
import java.util.*;

/**
 * Classloader that generates classes on the fly.
 *
 * This classloader can load classes with name starting with 'Class'. It will
 * use TemplateClass as template and will replace class name in the bytecode of
 * template class. It can be used for example to detect memory leaks in class
 * loading or to quickly fill Metaspace.
 */
class TemplateClass {
}

public class GeneratingClassLoader extends ClassLoader {

    public synchronized Class loadClass(String name) throws ClassNotFoundException {
        return loadClass(name, false);
    }

    public synchronized Class loadClass(String name, boolean resolve)
            throws ClassNotFoundException {
        Class c = findLoadedClass(name);
        if (c != null) {
            return c;
        }
        if (!name.startsWith(PREFIX)) {
            return super.loadClass(name, resolve);
        }
        if (name.length() != templateClassName.length()) {
            throw new ClassNotFoundException("Only can load classes with name.length() = " + getNameLength() + " got: '" + name + "' length: " + name.length());
        }
        byte[] bytecode = getPatchedByteCode(name);
        c = defineClass(name, bytecode, 0, bytecode.length);
        if (resolve) {
            resolveClass(c);
        }
        return c;
    }

    /**
     * Create generating class loader that will use class file for given class
     * from classpath as template.
     */
    public GeneratingClassLoader(String templateClassName) {
        this.templateClassName = templateClassName;
        classPath = System.getProperty("java.class.path").split(File.pathSeparator);
        try {
            templateClassNameBytes = templateClassName.getBytes(encoding);
        } catch (UnsupportedEncodingException e) {
            throw new RuntimeException(e);
        }
    }

    /**
     * Create generating class loader that will use class file for
     * nsk.share.classload.TemplateClass as template.
     */
    public GeneratingClassLoader() {
        this(TemplateClass.class.getName());
    }

    public int getNameLength() {
        return templateClassName.length();
    }

    String getPrefix() {
        return PREFIX;
    }

    public String getClassName(int number) {
        StringBuffer sb = new StringBuffer();
        sb.append(PREFIX);
        sb.append(number);
        int n = templateClassName.length() - sb.length();
        for (int i = 0; i < n; ++i) {
            sb.append("_");
        }
        return sb.toString();
    }

    private byte[] getPatchedByteCode(String name) throws ClassNotFoundException {
        try {
            byte[] bytecode = getByteCode();
            String fname = name.replace(".", File.separator);
            byte[] replaceBytes = fname.getBytes(encoding);
            for (int offset : offsets) {
                for (int i = 0; i < replaceBytes.length; ++i) {
                    bytecode[offset + i] = replaceBytes[i];
                }
            }
            return bytecode;
        } catch (UnsupportedEncodingException e) {
            throw new RuntimeException(e);
        }
    }

    private byte[] getByteCode() throws ClassNotFoundException {
        if (bytecode == null) {
            readByteCode();
        }
        if (offsets == null) {
            getOffsets(bytecode);
            if (offsets == null) {
                throw new RuntimeException("Class name not found in template class file");
            }
        }
        return (byte[]) bytecode.clone();
    }

    private void readByteCode() throws ClassNotFoundException {
        String fname = templateClassName.replace(".", File.separator) + ".class";
        File target = null;
        for (int i = 0; i < classPath.length; ++i) {
            target = new File(classPath[i] + File.separator + fname);
            if (target.exists()) {
                break;
            }
        }

        if (target == null || !target.exists()) {
            throw new ClassNotFoundException("File not found: " + target);
        }
        try {
            bytecode = ClassLoadUtils.readFile(target);
        } catch (IOException e) {
            throw new ClassNotFoundException(templateClassName, e);
        }
    }

    private void getOffsets(byte[] bytecode) {
        List<Integer> offsets = new ArrayList<Integer>();
        if (this.offsets == null) {
            String pname = templateClassName.replace(".", "/");
            try {
                byte[] pnameb = pname.getBytes(encoding);
                int i = 0;
                while (true) {
                    while (i < bytecode.length) {
                        int j = 0;
                        while (j < pnameb.length && bytecode[i + j] == pnameb[j]) {
                            ++j;
                        }
                        if (j == pnameb.length) {
                            break;
                        }
                        i++;
                    }
                    if (i == bytecode.length) {
                        break;
                    }
                    offsets.add(new Integer(i));
                    i++;
                }
            } catch (UnsupportedEncodingException e) {
                throw new RuntimeException(e);
            }
            this.offsets = new int[offsets.size()];
            for (int i = 0; i < offsets.size(); ++i) {
                this.offsets[i] = offsets.get(i).intValue();
            }
        }
    }

    public static final String DEFAULT_CLASSNAME = TemplateClass.class.getName();
    static final String PREFIX = "Class";

    private final String[] classPath;
    private byte[] bytecode;
    private int[] offsets;
    private final String encoding = "UTF8";
    private final String templateClassName;
    private final byte[] templateClassNameBytes;
}