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AspectJ tools most notably contains the AspectJ compiler (AJC). AJC applies aspects to Java classes during compilation, fully replacing Javac for plain Java classes and also compiling native AspectJ or annotation-based @AspectJ syntax. Furthermore, AJC can weave aspects into existing class files in a post-compile binary weaving step. This library is a superset of AspectJ weaver and hence also of AspectJ runtime.

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/* *******************************************************************
 * Copyright (c) 2003 Contributors.
 * All rights reserved.
 * This program and the accompanying materials are made available
 * under the terms of the Eclipse Public License v 2.0
 * which accompanies this distribution and is available at
 * https://www.eclipse.org/org/documents/epl-2.0/EPL-2.0.txt
 *
 * Contributors:
 *     Isberg        initial implementation
 * ******************************************************************/

package org.aspectj.util;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

/**
 * Load classes as File from File[] dirs or URL[] jars.
 */
public class UtilClassLoader extends URLClassLoader {

    /** seek classes in dirs first */
    List dirs;

    /** save URL[] only for toString */
    private URL[] urlsForDebugString;

    public UtilClassLoader(URL[] urls, File[] dirs) {
        super(urls);
        LangUtil.throwIaxIfNotAssignable(dirs, File.class, "dirs");
        this.urlsForDebugString = urls;
        List dcopy = new ArrayList<>();

        if (!LangUtil.isEmpty(dirs)) {
            dcopy.addAll(Arrays.asList(dirs));
        }
        this.dirs = Collections.unmodifiableList(dcopy);
    }


    public URL getResource(String name) {
        return ClassLoader.getSystemResource(name);
    }

    public InputStream getResourceAsStream(String name) {
        return ClassLoader.getSystemResourceAsStream(name);
    }

    public synchronized Class loadClass(String name, boolean resolve)
        throws ClassNotFoundException {
        // search the cache, our dirs (if maybe test),
        // the system, the superclass (URL[]),
        // and our dirs again (if not maybe test)
        ClassNotFoundException thrown = null;
        Class result =  findLoadedClass(name);
        if (null != result) {
            resolve = false;
        } else {
            try {
                result = findSystemClass(name);
            } catch (ClassNotFoundException e) {
                thrown = e;
            }
        }
        if (null == result) {
            try {
                result = super.loadClass(name, resolve);
            } catch (ClassNotFoundException e) {
                thrown = e;
            }
            if (null != result) { // resolved by superclass
                return result;
            }
        }
        if (null == result) {
            byte[] data = readClass(name);
            if (data != null) {
                result = defineClass(name, data, 0, data.length);
            } // handle ClassFormatError?
        }

        if (null == result) {
            throw (null != thrown ? thrown : new ClassNotFoundException(name));
        }
        if (resolve) {
            resolveClass(result);
        }
        return result;
    }

    /** @return null if class not found or byte[] of class otherwise */
    private byte[] readClass(String className) throws ClassNotFoundException {
        final String fileName = className.replace('.', '/')+".class";
		for (File dir : dirs) {
			File file = new File(dir, fileName);
			if (file.canRead()) {
				return getClassData(file);
			}
		}
        return null;
    }

    private byte[] getClassData(File f) {
        try {
            FileInputStream stream= new FileInputStream(f);
            ByteArrayOutputStream out= new ByteArrayOutputStream(1000);
            byte[] b= new byte[4096];
            int n;
            while ((n= stream.read(b)) != -1) {
                out.write(b, 0, n);
            }
            stream.close();
            out.close();
            return out.toByteArray();
        } catch (IOException e) {
        }
        return null;
    }

    /** @return String with debug info: urls and classes used */
    public String toString() {
        return "UtilClassLoader(urls="
            + Arrays.asList(urlsForDebugString)
            + ", dirs="
            + dirs
            + ")";
    }
}