Extract class files which contains Java Class Library and other libraries

gistfile1.sh

$ javac PackageReflection.java
$ java PackageReflection > packages.txt
$ grep "java.lang.String" packages.txt
java/lang/String$1.class
java/lang/String$CaseInsensitiveComparator.class
java/lang/String.class
java/lang/StringBuffer.class
java/lang/StringBuilder.class
java/lang/StringValue$1.class
java/lang/StringValue$StringCache.class
java/lang/StringValue$StringCacheEntry.class
java/lang/StringValue$StringProfile.class
java/lang/StringValue.class
java/beans/java_lang_String_PersistenceDelegate.class
java/lang/String$1.class
java/lang/StringCoding$1.class
java/lang/StringIndexOutOfBoundsException.class
java/lang/StringValue.class
java/lang/StringCoding$StringEncoder.class
java/lang/StringCoding$StringDecoder.class
java/lang/StringCoding.class
java/lang/StringBuilder.class
java/lang/String$CaseInsensitiveComparator.class
java/lang/StringBuffer.class
java/lang/String.class
$ grep "java.util.ArrayList" packages.txt
java/util/ArrayList.class
$

PackageReflection.java

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

public class PackageReflection {
    public static void main(String[] args) {
        ArrayList<String> paths = getLibraryPaths();
        for (String path : paths) {
            if (path.endsWith(".jar") || path.endsWith(".zip")) {
                try {
                    ArrayList<String> classNames = getClassNamesInFile(path);
                    for (String className : classNames) {
                        System.out.println(className);
                    }
                } catch (IOException e) {
                    continue;
                }
            }
        }
    }

    public static ArrayList<String> getLibraryPaths() {
        ArrayList<String> paths = new ArrayList<String>();
        String path = System.getProperty("java.home") + File.separator + ".." + File.separator + "Classes" + File.separator;
        File dir = new File(path);
        File[] files = dir.listFiles();
        for (File file : files) {
            paths.add(file.getAbsolutePath());
        }
        return paths;
    }

    public static ArrayList<String> getClassNamesInFile(String path) throws IOException {
        ArrayList<String> classNames = new ArrayList<String>();
        ZipFile file = new ZipFile(path);
        Enumeration<? extends ZipEntry> entries = file.entries();
        while (entries.hasMoreElements()) {
            ZipEntry entry = entries.nextElement();
            if (entry != null && entry.getName().endsWith(".class")) {
                classNames.add(entry.getName());
            }
        }
        return classNames;
    }
}