深入探究Java中的类加载机制

public static int v = 8080;

public static final int v = 8080;

protected Class<?> loadClass(String name, boolean resolve)
        throws ClassNotFoundException
    {
        synchronized (getClassLoadingLock(name)) {
            // First, check if the class has already been loaded
            // 如果 Java 虚拟机已将此加载器记录为具有给定二进制名称的某个类的启动加载器，
            //则返回该二进制名称的类。
            Class<?> c = findLoadedClass(name);
            if (c == null) {
                long t0 = System.nanoTime();
                try {
                    if (parent != null) {
                        c = parent.loadClass(name, false);//继续查找父类的类加载
                    } else {
                        c = findBootstrapClassOrNull(name);//返回启动类加载器加载的类
                    }
                } catch (ClassNotFoundException e) {
                    // ClassNotFoundException thrown if class not found
                    // from the non-null parent class loader
                }

                if (c == null) {
                    // If still not found, then invoke findClass in order
                    // to find the class.
                    long t1 = System.nanoTime();
                    c = findClass(name);

                    // this is the defining class loader; record the stats
                    sun.misc.PerfCounter.getParentDelegationTime().addTime(t1 - t0);
                    sun.misc.PerfCounter.getFindClassTime().addElapsedTimeFrom(t1);
                    sun.misc.PerfCounter.getFindClasses().increment();
                }
            }
            if (resolve) {
                resolveClass(c);
            }
            return c;
        }
    }

protected Class<?> findClass(String name) throws ClassNotFoundException {
	  // 获取类的字节数组
      byte[] classData = getClassData(name);  
      if (classData == null) {
          throw new ClassNotFoundException();
      } else {
	      //使用defineClass生成class对象
          return defineClass(name, classData, 0, classData.length);
      }
  }

package java.lang;

import java.io.InputStream;
import java.io.IOException;
import java.io.File;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.net.MalformedURLException;
import java.net.URL;
import java.security.AccessController;
import java.security.AccessControlContext;
import java.security.CodeSource;
import java.security.Policy;
import java.security.PrivilegedAction;
import java.security.PrivilegedActionException;
import java.security.PrivilegedExceptionAction;
import java.security.ProtectionDomain;
import java.security.cert.Certificate;
import java.util.Collections;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Set;
import java.util.Stack;
import java.util.Map;
import java.util.Vector;
import java.util.Hashtable;
import java.util.WeakHashMap;
import java.util.concurrent.ConcurrentHashMap;
import sun.misc.CompoundEnumeration;
import sun.misc.Resource;
import sun.misc.URLClassPath;
import sun.misc.VM;
import sun.reflect.CallerSensitive;
import sun.reflect.Reflection;
import sun.reflect.misc.ReflectUtil;
import sun.security.util.SecurityConstants;


public abstract class ClassLoader {

    private static native void registerNatives();
    static {
        registerNatives();
    }

    // The parent class loader for delegation
    // Note: VM hardcoded the offset of this field, thus all new fields
    // must be added *after* it.
    private final ClassLoader parent;

    
    private static class ParallelLoaders {
        private ParallelLoaders() {}

        // the set of parallel capable loader types
        private static final Set<Class<? extends ClassLoader>> loaderTypes =
            Collections.newSetFromMap(
                new WeakHashMap<Class<? extends ClassLoader>, Boolean>());
        static {
            synchronized (loaderTypes) { loaderTypes.add(ClassLoader.class); }
        }

        
        static boolean register(Class<? extends ClassLoader> c) {
            synchronized (loaderTypes) {
                if (loaderTypes.contains(c.getSuperclass())) {
                    // register the class loader as parallel capable
                    // if and only if all of its super classes are.
                    // Note: given current classloading sequence, if
                    // the immediate super class is parallel capable,
                    // all the super classes higher up must be too.
                    loaderTypes.add(c);
                    return true;
                } else {
                    return false;
                }
            }
        }

        
        static boolean isRegistered(Class<? extends ClassLoader> c) {
            synchronized (loaderTypes) {
                return loaderTypes.contains(c);
            }
        }
    }

    // Maps class name to the corresponding lock object when the current
    // class loader is parallel capable.
    // Note: VM also uses this field to decide if the current class loader
    // is parallel capable and the appropriate lock object for class loading.
    private final ConcurrentHashMap<String, Object> parallelLockMap;

    // Hashtable that maps packages to certs
    private final Map <String, Certificate[]> package2certs;

    // Shared among all packages with unsigned classes
    private static final Certificate[] nocerts = new Certificate[0];

    // The classes loaded by this class loader. The only purpose of this table
    // is to keep the classes from being GC'ed until the loader is GC'ed.
    private final Vector<Class<?>> classes = new Vector<>();

    // The "default" domain. Set as the default ProtectionDomain on newly
    // created classes.
    private final ProtectionDomain defaultDomain =
        new ProtectionDomain(new CodeSource(null, (Certificate[]) null),
                             null, this, null);

    // The initiating protection domains for all classes loaded by this loader
    private final Set<ProtectionDomain> domains;

    // Invoked by the VM to record every loaded class with this loader.
    void addClass(Class<?> c) {
        classes.addElement(c);
    }

    // The packages defined in this class loader.  Each package name is mapped
    // to its corresponding Package object.
    // @GuardedBy("itself")
    private final HashMap<String, Package> packages = new HashMap<>();

    private static Void checkCreateClassLoader() {
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            security.checkCreateClassLoader();
        }
        return null;
    }

    private ClassLoader(Void unused, ClassLoader parent) {
        this.parent = parent;
        if (ParallelLoaders.isRegistered(this.getClass())) {
            parallelLockMap = new ConcurrentHashMap<>();
            package2certs = new ConcurrentHashMap<>();
            domains =
                Collections.synchronizedSet(new HashSet<ProtectionDomain>());
            assertionLock = new Object();
        } else {
            // no finer-grained lock; lock on the classloader instance
            parallelLockMap = null;
            package2certs = new Hashtable<>();
            domains = new HashSet<>();
            assertionLock = this;
        }
    }

    
    protected ClassLoader(ClassLoader parent) {
        this(checkCreateClassLoader(), parent);
    }

    
    protected ClassLoader() {
        this(checkCreateClassLoader(), getSystemClassLoader());
    }

    // -- Class --

    
    public Class<?> loadClass(String name) throws ClassNotFoundException {
        return loadClass(name, false);
    }

    
    protected Class<?> loadClass(String name, boolean resolve)
        throws ClassNotFoundException
    {
        synchronized (getClassLoadingLock(name)) {
            // First, check if the class has already been loaded
            Class<?> c = findLoadedClass(name);
            if (c == null) {
                long t0 = System.nanoTime();
                try {
                    if (parent != null) {
                        c = parent.loadClass(name, false);
                    } else {
                        c = findBootstrapClassOrNull(name);
                    }
                } catch (ClassNotFoundException e) {
                    // ClassNotFoundException thrown if class not found
                    // from the non-null parent class loader
                }

                if (c == null) {
                    // If still not found, then invoke findClass in order
                    // to find the class.
                    long t1 = System.nanoTime();
                    c = findClass(name);

                    // this is the defining class loader; record the stats
                    sun.misc.PerfCounter.getParentDelegationTime().addTime(t1 - t0);
                    sun.misc.PerfCounter.getFindClassTime().addElapsedTimeFrom(t1);
                    sun.misc.PerfCounter.getFindClasses().increment();
                }
            }
            if (resolve) {
                resolveClass(c);
            }
            return c;
        }
    }

    
    protected Object getClassLoadingLock(String className) {
        Object lock = this;
        if (parallelLockMap != null) {
            Object newLock = new Object();
            lock = parallelLockMap.putIfAbsent(className, newLock);
            if (lock == null) {
                lock = newLock;
            }
        }
        return lock;
    }

    // This method is invoked by the virtual machine to load a class.
    private Class<?> loadClassInternal(String name)
        throws ClassNotFoundException
    {
        // For backward compatibility, explicitly lock on 'this' when
        // the current class loader is not parallel capable.
        if (parallelLockMap == null) {
            synchronized (this) {
                 return loadClass(name);
            }
        } else {
            return loadClass(name);
        }
    }

    // Invoked by the VM after loading class with this loader.
    private void checkPackageAccess(Class<?> cls, ProtectionDomain pd) {
        final SecurityManager sm = System.getSecurityManager();
        if (sm != null) {
            if (ReflectUtil.isNonPublicProxyClass(cls)) {
                for (Class<?> intf: cls.getInterfaces()) {
                    checkPackageAccess(intf, pd);
                }
                return;
            }

            final String name = cls.getName();
            final int i = name.lastIndexOf('.');
            if (i != -1) {
                AccessController.doPrivileged(new PrivilegedAction<Void>() {
                    public Void run() {
                        sm.checkPackageAccess(name.substring(0, i));
                        return null;
                    }
                }, new AccessControlContext(new ProtectionDomain[] {pd}));
            }
        }
        domains.add(pd);
    }

    
    protected Class<?> findClass(String name) throws ClassNotFoundException {
        throw new ClassNotFoundException(name);
    }

    
    @Deprecated
    protected final Class<?> defineClass(byte[] b, int off, int len)
        throws ClassFormatError
    {
        return defineClass(null, b, off, len, null);
    }

    
    protected final Class<?> defineClass(String name, byte[] b, int off, int len)
        throws ClassFormatError
    {
        return defineClass(name, b, off, len, null);
    }

    
    private ProtectionDomain preDefineClass(String name,
                                            ProtectionDomain pd)
    {
        if (!checkName(name))
            throw new NoClassDefFoundError("IllegalName: " + name);

        // Note:  Checking logic in java.lang.invoke.MemberName.checkForTypeAlias
        // relies on the fact that spoofing is impossible if a class has a name
        // of the form "java.*"
        if ((name != null) && name.startsWith("java.")) {
            throw new SecurityException
                ("Prohibited package name: " +
                 name.substring(0, name.lastIndexOf('.')));
        }
        if (pd == null) {
            pd = defaultDomain;
        }

        if (name != null) checkCerts(name, pd.getCodeSource());

        return pd;
    }

    private String defineClassSourceLocation(ProtectionDomain pd)
    {
        CodeSource cs = pd.getCodeSource();
        String source = null;
        if (cs != null && cs.getLocation() != null) {
            source = cs.getLocation().toString();
        }
        return source;
    }

    private void postDefineClass(Class<?> c, ProtectionDomain pd)
    {
        if (pd.getCodeSource() != null) {
            Certificate certs[] = pd.getCodeSource().getCertificates();
            if (certs != null)
                setSigners(c, certs);
        }
    }

    
    protected final Class<?> defineClass(String name, byte[] b, int off, int len,
                                         ProtectionDomain protectionDomain)
        throws ClassFormatError
    {
        protectionDomain = preDefineClass(name, protectionDomain);
        String source = defineClassSourceLocation(protectionDomain);
        Class<?> c = defineClass1(name, b, off, len, protectionDomain, source);
        postDefineClass(c, protectionDomain);
        return c;
    }

    
    protected final Class<?> defineClass(String name, java.nio.ByteBuffer b,
                                         ProtectionDomain protectionDomain)
        throws ClassFormatError
    {
        int len = b.remaining();

        // Use byte[] if not a direct ByteBufer:
        if (!b.isDirect()) {
            if (b.hasArray()) {
                return defineClass(name, b.array(),
                                   b.position() + b.arrayOffset(), len,
                                   protectionDomain);
            } else {
                // no array, or read-only array
                byte[] tb = new byte[len];
                b.get(tb);  // get bytes out of byte buffer.
                return defineClass(name, tb, 0, len, protectionDomain);
            }
        }

        protectionDomain = preDefineClass(name, protectionDomain);
        String source = defineClassSourceLocation(protectionDomain);
        Class<?> c = defineClass2(name, b, b.position(), len, protectionDomain, source);
        postDefineClass(c, protectionDomain);
        return c;
    }

    private native Class<?> defineClass0(String name, byte[] b, int off, int len,
                                         ProtectionDomain pd);

    private native Class<?> defineClass1(String name, byte[] b, int off, int len,
                                         ProtectionDomain pd, String source);

    private native Class<?> defineClass2(String name, java.nio.ByteBuffer b,
                                         int off, int len, ProtectionDomain pd,
                                         String source);

    // true if the name is null or has the potential to be a valid binary name
    private boolean checkName(String name) {
        if ((name == null) || (name.length() == 0))
            return true;
        if ((name.indexOf('/') != -1)
            || (!VM.allowArraySyntax() && (name.charAt(0) == '[')))
            return false;
        return true;
    }

    private void checkCerts(String name, CodeSource cs) {
        int i = name.lastIndexOf('.');
        String pname = (i == -1) ? "" : name.substring(0, i);

        Certificate[] certs = null;
        if (cs != null) {
            certs = cs.getCertificates();
        }
        Certificate[] pcerts = null;
        if (parallelLockMap == null) {
            synchronized (this) {
                pcerts = package2certs.get(pname);
                if (pcerts == null) {
                    package2certs.put(pname, (certs == null? nocerts:certs));
                }
            }
        } else {
            pcerts = ((ConcurrentHashMap<String, Certificate[]>)package2certs).
                putIfAbsent(pname, (certs == null? nocerts:certs));
        }
        if (pcerts != null && !compareCerts(pcerts, certs)) {
            throw new SecurityException("class \""+ name +
                 "\"'s signer information does not match signer information of other classes in the same package");
        }
    }

    
    private boolean compareCerts(Certificate[] pcerts,
                                 Certificate[] certs)
    {
        // certs can be null, indicating no certs.
        if ((certs == null) || (certs.length == 0)) {
            return pcerts.length == 0;
        }

        // the length must be the same at this point
        if (certs.length != pcerts.length)
            return false;

        // go through and make sure all the certs in one array
        // are in the other and vice-versa.
        boolean match;
        for (int i = 0; i < certs.length; i++) {
            match = false;
            for (int j = 0; j < pcerts.length; j++) {
                if (certs[i].equals(pcerts[j])) {
                    match = true;
                    break;
                }
            }
            if (!match) return false;
        }

        // now do the same for pcerts
        for (int i = 0; i < pcerts.length; i++) {
            match = false;
            for (int j = 0; j < certs.length; j++) {
                if (pcerts[i].equals(certs[j])) {
                    match = true;
                    break;
                }
            }
            if (!match) return false;
        }

        return true;
    }

    
    protected final void resolveClass(Class<?> c) {
        resolveClass0(c);
    }

    private native void resolveClass0(Class<?> c);

    
    protected final Class<?> findSystemClass(String name)
        throws ClassNotFoundException
    {
        ClassLoader system = getSystemClassLoader();
        if (system == null) {
            if (!checkName(name))
                throw new ClassNotFoundException(name);
            Class<?> cls = findBootstrapClass(name);
            if (cls == null) {
                throw new ClassNotFoundException(name);
            }
            return cls;
        }
        return system.loadClass(name);
    }

    
    private Class<?> findBootstrapClassOrNull(String name)
    {
        if (!checkName(name)) return null;

        return findBootstrapClass(name);
    }

    // return null if not found
    private native Class<?> findBootstrapClass(String name);

    
    protected final Class<?> findLoadedClass(String name) {
        if (!checkName(name))
            return null;
        return findLoadedClass0(name);
    }

    private native final Class<?> findLoadedClass0(String name);

    
    protected final void setSigners(Class<?> c, Object[] signers) {
        c.setSigners(signers);
    }


    // -- Resource --

    
    public URL getResource(String name) {
        URL url;
        if (parent != null) {
            url = parent.getResource(name);
        } else {
            url = getBootstrapResource(name);
        }
        if (url == null) {
            url = findResource(name);
        }
        return url;
    }

    
    public Enumeration<URL> getResources(String name) throws IOException {
        @SuppressWarnings("unchecked")
        Enumeration<URL>[] tmp = (Enumeration<URL>[]) new Enumeration<?>[2];
        if (parent != null) {
            tmp[0] = parent.getResources(name);
        } else {
            tmp[0] = getBootstrapResources(name);
        }
        tmp[1] = findResources(name);

        return new CompoundEnumeration<>(tmp);
    }

    
    protected URL findResource(String name) {
        return null;
    }

    
    protected Enumeration<URL> findResources(String name) throws IOException {
        return java.util.Collections.emptyEnumeration();
    }

    
    @CallerSensitive
    protected static boolean registerAsParallelCapable() {
        Class<? extends ClassLoader> callerClass =
            Reflection.getCallerClass().asSubclass(ClassLoader.class);
        return ParallelLoaders.register(callerClass);
    }

    
    public static URL getSystemResource(String name) {
        ClassLoader system = getSystemClassLoader();
        if (system == null) {
            return getBootstrapResource(name);
        }
        return system.getResource(name);
    }

    
    public static Enumeration<URL> getSystemResources(String name)
        throws IOException
    {
        ClassLoader system = getSystemClassLoader();
        if (system == null) {
            return getBootstrapResources(name);
        }
        return system.getResources(name);
    }

    
    private static URL getBootstrapResource(String name) {
        URLClassPath ucp = getBootstrapClassPath();
        Resource res = ucp.getResource(name);
        return res != null ? res.getURL() : null;
    }

    
    private static Enumeration<URL> getBootstrapResources(String name)
        throws IOException
    {
        final Enumeration<Resource> e =
            getBootstrapClassPath().getResources(name);
        return new Enumeration<URL> () {
            public URL nextElement() {
                return e.nextElement().getURL();
            }
            public boolean hasMoreElements() {
                return e.hasMoreElements();
            }
        };
    }

    // Returns the URLClassPath that is used for finding system resources.
    static URLClassPath getBootstrapClassPath() {
        return sun.misc.Launcher.getBootstrapClassPath();
    }


    
    public InputStream getResourceAsStream(String name) {
        URL url = getResource(name);
        try {
            return url != null ? url.openStream() : null;
        } catch (IOException e) {
            return null;
        }
    }

    
    public static InputStream getSystemResourceAsStream(String name) {
        URL url = getSystemResource(name);
        try {
            return url != null ? url.openStream() : null;
        } catch (IOException e) {
            return null;
        }
    }


    // -- Hierarchy --

    
    @CallerSensitive
    public final ClassLoader getParent() {
        if (parent == null)
            return null;
        SecurityManager sm = System.getSecurityManager();
        if (sm != null) {
            // Check access to the parent class loader
            // If the caller's class loader is same as this class loader,
            // permission check is performed.
            checkClassLoaderPermission(parent, Reflection.getCallerClass());
        }
        return parent;
    }

    
    @CallerSensitive
    public static ClassLoader getSystemClassLoader() {
        initSystemClassLoader();
        if (scl == null) {
            return null;
        }
        SecurityManager sm = System.getSecurityManager();
        if (sm != null) {
            checkClassLoaderPermission(scl, Reflection.getCallerClass());
        }
        return scl;
    }

    private static synchronized void initSystemClassLoader() {
        if (!sclSet) {
            if (scl != null)
                throw new IllegalStateException("recursive invocation");
            sun.misc.Launcher l = sun.misc.Launcher.getLauncher();
            if (l != null) {
                Throwable oops = null;
                scl = l.getClassLoader();
                try {
                    scl = AccessController.doPrivileged(
                        new SystemClassLoaderAction(scl));
                } catch (PrivilegedActionException pae) {
                    oops = pae.getCause();
                    if (oops instanceof InvocationTargetException) {
                        oops = oops.getCause();
                    }
                }
                if (oops != null) {
                    if (oops instanceof Error) {
                        throw (Error) oops;
                    } else {
                        // wrap the exception
                        throw new Error(oops);
                    }
                }
            }
            sclSet = true;
        }
    }

    // Returns true if the specified class loader can be found in this class
    // loader's delegation chain.
    boolean isAncestor(ClassLoader cl) {
        ClassLoader acl = this;
        do {
            acl = acl.parent;
            if (cl == acl) {
                return true;
            }
        } while (acl != null);
        return false;
    }

    // Tests if class loader access requires "getClassLoader" permission
    // check.  A class loader 'from' can access class loader 'to' if
    // class loader 'from' is same as class loader 'to' or an ancestor
    // of 'to'.  The class loader in a system domain can access
    // any class loader.
    private static boolean needsClassLoaderPermissionCheck(ClassLoader from,
                                                           ClassLoader to)
    {
        if (from == to)
            return false;

        if (from == null)
            return false;

        return !to.isAncestor(from);
    }

    // Returns the class's class loader, or null if none.
    static ClassLoader getClassLoader(Class<?> caller) {
        // This can be null if the VM is requesting it
        if (caller == null) {
            return null;
        }
        // Circumvent security check since this is package-private
        return caller.getClassLoader0();
    }

    
    static void checkClassLoaderPermission(ClassLoader cl, Class<?> caller) {
        SecurityManager sm = System.getSecurityManager();
        if (sm != null) {
            // caller can be null if the VM is requesting it
            ClassLoader ccl = getClassLoader(caller);
            if (needsClassLoaderPermissionCheck(ccl, cl)) {
                sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
            }
        }
    }

    // The class loader for the system
    // @GuardedBy("ClassLoader.class")
    private static ClassLoader scl;

    // Set to true once the system class loader has been set
    // @GuardedBy("ClassLoader.class")
    private static boolean sclSet;


    // -- Package --

    
    protected Package definePackage(String name, String specTitle,
                                    String specVersion, String specVendor,
                                    String implTitle, String implVersion,
                                    String implVendor, URL sealBase)
        throws IllegalArgumentException
    {
        synchronized (packages) {
            Package pkg = getPackage(name);
            if (pkg != null) {
                throw new IllegalArgumentException(name);
            }
            pkg = new Package(name, specTitle, specVersion, specVendor,
                              implTitle, implVersion, implVendor,
                              sealBase, this);
            packages.put(name, pkg);
            return pkg;
        }
    }

    
    protected Package getPackage(String name) {
        Package pkg;
        synchronized (packages) {
            pkg = packages.get(name);
        }
        if (pkg == null) {
            if (parent != null) {
                pkg = parent.getPackage(name);
            } else {
                pkg = Package.getSystemPackage(name);
            }
            if (pkg != null) {
                synchronized (packages) {
                    Package pkg2 = packages.get(name);
                    if (pkg2 == null) {
                        packages.put(name, pkg);
                    } else {
                        pkg = pkg2;
                    }
                }
            }
        }
        return pkg;
    }

    
    protected Package[] getPackages() {
        Map<String, Package> map;
        synchronized (packages) {
            map = new HashMap<>(packages);
        }
        Package[] pkgs;
        if (parent != null) {
            pkgs = parent.getPackages();
        } else {
            pkgs = Package.getSystemPackages();
        }
        if (pkgs != null) {
            for (int i = 0; i < pkgs.length; i++) {
                String pkgName = pkgs[i].getName();
                if (map.get(pkgName) == null) {
                    map.put(pkgName, pkgs[i]);
                }
            }
        }
        return map.values().toArray(new Package[map.size()]);
    }


    // -- Native library access --

    
    protected String findLibrary(String libname) {
        return null;
    }

    
    static class NativeLibrary {
        // opaque handle to native library, used in native code.
        long handle;
        // the version of JNI environment the native library requires.
        private int jniVersion;
        // the class from which the library is loaded, also indicates
        // the loader this native library belongs.
        private final Class<?> fromClass;
        // the canonicalized name of the native library.
        // or static library name
        String name;
        // Indicates if the native library is linked into the VM
        boolean isBuiltin;
        // Indicates if the native library is loaded
        boolean loaded;
        native void load(String name, boolean isBuiltin);

        native long find(String name);
        native void unload(String name, boolean isBuiltin);

        public NativeLibrary(Class<?> fromClass, String name, boolean isBuiltin) {
            this.name = name;
            this.fromClass = fromClass;
            this.isBuiltin = isBuiltin;
        }

        protected void finalize() {
            synchronized (loadedLibraryNames) {
                if (fromClass.getClassLoader() != null && loaded) {
                    
                    int size = loadedLibraryNames.size();
                    for (int i = 0; i < size; i++) {
                        if (name.equals(loadedLibraryNames.elementAt(i))) {
                            loadedLibraryNames.removeElementAt(i);
                            break;
                        }
                    }
                    
                    ClassLoader.nativeLibraryContext.push(this);
                    try {
                        unload(name, isBuiltin);
                    } finally {
                        ClassLoader.nativeLibraryContext.pop();
                    }
                }
            }
        }
        // Invoked in the VM to determine the context class in
        // JNI_Load/JNI_Unload
        static Class<?> getFromClass() {
            return ClassLoader.nativeLibraryContext.peek().fromClass;
        }
    }

    // All native library names we've loaded.
    private static Vector<String> loadedLibraryNames = new Vector<>();

    // Native libraries belonging to system classes.
    private static Vector<NativeLibrary> systemNativeLibraries
        = new Vector<>();

    // Native libraries associated with the class loader.
    private Vector<NativeLibrary> nativeLibraries = new Vector<>();

    // native libraries being loaded/unloaded.
    private static Stack<NativeLibrary> nativeLibraryContext = new Stack<>();

    // The paths searched for libraries
    private static String usr_paths[];
    private static String sys_paths[];

    private static String[] initializePath(String propname) {
        String ldpath = System.getProperty(propname, "");
        String ps = File.pathSeparator;
        int ldlen = ldpath.length();
        int i, j, n;
        // Count the separators in the path
        i = ldpath.indexOf(ps);
        n = 0;
        while (i >= 0) {
            n++;
            i = ldpath.indexOf(ps, i + 1);
        }

        // allocate the array of paths - n :'s = n + 1 path elements
        String[] paths = new String[n + 1];

        // Fill the array with paths from the ldpath
        n = i = 0;
        j = ldpath.indexOf(ps);
        while (j >= 0) {
            if (j - i > 0) {
                paths[n++] = ldpath.substring(i, j);
            } else if (j - i == 0) {
                paths[n++] = ".";
            }
            i = j + 1;
            j = ldpath.indexOf(ps, i);
        }
        paths[n] = ldpath.substring(i, ldlen);
        return paths;
    }

    // Invoked in the java.lang.Runtime class to implement load and loadLibrary.
    static void loadLibrary(Class<?> fromClass, String name,
                            boolean isAbsolute) {
        ClassLoader loader =
            (fromClass == null) ? null : fromClass.getClassLoader();
        if (sys_paths == null) {
            usr_paths = initializePath("java.library.path");
            sys_paths = initializePath("sun.boot.library.path");
        }
        if (isAbsolute) {
            if (loadLibrary0(fromClass, new File(name))) {
                return;
            }
            throw new UnsatisfiedLinkError("Can't load library: " + name);
        }
        if (loader != null) {
            String libfilename = loader.findLibrary(name);
            if (libfilename != null) {
                File libfile = new File(libfilename);
                if (!libfile.isAbsolute()) {
                    throw new UnsatisfiedLinkError(
    "ClassLoader.findLibrary failed to return an absolute path: " + libfilename);
                }
                if (loadLibrary0(fromClass, libfile)) {
                    return;
                }
                throw new UnsatisfiedLinkError("Can't load " + libfilename);
            }
        }
        for (int i = 0 ; i < sys_paths.length ; i++) {
            File libfile = new File(sys_paths[i], System.mapLibraryName(name));
            if (loadLibrary0(fromClass, libfile)) {
                return;
            }
            libfile = ClassLoaderHelper.mapAlternativeName(libfile);
            if (libfile != null && loadLibrary0(fromClass, libfile)) {
                return;
            }
        }
        if (loader != null) {
            for (int i = 0 ; i < usr_paths.length ; i++) {
                File libfile = new File(usr_paths[i],
                                        System.mapLibraryName(name));
                if (loadLibrary0(fromClass, libfile)) {
                    return;
                }
                libfile = ClassLoaderHelper.mapAlternativeName(libfile);
                if (libfile != null && loadLibrary0(fromClass, libfile)) {
                    return;
                }
            }
        }
        // Oops, it failed
        throw new UnsatisfiedLinkError("no " + name + " in java.library.path");
    }

    private static native String findBuiltinLib(String name);

    private static boolean loadLibrary0(Class<?> fromClass, final File file) {
        // Check to see if we're attempting to access a static library
        String name = findBuiltinLib(file.getName());
        boolean isBuiltin = (name != null);
        if (!isBuiltin) {
            boolean exists = AccessController.doPrivileged(
                new PrivilegedAction<Object>() {
                    public Object run() {
                        return file.exists() ? Boolean.TRUE : null;
                    }})
                != null;
            if (!exists) {
                return false;
            }
            try {
                name = file.getCanonicalPath();
            } catch (IOException e) {
                return false;
            }
        }
        ClassLoader loader =
            (fromClass == null) ? null : fromClass.getClassLoader();
        Vector<NativeLibrary> libs =
            loader != null ? loader.nativeLibraries : systemNativeLibraries;
        synchronized (libs) {
            int size = libs.size();
            for (int i = 0; i < size; i++) {
                NativeLibrary lib = libs.elementAt(i);
                if (name.equals(lib.name)) {
                    return true;
                }
            }

            synchronized (loadedLibraryNames) {
                if (loadedLibraryNames.contains(name)) {
                    throw new UnsatisfiedLinkError
                        ("Native Library " +
                         name +
                         " already loaded in another classloader");
                }
                
                int n = nativeLibraryContext.size();
                for (int i = 0; i < n; i++) {
                    NativeLibrary lib = nativeLibraryContext.elementAt(i);
                    if (name.equals(lib.name)) {
                        if (loader == lib.fromClass.getClassLoader()) {
                            return true;
                        } else {
                            throw new UnsatisfiedLinkError
                                ("Native Library " +
                                 name +
                                 " is being loaded in another classloader");
                        }
                    }
                }
                NativeLibrary lib = new NativeLibrary(fromClass, name, isBuiltin);
                nativeLibraryContext.push(lib);
                try {
                    lib.load(name, isBuiltin);
                } finally {
                    nativeLibraryContext.pop();
                }
                if (lib.loaded) {
                    loadedLibraryNames.addElement(name);
                    libs.addElement(lib);
                    return true;
                }
                return false;
            }
        }
    }

    // Invoked in the VM class linking code.
    static long findNative(ClassLoader loader, String name) {
        Vector<NativeLibrary> libs =
            loader != null ? loader.nativeLibraries : systemNativeLibraries;
        synchronized (libs) {
            int size = libs.size();
            for (int i = 0; i < size; i++) {
                NativeLibrary lib = libs.elementAt(i);
                long entry = lib.find(name);
                if (entry != 0)
                    return entry;
            }
        }
        return 0;
    }


    // -- Assertion management --

    final Object assertionLock;

    // The default toggle for assertion checking.
    // @GuardedBy("assertionLock")
    private boolean defaultAssertionStatus = false;

    // Maps String packageName to Boolean package default assertion status Note
    // that the default package is placed under a null map key.  If this field
    // is null then we are delegating assertion status queries to the VM, i.e.,
    // none of this ClassLoader's assertion status modification methods have
    // been invoked.
    // @GuardedBy("assertionLock")
    private Map<String, Boolean> packageAssertionStatus = null;

    // Maps String fullyQualifiedClassName to Boolean assertionStatus If this
    // field is null then we are delegating assertion status queries to the VM,
    // i.e., none of this ClassLoader's assertion status modification methods
    // have been invoked.
    // @GuardedBy("assertionLock")
    Map<String, Boolean> classAssertionStatus = null;

    
    public void setDefaultAssertionStatus(boolean enabled) {
        synchronized (assertionLock) {
            if (classAssertionStatus == null)
                initializeJavaAssertionMaps();

            defaultAssertionStatus = enabled;
        }
    }

    
    public void setPackageAssertionStatus(String packageName,
                                          boolean enabled) {
        synchronized (assertionLock) {
            if (packageAssertionStatus == null)
                initializeJavaAssertionMaps();

            packageAssertionStatus.put(packageName, enabled);
        }
    }

    
    public void setClassAssertionStatus(String className, boolean enabled) {
        synchronized (assertionLock) {
            if (classAssertionStatus == null)
                initializeJavaAssertionMaps();

            classAssertionStatus.put(className, enabled);
        }
    }

    
    public void clearAssertionStatus() {
        
        synchronized (assertionLock) {
            classAssertionStatus = new HashMap<>();
            packageAssertionStatus = new HashMap<>();
            defaultAssertionStatus = false;
        }
    }

    
    boolean desiredAssertionStatus(String className) {
        synchronized (assertionLock) {
            // assert classAssertionStatus   != null;
            // assert packageAssertionStatus != null;

            // Check for a class entry
            Boolean result = classAssertionStatus.get(className);
            if (result != null)
                return result.booleanValue();

            // Check for most specific package entry
            int dotIndex = className.lastIndexOf(".");
            if (dotIndex < 0) { // default package
                result = packageAssertionStatus.get(null);
                if (result != null)
                    return result.booleanValue();
            }
            while(dotIndex > 0) {
                className = className.substring(0, dotIndex);
                result = packageAssertionStatus.get(className);
                if (result != null)
                    return result.booleanValue();
                dotIndex = className.lastIndexOf(".", dotIndex-1);
            }

            // Return the classloader default
            return defaultAssertionStatus;
        }
    }

    // Set up the assertions with information provided by the VM.
    // Note: Should only be called inside a synchronized block
    private void initializeJavaAssertionMaps() {
        // assert Thread.holdsLock(assertionLock);

        classAssertionStatus = new HashMap<>();
        packageAssertionStatus = new HashMap<>();
        AssertionStatusDirectives directives = retrieveDirectives();

        for(int i = 0; i < directives.classes.length; i++)
            classAssertionStatus.put(directives.classes[i],
                                     directives.classEnabled[i]);

        for(int i = 0; i < directives.packages.length; i++)
            packageAssertionStatus.put(directives.packages[i],
                                       directives.packageEnabled[i]);

        defaultAssertionStatus = directives.deflt;
    }

    // Retrieves the assertion directives from the VM.
    private static native AssertionStatusDirectives retrieveDirectives();
}


class SystemClassLoaderAction
    implements PrivilegedExceptionAction<ClassLoader> {
    private ClassLoader parent;

    SystemClassLoaderAction(ClassLoader parent) {
        this.parent = parent;
    }

    public ClassLoader run() throws Exception {
        String cls = System.getProperty("java.system.class.loader");
        if (cls == null) {
            return parent;
        }

        Constructor<?> ctor = Class.forName(cls, true, parent)
            .getDeclaredConstructor(new Class<?>[] { ClassLoader.class });
        ClassLoader sys = (ClassLoader) ctor.newInstance(
            new Object[] { parent });
        Thread.currentThread().setContextClassLoader(sys);
        return sys;
    }
}