2.6URLClassLoader源码解析

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* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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package java.net;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.lang.ref.*;
import java.io.*;
import java.net.URL;
import java.net.URLConnection;
import java.net.URLStreamHandlerFactory;
import java.util.Enumeration;
import java.util.*;
import java.util.jar.Manifest;
import java.util.jar.JarFile;
import java.util.jar.Attributes;
import java.util.jar.Attributes.Name;
import java.security.CodeSigner;
import java.security.PrivilegedAction;
import java.security.PrivilegedExceptionAction;
import java.security.AccessController;
import java.security.AccessControlContext;
import java.security.SecureClassLoader;
import java.security.CodeSource;
import java.security.Permission;
import java.security.PermissionCollection;
import sun.misc.Resource;
import sun.misc.URLClassPath;
import sun.net.www.ParseUtil;
import sun.security.util.SecurityConstants;
/**
* This class loader is used to load classes and resources from a search
* path of URLs referring to both JAR files and directories. Any URL that
* ends with a '/' is assumed to refer to a directory. Otherwise, the URL
* is assumed to refer to a JAR file which will be opened as needed.
*
* The AccessControlContext of the thread that created the instance of
* URLClassLoader will be used when subsequently loading classes and
* resources.
*
* The classes that are loaded are by default granted permission only to
* access the URLs specified when the URLClassLoader was created.
*
* @author David Connelly
* @since 1.2
*/
public class URLClassLoader extends SecureClassLoader implements Closeable {
/* The search path for classes and resources */
private final URLClassPath ucp;
/* The context to be used when loading classes and resources */
private final AccessControlContext acc;
/**
* Constructs a new URLClassLoader for the given URLs. The URLs will be
* searched in the order specified for classes and resources after first
* searching in the specified parent class loader. Any URL that ends with
* a '/' is assumed to refer to a directory. Otherwise, the URL is assumed
* to refer to a JAR file which will be downloaded and opened as needed.
*
* If there is a security manager, this method first
* calls the security manager's {@code checkCreateClassLoader} method
* to ensure creation of a class loader is allowed.
*
* @param urls the URLs from which to load classes and resources
* @param parent the parent class loader for delegation
* @exception SecurityException if a security manager exists and its
* {@code checkCreateClassLoader} method doesn't allow
* creation of a class loader.
* @see SecurityManager#checkCreateClassLoader
*/
public URLClassLoader(URL[] urls, ClassLoader parent) {
super(parent);
// this is to make the stack depth consistent with 1.1
SecurityManager security = System.getSecurityManager();
if (security != null) {
security.checkCreateClassLoader();
}
ucp = new URLClassPath(urls);
this.acc = AccessController.getContext();
}
URLClassLoader(URL[] urls, ClassLoader parent,
AccessControlContext acc) {
super(parent);
// this is to make the stack depth consistent with 1.1
SecurityManager security = System.getSecurityManager();
if (security != null) {
security.checkCreateClassLoader();
}
ucp = new URLClassPath(urls);
this.acc = acc;
}
/**
* Constructs a new URLClassLoader for the specified URLs using the
* default delegation parent <code>ClassLoader</code>. The URLs will
* be searched in the order specified for classes and resources after
* first searching in the parent class loader. Any URL that ends with
* a '/' is assumed to refer to a directory. Otherwise, the URL is
* assumed to refer to a JAR file which will be downloaded and opened
* as needed.
*
* If there is a security manager, this method first
* calls the security manager's <code>checkCreateClassLoader</code> method
* to ensure creation of a class loader is allowed.
*
* @param urls the URLs from which to load classes and resources
*
* @exception SecurityException if a security manager exists and its
* <code>checkCreateClassLoader</code> method doesn't allow
* creation of a class loader.
* @see SecurityManager#checkCreateClassLoader
*/
public URLClassLoader(URL[] urls) {
super();
// this is to make the stack depth consistent with 1.1
SecurityManager security = System.getSecurityManager();
if (security != null) {
security.checkCreateClassLoader();
}
ucp = new URLClassPath(urls);
this.acc = AccessController.getContext();
}
URLClassLoader(URL[] urls, AccessControlContext acc) {
super();
// this is to make the stack depth consistent with 1.1
SecurityManager security = System.getSecurityManager();
if (security != null) {
security.checkCreateClassLoader();
}
ucp = new URLClassPath(urls);
this.acc = acc;
}
/**
* Constructs a new URLClassLoader for the specified URLs, parent
* class loader, and URLStreamHandlerFactory. The parent argument
* will be used as the parent class loader for delegation. The
* factory argument will be used as the stream handler factory to
* obtain protocol handlers when creating new jar URLs.
*
* If there is a security manager, this method first
* calls the security manager's <code>checkCreateClassLoader</code> method
* to ensure creation of a class loader is allowed.
*
* @param urls the URLs from which to load classes and resources
* @param parent the parent class loader for delegation
* @param factory the URLStreamHandlerFactory to use when creating URLs
*
* @exception SecurityException if a security manager exists and its
* <code>checkCreateClassLoader</code> method doesn't allow
* creation of a class loader.
* @see SecurityManager#checkCreateClassLoader
*/
public URLClassLoader(URL[] urls, ClassLoader parent,
URLStreamHandlerFactory factory) {
super(parent);
// this is to make the stack depth consistent with 1.1
SecurityManager security = System.getSecurityManager();
if (security != null) {
security.checkCreateClassLoader();
}
ucp = new URLClassPath(urls, factory);
acc = AccessController.getContext();
}
/* A map (used as a set) to keep track of closeable local resources
* (either JarFiles or FileInputStreams). We don't care about
* Http resources since they don't need to be closed.
*
* If the resource is coming from a jar file
* we keep a (weak) reference to the JarFile object which can
* be closed if URLClassLoader.close() called. Due to jar file
* caching there will typically be only one JarFile object
* per underlying jar file.
*
* For file resources, which is probably a less common situation
* we have to keep a weak reference to each stream.
*/
private WeakHashMap<Closeable,Void>
closeables = new WeakHashMap<>();
/**
* Returns an input stream for reading the specified resource.
* If this loader is closed, then any resources opened by this method
* will be closed.
*
* The search order is described in the documentation for {@link
* #getResource(String)}.
*
* @param name
* The resource name
*
* @return An input stream for reading the resource, or <tt>null</tt>
* if the resource could not be found
*
* @since 1.7
*/
public InputStream getResourceAsStream(String name) {
URL url = getResource(name);
try {
if (url == null) {
return null;
}
URLConnection urlc = url.openConnection();
InputStream is = urlc.getInputStream();
if (urlc instanceof JarURLConnection) {
JarURLConnection juc = (JarURLConnection)urlc;
JarFile jar = juc.getJarFile();
synchronized (closeables) {
if (!closeables.containsKey(jar)) {
closeables.put(jar, null);
}
}
} else if (urlc instanceof sun.net.www.protocol.file.FileURLConnection) {
synchronized (closeables) {
closeables.put(is, null);
}
}
return is;
} catch (IOException e) {
return null;
}
}
/**
* Closes this URLClassLoader, so that it can no longer be used to load
* new classes or resources that are defined by this loader.
* Classes and resources defined by any of this loader's parents in the
* delegation hierarchy are still accessible. Also, any classes or resources
* that are already loaded, are still accessible.
*
* In the case of jar: and file: URLs, it also closes any files
* that were opened by it. If another thread is loading a
* class when the {@code close} method is invoked, then the result of
* that load is undefined.
*
* The method makes a best effort attempt to close all opened files,
* by catching {@link IOException}s internally. Unchecked exceptions
* and errors are not caught. Calling close on an already closed
* loader has no effect.
*
* @throws IOException if closing any file opened by this class loader
* resulted in an IOException. Any such exceptions are caught internally.
* If only one is caught, then it is re-thrown. If more than one exception
* is caught, then the second and following exceptions are added
* as suppressed exceptions of the first one caught, which is then re-thrown.
*
* @throws SecurityException if a security manager is set, and it denies
* {@link RuntimePermission}<tt>("closeClassLoader")</tt>
*
* @since 1.7
*/
public void close() throws IOException {
SecurityManager security = System.getSecurityManager();
if (security != null) {
security.checkPermission(new RuntimePermission("closeClassLoader"));
}
List<IOException> errors = ucp.closeLoaders();
// now close any remaining streams.
synchronized (closeables) {
Set<Closeable> keys = closeables.keySet();
for (Closeable c : keys) {
try {
c.close();
} catch (IOException ioex) {
errors.add(ioex);
}
}
closeables.clear();
}
if (errors.isEmpty()) {
return;
}
IOException firstex = errors.remove(0);
// Suppress any remaining exceptions
for (IOException error: errors) {
firstex.addSuppressed(error);
}
throw firstex;
}
/**
* Appends the specified URL to the list of URLs to search for
* classes and resources.
*
* If the URL specified is <code>null</code> or is already in the
* list of URLs, or if this loader is closed, then invoking this
* method has no effect.
*
* @param url the URL to be added to the search path of URLs
*/
protected void addURL(URL url) {
ucp.addURL(url);
}
/**
* Returns the search path of URLs for loading classes and resources.
* This includes the original list of URLs specified to the constructor,
* along with any URLs subsequently appended by the addURL() method.
* @return the search path of URLs for loading classes and resources.
*/
public URL[] getURLs() {
return ucp.getURLs();
}
/**
* Finds and loads the class with the specified name from the URL search
* path. Any URLs referring to JAR files are loaded and opened as needed
* until the class is found.
*
* @param name the name of the class
* @return the resulting class
* @exception ClassNotFoundException if the class could not be found,
* or if the loader is closed.
*/
protected Class<?> findClass(final String name)
throws ClassNotFoundException
{
try {
return AccessController.doPrivileged(
new PrivilegedExceptionAction<Class>() {
public Class run() throws ClassNotFoundException {
String path = name.replace('.', '/').concat(".class");
Resource res = ucp.getResource(path, false);
if (res != null) {
try {
return defineClass(name, res);
} catch (IOException e) {
throw new ClassNotFoundException(name, e);
}
} else {
throw new ClassNotFoundException(name);
}
}
}, acc);
} catch (java.security.PrivilegedActionException pae) {
throw (ClassNotFoundException) pae.getException();
}
}
/*
* Retrieve the package using the specified package name.
* If non-null, verify the package using the specified code
* source and manifest.
*/
private Package getAndVerifyPackage(String pkgname,
Manifest man, URL url) {
Package pkg = getPackage(pkgname);
if (pkg != null) {
// Package found, so check package sealing.
if (pkg.isSealed()) {
// Verify that code source URL is the same.
if (!pkg.isSealed(url)) {
throw new SecurityException(
"sealing violation: package " + pkgname + " is sealed");
}
} else {
// Make sure we are not attempting to seal the package
// at this code source URL.
if ((man != null) && isSealed(pkgname, man)) {
throw new SecurityException(
"sealing violation: can't seal package " + pkgname +
": already loaded");
}
}
}
return pkg;
}
/*
* Defines a Class using the class bytes obtained from the specified
* Resource. The resulting Class must be resolved before it can be
* used.
*/
private Class defineClass(String name, Resource res) throws IOException {
long t0 = System.nanoTime();
int i = name.lastIndexOf('.');
URL url = res.getCodeSourceURL();
if (i != -1) {
String pkgname = name.substring(0, i);
// Check if package already loaded.
Manifest man = res.getManifest();
if (getAndVerifyPackage(pkgname, man, url) == null) {
try {
if (man != null) {
definePackage(pkgname, man, url);
} else {
definePackage(pkgname, null, null, null, null, null, null, null);
}
} catch (IllegalArgumentException iae) {
// parallel-capable class loaders: re-verify in case of a
// race condition
if (getAndVerifyPackage(pkgname, man, url) == null) {
// Should never happen
throw new AssertionError("Cannot find package " +
pkgname);
}
}
}
}
// Now read the class bytes and define the class
java.nio.ByteBuffer bb = res.getByteBuffer();
if (bb != null) {
// Use (direct) ByteBuffer:
CodeSigner[] signers = res.getCodeSigners();
CodeSource cs = new CodeSource(url, signers);
sun.misc.PerfCounter.getReadClassBytesTime().addElapsedTimeFrom(t0);
return defineClass(name, bb, cs);
} else {
byte[] b = res.getBytes();
// must read certificates AFTER reading bytes.
CodeSigner[] signers = res.getCodeSigners();
CodeSource cs = new CodeSource(url, signers);
sun.misc.PerfCounter.getReadClassBytesTime().addElapsedTimeFrom(t0);
return defineClass(name, b, 0, b.length, cs);
}
}
/**
* Defines a new package by name in this ClassLoader. The attributes
* contained in the specified Manifest will be used to obtain package
* version and sealing information. For sealed packages, the additional
* URL specifies the code source URL from which the package was loaded.
*
* @param name the package name
* @param man the Manifest containing package version and sealing
* information
* @param url the code source url for the package, or null if none
* @exception IllegalArgumentException if the package name duplicates
* an existing package either in this class loader or one
* of its ancestors
* @return the newly defined Package object
*/
protected Package definePackage(String name, Manifest man, URL url)
throws IllegalArgumentException
{
String path = name.replace('.', '/').concat("/");
String specTitle = null, specVersion = null, specVendor = null;
String implTitle = null, implVersion = null, implVendor = null;
String sealed = null;
URL sealBase = null;
Attributes attr = man.getAttributes(path);
if (attr != null) {
specTitle = attr.getValue(Name.SPECIFICATION_TITLE);
specVersion = attr.getValue(Name.SPECIFICATION_VERSION);
specVendor = attr.getValue(Name.SPECIFICATION_VENDOR);
implTitle = attr.getValue(Name.IMPLEMENTATION_TITLE);
implVersion = attr.getValue(Name.IMPLEMENTATION_VERSION);
implVendor = attr.getValue(Name.IMPLEMENTATION_VENDOR);
sealed = attr.getValue(Name.SEALED);
}
attr = man.getMainAttributes();
if (attr != null) {
if (specTitle == null) {
specTitle = attr.getValue(Name.SPECIFICATION_TITLE);
}
if (specVersion == null) {
specVersion = attr.getValue(Name.SPECIFICATION_VERSION);
}
if (specVendor == null) {
specVendor = attr.getValue(Name.SPECIFICATION_VENDOR);
}
if (implTitle == null) {
implTitle = attr.getValue(Name.IMPLEMENTATION_TITLE);
}
if (implVersion == null) {
implVersion = attr.getValue(Name.IMPLEMENTATION_VERSION);
}
if (implVendor == null) {
implVendor = attr.getValue(Name.IMPLEMENTATION_VENDOR);
}
if (sealed == null) {
sealed = attr.getValue(Name.SEALED);
}
}
if ("true".equalsIgnoreCase(sealed)) {
sealBase = url;
}
return definePackage(name, specTitle, specVersion, specVendor,
implTitle, implVersion, implVendor, sealBase);
}
/*
* Returns true if the specified package name is sealed according to the
* given manifest.
*/
private boolean isSealed(String name, Manifest man) {
String path = name.replace('.', '/').concat("/");
Attributes attr = man.getAttributes(path);
String sealed = null;
if (attr != null) {
sealed = attr.getValue(Name.SEALED);
}
if (sealed == null) {
if ((attr = man.getMainAttributes()) != null) {
sealed = attr.getValue(Name.SEALED);
}
}
return "true".equalsIgnoreCase(sealed);
}
/**
* Finds the resource with the specified name on the URL search path.
*
* @param name the name of the resource
* @return a <code>URL</code> for the resource, or <code>null</code>
* if the resource could not be found, or if the loader is closed.
*/
public URL findResource(final String name) {
/*
* The same restriction to finding classes applies to resources
*/
URL url = AccessController.doPrivileged(
new PrivilegedAction<URL>() {
public URL run() {
return ucp.findResource(name, true);
}
}, acc);
return url != null ? ucp.checkURL(url) : null;
}
/**
* Returns an Enumeration of URLs representing all of the resources
* on the URL search path having the specified name.
*
* @param name the resource name
* @exception IOException if an I/O exception occurs
* @return an <code>Enumeration</code> of <code>URL</code>s
* If the loader is closed, the Enumeration will be empty.
*/
public Enumeration<URL> findResources(final String name)
throws IOException
{
final Enumeration<URL> e = ucp.findResources(name, true);
return new Enumeration<URL>() {
private URL url = null;
private boolean next() {
if (url != null) {
return true;
}
do {
URL u = AccessController.doPrivileged(
new PrivilegedAction<URL>() {
public URL run() {
if (!e.hasMoreElements())
return null;
return e.nextElement();
}
}, acc);
if (u == null)
break;
url = ucp.checkURL(u);
} while (url == null);
return url != null;
}
public URL nextElement() {
if (!next()) {
throw new NoSuchElementException();
}
URL u = url;
url = null;
return u;
}
public boolean hasMoreElements() {
return next();
}
};
}
/**
* Returns the permissions for the given codesource object.
* The implementation of this method first calls super.getPermissions
* and then adds permissions based on the URL of the codesource.
*
* If the protocol of this URL is "jar", then the permission granted
* is based on the permission that is required by the URL of the Jar
* file.
*
* If the protocol is "file" and there is an authority component, then
* permission to connect to and accept connections from that authority
* may be granted. If the protocol is "file"
* and the path specifies a file, then permission to read that
* file is granted. If protocol is "file" and the path is
* a directory, permission is granted to read all files
* and (recursively) all files and subdirectories contained in
* that directory.
*
* If the protocol is not "file", then permission
* to connect to and accept connections from the URL's host is granted.
* @param codesource the codesource
* @return the permissions granted to the codesource
*/
protected PermissionCollection getPermissions(CodeSource codesource)
{
PermissionCollection perms = super.getPermissions(codesource);
URL url = codesource.getLocation();
Permission p;
URLConnection urlConnection;
try {
urlConnection = url.openConnection();
p = urlConnection.getPermission();
} catch (java.io.IOException ioe) {
p = null;
urlConnection = null;
}
if (p instanceof FilePermission) {
// if the permission has a separator char on the end,
// it means the codebase is a directory, and we need
// to add an additional permission to read recursively
String path = p.getName();
if (path.endsWith(File.separator)) {
path += "-";
p = new FilePermission(path, SecurityConstants.FILE_READ_ACTION);
}
} else if ((p == null) && (url.getProtocol().equals("file"))) {
String path = url.getFile().replace('/', File.separatorChar);
path = ParseUtil.decode(path);
if (path.endsWith(File.separator))
path += "-";
p = new FilePermission(path, SecurityConstants.FILE_READ_ACTION);
} else {
/**
* Not loading from a 'file:' URL so we want to give the class
* permission to connect to and accept from the remote host
* after we've made sure the host is the correct one and is valid.
*/
URL locUrl = url;
if (urlConnection instanceof JarURLConnection) {
locUrl = ((JarURLConnection)urlConnection).getJarFileURL();
}
String host = locUrl.getHost();
if (host != null && (host.length() > 0))
p = new SocketPermission(host,
SecurityConstants.SOCKET_CONNECT_ACCEPT_ACTION);
}
// make sure the person that created this class loader
// would have this permission
if (p != null) {
final SecurityManager sm = System.getSecurityManager();
if (sm != null) {
final Permission fp = p;
AccessController.doPrivileged(new PrivilegedAction<Void>() {
public Void run() throws SecurityException {
sm.checkPermission(fp);
return null;
}
}, acc);
}
perms.add(p);
}
return perms;
}
/**
* Creates a new instance of URLClassLoader for the specified
* URLs and parent class loader. If a security manager is
* installed, the <code>loadClass</code> method of the URLClassLoader
* returned by this method will invoke the
* <code>SecurityManager.checkPackageAccess</code> method before
* loading the class.
*
* @param urls the URLs to search for classes and resources
* @param parent the parent class loader for delegation
* @return the resulting class loader
*/
public static URLClassLoader newInstance(final URL[] urls,
final ClassLoader parent) {
// Save the caller's context
final AccessControlContext acc = AccessController.getContext();
// Need a privileged block to create the class loader
URLClassLoader ucl = AccessController.doPrivileged(
new PrivilegedAction<URLClassLoader>() {
public URLClassLoader run() {
return new FactoryURLClassLoader(urls, parent, acc);
}
});
return ucl;
}
/**
* Creates a new instance of URLClassLoader for the specified
* URLs and default parent class loader. If a security manager is
* installed, the <code>loadClass</code> method of the URLClassLoader
* returned by this method will invoke the
* <code>SecurityManager.checkPackageAccess</code> before
* loading the class.
*
* @param urls the URLs to search for classes and resources
* @return the resulting class loader
*/
public static URLClassLoader newInstance(final URL[] urls) {
// Save the caller's context
final AccessControlContext acc = AccessController.getContext();
// Need a privileged block to create the class loader
URLClassLoader ucl = AccessController.doPrivileged(
new PrivilegedAction<URLClassLoader>() {
public URLClassLoader run() {
return new FactoryURLClassLoader(urls, acc);
}
});
return ucl;
}
static {
sun.misc.SharedSecrets.setJavaNetAccess (
new sun.misc.JavaNetAccess() {
public URLClassPath getURLClassPath (URLClassLoader u) {
return u.ucp;
}
}
);
ClassLoader.registerAsParallelCapable();
}
}
final class FactoryURLClassLoader extends URLClassLoader {
static {
ClassLoader.registerAsParallelCapable();
}
FactoryURLClassLoader(URL[] urls, ClassLoader parent,
AccessControlContext acc) {
super(urls, parent, acc);
}
FactoryURLClassLoader(URL[] urls, AccessControlContext acc) {
super(urls, acc);
}
public final Class loadClass(String name, boolean resolve)
throws ClassNotFoundException
{
// First check if we have permission to access the package. This
// should go away once we've added support for exported packages.
SecurityManager sm = System.getSecurityManager();
if (sm != null) {
int i = name.lastIndexOf('.');
if (i != -1) {
sm.checkPackageAccess(name.substring(0, i));
}
}
return super.loadClass(name, resolve);
}
}

2.6URLClassLoader源码解析

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