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products/sources/formale Sprachen/Java/Openjdk/src/java.base/share/classes/java/net/ (Sun/Oracle ^©) Datei vom 13.11.2022 mit Größe 74 kB

Quelle URL.java Sprache: JAVA

/*
* Copyright (c) 1995, 2022, 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. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* 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 java.net;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.net.spi.URLStreamHandlerProvider;
import java.nio.file.Path;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Hashtable;
import java.io.InvalidObjectException;
import java.io.ObjectStreamException;
import java.io.ObjectStreamField;
import java.io.ObjectInputStream.GetField;
import java.util.Iterator;
import java.util.Locale;
import java.util.NoSuchElementException;
import java.util.ServiceConfigurationError;
import java.util.ServiceLoader;

import jdk.internal.access.JavaNetURLAccess;
import jdk.internal.access.SharedSecrets;
import jdk.internal.misc.ThreadTracker;
import jdk.internal.misc.VM;
import sun.net.util.IPAddressUtil;
import sun.security.util.SecurityConstants;
import sun.security.action.GetPropertyAction;

/**
* Class {@code URL} represents a Uniform Resource
* Locator, a pointer to a "resource" on the World
* Wide Web. A resource can be something as simple as a file or a
* directory, or it can be a reference to a more complicated object,
* such as a query to a database or to a search engine. More
* information on the types of URLs and their formats can be found at:
* <a href=
* "http://web.archive.org/web/20051219043731/http://archive.ncsa.uiuc.edu/SDG/Software/Mosaic/Demo/url-primer.html">
* Types of URL</a>
* 
* In general, a URL can be broken into several parts. Consider the
* following example:
* <blockquote><pre>
* http://www.example.com/docs/resource1.html
* </pre></blockquote>
* 
* The URL above indicates that the protocol to use is
* {@code http} (HyperText Transfer Protocol) and that the
* information resides on a host machine named
* {@code www.example.com}. The information on that host
* machine is named {@code /docs/resource1.html}. The exact
* meaning of this name on the host machine is both protocol
* dependent and host dependent. The information normally resides in
* a file, but it could be generated on the fly. This component of
* the URL is called the path component.
* 
* A URL can optionally specify a "port", which is the
* port number to which the TCP connection is made on the remote host
* machine. If the port is not specified, the default port for
* the protocol is used instead. For example, the default port for
* {@code http} is {@code 80}. An alternative port could be
* specified as:
* <blockquote><pre>
* http://www.example.com:1080/docs/resource1.html
* </pre></blockquote>
* 
* The syntax of {@code URL} is defined by <a
* href="http://www.ietf.org/rfc/rfc2396.txt">RFC 2396: Uniform
* Resource Identifiers (URI): Generic Syntax</a>, amended by <a
* href="http://www.ietf.org/rfc/rfc2732.txt">RFC 2732: Format for
* Literal IPv6 Addresses in URLs</a>. The Literal IPv6 address format
* also supports scope_ids. The syntax and usage of scope_ids is described
* <a href="Inet6Address.html#scoped">here</a>.
* 
* A URL may have appended to it a "fragment", also known
* as a "ref" or a "reference". The fragment is indicated by the sharp
* sign character "#" followed by more characters. For example,
* <blockquote><pre>
* http://www.example.com/index.html#chapter1
* </pre></blockquote>
* 
* This fragment is not technically part of the URL. Rather, it
* indicates that after the specified resource is retrieved, the
* application is specifically interested in that part of the
* document that has the tag {@code chapter1} attached to it. The
* meaning of a tag is resource specific.
* 
* An application can also specify a "relative URL",
* which contains only enough information to reach the resource
* relative to another URL. Relative URLs are frequently used within
* HTML pages. For example, if the contents of the URL:
* <blockquote><pre>
* http://www.example.com/index.html
* </pre></blockquote>
* contained within it the relative URL:
* <blockquote><pre>
* FAQ.html
* </pre></blockquote>
* it would be a shorthand for:
* <blockquote><pre>
* http://www.example.com/FAQ.html
* </pre></blockquote>
* 
* The relative URL need not specify all the components of a URL. If
* the protocol, host name, or port number is missing, the value is
* inherited from the fully specified URL. The file component must be
* specified. The optional fragment is not inherited.
*
* <h2><a id="constructor-deprecation"></a>Constructing instances of {@code URL}</h2>
*
* The {@code java.net.URL} constructors are deprecated.
* Developers are encouraged to use {@link URI java.net.URI} to parse
* or construct a {@code URL}. In cases where an instance of {@code
* java.net.URL} is needed to open a connection, {@link URI} can be used
* to construct or parse the URL string, possibly calling {@link
* URI#parseServerAuthority()} to validate that the authority component
* can be parsed as a server-based authority, and then calling
* {@link URI#toURL()} to create the {@code URL} instance.
* 
* The URL constructors are specified to throw
* {@link MalformedURLException} but the actual parsing/validation
* that is performed is implementation dependent. Some parsing/validation
* may be delayed until later, when the underlying {@linkplain
* URLStreamHandler stream handler's implementation} is called.
* Being able to construct an instance of {@code URL} doesn't
* provide any guarantee about its conformance to the URL
* syntax specification.
* 
* The URL class does not itself encode or decode any URL components
* according to the escaping mechanism defined in RFC2396. It is the
* responsibility of the caller to encode any fields, which need to be
* escaped prior to calling URL, and also to decode any escaped fields,
* that are returned from URL. Furthermore, because URL has no knowledge
* of URL escaping, it does not recognise equivalence between the encoded
* or decoded form of the same URL. For example, the two URLs: 
* <pre> http://foo.com/hello world/ and http://foo.com/hello%20world</pre>
* would be considered not equal to each other.
* 
* Note, the {@link java.net.URI} class does perform escaping of its
* component fields in certain circumstances. The recommended way
* to manage the encoding and decoding of URLs is to use {@link java.net.URI},
* and to convert between these two classes using {@link #toURI()} and
* {@link URI#toURL()}.
* 
* The {@link URLEncoder} and {@link URLDecoder} classes can also be
* used, but only for HTML form encoding, which is not the same
* as the encoding scheme defined in RFC2396.
*
* @apiNote
*
* <a id="integrity"></a>
* Applications working with file paths and file URIs should take great
* care to use the appropriate methods to convert between the two.
* The {@link Path#of(URI)} factory method and the {@link File#File(URI)}
* constructor can be used to create {@link Path} or {@link File}
* objects from a file URI. {@link Path#toUri()} and {@link File#toURI()}
* can be used to create a {@link URI} from a file path, which can be
* converted to URL using {@link URI#toURL()}.
* Applications should never try to {@linkplain #URL(String, String, String)
* construct} or {@linkplain #URL(String) parse} a {@code URL}
* from the direct string representation of a {@code File} or {@code Path}
* instance.
* 
* Before constructing a {@code URL} from a {@code URI}, and depending
* on the protocol involved, applications should consider validating
* whether the URI authority {@linkplain URI#parseServerAuthority()
* can be parsed as server-based}.
* 
* Some components of a URL or URI, such as userinfo, may
* be abused to construct misleading URLs or URIs. Applications
* that deal with URLs or URIs should take into account
* the recommendations advised in <a
* href="https://tools.ietf.org/html/rfc3986#section-7">RFC3986,
* Section 7, Security Considerations</a>.
* 
* All {@code URL} constructors may throw {@link MalformedURLException}.
* In particular, if the underlying {@link URLStreamHandler}
* implementation rejects, or is known to reject, any of the parameters,
* {@link MalformedURLException} may be thrown.
* Typically, a constructor that calls the stream handler's {@linkplain
* URLStreamHandler#parseURL(URL, String, int, int) parseURL method} may
* throw {@code MalformedURLException} if the underlying stream handler
* implementation of that method throws {@code IllegalArgumentException}.
* However, which checks are performed, or not, by the stream handlers
* is implementation dependent, and callers should not rely on such
* checks for full URL validation.
*
* @author James Gosling
* @since 1.0
*/
public final class URL implements java.io.Serializable {

 static final String BUILTIN_HANDLERS_PREFIX = "sun.net.www.protocol";
 @java.io.Serial
 static final long serialVersionUID = -7627629688361524110L;

 /**
 * The property which specifies the package prefix list to be scanned
 * for protocol handlers. The value of this property (if any) should
 * be a vertical bar delimited list of package names to search through
 * for a protocol handler to load. The policy of this class is that
 * all protocol handlers will be in a class called <protocolname>.Handler,
 * and each package in the list is examined in turn for a matching
 * handler. If none are found (or the property is not specified), the
 * default package prefix, sun.net.www.protocol, is used. The search
 * proceeds from the first package in the list to the last and stops
 * when a match is found.
 */
 private static final String protocolPathProp = "java.protocol.handler.pkgs";

 /**
 * The protocol to use (ftp, http, nntp, ... etc.) .
 * @serial
 */
 private String protocol;

 /**
 * The host name to connect to.
 * @serial
 */
 private String host;

 /**
 * The protocol port to connect to.
 * @serial
 */
 private int port = -1;

 /**
 * The specified file name on that host. {@code file} is
 * defined as {@code path[?query]}
 * @serial
 */
 private String file;

 /**
 * The query part of this URL.
 */
 private transient String query;

 /**
 * The authority part of this URL.
 * @serial
 */
 private String authority;

 /**
 * The path part of this URL.
 */
 private transient String path;

 /**
 * The userinfo part of this URL.
 */
 private transient String userInfo;

 /**
 * # reference.
 * @serial
 */
 private String ref;

 /**
 * The host's IP address, used in equals and hashCode.
 * Computed on demand. An uninitialized or unknown hostAddress is null.
 */
 private transient InetAddress hostAddress;

 /**
 * The URLStreamHandler for this URL.
 */
 transient URLStreamHandler handler;

 /* Our hash code.
 * @serial
 */
 private int hashCode = -1;

 private transient UrlDeserializedState tempState;

 /**
 * Creates a {@code URL} object from the specified
 * {@code protocol}, {@code host}, {@code port}
 * number, and {@code file}.
 *
 * {@code host} can be expressed as a host name or a literal
 * IP address. If IPv6 literal address is used, it should be
 * enclosed in square brackets ({@code '['} and {@code ']'}), as
 * specified by <a
 * href="http://www.ietf.org/rfc/rfc2732.txt">RFC 2732</a>;
 * However, the literal IPv6 address format defined in <a
 * href="http://www.ietf.org/rfc/rfc2373.txt">RFC 2373: IP
 * Version 6 Addressing Architecture</a> is also accepted.
 *
 * Specifying a {@code port} number of {@code -1}
 * indicates that the URL should use the default port for the
 * protocol.
 *
 * If this is the first URL object being created with the specified
 * protocol, a stream protocol handler object, an instance of
 * class {@code URLStreamHandler}, is created for that protocol:
 * <ol>
 * <li>If the application has previously set up an instance of
 * {@code URLStreamHandlerFactory} as the stream handler factory,
 * then the {@code createURLStreamHandler} method of that instance
 * is called with the protocol string as an argument to create the
 * stream protocol handler.
 * <li>If no {@code URLStreamHandlerFactory} has yet been set up,
 * or if the factory's {@code createURLStreamHandler} method
 * returns {@code null}, then the {@linkplain java.util.ServiceLoader
 * ServiceLoader} mechanism is used to locate {@linkplain
 * java.net.spi.URLStreamHandlerProvider URLStreamHandlerProvider}
 * implementations using the system class
 * loader. The order that providers are located is implementation
 * specific, and an implementation is free to cache the located
 * providers. A {@linkplain java.util.ServiceConfigurationError
 * ServiceConfigurationError}, {@code Error} or {@code RuntimeException}
 * thrown from the {@code createURLStreamHandler}, if encountered, will
 * be propagated to the calling thread. The {@code
 * createURLStreamHandler} method of each provider, if instantiated, is
 * invoked, with the protocol string, until a provider returns non-null,
 * or all providers have been exhausted.
 * <li>If the previous step fails to find a protocol handler, the
 * constructor reads the value of the system property:
 * <blockquote>{@systemProperty
 * java.protocol.handler.pkgs
 * }</blockquote>
 * If the value of that system property is not {@code null},
 * it is interpreted as a list of packages separated by a vertical
 * slash character '{@code |}'. The constructor tries to load
 * the class named:
 * <blockquote>{@code
 * <package>.<protocol>.Handler
 * }</blockquote>
 * where {@code <package>} is replaced by the name of the package
 * and {@code <protocol>} is replaced by the name of the protocol.
 * If this class does not exist, or if the class exists but it is not
 * a subclass of {@code URLStreamHandler}, then the next package
 * in the list is tried.
 * <li>If the previous step fails to find a protocol handler, then the
 * constructor tries to load a built-in protocol handler.
 * If this class does not exist, or if the class exists but it is not a
 * subclass of {@code URLStreamHandler}, then a
 * {@code MalformedURLException} is thrown.
 * </ol>
 *
 * Protocol handlers for the following protocols are guaranteed
 * to exist on the search path:
 * <ul>
 * <li>{@code http}</li>
 * <li>{@code https}</li>
 * <li>{@code file}</li>
 * <li>{@code jar}</li>
 * </ul>
 * Protocol handlers for additional protocols may also be available.
 * Some protocol handlers, for example those used for loading platform
 * classes or classes on the class path, may not be overridden. The details
 * of such restrictions, and when those restrictions apply (during
 * initialization of the runtime for example), are implementation specific
 * and therefore not specified
 *
 * No validation of the inputs is performed by this constructor.
 *
 * @param protocol the name of the protocol to use.
 * @param host the name of the host.
 * @param port the port number on the host.
 * @param file the file on the host
 * @throws MalformedURLException if an unknown protocol or the port
 * is a negative number other than -1, or if the
 * underlying stream handler implementation rejects,
 * or is known to reject, the {@code URL}
 * @see java.lang.System#getProperty(java.lang.String)
 * @see java.net.URL#setURLStreamHandlerFactory(
 * java.net.URLStreamHandlerFactory)
 * @see java.net.URLStreamHandler
 * @see java.net.URLStreamHandlerFactory#createURLStreamHandler(
 * java.lang.String)
 * @deprecated Use {@link URI#toURL()} to construct an instance of URL. See the note on
 * <a href="#constructor-deprecation">constructor deprecation</a> for more
 * details.
 */
 @Deprecated(since = "20")
 public URL(String protocol, String host, int port, String file)
 throws MalformedURLException
 {
 this(protocol, host, port, file, null);
 }

 /**
 * Creates a URL from the specified {@code protocol}
 * name, {@code host} name, and {@code file} name. The
 * default port for the specified protocol is used.
 * 
 * This constructor is equivalent to the four-argument
 * constructor with the only difference of using the
 * default port for the specified protocol.
 *
 * No validation of the inputs is performed by this constructor.
 *
 * @param protocol the name of the protocol to use.
 * @param host the name of the host.
 * @param file the file on the host.
 * @throws MalformedURLException if an unknown protocol is specified,
 * or if the underlying stream handler implementation
 * rejects, or is known to reject, the {@code URL}
 * @see java.net.URL#URL(java.lang.String, java.lang.String,
 * int, java.lang.String)
 * @deprecated Use {@link URI#toURL()} to construct an instance of URL. See the note on
 * <a href="#constructor-deprecation">constructor deprecation</a> for more
 * details.
 */
 @Deprecated(since = "20")
 public URL(String protocol, String host, String file)
 throws MalformedURLException {
 this(protocol, host, -1, file);
 }

 /**
 * Creates a {@code URL} object from the specified
 * {@code protocol}, {@code host}, {@code port}
 * number, {@code file}, and {@code handler}. Specifying
 * a {@code port} number of {@code -1} indicates that
 * the URL should use the default port for the protocol. Specifying
 * a {@code handler} of {@code null} indicates that the URL
 * should use a default stream handler for the protocol, as outlined
 * for:
 * {@link java.net.URL#URL(java.lang.String, java.lang.String, int,
 * java.lang.String)}
 *
 * If the handler is not null and there is a security manager,
 * the security manager's {@code checkPermission}
 * method is called with a
 * {@code NetPermission("specifyStreamHandler")} permission.
 * This may result in a SecurityException.
 *
 * No validation of the inputs is performed by this constructor.
 *
 * @param protocol the name of the protocol to use.
 * @param host the name of the host.
 * @param port the port number on the host.
 * @param file the file on the host
 * @param handler the stream handler for the URL.
 * @throws MalformedURLException if an unknown protocol or the port
 * is a negative number other than -1,
 * or if the underlying stream handler implementation
 * rejects, or is known to reject, the {@code URL}
 * @throws SecurityException
 * if a security manager exists and its
 * {@code checkPermission} method doesn't allow
 * specifying a stream handler explicitly.
 * @see java.lang.System#getProperty(java.lang.String)
 * @see java.net.URL#setURLStreamHandlerFactory(
 * java.net.URLStreamHandlerFactory)
 * @see java.net.URLStreamHandler
 * @see java.net.URLStreamHandlerFactory#createURLStreamHandler(
 * java.lang.String)
 * @see SecurityManager#checkPermission
 * @see java.net.NetPermission
 * @deprecated
 * Use {@link #of(URI, URLStreamHandler)} to construct an instance of URL
 * associated with a custom protocol handler.
 * See the note on <a href="#constructor-deprecation">constructor deprecation</a>
 * for more details.
 */
 @Deprecated(since = "20")
 public URL(String protocol, String host, int port, String file,
 URLStreamHandler handler) throws MalformedURLException {
 if (handler != null) {
 @SuppressWarnings("removal")
 SecurityManager sm = System.getSecurityManager();
 if (sm != null) {
 // check for permission to specify a handler
 checkSpecifyHandler(sm);
 }
 }

 protocol = lowerCaseProtocol(protocol);
 this.protocol = protocol;
 if (host != null) {

 /**
 * if host is a literal IPv6 address,
 * we will make it conform to RFC 2732
 */
 if (host.indexOf(':') >= 0 && !host.startsWith("[")) {
 host = "["+host+"]";
 }
 this.host = host;

 if (port < -1) {
 throw new MalformedURLException("Invalid port number :" +
 port);
 }
 this.port = port;
 authority = (port == -1) ? host : host + ":" + port;
 }

 int index = file.indexOf('#');
 this.ref = index < 0 ? null : file.substring(index + 1);
 file = index < 0 ? file : file.substring(0, index);
 int q = file.lastIndexOf('?');
 if (q != -1) {
 this.query = file.substring(q + 1);
 this.path = file.substring(0, q);
 this.file = path + "?" + query;
 } else {
 this.path = file;
 this.file = path;
 }

 // Note: we don't do full validation of the URL here. Too risky to change
 // right now, but worth considering for future reference. -br
 if (handler == null &&
 (handler = getURLStreamHandler(protocol)) == null) {
 throw new MalformedURLException("unknown protocol: " + protocol);
 }
 this.handler = handler;
 if (host != null && isBuiltinStreamHandler(handler)) {
 String s = IPAddressUtil.checkExternalForm(this);
 if (s != null) {
 throw new MalformedURLException(s);
 }
 }
 if ("jar".equalsIgnoreCase(protocol)) {
 if (handler instanceof sun.net.www.protocol.jar.Handler) {
 // URL.openConnection() would throw a confusing exception
 // so generate a better exception here instead.
 String s = ((sun.net.www.protocol.jar.Handler) handler).checkNestedProtocol(file);
 if (s != null) {
 throw new MalformedURLException(s);
 }
 }
 }
 }

 /**
 * Creates a {@code URL} object from the {@code String}
 * representation.
 * 
 * This constructor is equivalent to a call to the two-argument
 * constructor with a {@code null} first argument.
 *
 * @param spec the {@code String} to parse as a URL.
 * @throws MalformedURLException if no protocol is specified, or an
 * unknown protocol is found, or {@code spec} is {@code null},
 * or the parsed URL fails to comply with the specific syntax
 * of the associated protocol, or the
 * underlying stream handler's {@linkplain
 * URLStreamHandler#parseURL parseURL method} throws
 * {@code IllegalArgumentException}
 * @see java.net.URL#URL(java.net.URL, java.lang.String)
 * @deprecated Use {@link URI#toURL()} to construct an instance of URL. See the note on
 * <a href="#constructor-deprecation">constructor deprecation</a> for more
 * details.
 */
 @Deprecated(since = "20")
 public URL(String spec) throws MalformedURLException {
 this(null, spec);
 }

 /**
 * Creates a URL by parsing the given spec within a specified context.
 *
 * The new URL is created from the given context URL and the spec
 * argument as described in
 * RFC2396 "Uniform Resource Identifiers : Generic Syntax" :
 * <blockquote><pre>
 * <scheme>://<authority><path>?<query>#<fragment>
 * </pre></blockquote>
 * The reference is parsed into the scheme, authority, path, query and
 * fragment parts. If the path component is empty and the scheme,
 * authority, and query components are undefined, then the new URL is a
 * reference to the current document. Otherwise, the fragment and query
 * parts present in the spec are used in the new URL.
 * 
 * If the scheme component is defined in the given spec and does not match
 * the scheme of the context, then the new URL is created as an absolute
 * URL based on the spec alone. Otherwise the scheme component is inherited
 * from the context URL.
 * 
 * If the authority component is present in the spec then the spec is
 * treated as absolute and the spec authority and path will replace the
 * context authority and path. If the authority component is absent in the
 * spec then the authority of the new URL will be inherited from the
 * context.
 * 
 * If the spec's path component begins with a slash character
 * "/" then the
 * path is treated as absolute and the spec path replaces the context path.
 * 
 * Otherwise, the path is treated as a relative path and is appended to the
 * context path, as described in RFC2396. Also, in this case,
 * the path is canonicalized through the removal of directory
 * changes made by occurrences of ".." and ".".
 * 
 * For a more detailed description of URL parsing, refer to RFC2396.
 *
 * @implSpec Parsing the URL includes calling the {@link
 * URLStreamHandler#parseURL(URL, String, int, int) parseURL} method on the
 * selected handler.
 *
 * @param context the context in which to parse the specification.
 * @param spec the {@code String} to parse as a URL.
 * @throws MalformedURLException if no protocol is specified, or an
 * unknown protocol is found, or {@code spec} is {@code null},
 * or the parsed URL fails to comply with the specific syntax
 * of the associated protocol, or the
 * underlying stream handler's {@linkplain
 * URLStreamHandler#parseURL parseURL method} throws
 * {@code IllegalArgumentException}
 * @see java.net.URL#URL(java.lang.String, java.lang.String,
 * int, java.lang.String)
 * @see java.net.URLStreamHandler
 * @see java.net.URLStreamHandler#parseURL(java.net.URL,
 * java.lang.String, int, int)
 * @deprecated Use {@link URI#toURL()} to construct an instance of URL. See the note on
 * <a href="#constructor-deprecation">constructor deprecation</a> for more
 * details.
 */
 @Deprecated(since = "20")
 public URL(URL context, String spec) throws MalformedURLException {
 this(context, spec, null);
 }

 /**
 * Creates a URL by parsing the given spec with the specified handler
 * within a specified context. If the handler is null, the parsing
 * occurs as with the two argument constructor.
 *
 * @implSpec Parsing the URL includes calling the {@link
 * URLStreamHandler#parseURL(URL, String, int, int) parseURL} method on the
 * selected handler.
 *
 * @param context the context in which to parse the specification.
 * @param spec the {@code String} to parse as a URL.
 * @param handler the stream handler for the URL.
 * @throws MalformedURLException if no protocol is specified, or an
 * unknown protocol is found, or {@code spec} is {@code null},
 * or the parsed URL fails to comply with the specific syntax
 * of the associated protocol, or the
 * underlying stream handler's {@linkplain
 * URLStreamHandler#parseURL(URL, String, int, int)
 * parseURL method} throws {@code IllegalArgumentException}
 * @throws SecurityException
 * if a security manager exists and its
 * {@code checkPermission} method doesn't allow
 * specifying a stream handler.
 * @see java.net.URL#URL(java.lang.String, java.lang.String,
 * int, java.lang.String)
 * @see java.net.URLStreamHandler
 * @see java.net.URLStreamHandler#parseURL(java.net.URL,
 * java.lang.String, int, int)
 * @deprecated
 * Use {@link #of(URI, URLStreamHandler)} to construct an instance of URL
 * associated with a custom protocol handler.
 * See the note on <a href="#constructor-deprecation">constructor deprecation</a>
 * for more details.
 */
 @Deprecated(since = "20")
 public URL(URL context, String spec, URLStreamHandler handler)
 throws MalformedURLException
 {
 String original = spec;
 int i, limit, c;
 int start = 0;
 String newProtocol = null;
 boolean aRef=false;
 boolean isRelative = false;

 // Check for permission to specify a handler
 if (handler != null) {
 @SuppressWarnings("removal")
 SecurityManager sm = System.getSecurityManager();
 if (sm != null) {
 checkSpecifyHandler(sm);
 }
 }

 try {
 limit = spec.length();
 while ((limit > 0) && (spec.charAt(limit - 1) <= ' ')) {
 limit--; //eliminate trailing whitespace
 }
 while ((start < limit) && (spec.charAt(start) <= ' ')) {
 start++; // eliminate leading whitespace
 }

 if (spec.regionMatches(true, start, "url:", 0, 4)) {
 start += 4;
 }
 if (start < spec.length() && spec.charAt(start) == '#') {
 /* we're assuming this is a ref relative to the context URL.
 * This means protocols cannot start w/ '#', but we must parse
 * ref URL's like: "hello:there" w/ a ':' in them.
 */
 aRef=true;
 }
 for (i = start ; !aRef && (i < limit) &&
 ((c = spec.charAt(i)) != '/') ; i++) {
 if (c == ':') {
 String s = lowerCaseProtocol(spec.substring(start, i));
 if (isValidProtocol(s)) {
 newProtocol = s;
 start = i + 1;
 }
 break;
 }
 }

 // Only use our context if the protocols match.
 protocol = newProtocol;
 if ((context != null) && ((newProtocol == null) ||
 newProtocol.equalsIgnoreCase(context.protocol))) {
 // inherit the protocol handler from the context
 // if not specified to the constructor
 if (handler == null) {
 handler = context.handler;
 }

 // If the context is a hierarchical URL scheme and the spec
 // contains a matching scheme then maintain backwards
 // compatibility and treat it as if the spec didn't contain
 // the scheme; see 5.2.3 of RFC2396
 if (context.path != null && context.path.startsWith("/"))
 newProtocol = null;

 if (newProtocol == null) {
 protocol = context.protocol;
 authority = context.authority;
 userInfo = context.userInfo;
 host = context.host;
 port = context.port;
 file = context.file;
 path = context.path;
 isRelative = true;
 }
 }

 if (protocol == null) {
 throw new MalformedURLException("no protocol: "+original);
 }

 // Get the protocol handler if not specified or the protocol
 // of the context could not be used
 if (handler == null &&
 (handler = getURLStreamHandler(protocol)) == null) {
 throw new MalformedURLException("unknown protocol: "+protocol);
 }

 this.handler = handler;

 i = spec.indexOf('#', start);
 if (i >= 0) {
 ref = spec.substring(i + 1, limit);
 limit = i;
 }

 /*
 * Handle special case inheritance of query and fragment
 * implied by RFC2396 section 5.2.2.
 */
 if (isRelative && start == limit) {
 query = context.query;
 if (ref == null) {
 ref = context.ref;
 }
 }

 handler.parseURL(this, spec, start, limit);

 } catch(MalformedURLException e) {
 throw e;
 } catch(Exception e) {
 MalformedURLException exception = new MalformedURLException(e.getMessage());
 exception.initCause(e);
 throw exception;
 }
 }

 /**
 * Creates a URL from a URI, as if by invoking {@code uri.toURL()}, but
 * associating it with the given {@code URLStreamHandler}, if allowed.
 *
 * @apiNote
 * Applications should consider performing additional integrity
 * checks before constructing a {@code URL} and opening a connection.
 * See the <a href=#integrity>API note</a> in the class level API
 * documentation.
 *
 * @implSpec The implementation of this method includes calling the {@link
 * URLStreamHandler#parseURL(URL, String, int, int) parseURL} method on the
 * selected handler.
 *
 * @param uri the {@code URI} from which the returned {@code URL} should
 * be built
 * @param handler a custom protocol stream handler for
 * the returned {@code URL}. Can be {@code null},
 * in which case the default stream handler for
 * the protocol if any, will be used.
 *
 * @return a new {@code URL} instance created from the given {@code URI}
 * and associated with the given {@code URLStreamHandler}, if any
 *
 * @throws NullPointerException if {@code uri} is {@code null}
 *
 * @throws IllegalArgumentException if no protocol is specified
 * (the {@linkplain URI#getScheme() uri scheme} is {@code null}), or
 * if the {@code URLStreamHandler} is not {@code null} and can not be
 * set for the given protocol
 *
 * @throws MalformedURLException if an unknown protocol is found,
 * or the given URI fails to comply with the specific
 * syntax of the associated protocol, or the
 * underlying stream handler's {@linkplain
 * URLStreamHandler#parseURL(URL, String, int, int)
 * parseURL method} throws {@code IllegalArgumentException}
 *
 * @throws SecurityException
 * if a security manager exists and its
 * {@code checkPermission} method doesn't allow
 * specifying a stream handler
 *
 * @see java.net.URI#toURL()
 *
 * @since 20
 */
 public static URL of(URI uri, URLStreamHandler handler)
 throws MalformedURLException {
 if (!uri.isAbsolute()) {
 throw new IllegalArgumentException("URI is not absolute");
 }

 String protocol = uri.getScheme();

 // fast path for canonical jrt:/... URLs
 //
 // In general we need to go via Handler.parseURL, but for the jrt
 // protocol we enforce that the Handler is not overridable and can
 // optimize URI to URL conversion.
 //
 // Case-sensitive comparison for performance; malformed protocols will
 // be handled correctly by the slow path.
 if (handler == null && protocol.equals("jrt") && !uri.isOpaque()
 && uri.getRawAuthority() == null
 && uri.getRawFragment() == null) {

 String query = uri.getRawQuery();
 String path = uri.getRawPath();
 String file = (query == null) ? path : path + "?" + query;

 // URL represent undefined host as empty string while URI use null
 String host = uri.getHost();
 if (host == null) {
 host = "";
 }

 int port = uri.getPort();

 return new URL("jrt", host, port, file, null);
 }

 // slow path (will work for non-canonical forms of jrt: too)

 if ("url".equalsIgnoreCase(protocol)) {;
 String uristr = uri.toString();
 try {
 URI inner = new URI(uristr.substring(4));
 if (inner.isAbsolute()) {
 protocol = inner.getScheme();
 }
 } catch (URISyntaxException use) {
 throw new MalformedURLException(use.getMessage());
 }
 }

 if (handler != null && !isOverrideable(protocol)) {
 throw new IllegalArgumentException("Can't override URLStreamHandler for protocol "
 + protocol);
 }

 return new URL((URL)null, uri.toString(), handler);
 }

 /*
 * Returns true if specified string is a valid protocol name.
 */
 private boolean isValidProtocol(String protocol) {
 int len = protocol.length();
 if (len < 1)
 return false;
 char c = protocol.charAt(0);
 if (!Character.isLetter(c))
 return false;
 for (int i = 1; i < len; i++) {
 c = protocol.charAt(i);
 if (!Character.isLetterOrDigit(c) && c != '.' && c != '+' &&
 c != '-') {
 return false;
 }
 }
 return true;
 }

 /*
 * Checks for permission to specify a stream handler.
 */
 private void checkSpecifyHandler(@SuppressWarnings("removal") SecurityManager sm) {
 sm.checkPermission(SecurityConstants.SPECIFY_HANDLER_PERMISSION);
 }

 /**
 * Sets the specified 8 fields of the URL. This is not a public method so
 * that only URLStreamHandlers can modify URL fields. URLs are otherwise
 * constant.
 *
 * @param protocol the name of the protocol to use
 * @param host the name of the host
 * @param port the port number on the host
 * @param authority the authority part for the url
 * @param userInfo the username and password
 * @param path the file on the host
 * @param ref the internal reference in the URL
 * @param query the query part of this URL
 * @since 1.3
 */
 void set(String protocol, String host, int port,
 String authority, String userInfo, String path,
 String query, String ref) {
 synchronized (this) {
 this.protocol = protocol;
 this.host = host;
 this.port = port;
 this.file = query == null ? path : path + "?" + query;
 this.userInfo = userInfo;
 this.path = path;
 this.ref = ref;
 /* This is very important. We must recompute this after the
 * URL has been changed. */
 hashCode = -1;
 hostAddress = null;
 this.query = query;
 this.authority = authority;
 }
 }

 /**
 * Returns the address of the host represented by this URL.
 * A {@link SecurityException} or an {@link UnknownHostException}
 * while getting the host address will result in this method returning
 * {@code null}
 *
 * @return an {@link InetAddress} representing the host
 */
 synchronized InetAddress getHostAddress() {
 if (hostAddress != null) {
 return hostAddress;
 }

 if (host == null || host.isEmpty()) {
 return null;
 }
 try {
 hostAddress = InetAddress.getByName(host);
 } catch (UnknownHostException | SecurityException ex) {
 return null;
 }
 return hostAddress;
 }

 /**
 * Gets the query part of this {@code URL}.
 *
 * @return the query part of this {@code URL},
 * or <CODE>null</CODE> if one does not exist
 * @since 1.3
 */
 public String getQuery() {
 return query;
 }

 /**
 * Gets the path part of this {@code URL}.
 *
 * @return the path part of this {@code URL}, or an
 * empty string if one does not exist
 * @since 1.3
 */
 public String getPath() {
 return path;
 }

 /**
 * Gets the userInfo part of this {@code URL}.
 *
 * @return the userInfo part of this {@code URL}, or
 * <CODE>null</CODE> if one does not exist
 * @since 1.3
 */
 public String getUserInfo() {
 return userInfo;
 }

 /**
 * Gets the authority part of this {@code URL}.
 *
 * @return the authority part of this {@code URL}
 * @since 1.3
 */
 public String getAuthority() {
 return authority;
 }

 /**
 * Gets the port number of this {@code URL}.
 *
 * @return the port number, or -1 if the port is not set
 */
 public int getPort() {
 return port;
 }

 /**
 * Gets the default port number of the protocol associated
 * with this {@code URL}. If the URL scheme or the URLStreamHandler
 * for the URL do not define a default port number,
 * then -1 is returned.
 *
 * @return the port number
 * @since 1.4
 */
 public int getDefaultPort() {
 return handler.getDefaultPort();
 }

 /**
 * Gets the protocol name of this {@code URL}.
 *
 * @return the protocol of this {@code URL}.
 */
 public String getProtocol() {
 return protocol;
 }

 /**
 * Gets the host name of this {@code URL}, if applicable.
 * The format of the host conforms to RFC 2732, i.e. for a
 * literal IPv6 address, this method will return the IPv6 address
 * enclosed in square brackets ({@code '['} and {@code ']'}).
 *
 * @return the host name of this {@code URL}.
 */
 public String getHost() {
 return host;
 }

 /**
 * Gets the file name of this {@code URL}.
 * The returned file portion will be
 * the same as <CODE>getPath()</CODE>, plus the concatenation of
 * the value of <CODE>getQuery()</CODE>, if any. If there is
 * no query portion, this method and <CODE>getPath()</CODE> will
 * return identical results.
 *
 * @return the file name of this {@code URL},
 * or an empty string if one does not exist
 */
 public String getFile() {
 return file;
 }

 /**
 * Gets the anchor (also known as the "reference") of this
 * {@code URL}.
 *
 * @return the anchor (also known as the "reference") of this
 * {@code URL}, or <CODE>null</CODE> if one does not exist
 */
 public String getRef() {
 return ref;
 }

 /**
 * Compares this URL for equality with another object.
 *
 * If the given object is not a URL then this method immediately returns
 * {@code false}.
 *
 * Two URL objects are equal if they have the same protocol, reference
 * equivalent hosts, have the same port number on the host, and the same
 * file and fragment of the file.
 *
 * Two hosts are considered equivalent if both host names can be resolved
 * into the same IP addresses; else if either host name can't be
 * resolved, the host names must be equal without regard to case; or both
 * host names equal to null.
 *
 * Since hosts comparison requires name resolution, this operation is a
 * blocking operation. 
 *
 * Note: The defined behavior for {@code equals} is known to
 * be inconsistent with virtual hosting in HTTP.
 *
 * @param obj the URL to compare against.
 * @return {@code true} if the objects are the same;
 * {@code false} otherwise.
 */
 public boolean equals(Object obj) {
 if (!(obj instanceof URL u2))
 return false;

 return handler.equals(this, u2);
 }

 /**
 * Creates an integer suitable for hash table indexing.
 *
 * The hash code is based upon all the URL components relevant for URL
 * comparison. As such, this operation is a blocking operation.
 *
 * @return a hash code for this {@code URL}.
 */
 public synchronized int hashCode() {
 if (hashCode != -1)
 return hashCode;

 hashCode = handler.hashCode(this);
 return hashCode;
 }

 /**
 * Compares two URLs, excluding the fragment component.
 *
 * Returns {@code true} if this {@code URL} and the
 * {@code other} argument are equal without taking the
 * fragment component into consideration.
 *
 * @param other the {@code URL} to compare against.
 * @return {@code true} if they reference the same remote object;
 * {@code false} otherwise.
 */
 public boolean sameFile(URL other) {
 return handler.sameFile(this, other);
 }

 /**
 * Constructs a string representation of this {@code URL}. The
 * string is created by calling the {@code toExternalForm}
 * method of the stream protocol handler for this object.
 *
 * @return a string representation of this object.
 * @see java.net.URL#URL(java.lang.String, java.lang.String, int,
 * java.lang.String)
 * @see java.net.URLStreamHandler#toExternalForm(java.net.URL)
 */
 public String toString() {
 return toExternalForm();
 }

 /**
 * Constructs a string representation of this {@code URL}. The
 * string is created by calling the {@code toExternalForm}
 * method of the stream protocol handler for this object.
 *
 * @return a string representation of this object.
 * @see java.net.URL#URL(java.lang.String, java.lang.String,
 * int, java.lang.String)
 * @see java.net.URLStreamHandler#toExternalForm(java.net.URL)
 */
 public String toExternalForm() {
 return handler.toExternalForm(this);
 }

 /**
 * Returns a {@link java.net.URI} equivalent to this URL.
 * This method functions in the same way as {@code new URI (this.toString())}.
 * Note, any URL instance that complies with RFC 2396 can be converted
 * to a URI. However, some URLs that are not strictly in compliance
 * can not be converted to a URI.
 *
 * @throws URISyntaxException if this URL is not formatted strictly according to
 * RFC2396 and cannot be converted to a URI.
 *
 * @return a URI instance equivalent to this URL.
 * @since 1.5
 */
 public URI toURI() throws URISyntaxException {
 URI uri = new URI(toString());
 if (authority != null && isBuiltinStreamHandler(handler)) {
 String s = IPAddressUtil.checkAuthority(this);
 if (s != null) throw new URISyntaxException(authority, s);
 }
 return uri;
 }

 /**
 * Returns a {@link java.net.URLConnection URLConnection} instance that
 * represents a connection to the remote object referred to by the
 * {@code URL}.
 *
 * A new instance of {@linkplain java.net.URLConnection URLConnection} is
 * created every time when invoking the
 * {@linkplain java.net.URLStreamHandler#openConnection(URL)
 * URLStreamHandler.openConnection(URL)} method of the protocol handler for
 * this URL.
 *
 * It should be noted that a URLConnection instance does not establish
 * the actual network connection on creation. This will happen only when
 * calling {@linkplain java.net.URLConnection#connect() URLConnection.connect()}.
 *
 * If for the URL's protocol (such as HTTP or JAR), there
 * exists a public, specialized URLConnection subclass belonging
 * to one of the following packages or one of their subpackages:
 * java.lang, java.io, java.util, java.net, the connection
 * returned will be of that subclass. For example, for HTTP an
 * HttpURLConnection will be returned, and for JAR a
 * JarURLConnection will be returned.
 *
 * @return a {@link java.net.URLConnection URLConnection} linking
 * to the URL.
 * @throws IOException if an I/O exception occurs.
 * @see java.net.URL#URL(java.lang.String, java.lang.String,
 * int, java.lang.String)
 */
 public URLConnection openConnection() throws java.io.IOException {
 return handler.openConnection(this);
 }

 /**
 * Same as {@link #openConnection()}, except that the connection will be
 * made through the specified proxy; Protocol handlers that do not
 * support proxying will ignore the proxy parameter and make a
 * normal connection.
 *
 * Invoking this method preempts the system's default
 * {@link java.net.ProxySelector ProxySelector} settings.
 *
 * @param proxy the Proxy through which this connection
 * will be made. If direct connection is desired,
 * Proxy.NO_PROXY should be specified.
 * @return a {@code URLConnection} to the URL.
 * @throws IOException if an I/O exception occurs.
 * @throws SecurityException if a security manager is present
 * and the caller doesn't have permission to connect
 * to the proxy.
 * @throws IllegalArgumentException will be thrown if proxy is null,
 * or proxy has the wrong type
 * @throws UnsupportedOperationException if the subclass that
 * implements the protocol handler doesn't support
 * this method.
 * @see java.net.URL#URL(java.lang.String, java.lang.String,
 * int, java.lang.String)
 * @see java.net.URLConnection
 * @see java.net.URLStreamHandler#openConnection(java.net.URL,
 * java.net.Proxy)
 * @since 1.5
 */
 public URLConnection openConnection(Proxy proxy)
 throws java.io.IOException {
 if (proxy == null) {
 throw new IllegalArgumentException("proxy can not be null");
 }

 // Create a copy of Proxy as a security measure
 Proxy p = proxy == Proxy.NO_PROXY ? Proxy.NO_PROXY : sun.net.ApplicationProxy.create(proxy);
 @SuppressWarnings("removal")
 SecurityManager sm = System.getSecurityManager();
 if (p.type() != Proxy.Type.DIRECT && sm != null) {
 InetSocketAddress epoint = (InetSocketAddress) p.address();
 if (epoint.isUnresolved())
 sm.checkConnect(epoint.getHostName(), epoint.getPort());
 else
 sm.checkConnect(epoint.getAddress().getHostAddress(),
 epoint.getPort());
 }
 return handler.openConnection(this, p);
 }

 /**
 * Opens a connection to this {@code URL} and returns an
 * {@code InputStream} for reading from that connection. This
 * method is a shorthand for:
 * <blockquote><pre>
 * openConnection().getInputStream()
 * </pre></blockquote>
 *
 * @return an input stream for reading from the URL connection.
 * @throws IOException if an I/O exception occurs.
 * @see java.net.URL#openConnection()
 * @see java.net.URLConnection#getInputStream()
 */
 public final InputStream openStream() throws java.io.IOException {
 return openConnection().getInputStream();
 }

 /**
 * Gets the contents of this URL. This method is a shorthand for:
 * <blockquote><pre>
 * openConnection().getContent()
 * </pre></blockquote>
 *
 * @return the contents of this URL.
 * @throws IOException if an I/O exception occurs.
 * @see java.net.URLConnection#getContent()
 */
 public final Object getContent() throws java.io.IOException {
 return openConnection().getContent();
 }

 /**
 * Gets the contents of this URL. This method is a shorthand for:
 * <blockquote><pre>
 * openConnection().getContent(classes)
 * </pre></blockquote>
 *
 * @param classes an array of Java types
 * @return the content object of this URL that is the first match of
 * the types specified in the classes array.
 * null if none of the requested types are supported.
 * @throws IOException if an I/O exception occurs.
 * @see java.net.URLConnection#getContent(Class[])
 * @since 1.3
 */
 public final Object getContent(Class<?>[] classes)
 throws java.io.IOException {
 return openConnection().getContent(classes);
 }

 /**
 * The URLStreamHandler factory.
 */
 private static volatile URLStreamHandlerFactory factory;

 /**
 * Sets an application's {@code URLStreamHandlerFactory}.
 * This method can be called at most once in a given Java Virtual
 * Machine.
 *
 * The {@code URLStreamHandlerFactory} instance is used to
 *construct a stream protocol handler from a protocol name.
 *
 * If there is a security manager, this method first calls
 * the security manager's {@code checkSetFactory} method
 * to ensure the operation is allowed.
 * This could result in a SecurityException.
 *
 * @param fac the desired factory.
 * @throws Error if the application has already set a factory.
 * @throws SecurityException if a security manager exists and its
 * {@code checkSetFactory} method doesn't allow
 * the operation.
 * @see java.net.URL#URL(java.lang.String, java.lang.String,
 * int, java.lang.String)
 * @see java.net.URLStreamHandlerFactory
 * @see SecurityManager#checkSetFactory
 */
 public static void setURLStreamHandlerFactory(URLStreamHandlerFactory fac) {
 synchronized (streamHandlerLock) {
 if (factory != null) {
 throw new Error("factory already defined");
 }
 @SuppressWarnings("removal")
 SecurityManager security = System.getSecurityManager();
 if (security != null) {
 security.checkSetFactory();
 }
 handlers.clear();

 // safe publication of URLStreamHandlerFactory with volatile write
 factory = fac;
 }
 }

 private static final URLStreamHandlerFactory defaultFactory = new DefaultFactory();

 private static class DefaultFactory implements URLStreamHandlerFactory {
 private static final String PREFIX = "sun.net.www.protocol.";

 public URLStreamHandler createURLStreamHandler(String protocol) {
 // Avoid using reflection during bootstrap
 switch (protocol) {
 case "file":
 return new sun.net.www.protocol.file.Handler();
 case "jar":
 return new sun.net.www.protocol.jar.Handler();
 case "jrt":
 return new sun.net.www.protocol.jrt.Handler();
 }
 String name = PREFIX + protocol + ".Handler";
 try {
 Object o = Class.forName(name).getDeclaredConstructor().newInstance();
 return (URLStreamHandler)o;
 } catch (Exception e) {
 // For compatibility, all Exceptions are ignored.
 // any number of exceptions can get thrown here
 }
 return null;
 }
 }

 private static URLStreamHandler lookupViaProperty(String protocol) {
 String packagePrefixList =
 GetPropertyAction.privilegedGetProperty(protocolPathProp);
 if (packagePrefixList == null) {
 // not set
 return null;
 }

 String[] packagePrefixes = packagePrefixList.split("\\|");
 URLStreamHandler handler = null;
 for (int i=0; handler == null && i<packagePrefixes.length; i++) {
 String packagePrefix = packagePrefixes[i].trim();
 try {
 String clsName = packagePrefix + "." + protocol + ".Handler";
 Class<?> cls = null;
 try {
 cls = Class.forName(clsName);
 } catch (ClassNotFoundException e) {
 ClassLoader cl = ClassLoader.getSystemClassLoader();
 if (cl != null) {
 cls = cl.loadClass(clsName);
 }
 }
 if (cls != null) {
 @SuppressWarnings("deprecation")
 Object tmp = cls.newInstance();
 handler = (URLStreamHandler)tmp;
 }
 } catch (Exception e) {
 // any number of exceptions can get thrown here
 }
 }
 return handler;
 }

 private static Iterator<URLStreamHandlerProvider> providers() {
 return new Iterator<>() {

 ClassLoader cl = ClassLoader.getSystemClassLoader();
 ServiceLoader<URLStreamHandlerProvider> sl =
 ServiceLoader.load(URLStreamHandlerProvider.class, cl);
 Iterator<URLStreamHandlerProvider> i = sl.iterator();

 URLStreamHandlerProvider next = null;

 private boolean getNext() {
 while (next == null) {
 try {
 if (!i.hasNext())
 return false;
 next = i.next();
 } catch (ServiceConfigurationError sce) {
 if (sce.getCause() instanceof SecurityException) {
 // Ignore security exceptions
 continue;
 }
 throw sce;
 }
 }
 return true;
 }

 public boolean hasNext() {
 return getNext();
 }

 public URLStreamHandlerProvider next() {
 if (!getNext())
 throw new NoSuchElementException();
 URLStreamHandlerProvider n = next;
 next = null;
 return n;
 }
 };
 }

 private static class ThreadTrackHolder {
 static final ThreadTracker TRACKER = new ThreadTracker();
 }

 private static Object tryBeginLookup() {
 return ThreadTrackHolder.TRACKER.tryBegin();
 }

 private static void endLookup(Object key) {
 ThreadTrackHolder.TRACKER.end(key);
 }

 @SuppressWarnings("removal")
 private static URLStreamHandler lookupViaProviders(final String protocol) {
 Object key = tryBeginLookup();
 if (key == null) {
 throw new Error("Circular loading of URL stream handler providers detected");
 }
 try {
 return AccessController.doPrivileged(
 new PrivilegedAction<>() {
 public URLStreamHandler run() {
 Iterator<URLStreamHandlerProvider> itr = providers();
 while (itr.hasNext()) {
 URLStreamHandlerProvider f = itr.next();
 URLStreamHandler h = f.createURLStreamHandler(protocol);
 if (h != null)
 return h;
 }
 return null;
 }
 });
 } finally {
 endLookup(key);
 }
 }

 /**
 * Returns the protocol in lower case. Special cases known protocols
 * to avoid loading locale classes during startup.
 */
 static String lowerCaseProtocol(String protocol) {
 if (protocol.equals("jrt")) {
 return "jrt";
 } else if (protocol.equals("file")) {
 return "file";
 } else if (protocol.equals("jar")) {
 return "jar";
 } else {
 return protocol.toLowerCase(Locale.ROOT);
 }
 }

 /**
 * Non-overrideable protocols: "jrt" and "file"
 *
 * Character-based comparison for performance reasons; also ensures
 * case-insensitive comparison in a locale-independent fashion.
 */
 static boolean isOverrideable(String protocol) {
 if (protocol.length() == 3) {
 if ((Character.toLowerCase(protocol.charAt(0)) == 'j') &&
 (Character.toLowerCase(protocol.charAt(1)) == 'r') &&
 (Character.toLowerCase(protocol.charAt(2)) == 't')) {
 return false;
 }
 } else if (protocol.length() == 4) {
 if ((Character.toLowerCase(protocol.charAt(0)) == 'f') &&
 (Character.toLowerCase(protocol.charAt(1)) == 'i') &&
 (Character.toLowerCase(protocol.charAt(2)) == 'l') &&
 (Character.toLowerCase(protocol.charAt(3)) == 'e')) {
 return false;
 }
 }
 return true;
 }

 /**
 * A table of protocol handlers.
 */
 static Hashtable<String,URLStreamHandler> handlers = new Hashtable<>();
 private static final Object streamHandlerLock = new Object();

 /**
 * Returns the Stream Handler.
 * @param protocol the protocol to use
 */
 static URLStreamHandler getURLStreamHandler(String protocol) {

 URLStreamHandler handler = handlers.get(protocol);

 if (handler != null) {
 return handler;
 }

 URLStreamHandlerFactory fac;
 boolean checkedWithFactory = false;
 boolean overrideableProtocol = isOverrideable(protocol);

 if (overrideableProtocol && VM.isBooted()) {
 // Use the factory (if any). Volatile read makes
 // URLStreamHandlerFactory appear fully initialized to current thread.
 fac = factory;
 if (fac != null) {
 handler = fac.createURLStreamHandler(protocol);
 checkedWithFactory = true;
 }

 if (handler == null && !protocol.equalsIgnoreCase("jar")) {
 handler = lookupViaProviders(protocol);
 }

 if (handler == null) {
 handler = lookupViaProperty(protocol);
 }
 }

 if (handler == null) {
 // Try the built-in protocol handler
 handler = defaultFactory.createURLStreamHandler(protocol);
 }

 synchronized (streamHandlerLock) {
 URLStreamHandler handler2 = null;

 // Check again with hashtable just in case another
 // thread created a handler since we last checked
 handler2 = handlers.get(protocol);

 if (handler2 != null) {
 return handler2;
 }

 // Check with factory if another thread set a
 // factory since our last check
 if (overrideableProtocol && !checkedWithFactory &&
--> --------------------

--> maximum size reached

--> --------------------

quality95%

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