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feat(shared): add custom ServiceLoader implementation

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This commit is contained in:
Akash Yadav
2023-04-30 22:42:12 +05:30
parent 2b5e78fd90
commit f87748740b
3 changed files with 669 additions and 0 deletions
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lookup/src/main/java/com/itsaky/androidide/lookup/internal/DefaultLookup.java → app/src/main/java/com/itsaky/androidide/lookup/DefaultLookup.java
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shared/src/main/java/com/itsaky/androidide/utils/ServiceLoader.java
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/*
* This file is part of AndroidIDE.
*
* AndroidIDE is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* AndroidIDE 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 for more details.
*
* You should have received a copy of the GNU General Public License
* along with AndroidIDE. If not, see <https://www.gnu.org/licenses/>.
*/
/*
* Copyright (C) 2014 The Android Open Source Project
* Copyright (c) 2005, 2013, 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 com.itsaky.androidide.utils;
import androidx.annotation.NonNull;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.URL;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Objects;
import java.util.Optional;
import java.util.ServiceConfigurationError;
/**
* A simple service-provider loading facility. This class is an adaptation of the
* {@link java.util.ServiceLoader ServiceLoader} to avoid the usage of {@link Class#newInstance()}
* and use
* {@link java.lang.reflect.Constructor#newInstance(Object...) Constructor.newInstance(Object...)}
* for class instance creation.
*
* <p> A <i>service</i> is a well-known set of interfaces and (usually
* abstract) classes. A <i>service provider</i> is a specific implementation of a service. The
* classes in a provider typically implement the interfaces and subclass the classes defined in the
* service itself. Service providers can be installed in an implementation of the Java platform in
* the form of extensions, that is, jar files placed into any of the usual extension directories.
* Providers can also be made available by adding them to the application's class path or by some
* other platform-specific means.
*
* <p> For the purpose of loading, a service is represented by a single type,
* that is, a single interface or abstract class. (A concrete class can be used, but this is not
* recommended.) A provider of a given service contains one or more concrete classes that extend
* this <i>service type</i> with data and code specific to the provider. The <i>provider class</i>
* is typically not the entire provider itself but rather a proxy which contains enough information
* to decide whether the provider is able to satisfy a particular request together with code that
* can create the actual provider on demand. The details of provider classes tend to be highly
* service-specific; no single class or interface could possibly unify them, so no such type is
* defined here. The only requirement enforced by this facility is that provider classes must have
* a zero-argument constructor so that they can be instantiated during loading.
*
* <p><a name="format"> A service provider is identified by placing a
* <i>provider-configuration file</i> in the resource directory
* <tt>META-INF/services</tt>.</a> The file's name is the fully-qualified <a
* href="../lang/ClassLoader.html#name">binary name</a> of the service's type. The file contains a
* list of fully-qualified binary names of concrete provider classes, one per line. Space and tab
* characters surrounding each name, as well as blank lines, are ignored. The comment character is
* <tt>'#'</tt> (<tt>'&#92;u0023'</tt>,
* <font style="font-size:smaller;">NUMBER SIGN</font>); on
* each line all characters following the first comment character are ignored. The file must be
* encoded in UTF-8.
*
* <p> If a particular concrete provider class is named in more than one
* configuration file, or is named in the same configuration file more than once, then the
* duplicates are ignored. The configuration file naming a particular provider need not be in the
* same jar file or other distribution unit as the provider itself. The provider must be accessible
* from the same class loader that was initially queried to locate the configuration file; note that
* this is not necessarily the class loader from which the file was actually loaded.
*
* <p> Providers are located and instantiated lazily, that is, on demand. A
* service loader maintains a cache of the providers that have been loaded so far. Each invocation
* of the {@link #iterator iterator} method returns an iterator that first yields all of the
* elements of the cache, in instantiation order, and then lazily locates and instantiates any
* remaining providers, adding each one to the cache in turn. The cache can be cleared via the
* {@link #reload reload} method.
*
* <p> Service loaders always execute in the security context of the caller.
* Trusted system code should typically invoke the methods in this class, and the methods of the
* iterators which they return, from within a privileged security context.
*
* <p> Instances of this class are not safe for use by multiple concurrent
* threads.
*
* <p> Unless otherwise specified, passing a <tt>null</tt> argument to any
* method in this class will cause a {@link NullPointerException} to be thrown.
*
* <p><span style="font-weight: bold; padding-right: 1em">Example</span>
* Suppose we have a service type <tt>com.example.CodecSet</tt> which is intended to represent sets
* of encoder/decoder pairs for some protocol. In this case it is an abstract class with two
* abstract methods:
*
* <blockquote><pre>
* public abstract Encoder getEncoder(String encodingName);
* public abstract Decoder getDecoder(String encodingName);</pre></blockquote>
* <p>
* Each method returns an appropriate object or <tt>null</tt> if the provider does not support the
* given encoding. Typical providers support more than one encoding.
*
* <p> If <tt>com.example.impl.StandardCodecs</tt> is an implementation of the
* <tt>CodecSet</tt> service then its jar file also contains a file named
*
* <blockquote><pre>
* META-INF/services/com.example.CodecSet</pre></blockquote>
*
* <p> This file contains the single line:
*
* <blockquote><pre>
* com.example.impl.StandardCodecs # Standard codecs</pre></blockquote>
*
* <p> The <tt>CodecSet</tt> class creates and saves a single service instance
* at initialization:
*
* <blockquote><pre>
* private static ServiceLoader&lt;CodecSet&gt; codecSetLoader
* = ServiceLoader.load(CodecSet.class);</pre></blockquote>
*
* <p> To locate an encoder for a given encoding name it defines a static
* factory method which iterates through the known and available providers, returning only when it
* has located a suitable encoder or has run out of providers.
*
* <blockquote><pre>
* public static Encoder getEncoder(String encodingName) {
* for (CodecSet cp : codecSetLoader) {
* Encoder enc = cp.getEncoder(encodingName);
* if (enc != null)
* return enc;
* }
* return null;
* }</pre></blockquote>
*
* <p> A <tt>getDecoder</tt> method is defined similarly.
*
* <p><span style="font-weight: bold; padding-right: 1em">Usage Note</span> If
* the class path of a class loader that is used for provider loading includes remote network URLs
* then those URLs will be dereferenced in the process of searching for provider-configuration
* files.
*
* <p> This activity is normal, although it may cause puzzling entries to be
* created in web-server logs. If a web server is not configured correctly, however, then this
* activity may cause the provider-loading algorithm to fail spuriously.
*
* <p> A web server should return an HTTP 404 (Not Found) response when a
* requested resource does not exist. Sometimes, however, web servers are erroneously configured to
* return an HTTP 200 (OK) response along with a helpful HTML error page in such cases. This will
* cause a {@link ServiceConfigurationError} to be thrown when this class attempts to parse the HTML
* page as a provider-configuration file. The best solution to this problem is to fix the
* misconfigured web server to return the correct response code (HTTP 404) along with the HTML error
* page.
*
* @param <S> The type of the service to be loaded by this loader
* @author Mark Reinhold
* @since 1.6
*/
public final class ServiceLoader<S> implements Iterable<S> {
private static final String PREFIX = "META-INF/services/";
// The class or interface representing the service being loaded
private final Class<S> service;
// The class loader used to locate, load, and instantiate providers
private final ClassLoader loader;
// The access control context taken when the ServiceLoader is created
// Android-changed: do not use legacy security code.
// private final AccessControlContext acc;
// Cached providers, in instantiation order
private final LinkedHashMap<String, S> providers = new LinkedHashMap<>();
// The current lazy-lookup iterator
private LazyIterator lookupIterator;
/**
* Clear this loader's provider cache so that all providers will be reloaded.
*
* <p> After invoking this method, subsequent invocations of the {@link
* #iterator() iterator} method will lazily look up and instantiate providers from scratch, just
* as is done by a newly-created loader.
*
* <p> This method is intended for use in situations in which new providers
* can be installed into a running Java virtual machine.
*/
public void reload() {
providers.clear();
lookupIterator = new LazyIterator(service, loader);
}
private ServiceLoader(Class<S> svc, ClassLoader cl) {
service = Objects.requireNonNull(svc, "Service interface cannot be null");
loader = (cl == null) ? ClassLoader.getSystemClassLoader() : cl;
// Android-changed: Do not use legacy security code.
// On Android, System.getSecurityManager() is always null.
// acc = (System.getSecurityManager() != null) ? AccessController.getContext() : null;
reload();
}
private static void fail(Class<?> service, String msg, Throwable cause)
throws ServiceConfigurationError {
throw new ServiceConfigurationError(service.getName() + ": " + msg, cause);
}
private static void fail(Class<?> service, String msg) throws ServiceConfigurationError {
throw new ServiceConfigurationError(service.getName() + ": " + msg);
}
private static void fail(Class<?> service, URL u, int line, String msg)
throws ServiceConfigurationError {
fail(service, u + ":" + line + ": " + msg);
}
// Parse a single line from the given configuration file, adding the name
// on the line to the names list.
//
private int parseLine(Class<?> service, URL u, BufferedReader r, int lc, List<String> names)
throws IOException, ServiceConfigurationError {
String ln = r.readLine();
if (ln == null) {
return -1;
}
int ci = ln.indexOf('#');
if (ci >= 0) {
ln = ln.substring(0, ci);
}
ln = ln.trim();
int n = ln.length();
if (n != 0) {
if ((ln.indexOf(' ') >= 0) || (ln.indexOf('\t') >= 0)) {
fail(service, u, lc, "Illegal configuration-file syntax");
}
int cp = ln.codePointAt(0);
if (!Character.isJavaIdentifierStart(cp)) {
fail(service, u, lc, "Illegal provider-class name: " + ln);
}
for (int i = Character.charCount(cp); i < n; i += Character.charCount(cp)) {
cp = ln.codePointAt(i);
if (!Character.isJavaIdentifierPart(cp) && (cp != '.')) {
fail(service, u, lc, "Illegal provider-class name: " + ln);
}
}
if (!providers.containsKey(ln) && !names.contains(ln)) {
names.add(ln);
}
}
return lc + 1;
}
// Parse the content of the given URL as a provider-configuration file.
//
// @param service
// The service type for which providers are being sought;
// used to construct error detail strings
//
// @param u
// The URL naming the configuration file to be parsed
//
// @return A (possibly empty) iterator that will yield the provider-class
// names in the given configuration file that are not yet members
// of the returned set
//
// @throws ServiceConfigurationError
// If an I/O error occurs while reading from the given URL, or
// if a configuration-file format error is detected
//
private Iterator<String> parse(Class<?> service, URL u) throws ServiceConfigurationError {
InputStream in = null;
BufferedReader r = null;
ArrayList<String> names = new ArrayList<>();
try {
in = u.openStream();
r = new BufferedReader(new InputStreamReader(in, StandardCharsets.UTF_8));
int lc = 1;
//noinspection StatementWithEmptyBody
while ((lc = parseLine(service, u, r, lc, names)) >= 0);
} catch (IOException x) {
fail(service, "Error reading configuration file", x);
} finally {
try {
if (r != null) {
r.close();
}
if (in != null) {
in.close();
}
} catch (IOException y) {
fail(service, "Error closing configuration file", y);
}
}
return names.iterator();
}
// Private inner class implementing fully-lazy provider lookup
//
private class LazyIterator implements Iterator<S> {
Class<S> service;
ClassLoader loader;
Enumeration<URL> configs = null;
Iterator<String> pending = null;
String nextName = null;
private LazyIterator(Class<S> service, ClassLoader loader) {
this.service = service;
this.loader = loader;
}
private boolean hasNextService() {
if (nextName != null) {
return true;
}
if (configs == null) {
try {
String fullName = PREFIX + service.getName();
if (loader == null) {
configs = ClassLoader.getSystemResources(fullName);
} else {
configs = loader.getResources(fullName);
}
} catch (IOException x) {
fail(service, "Error locating configuration files", x);
}
}
while ((pending == null) || !pending.hasNext()) {
if (!configs.hasMoreElements()) {
return false;
}
pending = parse(service, configs.nextElement());
}
nextName = pending.next();
return true;
}
private S nextService() {
if (!hasNextService()) {
throw new NoSuchElementException();
}
String cn = nextName;
nextName = null;
Class<?> c = null;
try {
c = Class.forName(cn, false, loader);
} catch (ClassNotFoundException x) {
fail(service,
// Android-changed: Let the ServiceConfigurationError have a cause.
"Provider " + cn + " not found", x);
// "Provider " + cn + " not found");
}
if (!service.isAssignableFrom(c)) {
// Android-changed: Let the ServiceConfigurationError have a cause.
ClassCastException cce = new ClassCastException(
service.getCanonicalName() + " is not assignable from " + c.getCanonicalName());
fail(service, "Provider " + cn + " not a subtype", cce);
}
try {
S p = service.cast(c.getConstructor().newInstance());
providers.put(cn, p);
return p;
} catch (Throwable x) {
fail(service, "Provider " + cn + " could not be instantiated", x);
}
throw new Error(); // This cannot happen
}
public boolean hasNext() {
// Android-changed: do not use legacy security code
/* if (acc == null) { */
return hasNextService();
/*
} else {
PrivilegedAction<Boolean> action = new PrivilegedAction<Boolean>() {
public Boolean run() { return hasNextService(); }
};
return AccessController.doPrivileged(action, acc);
}
*/
}
public S next() {
// Android-changed: do not use legacy security code
/* if (acc == null) { */
return nextService();
/*
} else {
PrivilegedAction<S> action = new PrivilegedAction<S>() {
public S run() { return nextService(); }
};
return AccessController.doPrivileged(action, acc);
}
*/
}
public void remove() {
throw new UnsupportedOperationException();
}
}
/**
* Lazily loads the available providers of this loader's service.
*
* <p> The iterator returned by this method first yields all of the
* elements of the provider cache, in instantiation order. It then lazily loads and instantiates
* any remaining providers, adding each one to the cache in turn.
*
* <p> To achieve laziness the actual work of parsing the available
* provider-configuration files and instantiating providers must be done by the iterator itself.
* Its {@link java.util.Iterator#hasNext hasNext} and {@link java.util.Iterator#next next} methods
* can therefore throw a {@link ServiceConfigurationError} if a provider-configuration file
* violates the specified format, or if it names a provider class that cannot be found and
* instantiated, or if the result of instantiating the class is not assignable to the service
* type, or if any other kind of exception or error is thrown as the next provider is located and
* instantiated. To write robust code it is only necessary to catch
* {@link ServiceConfigurationError} when using a service iterator.
*
* <p> If such an error is thrown then subsequent invocations of the
* iterator will make a best effort to locate and instantiate the next available provider, but in
* general such recovery cannot be guaranteed.
* <blockquote style="font-size: smaller; line-height: 1.2"><span
* style="padding-right: 1em; font-weight: bold">Design Note</span> Throwing an error in these
* cases may seem extreme. The rationale for this behavior is that a malformed
* provider-configuration file, like a malformed class file, indicates a serious problem with the
* way the Java virtual machine is configured or is being used. As such it is preferable to throw
* an error rather than try to recover or, even worse, fail silently.</blockquote>
*
* <p> The iterator returned by this method does not support removal.
* Invoking its {@link java.util.Iterator#remove() remove} method will cause an
* {@link UnsupportedOperationException} to be thrown.
*
* @return An iterator that lazily loads providers for this loader's service
* @implNote When adding providers to the cache, the {@link #iterator Iterator} processes
* resources in the order that the
* {@link java.lang.ClassLoader#getResources(java.lang.String) ClassLoader.getResources(String)}
* method finds the service configuration files.
*/
@NonNull
public Iterator<S> iterator() {
return new Iterator<S>() {
final Iterator<Map.Entry<String, S>> knownProviders = providers.entrySet().iterator();
public boolean hasNext() {
if (knownProviders.hasNext()) {
return true;
}
return lookupIterator.hasNext();
}
public S next() {
if (knownProviders.hasNext()) {
return knownProviders.next().getValue();
}
return lookupIterator.next();
}
public void remove() {
throw new UnsupportedOperationException();
}
};
}
/**
* Creates a new service loader for the given service type and class loader.
*
* @param <S> the class of the service type
* @param service The interface or abstract class representing the service
* @param loader The class loader to be used to load provider-configuration files and provider
* classes, or <tt>null</tt> if the system class loader (or, failing that, the
* bootstrap class loader) is to be used
* @return A new service loader
*/
public static <S> ServiceLoader<S> load(Class<S> service, ClassLoader loader) {
return new ServiceLoader<>(service, loader);
}
/**
* Creates a new service loader for the given service type, using the current thread's
* {@linkplain java.lang.Thread#getContextClassLoader context class loader}.
*
* <p> An invocation of this convenience method of the form
*
* <blockquote><pre>
* ServiceLoader.load(<i>service</i>)</pre></blockquote>
* <p>
* is equivalent to
*
* <blockquote><pre>
* ServiceLoader.load(<i>service</i>,
* Thread.currentThread().getContextClassLoader())</pre></blockquote>
*
* @param <S> the class of the service type
* @param service The interface or abstract class representing the service
* @return A new service loader
*/
public static <S> ServiceLoader<S> load(Class<S> service) {
ClassLoader cl = Thread.currentThread().getContextClassLoader();
return ServiceLoader.load(service, cl);
}
/**
* Creates a new service loader for the given service type, using the extension class loader.
*
* <p> This convenience method simply locates the extension class loader,
* call it <tt><i>extClassLoader</i></tt>, and then returns
*
* <blockquote><pre>
* ServiceLoader.load(<i>service</i>, <i>extClassLoader</i>)</pre></blockquote>
*
* <p> If the extension class loader cannot be found then the system class
* loader is used; if there is no system class loader then the bootstrap class loader is used.
*
* <p> This method is intended for use when only installed providers are
* desired. The resulting service will only find and load providers that have been installed into
* the current Java virtual machine; providers on the application's class path will be ignored.
*
* @param <S> the class of the service type
* @param service The interface or abstract class representing the service
* @return A new service loader
*/
public static <S> ServiceLoader<S> loadInstalled(Class<S> service) {
ClassLoader cl = ClassLoader.getSystemClassLoader();
ClassLoader prev = null;
while (cl != null) {
prev = cl;
cl = cl.getParent();
}
return ServiceLoader.load(service, prev);
}
// BEGIN Android-added: loadFromSystemProperty(), for internal use.
// Instantiates a class from a system property (used elsewhere in libcore).
/**
* Internal API to support built-in SPIs that check a system property first. Returns an instance
* specified by a property with the class' binary name, or null if no such property is set.
*
* @hide
*/
public static <S> S loadFromSystemProperty(final Class<S> service) {
try {
final String className = System.getProperty(service.getName());
if (className != null) {
Class<?> c = ClassLoader.getSystemClassLoader().loadClass(className);
return (S) c.getConstructor().newInstance();
}
return null;
} catch (Exception e) {
throw new Error(e);
}
}
// END Android-added: loadFromSystemProperty(), for internal use.
/**
* Load the first available service provider of this loader's service. This convenience method is
* equivalent to invoking the {@link #iterator() iterator()} method and obtaining the first
* element. It therefore returns the first element from the provider cache if possible, it
* otherwise attempts to load and instantiate the first provider.
*
* <p> The following example loads the first available service provider. If
* no service providers are located then it uses a default implementation.
* <pre>{@code
* CodecFactory factory = ServiceLoader.load(CodecFactory.class)
* .findFirst()
* .orElse(DEFAULT_CODECSET_FACTORY);
* }</pre>
*
* @return The first service provider or empty {@code Optional} if no service providers are
* located
* @throws ServiceConfigurationError If a provider class cannot be loaded for any of the reasons
* specified in the <a href="#errors">Errors</a> section above.
* @since 9
*/
public Optional<S> findFirst() {
Iterator<S> iterator = iterator();
if (iterator.hasNext()) {
return Optional.of(iterator.next());
} else {
return Optional.empty();
}
}
/**
* Loads the first available service provider of this loader's service. Throws
* {@link ServiceNotFoundException} if the service provider cannot be found.
*
* @return The first service provider.
* @throws ServiceNotFoundException If no service provider is found for the service.
* @see #findFirst()
*/
public S findFirstOrThrow() throws ServiceNotFoundException {
final var first = findFirst();
if (first.isPresent()) {
return first.get();
}
throw new ServiceNotFoundException(service);
}
/**
* Returns a string describing this service.
*
* @return A descriptive string
*/
public String toString() {
return "java.util.ServiceLoader[" + service.getName() + "]";
}
}
shared/src/main/java/com/itsaky/androidide/utils/ServiceNotFoundException.java
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/*
* This file is part of AndroidIDE.
*
* AndroidIDE is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* AndroidIDE 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 for more details.
*
* You should have received a copy of the GNU General Public License
* along with AndroidIDE. If not, see <https://www.gnu.org/licenses/>.
*/
package com.itsaky.androidide.utils;
import java.util.Objects;
/**
* Exception thrown when a service cannot be loaded by {@link ServiceLoader}.
*
* @author Akash Yadav
*/
class ServiceNotFoundException extends IllegalStateException {
public ServiceNotFoundException(Class<?> service) {
super("Cannot find service " + service);
}
}