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/*
* #%L
* SciJava Common shared library for SciJava software.
* %%
* Copyright (C) 2009 - 2026 SciJava developers.
* %%
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
* #L%
*/
package org.scijava;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import org.scijava.event.ContextCreatedEvent;
import org.scijava.event.ContextDisposingEvent;
import org.scijava.event.EventHandler;
import org.scijava.event.EventService;
import org.scijava.log.LogService;
import org.scijava.plugin.Parameter;
import org.scijava.plugin.PluginIndex;
import org.scijava.service.Service;
import org.scijava.service.ServiceHelper;
import org.scijava.service.ServiceIndex;
import org.scijava.util.ClassUtils;
import org.scijava.util.Query;
import org.scijava.util.Types;
/**
* Top-level SciJava application context, which initializes and maintains a list
* of services.
*
* @author Curtis Rueden
* @see Service
*/
public class Context implements Disposable, AutoCloseable {
// -- Constants --
/**
* System property indicating whether the context should fail fast when
* attempting to instantiate a required service which is invalid or missing.
* If this property is set to "false" then the context creation will attempt
* to continue even when a required service cannot be instantiated. Otherwise,
* the constructor will throw an {@link IllegalArgumentException} in that
* situation.
*/
public static final String STRICT_PROPERTY = "scijava.context.strict";
/** Set of currently active (not disposed) application contexts. */
private static final Map<Context, Boolean> CONTEXTS =
new ConcurrentHashMap<>(); // NB: ConcurrentHashMap disallows nulls.
// -- Static fields --
private static Thread shutdownThread = null;
// -- Fields --
/** Index of the application context's services. */
private final ServiceIndex serviceIndex;
/** Master index of all plugins known to the application context. */
private final PluginIndex pluginIndex;
/**
* Whether context creation and injection should behave strictly, failing fast
* when attempting to instantiate a required service which is invalid or
* missing.
* <ul>
* <li>If the flag is false, then the context creation will attempt to
* continue even when a required service cannot be instantiated. Otherwise,
* the constructor will throw an {@link IllegalArgumentException} in that
* situation.</li>
* <li>If this flag is false, then a call to {@link Context#inject(Object)}
* will attempt to catch any errors that occur during context injection
* (notably: {@link NoClassDefFoundError} when scanning for event handler
* methods), logging them as errors.</li>
* </ul>
*/
private boolean strict;
/**
* False if the context is currently active; true if the context
* has already been disposed, or is in the process of being disposed.
*/
private volatile boolean disposed;
/**
* Creates a new SciJava application context with all available services.
*
* @see #Context(Collection, PluginIndex, boolean)
*/
public Context() {
this(false);
}
/**
* Creates a new SciJava application context.
*
* @param empty If true, the context will be empty of services; otherwise, it
* will be initialized with all available services.
* @see #Context(boolean, boolean)
*/
public Context(final boolean empty) {
this(empty, false);
}
/**
* Creates a new SciJava application context.
*
* @param noServices If true, the context will contain no services; otherwise,
* it will be initialized with all available services.
* @param noPlugins If true, the context will contain no plugins; otherwise,
* it will be initialized with all available plugins.
* @see #Context(Collection, PluginIndex, boolean)
*/
public Context(final boolean noServices, final boolean noPlugins) {
this(services(noServices), plugins(noPlugins));
}
/**
* Creates a new SciJava application context with the specified services (and
* any required service dependencies).
* <p>
* <b>Developer's note:</b> This constructor's argument is raw (i.e.,
* {@code Class...} instead of {@code Class<? extends Service>...}) because
* otherwise, downstream invocations (e.g.,
* {@code new Context(DisplayService.class)}) yield the potentially confusing
* warning:
* </p>
* <blockquote>Type safety: A generic array of
* {@code Class<? extends Service>} is created for a varargs
* parameter</blockquote>
* <p>
* To avoid this, we have opted to use raw types and suppress the relevant
* warnings here instead.
* </p>
*
* @param serviceClasses A list of types that implement the {@link Service}
* interface (e.g., {@code DisplayService.class}). Compatible
* services will be loaded in the order given, <em>regardless of
* their relative priorities</em>.
* @see #Context(Collection, PluginIndex, boolean)
* @throws ClassCastException If any of the given arguments do not implement
* the {@link Service} interface.
*/
public Context(@SuppressWarnings("rawtypes") final Class... serviceClasses) {
this(serviceClassList(serviceClasses));
}
/**
* Creates a new SciJava application context with the specified services (and
* any required service dependencies).
*
* @param serviceClasses A collection of types that implement the
* {@link Service} interface (e.g., {@code DisplayService.class}).
* Compatible services will be loaded according to the order of the
* collection, <em>regardless of their relative priorities</em>.
* @see #Context(Collection, PluginIndex, boolean)
*/
public Context(final Collection<Class<? extends Service>> serviceClasses) {
this(serviceClasses, null);
}
/**
* Creates a new SciJava application context with the specified services (and
* any required service dependencies).
*
* @param serviceClasses A collection of types that implement the
* {@link Service} interface (e.g., {@code DisplayService.class}).
* Compatible services will be loaded according to the order of the
* collection, <em>regardless of their relative priorities</em>.
* @param strict Whether context creation will fail fast when there is an
* error instantiating a required service.
* @see #Context(Collection, PluginIndex, boolean)
*/
public Context(final Collection<Class<? extends Service>> serviceClasses,
final boolean strict)
{
this(serviceClasses, null, strict);
}
/**
* Creates a new SciJava application context with all available services from
* the specified PluginIndex. This allows a base set of available plugins to
* be defined, and is useful when plugins that would not be returned by the
* {@link PluginIndex}'s {@link org.scijava.plugin.PluginFinder} are desired.
*
* @param pluginIndex The plugin index to use when discovering and indexing
* plugins. If you wish to completely control how services are
* discovered (i.e., use your own
* {@link org.scijava.plugin.PluginFinder} implementation), then you
* can pass a custom {@link PluginIndex} here. Passing null will
* result in a default plugin index being constructed and used.
* @see #Context(Collection, PluginIndex, boolean)
*/
public Context(final PluginIndex pluginIndex) {
this(services(false), pluginIndex);
}
/**
* Creates a new SciJava application context with the specified services (and
* any required service dependencies). Service dependency candidates are
* selected from those discovered by the given {@link PluginIndex}'s
* associated {@link org.scijava.plugin.PluginFinder}.
*
* @param serviceClasses A collection of types that implement the
* {@link Service} interface (e.g., {@code DisplayService.class}).
* Compatible services will be loaded according to the order of the
* collection, <em>regardless of their relative priorities</em>.
* @param pluginIndex The plugin index to use when discovering and indexing
* plugins. If you wish to completely control how services are
* discovered (i.e., use your own
* {@link org.scijava.plugin.PluginFinder} implementation), then you
* can pass a custom {@link PluginIndex} here. Passing null will
* result in a default plugin index being constructed and used.
* @see #Context(Collection, PluginIndex, boolean)
*/
public Context(final Collection<Class<? extends Service>> serviceClasses,
final PluginIndex pluginIndex)
{
this(serviceClasses, pluginIndex, strict());
}
/**
* Creates a new SciJava application context with the specified services (and
* any required service dependencies). Service dependency candidates are
* selected from those discovered by the given {@link PluginIndex}'s
* associated {@link org.scijava.plugin.PluginFinder}.
* <p>
* NB: Context creation is an important step of a SciJava application's
* lifecycle. Particularly in environments where more than one implementation
* exists for various services, careful consideration should be exercised
* regarding what classes and plugins are provided to the Context, and what
* needs to occur during the initialization of these services (especially
* those of lower priority). See {@link ServiceHelper#loadServices()} for more
* information.
* </p>
* <p>
* NB: Instiantiation of a Context has an implied requirement of a
* corresponding call to {@link Context#dispose()} at the end of the SciJava
* applicaton's lifecycle. This cleans up any remaining resources and allows
* the JVM to exit gracefully. This is called automatically when constructed as
* an {@link AutoCloseable}.
* </p>
*
* @param serviceClasses A collection of types that implement the
* {@link Service} interface (e.g., {@code DisplayService.class}).
* Compatible services will be loaded according to the order of the
* collection, <em>regardless of their relative priorities</em>.
* @param pluginIndex The plugin index to use when discovering and indexing
* plugins. If you wish to completely control how services are
* discovered (i.e., use your own
* {@link org.scijava.plugin.PluginFinder} implementation), then you
* can pass a custom {@link PluginIndex} here. Passing null will
* result in a default plugin index being constructed and used.
* @param strict Whether context creation will fail fast when there is an
* error instantiating a required service.
*/
public Context(final Collection<Class<? extends Service>> serviceClasses,
final PluginIndex pluginIndex, final boolean strict)
{
serviceIndex = new ServiceIndex();
this.pluginIndex = pluginIndex == null ? new PluginIndex() : pluginIndex;
this.pluginIndex.discover();
setStrict(strict);
if (!serviceClasses.isEmpty()) {
final ServiceHelper serviceHelper = //
new ServiceHelper(this, serviceClasses, strict);
serviceHelper.loadServices();
}
// If JVM shuts down with context still active, clean up after ourselves.
if (shutdownThread == null) {
synchronized (Context.class) {
if (shutdownThread == null) {
shutdownThread = new Thread(() -> {
final List<Context> contexts = new ArrayList<>(CONTEXTS.keySet());
for (final Context context : contexts) {
context.doDispose(false);
}
});
Runtime.getRuntime().addShutdownHook(shutdownThread);
}
}
}
CONTEXTS.put(this, true);
// Publish an event to indicate that context initialization is complete.
final EventService eventService = getService(EventService.class);
if (eventService != null) eventService.publish(new ContextCreatedEvent());
}
// -- Context methods --
public ServiceIndex getServiceIndex() {
return serviceIndex;
}
public PluginIndex getPluginIndex() {
return pluginIndex;
}
public boolean isStrict() {
return strict;
}
public void setStrict(final boolean strict) {
this.strict = strict;
}
/**
* Gets the service of the given class.
*
* @throws NoSuchServiceException if the context does not have the requested
* service.
*/
public <S extends Service> S service(final Class<S> c) {
final S service = getService(c);
if (service == null) {
throw new NoSuchServiceException("Service " + c.getName() +
" not found.");
}
return service;
}
/**
* Gets the service of the given class name (useful for scripts).
*
* @throws IllegalArgumentException if the class does not exist, or is not a
* service class.
* @throws NoSuchServiceException if the context does not have the requested
* service.
*/
public Service service(final String className) {
final Class<?> c = Types.load(className, false);
if (!Service.class.isAssignableFrom(c)) {
throw new IllegalArgumentException("Not a service class: " + c.getName());
}
@SuppressWarnings("unchecked")
final Class<? extends Service> serviceClass = (Class<? extends Service>) c;
return service(serviceClass);
}
/**
* Gets the service of the given class, or null if there is no matching
* service.
*/
public <S extends Service> S getService(final Class<S> c) {
return serviceIndex.getService(c);
}
/** Gets the service of the given class name (useful for scripts). */
public Service getService(final String className) {
final Class<?> c = Types.load(className);
if (c == null) return null;
if (!Service.class.isAssignableFrom(c)) return null; // not a service class
@SuppressWarnings("unchecked")
final Class<? extends Service> serviceClass = (Class<? extends Service>) c;
return getService(serviceClass);
}
/**
* Injects the application context into the given object. This does three
* distinct things:
* <ol>
* <li>If the given object has any non-final {@link Context} fields annotated
* with @{@link Parameter}, sets the value of those fields to this context.
* </li>
* <li>If the given object has any non-final {@link Service} fields annotated
* with @{@link Parameter}, sets the value of those fields to the
* corresponding service available from this context.</li>
* <li>Calls {@link EventService#subscribe(Object)} with the object to
* register any @{@link EventHandler} annotated methods as event subscribers.
* </li>
* </ol>
*
* @param o The object to which the context should be assigned.
* @throws IllegalStateException If the object already has a context.
* @throws IllegalArgumentException If the object has a required
* {@link Service} parameter (see {@link Parameter#required()})
* which is not available from this context.
*/
public void inject(final Object o) {
// Ensure parameter fields and event handler methods are cached for this
// object.
final Query query = new Query();
query.put(Parameter.class, Field.class);
query.put(EventHandler.class, Method.class);
ClassUtils.cacheAnnotatedObjects(o.getClass(), query);
// iterate over all @Parameter annotated fields
final List<Field> fields = getParameterFields(o);
for (final Field f : fields) {
inject(f, o);
}
// NB: Subscribe to all events handled by this object.
// This greatly simplifies event handling.
subscribeToEvents(o);
}
/**
* Reports whether a parameter of the given type would be assigned a value as
* a consequence of calling {@link #inject(Object)}.
* <p>
* This method is notably useful for downstream code to discern between
* {@link Parameter} fields whose values would be injected, versus those whose
* values would not, without needing to hardcode type comparison checks
* against the {@link Service} and {@link Context} types.
* </p>
*
* @param type The type of the @{@link Parameter}-annotated field.
* @return True iff a member field of the given type would have its value
* assigned.
*/
public boolean isInjectable(final Class<?> type) {
if (Service.class.isAssignableFrom(type)) return true;
return Context.class.isAssignableFrom(type) && type.isInstance(this);
}
// -- Disposable methods --
@Override
public void dispose() {
if (!disposed) doDispose(true);
}
// -- AutoCloseable methods --
@Override
public void close() {
dispose();
}
// -- Utility methods --
/**
* Utility method for converting a varargs list of service classes to a
* {@link List} of those classes.
*/
@SuppressWarnings({ "rawtypes", "unchecked" })
public static List<Class<? extends Service>> serviceClassList(
final Class... serviceClasses)
{
return serviceClasses != null ? //
Arrays.asList(serviceClasses) : Arrays.asList(Service.class);
}
/**
* Gets the class loader to use. This will be the current thread's context
* class loader if non-null; otherwise it will be the system class loader.
*
* @see Thread#getContextClassLoader()
* @see ClassLoader#getSystemClassLoader()
*/
public static ClassLoader getClassLoader() {
final ClassLoader contextCL = Thread.currentThread()
.getContextClassLoader();
return contextCL != null ? contextCL : ClassLoader.getSystemClassLoader();
}
// -- Helper methods --
private List<Field> getParameterFields(final Object o) {
try {
return ClassUtils.getAnnotatedFields(o.getClass(), Parameter.class);
}
catch (final Throwable t) {
handleSafely(t);
}
return Collections.emptyList();
}
private void inject(final Field f, final Object o) {
try {
f.setAccessible(true); // expose private fields
final Class<?> type = f.getType();
if (Service.class.isAssignableFrom(type)) {
final Service existingService = (Service) ClassUtils.getValue(f, o);
if (strict && existingService != null) {
throw new IllegalStateException("Context already injected: " + //
f.getDeclaringClass().getName() + "#" + f.getName());
}
// populate Service parameter
@SuppressWarnings("unchecked")
final Class<? extends Service> serviceType =
(Class<? extends Service>) type;
final Service service = getService(serviceType);
if (service == null && f.getAnnotation(Parameter.class).required()) {
throw new IllegalArgumentException(//
createMissingServiceMessage(serviceType));
}
if (existingService != null && existingService != service) {
// NB: Can only happen in non-strict mode.
throw new IllegalStateException("Mismatched context: " + //
f.getDeclaringClass().getName() + "#" + f.getName());
}
ClassUtils.setValue(f, o, service);
}
else if (Context.class.isAssignableFrom(type) && type.isInstance(this)) {
final Context existingContext = (Context) ClassUtils.getValue(f, o);
if (strict && existingContext != null) {
throw new IllegalStateException("Context already injected: " + //
f.getDeclaringClass().getName() + "#" + f.getName());
}
if (existingContext != null && existingContext != this) {
// NB: Can only happen in non-strict mode.
throw new IllegalStateException("Mismatched context: " + //
f.getDeclaringClass().getName() + "#" + f.getName());
}
// populate Context parameter
ClassUtils.setValue(f, o, this);
}
else if (!type.isPrimitive()) {
// the parameter is some other object; if it is non-null, we recurse
final Object value = ClassUtils.getValue(f, o);
if (value != null) inject(value);
}
}
catch (final Throwable t) {
handleSafely(t);
}
}
private void subscribeToEvents(final Object o) {
try {
final EventService eventService = getService(EventService.class);
if (eventService != null) eventService.subscribe(o);
}
catch (final Throwable t) {
handleSafely(t);
}
}
private void handleSafely(final Throwable t) {
if (isStrict()) {
// NB: Only rethrow unchecked exceptions.
if (t instanceof RuntimeException) throw (RuntimeException) t;
if (t instanceof Error) throw (Error) t;
}
final LogService log = getService(LogService.class);
if (log != null) log.error(t);
}
private String createMissingServiceMessage(
final Class<? extends Service> serviceType)
{
final String nl = System.getProperty("line.separator");
final ClassLoader classLoader = getClassLoader();
final StringBuilder msg = new StringBuilder(
"Required service is missing: " + serviceType.getName() + nl);
msg.append("Context: " + this + nl);
msg.append("ClassLoader: " + classLoader + nl);
// Add list of services known to context
msg.append(nl + "-- Services known to context --" + nl);
for (final Service knownService : serviceIndex.getAll()) {
msg.append(knownService + nl);
}
// Add list of classes known to classloader
msg.append(nl + "-- Classpath of ClassLoader --" + nl);
if (classLoader instanceof URLClassLoader) {
for (final URL url : ((URLClassLoader) classLoader).getURLs()) {
msg.append(url.getPath() + nl);
}
}
else {
msg.append(
"ClassLoader was not a URLClassLoader. Could not print classpath.");
}
return msg.toString();
}
private void doDispose(final boolean announce) {
synchronized (this) {
if (disposed) return;
disposed = true;
}
CONTEXTS.remove(this);
if (announce) {
final EventService eventService = getService(EventService.class);
if (eventService != null) eventService.publish(new ContextDisposingEvent());
}
// NB: Dispose services in reverse order.
// This may or may not actually be necessary, but seems safer, since
// dependent services will be disposed *before* their dependencies.
final List<Service> services = serviceIndex.getAll();
for (int s = services.size() - 1; s >= 0; s--) {
services.get(s).dispose();
}
}
private static PluginIndex plugins(final boolean empty) {
return empty ? new PluginIndex(null) : null;
}
private static List<Class<? extends Service>> services(final boolean empty) {
if (empty) return Collections.<Class<? extends Service>> emptyList();
return Arrays.<Class<? extends Service>> asList(Service.class);
}
private static boolean strict() {
return !"false".equals(System.getProperty(STRICT_PROPERTY));
}
}