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package org.openide.util;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.Set;
import org.openide.util.lookup.Lookups;
import org.openide.util.lookup.ProxyLookup;
/**
* A general registry permitting clients to find instances of services
* (implementation of a given interface).
* This class is inspired by the
* Jini
* registration and lookup mechanism. The difference is that the methods do
* not throw checked exceptions (as they usually work only locally and not over the network)
* and that the Lookup API concentrates on the lookup, not on the registration
* (although {@link Lookup#getDefault} is strongly encouraged to support
* {@link Lookups#metaInfServices} for registration in addition to whatever
* else it decides to support).
*
* For a general talk about the idea behind the lookup pattern please see
*
* - The Solution to Communication Between Components
* page
*
- the introduction to the lookup API via
* use cases
*
- the examples of how to write your own lookup
*
*
* @see org.openide.util.lookup.AbstractLookup
* @see Lookups
* @see LookupListener
* @see LookupEvent
* @author Jaroslav Tulach
*/
public abstract class Lookup {
/** A dummy lookup that never returns any results.
*/
public static final Lookup EMPTY = new Empty();
/** default instance */
private static Lookup defaultLookup;
/** Empty constructor for use by subclasses. */
public Lookup() {
}
/** Static method to obtain the global lookup in the whole system.
* The actual returned implementation can be different in different
* systems, but the default one is based on
* {@link org.openide.util.lookup.Lookups#metaInfServices}
* with the context classloader of the first caller. Each system is
* adviced to honor this and include some form of metaInfServices
* implementation in the returned lookup as usage of META-INF/services
* is a JDK standard.
*
* @return the global lookup in the system
*/
public static synchronized Lookup getDefault() {
if (defaultLookup != null) {
return defaultLookup;
}
// You can specify a Lookup impl using a system property if you like.
String className = System.getProperty("org.openide.util.Lookup" // NOI18N
);
if ("-".equals(className)) { // NOI18N
// Suppress even MetaInfServicesLookup.
return EMPTY;
}
ClassLoader l = Thread.currentThread().getContextClassLoader();
try {
if (className != null) {
defaultLookup = (Lookup) Class.forName(className, true, l).newInstance();
return defaultLookup;
}
} catch (Exception e) {
// do not use ErrorManager because we are in the startup code
// and ErrorManager might not be ready
e.printStackTrace();
}
// OK, none specified (successfully) in a system property.
// Try MetaInfServicesLookup as a default, which may also
// have a org.openide.util.Lookup line specifying the lookup.
Lookup misl = Lookups.metaInfServices(l);
defaultLookup = misl.lookup(Lookup.class);
if (defaultLookup != null) {
return defaultLookup;
}
// You may also specify a Lookup.Provider.
Lookup.Provider prov = misl.lookup(Lookup.Provider.class);
if (prov != null) {
defaultLookup = Lookups.proxy(prov);
return defaultLookup;
}
DefLookup def = new DefLookup();
def.init(l, misl);
return defaultLookup = def;
}
private static final class DefLookup extends ProxyLookup {
public DefLookup() {
super(new Lookup[0]);
}
public void init(ClassLoader loader, Lookup metaInfLookup) {
// Had no such line, use simple impl.
// It does however need to have ClassLoader available or many things will break.
// Use the thread context classloader in effect now.
Lookup clLookup = Lookups.singleton(loader);
setLookups(new Lookup[] { metaInfLookup, clLookup });
}
}
/** Called from MockServices to reset default lookup in case services change
*/
private static void resetDefaultLookup() {
if (defaultLookup instanceof DefLookup) {
DefLookup def = (DefLookup)defaultLookup;
ClassLoader l = Thread.currentThread().getContextClassLoader();
def.init(l, Lookups.metaInfServices(l));
}
}
/** Look up an object matching a given interface.
* This is the simplest method to use.
* If more than one object matches, the first will be returned.
* The template class may be a class or interface; the instance is
* guaranteed to be assignable to it.
*
* @param clazz class of the object we are searching for
* @return an object implementing the given class or null if no such
* implementation is found
*/
public abstract T lookup(Class clazz);
/** The general lookup method. Callers can get list of all instances and classes
* that match the given template, request more info about
* them in form of {@link Lookup.Item} and attach a listener to
* this be notified about changes. The general interface does not
* specify whether subsequent calls with the same template produce new
* instance of the {@link Lookup.Result} or return shared instance. The
* prefered behaviour however is to return shared one.
*
* @param template a template describing the services to look for
* @return an object containing the results
*/
public abstract Result lookup(Template template);
/** Look up the first item matching a given template.
* Includes not only the instance but other associated information.
* @param template the template to check
* @return a matching item or null
*
* @since 1.8
*/
public Item lookupItem(Template template) {
Result res = lookup(template);
Iterator> it = res.allItems().iterator();
return it.hasNext() ? it.next() : null;
}
/**
* Find a result corresponding to a given class.
* Equivalent to calling {@link #lookup(Lookup.Template)} but slightly more convenient.
* Subclasses may override this method to produce the same semantics more efficiently.
* @param clazz the supertype of the result
* @return a live object representing instances of that type
* @since org.openide.util 6.10
*/
public Lookup.Result lookupResult(Class clazz) {
return lookup(new Lookup.Template(clazz));
}
/**
* Find all instances corresponding to a given class.
* Equivalent to calling {@link #lookupResult} and asking for {@link Lookup.Result#allInstances} but slightly more convenient.
* Subclasses may override this method to produce the same semantics more efficiently.
*
* Example usage:
*
* for (MyService svc : Lookup.getDefault().lookupAll(MyService.class)) {
* svc.useMe();
* }
*
*
* @param clazz the supertype of the result
* @return all currently available instances of that type
* @since org.openide.util 6.10
*/
public Collection lookupAll(Class clazz) {
return lookupResult(clazz).allInstances();
}
/**
* Objects implementing interface Lookup.Provider are capable of
* and willing to provide a lookup (usually bound to the object).
* @since 3.6
*/
public interface Provider {
/**
* Returns lookup associated with the object.
* @return fully initialized lookup instance provided by this object
*/
Lookup getLookup();
}
/*
* I expect this class to grow in the future, but for now, it is
* enough to start with something simple.
*/
/** Template defining a pattern to filter instances by.
*/
public static final class Template extends Object {
/** cached hash code */
private int hashCode;
/** type of the service */
private Class type;
/** identity to search for */
private String id;
/** instance to search for */
private T instance;
/** General template to find all possible instances.
* @deprecated Use new Template (Object.class) which
* is going to be better typed with JDK1.5 templates and should produce
* the same result.
*/
@Deprecated
public Template() {
this(null);
}
/** Create a simple template matching by class.
* @param type the class of service we are looking for (subclasses will match)
*/
public Template(Class type) {
this(type, null, null);
}
/** Constructor to create new template.
* @param type the class of service we are looking for or null to leave unspecified
* @param id the ID of the item/service we are looking for or null to leave unspecified
* @param instance a specific known instance to look for or null to leave unspecified
*/
public Template(Class type, String id, T instance) {
this.type = extractType(type);
this.id = id;
this.instance = instance;
}
@SuppressWarnings("unchecked")
private Class extractType(Class type) {
return (type == null) ? (Class)Object.class : type;
}
/** Get the class (or superclass or interface) to search for.
* If it was not specified in the constructor, Object is used as
* this will match any instance.
* @return the class to search for
*/
public Class getType() {
return type;
}
/** Get the persistent identifier being searched for, if any.
* @return the ID or null
* @see Lookup.Item#getId
*
* @since 1.8
*/
public String getId() {
return id;
}
/** Get the specific instance being searched for, if any.
* Most useful for finding an Item when the instance
* is already known.
*
* @return the object to find or null
*
* @since 1.8
*/
public T getInstance() {
return instance;
}
/* Computes hashcode for this template. The hashcode is cached.
* @return hashcode
*/
public int hashCode() {
if (hashCode != 0) {
return hashCode;
}
hashCode = ((type == null) ? 1 : type.hashCode()) + ((id == null) ? 2 : id.hashCode()) +
((instance == null) ? 3 : 0);
return hashCode;
}
/* Checks whether two templates represent the same query.
* @param obj another template to check
* @return true if so, false otherwise
*/
public boolean equals(Object obj) {
if (!(obj instanceof Template)) {
return false;
}
Template t = (Template) obj;
if (hashCode() != t.hashCode()) {
// this is an optimalization - the hashCodes should have been
// precomputed
return false;
}
if (type != t.type) {
return false;
}
if (id == null) {
if (t.id != null) {
return false;
}
} else {
if (!id.equals(t.id)) {
return false;
}
}
if (instance == null) {
return (t.instance == null);
} else {
return instance.equals(t.instance);
}
}
/* for debugging */
public String toString() {
return "Lookup.Template[type=" + type + ",id=" + id + ",instance=" + instance + "]"; // NOI18N
}
}
/** Result of a lookup request.
* Allows access to all matching instances at once.
* Also permits listening to changes in the result.
* Result can contain duplicate items.
*/
public static abstract class Result extends Object {
/** Registers a listener that is invoked when there is a possible
* change in this result.
*
* @param l the listener to add
*/
public abstract void addLookupListener(LookupListener l);
/** Unregisters a listener previously added.
* @param l the listener to remove
*/
public abstract void removeLookupListener(LookupListener l);
/** Get all instances in the result. The return value type
* should be List instead of Collection, but it is too late to change it.
* @return unmodifiable collection of all instances that will never change its content
*/
public abstract Collection allInstances();
/** Get all classes represented in the result.
* That is, the set of concrete classes
* used by instances present in the result.
* All duplicate classes will be omitted.
* @return unmodifiable set of Class objects that will never change its content
*
* @since 1.8
*/
public Set> allClasses() {
return Collections.emptySet();
}
/** Get all registered items.
* This should include all pairs of instances together
* with their classes, IDs, and so on. The return value type
* should be List instead of Collection, but it is too late to change it.
* @return unmodifiable collection of {@link Lookup.Item} that will never change its content
*
* @since 1.8
*/
public Collection> allItems() {
return Collections.emptyList();
}
}
/** A single item in a lookup result.
* This wrapper provides unified access to not just the instance,
* but its class, a possible persistent identifier, and so on.
*
* @since 1.25
*/
public static abstract class Item extends Object {
/** Get the instance itself.
* @return the instance or null if the instance cannot be created
*/
public abstract T getInstance();
/** Get the implementing class of the instance.
* @return the class of the item
*/
public abstract Class getType();
// XXX can it be null??
/** Get a persistent indentifier for the item.
* This identifier should uniquely represent the item
* within its containing lookup (and if possible within the
* global lookup as a whole). For example, it might represent
* the source of the instance as a file name. The ID may be
* persisted and in a later session used to find the same instance
* as was encountered earlier, by means of passing it into a
* lookup template.
*
* @return a string ID of the item
*/
public abstract String getId();
/** Get a human presentable name for the item.
* This might be used when summarizing all the items found in a
* lookup result in some part of a GUI.
* @return the string suitable for presenting the object to a user
*/
public abstract String getDisplayName();
/* show ID for debugging */
public String toString() {
return getId();
}
}
//
// Implementation of the default lookup
//
private static final class Empty extends Lookup {
private static final Result NO_RESULT = new Result() {
public void addLookupListener(LookupListener l) {
}
public void removeLookupListener(LookupListener l) {
}
public Collection allInstances() {
return Collections.EMPTY_SET;
}
};
Empty() {
}
public T lookup(Class clazz) {
return null;
}
@SuppressWarnings("unchecked")
public Result lookup(Template template) {
return NO_RESULT;
}
}
}
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