pl.morgwai.base.guice.scopes.ContextScope Maven / Gradle / Ivy

Show more of this group Show more artifacts with this name
Show all versions of guice-context-scopes Show documentation

Classes for building Guice scopes, that get automatically transferred when dispatching work to other threads

There is a newer version: 10.0

// Copyright (c) Piotr Morgwai Kotarbinski, Licensed under the Apache License, Version 2.0
package pl.morgwai.base.guice.scopes;

import com.google.inject.Key;
import com.google.inject.Provider;
import com.google.inject.Scope;



/**
 * Scopes objects to a call context obtained from the associated {@link ContextTracker}.
 */
public class ContextScope> implements Scope {



	final ContextTracker tracker;

	final String name;
	public String getName() { return name; }



	public ContextScope(String name, ContextTracker tracker) {
		this.name = name;
		this.tracker = tracker;
	}



	/**
	 * @throws RuntimeException if there's no context for the current thread. This most commonly
	 * happens when providing a callback to some async method without transferring the context. Use
	 * static helper methods {@link ContextTrackingExecutor#getActiveContexts(ContextTracker...)}
	 * and {@link ContextTrackingExecutor#executeWithinAll(java.util.List, Runnable)} to fix it:
	 * 	 * class MyClass {
	 *
	 *     @Inject ContextTracker<ContextT1> tracker1;
	 *     @Inject ContextTracker<ContextT2> tracker2;
	 *
	 *     void myMethod(Object param) {
	 *         // myMethod code
	 *         var activeCtxList = ContextTrackingExecutor.getActiveContexts(tracker1, tracker2);
	 *         someAsyncMethod(param, (callbackParam) ->
	 *             ContextTrackingExecutor.executeWithinAll(activeCtxList, () -> {
	 *                 // callback code
	 *             }
	 *         ));
	 *     }
	 * }
	 */
	@Override
	public  Provider scope(Key key, Provider unscoped) {
		return () -> {
			try {
				return tracker.getCurrentContext().provideAttributeIfAbsent(key, unscoped);
			} catch (NullPointerException e) {
				// NPE here is a result of a bug that will be usually eliminated in development
				// phase and not happen in production, so we catch NPE instead of checking manually
				// each time.
				throw new RuntimeException("no context for thread "
						+ Thread.currentThread().getName() + " in scope " + name
						+ ". See javadoc for ContextScope.scope(...)");
			}
		};
	}



	@Override
	public String toString() {
		return name;
	}
}