com.google.jstestdriver.requesthandlers.RequestScope.java Source code

Introduction

Here is the source code for com.google.jstestdriver.requesthandlers.RequestScope.java

Source

/*
 * Copyright 2010 Google Inc.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */
package com.google.jstestdriver.requesthandlers;

import com.google.common.base.Preconditions;
import com.google.common.collect.Maps;
import com.google.inject.Guice;
import com.google.inject.Key;
import com.google.inject.OutOfScopeException;
import com.google.inject.Provider;
import com.google.inject.Scope;

import java.util.Map;

/**
 * The {@link Guice} {@link Scope} associated with HTTP requests. Maintains a
 * {@link Map} of {@link Key}s to {@link Object}s that exist within the scope
 * of the HTTP request.
 *
 * @author rdionne@google.com (Robert Dionne)
 */
class RequestScope implements Scope {

    private final ThreadLocal<Map<Key<?>, Object>> values = new ThreadLocal<Map<Key<?>, Object>>();

    /**
     * Enter the {@link RequestScope}.
     */
    public void enter() {
        Preconditions.checkState(values.get() == null, "Scope already entered.");
        values.set(Maps.<Key<?>, Object>newHashMap());
    }

    /**
     * Exit the {@link RequestScope}.
     */
    public void exit() {
        Preconditions.checkState(values.get() != null, "Scope not entered.");
        values.remove();
    }

    /**
     * Seed the {@link RequestScope} with an object of type T.
     *
     * @param key a {@link Key} that represents T
     * @param value the object of type T
     * @param <T> the type of {@code value}
     */
    public <T> void seed(Key<T> key, T value) {
        Map<Key<?>, Object> scopedObjects = getScopedObjectMap(key);

        // TODO(rdionne): replace error message
        Preconditions.checkState(!scopedObjects.containsKey(key), "Error");
        scopedObjects.put(key, value);
    }

    /**
     * Seed the {@link RequestScope} with an object of type T
     *
     * @param clazz {@code value}'s class
     * @param value the object of type T
     * @param <T> the type of {@code value}
     */
    public <T> void seed(Class<T> clazz, T value) {
        seed(Key.get(clazz), value);
    }

    public <T> Provider<T> scope(final Key<T> tKey, final Provider<T> tProvider) {
        return new Provider<T>() {
            public T get() {
                Map<Key<?>, Object> scopedObjects = getScopedObjectMap(tKey);

                @SuppressWarnings("unchecked")
                T current = (T) scopedObjects.get(tKey);
                if (current == null && !scopedObjects.containsKey(tKey)) {
                    current = tProvider.get();
                    scopedObjects.put(tKey, current);
                }
                return current;
            }
        };
    }

    private <T> Map<Key<?>, Object> getScopedObjectMap(Key<T> key) {
        Map<Key<?>, Object> scopedObjects = values.get();
        if (scopedObjects == null) {
            throw new OutOfScopeException(new StringBuilder("Cannot access ").append(key)
                    .append(" outside of a scoping block.").toString());
        }
        return scopedObjects;
    }
}