com.facebook.util.reflection.ForwardReferenceProxy.java Source code

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Here is the source code for com.facebook.util.reflection.ForwardReferenceProxy.java

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/*
 * Copyright (C) 2012 Facebook, 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.facebook.util.reflection;

import com.google.common.base.Preconditions;
import com.google.common.base.Supplier;
import com.google.common.base.Suppliers;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Proxy;
import java.util.concurrent.atomic.AtomicReference;

public class ForwardReferenceProxy<T> {
    private final AtomicReference<T> instanceRef;
    private final Supplier<T> proxySupplier;

    public ForwardReferenceProxy(final Class<T> clazz) {
        this.instanceRef = new AtomicReference<>();
        proxySupplier = Suppliers.memoize(new Supplier<T>() {
            @Override
            public T get() {
                return wrap(clazz, instanceRef);
            }
        });
    }

    public ForwardReferenceProxy<T> setInstance(T instance) {
        instanceRef.set(instance);

        return this;
    }

    public T get() {
        return proxySupplier.get();
    }

    private static <T> T wrap(Class<T> clazz, final AtomicReference<T> instance) {
        Preconditions.checkNotNull(instance, "must pass a non-null atomic reference");
        InvocationHandler handler = (proxy, method, args) -> method
                .invoke(Preconditions.checkNotNull(instance.get(), "instance has not been set"), args);

        T wrapper = (T) Proxy.newProxyInstance(clazz.getClassLoader(), new Class[] { clazz }, handler);

        return wrapper;
    }
}