RealmManager.java

/*
 * Copyright 2017 Gabor Varadi
 *
 * 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.zhuinden.realmmanager;

import java.io.Closeable;

import io.realm.Realm;

/**
 * The RealmManager allows creating a singleton Realm manager which can open thread-local instances.
 *
 * It also allows obtaining the open thread-local instance without incrementing the reference count.
 */
public class RealmManager {
    private final ThreadLocal<Realm> localRealms = new ThreadLocal<>();

    /**
     * Opens a reference-counted local Realm instance.
     *
     * @return the open Realm instance
     */
    public Realm openLocalInstance() {
        checkDefaultConfiguration();
        Realm realm = Realm.getDefaultInstance(); // <-- maybe this should be a parameter
        Realm localRealm = localRealms.get();
        if(localRealm == null || localRealm.isClosed()) {
            localRealms.set(realm);
        }
        return realm;
    }

    /**
     * Returns the local Realm instance without adding to the reference count.
     *
     * @return the local Realm instance
     * @throws IllegalStateException when no Realm is open
     */
    public Realm getLocalInstance() {
        Realm realm = localRealms.get();
        if(realm == null || realm.isClosed()) {
            throw new IllegalStateException(
                    "No open Realms were found on this thread.");
        }
        return realm;
    }

    /**
     * Closes local Realm instance, decrementing the reference count.
     *
     * @throws IllegalStateException if there is no open Realm.
     */
    public void closeLocalInstance() {
        checkDefaultConfiguration();
        Realm realm = localRealms.get();
        if(realm == null || realm.isClosed()) {
            throw new IllegalStateException(
                    "Cannot close a Realm that is not open.");
        }
        realm.close();
        // noinspection ConstantConditions
        if(Realm.getLocalInstanceCount(Realm.getDefaultConfiguration()) <= 0) {
            localRealms.set(null);
        }
    }

    private void checkDefaultConfiguration() {
        if(Realm.getDefaultConfiguration() == null) {
            throw new IllegalStateException("No default configuration is set.");
        }
    }
}