1 /* 2 * Copyright 2022 Google LLC 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 package com.google.android.libraries.mobiledatadownload.file.common; 17 18 import java.io.Closeable; 19 import java.io.IOException; 20 import javax.annotation.Nullable; 21 22 /** 23 * A wrapper for a Closeable resource that allows caller to free that resource from a 24 * try-with-resources block. 25 */ 26 public final class ReleasableResource<T extends Closeable> implements Closeable { 27 @Nullable private T resource; 28 ReleasableResource(T resource)29 private ReleasableResource(T resource) { 30 this.resource = resource; 31 } 32 33 /** 34 * Creates a ReleasableResource wrapped around a resource. 35 * 36 * @param resource the Closeable resource. 37 */ create(T resource)38 public static <T extends Closeable> ReleasableResource<T> create(T resource) { 39 return new ReleasableResource<T>(resource); 40 } 41 42 /** 43 * Returns the wrapped resource and releases ownership. The caller is responsible for ensuring the 44 * resource is closed. 45 * 46 * @return the wrapped resource. 47 */ 48 @Nullable release()49 public T release() { 50 T freed = resource; 51 resource = null; 52 return freed; 53 } 54 55 /** 56 * Returns the wrapped resource but does not release ownership. 57 * 58 * @return the wrapped resource. 59 */ 60 @Nullable get()61 public T get() { 62 return resource; 63 } 64 65 @Override close()66 public void close() throws IOException { 67 if (resource != null) { 68 resource.close(); 69 } 70 } 71 } 72