001/*
002 * Copyright (C) 2012 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
005 * in compliance with the License. You may obtain a copy of the License at
006 *
007 * http://www.apache.org/licenses/LICENSE-2.0
008 *
009 * Unless required by applicable law or agreed to in writing, software distributed under the License
010 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
011 * or implied. See the License for the specific language governing permissions and limitations under
012 * the License.
013 */
014
015package com.google.common.io;
016
017import static com.google.common.base.Preconditions.checkNotNull;
018import static com.google.common.base.Throwables.throwIfInstanceOf;
019import static com.google.common.base.Throwables.throwIfUnchecked;
020
021import com.google.common.annotations.GwtIncompatible;
022import com.google.common.annotations.J2ktIncompatible;
023import com.google.common.annotations.VisibleForTesting;
024import com.google.errorprone.annotations.CanIgnoreReturnValue;
025import java.io.Closeable;
026import java.io.IOException;
027import java.util.ArrayDeque;
028import java.util.Deque;
029import java.util.logging.Level;
030import org.checkerframework.checker.nullness.qual.Nullable;
031
032/**
033 * A {@link Closeable} that collects {@code Closeable} resources and closes them all when it is
034 * {@linkplain #close closed}. This was intended to approximately emulate the behavior of Java 7's
035 * <a href="http://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html"
036 * >try-with-resources</a> statement in JDK6-compatible code. Code using this should be
037 * approximately equivalent in behavior to the same code written with try-with-resources.
038 *
039 * <p>This class is intended to be used in the following pattern:
040 *
041 * <pre>{@code
042 * Closer closer = Closer.create();
043 * try {
044 *   InputStream in = closer.register(openInputStream());
045 *   OutputStream out = closer.register(openOutputStream());
046 *   // do stuff
047 * } catch (Throwable e) {
048 *   // ensure that any checked exception types other than IOException that could be thrown are
049 *   // provided here, e.g. throw closer.rethrow(e, CheckedException.class);
050 *   throw closer.rethrow(e);
051 * } finally {
052 *   closer.close();
053 * }
054 * }</pre>
055 *
056 * <p>Note that this try-catch-finally block is not equivalent to a try-catch-finally block using
057 * try-with-resources. To get the equivalent of that, you must wrap the above code in <i>another</i>
058 * try block in order to catch any exception that may be thrown (including from the call to {@code
059 * close()}).
060 *
061 * <p>This pattern ensures the following:
062 *
063 * <ul>
064 *   <li>Each {@code Closeable} resource that is successfully registered will be closed later.
065 *   <li>If a {@code Throwable} is thrown in the try block, no exceptions that occur when attempting
066 *       to close resources will be thrown from the finally block. The throwable from the try block
067 *       will be thrown.
068 *   <li>If no exceptions or errors were thrown in the try block, the <i>first</i> exception thrown
069 *       by an attempt to close a resource will be thrown.
070 *   <li>Any exception caught when attempting to close a resource that is <i>not</i> thrown (because
071 *       another exception is already being thrown) is <i>suppressed</i>.
072 * </ul>
073 *
074 * <p>An exception that is suppressed is added to the exception that <i>will</i> be thrown using
075 * {@code Throwable.addSuppressed(Throwable)}.
076 *
077 * @author Colin Decker
078 * @since 14.0
079 */
080// Coffee's for {@link Closer closers} only.
081@J2ktIncompatible
082@GwtIncompatible
083public final class Closer implements Closeable {
084  /** Creates a new {@link Closer}. */
085  public static Closer create() {
086    return new Closer(SUPPRESSING_SUPPRESSOR);
087  }
088
089  @VisibleForTesting final Suppressor suppressor;
090
091  // only need space for 2 elements in most cases, so try to use the smallest array possible
092  private final Deque<Closeable> stack = new ArrayDeque<>(4);
093  private @Nullable Throwable thrown;
094
095  @VisibleForTesting
096  Closer(Suppressor suppressor) {
097    this.suppressor = checkNotNull(suppressor); // checkNotNull to satisfy null tests
098  }
099
100  /**
101   * Registers the given {@code closeable} to be closed when this {@code Closer} is {@linkplain
102   * #close closed}.
103   *
104   * @return the given {@code closeable}
105   */
106  // close. this word no longer has any meaning to me.
107  @CanIgnoreReturnValue
108  @ParametricNullness
109  public <C extends @Nullable Closeable> C register(@ParametricNullness C closeable) {
110    if (closeable != null) {
111      stack.addFirst(closeable);
112    }
113
114    return closeable;
115  }
116
117  /**
118   * Stores the given throwable and rethrows it. It will be rethrown as is if it is an {@code
119   * IOException}, {@code RuntimeException} or {@code Error}. Otherwise, it will be rethrown wrapped
120   * in a {@code RuntimeException}. <b>Note:</b> Be sure to declare all of the checked exception
121   * types your try block can throw when calling an overload of this method so as to avoid losing
122   * the original exception type.
123   *
124   * <p>This method always throws, and as such should be called as {@code throw closer.rethrow(e);}
125   * to ensure the compiler knows that it will throw.
126   *
127   * @return this method does not return; it always throws
128   * @throws IOException when the given throwable is an IOException
129   */
130  public RuntimeException rethrow(Throwable e) throws IOException {
131    checkNotNull(e);
132    thrown = e;
133    throwIfInstanceOf(e, IOException.class);
134    throwIfUnchecked(e);
135    throw new RuntimeException(e);
136  }
137
138  /**
139   * Stores the given throwable and rethrows it. It will be rethrown as is if it is an {@code
140   * IOException}, {@code RuntimeException}, {@code Error} or a checked exception of the given type.
141   * Otherwise, it will be rethrown wrapped in a {@code RuntimeException}. <b>Note:</b> Be sure to
142   * declare all of the checked exception types your try block can throw when calling an overload of
143   * this method so as to avoid losing the original exception type.
144   *
145   * <p>This method always throws, and as such should be called as {@code throw closer.rethrow(e,
146   * ...);} to ensure the compiler knows that it will throw.
147   *
148   * @return this method does not return; it always throws
149   * @throws IOException when the given throwable is an IOException
150   * @throws X when the given throwable is of the declared type X
151   */
152  public <X extends Exception> RuntimeException rethrow(Throwable e, Class<X> declaredType)
153      throws IOException, X {
154    checkNotNull(e);
155    thrown = e;
156    throwIfInstanceOf(e, IOException.class);
157    throwIfInstanceOf(e, declaredType);
158    throwIfUnchecked(e);
159    throw new RuntimeException(e);
160  }
161
162  /**
163   * Stores the given throwable and rethrows it. It will be rethrown as is if it is an {@code
164   * IOException}, {@code RuntimeException}, {@code Error} or a checked exception of either of the
165   * given types. Otherwise, it will be rethrown wrapped in a {@code RuntimeException}. <b>Note:</b>
166   * Be sure to declare all of the checked exception types your try block can throw when calling an
167   * overload of this method so as to avoid losing the original exception type.
168   *
169   * <p>This method always throws, and as such should be called as {@code throw closer.rethrow(e,
170   * ...);} to ensure the compiler knows that it will throw.
171   *
172   * @return this method does not return; it always throws
173   * @throws IOException when the given throwable is an IOException
174   * @throws X1 when the given throwable is of the declared type X1
175   * @throws X2 when the given throwable is of the declared type X2
176   */
177  public <X1 extends Exception, X2 extends Exception> RuntimeException rethrow(
178      Throwable e, Class<X1> declaredType1, Class<X2> declaredType2) throws IOException, X1, X2 {
179    checkNotNull(e);
180    thrown = e;
181    throwIfInstanceOf(e, IOException.class);
182    throwIfInstanceOf(e, declaredType1);
183    throwIfInstanceOf(e, declaredType2);
184    throwIfUnchecked(e);
185    throw new RuntimeException(e);
186  }
187
188  /**
189   * Closes all {@code Closeable} instances that have been added to this {@code Closer}. If an
190   * exception was thrown in the try block and passed to one of the {@code exceptionThrown} methods,
191   * any exceptions thrown when attempting to close a closeable will be suppressed. Otherwise, the
192   * <i>first</i> exception to be thrown from an attempt to close a closeable will be thrown and any
193   * additional exceptions that are thrown after that will be suppressed.
194   */
195  @Override
196  public void close() throws IOException {
197    Throwable throwable = thrown;
198
199    // close closeables in LIFO order
200    while (!stack.isEmpty()) {
201      Closeable closeable = stack.removeFirst();
202      try {
203        closeable.close();
204      } catch (Throwable e) {
205        if (throwable == null) {
206          throwable = e;
207        } else {
208          suppressor.suppress(closeable, throwable, e);
209        }
210      }
211    }
212
213    if (thrown == null && throwable != null) {
214      throwIfInstanceOf(throwable, IOException.class);
215      throwIfUnchecked(throwable);
216      throw new AssertionError(throwable); // not possible
217    }
218  }
219
220  /** Suppression strategy interface. */
221  @VisibleForTesting
222  interface Suppressor {
223    /**
224     * Suppresses the given exception ({@code suppressed}) which was thrown when attempting to close
225     * the given closeable. {@code thrown} is the exception that is actually being thrown from the
226     * method. Implementations of this method should not throw under any circumstances.
227     */
228    void suppress(Closeable closeable, Throwable thrown, Throwable suppressed);
229  }
230
231  /**
232   * Suppresses exceptions by adding them to the exception that will be thrown using the
233   * addSuppressed(Throwable) mechanism.
234   */
235  private static final Suppressor SUPPRESSING_SUPPRESSOR =
236      (closeable, thrown, suppressed) -> {
237        // ensure no exceptions from addSuppressed
238        if (thrown == suppressed) {
239          return;
240        }
241        try {
242          thrown.addSuppressed(suppressed);
243        } catch (Throwable e) {
244          /*
245           * A Throwable is very unlikely, but we really don't want to throw from a Suppressor, so
246           * we catch everything. (Any Exception is either a RuntimeException or
247           * sneaky checked exception.) With no better options, we log anything to the same
248           * place as Closeables logs.
249           */
250          Closeables.logger.log(
251              Level.WARNING, "Suppressing exception thrown when closing " + closeable, suppressed);
252        }
253      };
254}