/*
* Copyright (C) 2012 The Guava Authors
*
* 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.common.io;
import static com.google.common.base.Preconditions.checkNotNull;
import com.google.common.annotations.Beta;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Throwables;
import java.io.Closeable;
import java.io.IOException;
import java.lang.reflect.Method;
import java.util.ArrayDeque;
import java.util.Deque;
import java.util.logging.Level;
import javax.annotation.Nullable;
/**
* A {@link Closeable} that collects {@code Closeable} resources and closes them all when it is
* {@linkplain #close closed}. This is intended to approximately emulate the behavior of Java 7's
* <a href="http://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html">
* try-with-resources</a> statement in JDK6-compatible code. Running on Java 7, code using this
* should be approximately equivalent in behavior to the same code written with try-with-resources.
* Running on Java 6, exceptions that cannot be thrown must be logged rather than being added to the
* thrown exception as a suppressed exception.
*
* <p>This class is intended to be used in the following pattern:
*
* <pre> {@code
* Closer closer = Closer.create();
* try {
* InputStream in = closer.register(openInputStream());
* OutputStream out = closer.register(openOutputStream());
* // do stuff
* } catch (Throwable e) {
* // ensure that any checked exception types other than IOException that could be thrown are
* // provided here, e.g. throw closer.rethrow(e, CheckedException.class);
* throw closer.rethrow(e);
* } finally {
* closer.close();
* }}</pre>
*
* <p>Note that this try-catch-finally block is not equivalent to a try-catch-finally block using
* try-with-resources. To get the equivalent of that, you must wrap the above code in <i>another</i>
* try block in order to catch any exception that may be thrown (including from the call to
* {@code close()}).
*
* <p>This pattern ensures the following:
*
* <ul>
* <li>Each {@code Closeable} resource that is successfully registered will be closed later.</li>
* <li>If a {@code Throwable} is thrown in the try block, no exceptions that occur when attempting
* to close resources will be thrown from the finally block. The throwable from the try block will
* be thrown.</li>
* <li>If no exceptions or errors were thrown in the try block, the <i>first</i> exception thrown
* by an attempt to close a resource will be thrown.</li>
* <li>Any exception caught when attempting to close a resource that is <i>not</i> thrown
* (because another exception is already being thrown) is <i>suppressed</i>.</li>
* </ul>
*
* <p>An exception that is suppressed is not thrown. The method of suppression used depends on the
* version of Java the code is running on:
*
* <ul>
* <li><b>Java 7+:</b> Exceptions are suppressed by adding them to the exception that <i>will</i>
* be thrown using {@code Throwable.addSuppressed(Throwable)}.</li>
* <li><b>Java 6:</b> Exceptions are suppressed by logging them instead.</li>
* </ul>
*
* @author Colin Decker
* @since 14.0
*/
// Coffee's for {@link Closer closers} only.
@Beta
public final class Closer implements Closeable {
/**
* The suppressor implementation to use for the current Java version.
*/
private static final Suppressor SUPPRESSOR = SuppressingSuppressor.isAvailable()
? SuppressingSuppressor.INSTANCE
: LoggingSuppressor.INSTANCE;
/**
* Creates a new {@link Closer}.
*/
public static Closer create() {
return new Closer(SUPPRESSOR);
}
@VisibleForTesting final Suppressor suppressor;
// only need space for 2 elements in most cases, so try to use the smallest array possible
private final Deque<Closeable> stack = new ArrayDeque<Closeable>(4);
private Throwable thrown;
@VisibleForTesting Closer(Suppressor suppressor) {
this.suppressor = checkNotNull(suppressor); // checkNotNull to satisfy null tests
}
/**
* Registers the given {@code closeable} to be closed when this {@code Closer} is
* {@linkplain #close closed}.
*
* @return the given {@code closeable}
*/
// close. this word no longer has any meaning to me.
public <C extends Closeable> C register(@Nullable C closeable) {
if (closeable != null) {
stack.addFirst(closeable);
}
return closeable;
}
/**
* Stores the given throwable and rethrows it. It will be rethrown as is if it is an
* {@code IOException}, {@code RuntimeException} or {@code Error}. Otherwise, it will be rethrown
* wrapped in a {@code RuntimeException}. <b>Note:</b> Be sure to declare all of the checked
* exception types your try block can throw when calling an overload of this method so as to avoid
* losing the original exception type.
*
* <p>This method always throws, and as such should be called as
* {@code throw closer.rethrow(e);} to ensure the compiler knows that it will throw.
*
* @return this method does not return; it always throws
* @throws IOException when the given throwable is an IOException
*/
public RuntimeException rethrow(Throwable e) throws IOException {
checkNotNull(e);
thrown = e;
Throwables.propagateIfPossible(e, IOException.class);
throw new RuntimeException(e);
}
/**
* Stores the given throwable and rethrows it. It will be rethrown as is if it is an
* {@code IOException}, {@code RuntimeException}, {@code Error} or a checked exception of the
* given type. Otherwise, it will be rethrown wrapped in a {@code RuntimeException}. <b>Note:</b>
* Be sure to declare all of the checked exception types your try block can throw when calling an
* overload of this method so as to avoid losing the original exception type.
*
* <p>This method always throws, and as such should be called as
* {@code throw closer.rethrow(e, ...);} to ensure the compiler knows that it will throw.
*
* @return this method does not return; it always throws
* @throws IOException when the given throwable is an IOException
* @throws X when the given throwable is of the declared type X
*/
public <X extends Exception> RuntimeException rethrow(Throwable e,
Class<X> declaredType) throws IOException, X {
checkNotNull(e);
thrown = e;
Throwables.propagateIfPossible(e, IOException.class);
Throwables.propagateIfPossible(e, declaredType);
throw new RuntimeException(e);
}
/**
* Stores the given throwable and rethrows it. It will be rethrown as is if it is an
* {@code IOException}, {@code RuntimeException}, {@code Error} or a checked exception of either
* of the given types. Otherwise, it will be rethrown wrapped in a {@code RuntimeException}.
* <b>Note:</b> Be sure to declare all of the checked exception types your try block can throw
* when calling an overload of this method so as to avoid losing the original exception type.
*
* <p>This method always throws, and as such should be called as
* {@code throw closer.rethrow(e, ...);} to ensure the compiler knows that it will throw.
*
* @return this method does not return; it always throws
* @throws IOException when the given throwable is an IOException
* @throws X1 when the given throwable is of the declared type X1
* @throws X2 when the given throwable is of the declared type X2
*/
public <X1 extends Exception, X2 extends Exception> RuntimeException rethrow(
Throwable e, Class<X1> declaredType1, Class<X2> declaredType2) throws IOException, X1, X2 {
checkNotNull(e);
thrown = e;
Throwables.propagateIfPossible(e, IOException.class);
Throwables.propagateIfPossible(e, declaredType1, declaredType2);
throw new RuntimeException(e);
}
/**
* Closes all {@code Closeable} instances that have been added to this {@code Closer}. If an
* exception was thrown in the try block and passed to one of the {@code exceptionThrown} methods,
* any exceptions thrown when attempting to close a closeable will be suppressed. Otherwise, the
* <i>first</i> exception to be thrown from an attempt to close a closeable will be thrown and any
* additional exceptions that are thrown after that will be suppressed.
*/
@Override
public void close() throws IOException {
Throwable throwable = thrown;
// close closeables in LIFO order
while (!stack.isEmpty()) {
Closeable closeable = stack.removeFirst();
try {
closeable.close();
} catch (Throwable e) {
if (throwable == null) {
throwable = e;
} else {
suppressor.suppress(closeable, throwable, e);
}
}
}
if (thrown == null && throwable != null) {
Throwables.propagateIfPossible(throwable, IOException.class);
throw new AssertionError(throwable); // not possible
}
}
/**
* Suppression strategy interface.
*/
@VisibleForTesting interface Suppressor {
/**
* Suppresses the given exception ({@code suppressed}) which was thrown when attempting to close
* the given closeable. {@code thrown} is the exception that is actually being thrown from the
* method. Implementations of this method should not throw under any circumstances.
*/
void suppress(Closeable closeable, Throwable thrown, Throwable suppressed);
}
/**
* Suppresses exceptions by logging them.
*/
@VisibleForTesting static final class LoggingSuppressor implements Suppressor {
static final LoggingSuppressor INSTANCE = new LoggingSuppressor();
@Override
public void suppress(Closeable closeable, Throwable thrown, Throwable suppressed) {
// log to the same place as Closeables
Closeables.logger.log(Level.WARNING,
"Suppressing exception thrown when closing " + closeable, suppressed);
}
}
/**
* Suppresses exceptions by adding them to the exception that will be thrown using JDK7's
* addSuppressed(Throwable) mechanism.
*/
@VisibleForTesting static final class SuppressingSuppressor implements Suppressor {
static final SuppressingSuppressor INSTANCE = new SuppressingSuppressor();
static boolean isAvailable() {
return addSuppressed != null;
}
static final Method addSuppressed = getAddSuppressed();
private static Method getAddSuppressed() {
try {
return Throwable.class.getMethod("addSuppressed", Throwable.class);
} catch (Throwable e) {
return null;
}
}
@Override
public void suppress(Closeable closeable, Throwable thrown, Throwable suppressed) {
// ensure no exceptions from addSuppressed
if (thrown == suppressed) {
return;
}
try {
addSuppressed.invoke(thrown, suppressed);
} catch (Throwable e) {
// if, somehow, IllegalAccessException or another exception is thrown, fall back to logging
LoggingSuppressor.INSTANCE.suppress(closeable, thrown, suppressed);
}
}
}
}