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; 018 019import com.google.common.annotations.Beta; 020import com.google.common.annotations.GwtIncompatible; 021import com.google.common.annotations.VisibleForTesting; 022import com.google.common.base.Throwables; 023import com.google.errorprone.annotations.CanIgnoreReturnValue; 024import java.io.Closeable; 025import java.io.IOException; 026import java.lang.reflect.Method; 027import java.util.ArrayDeque; 028import java.util.Deque; 029import java.util.logging.Level; 030import org.checkerframework.checker.nullness.qual.MonotonicNonNull; 031import org.checkerframework.checker.nullness.qual.Nullable; 032 033/** 034 * A {@link Closeable} that collects {@code Closeable} resources and closes them all when it is 035 * {@linkplain #close closed}. This is intended to approximately emulate the behavior of Java 7's <a 036 * href="http://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html" 037 * >try-with-resources</a> statement in JDK6-compatible code. Running on Java 7, code using this 038 * should be approximately equivalent in behavior to the same code written with try-with-resources. 039 * Running on Java 6, exceptions that cannot be thrown must be logged rather than being added to the 040 * thrown exception as a suppressed exception. 041 * 042 * <p>This class is intended to be used in the following pattern: 043 * 044 * <pre>{@code 045 * Closer closer = Closer.create(); 046 * try { 047 * InputStream in = closer.register(openInputStream()); 048 * OutputStream out = closer.register(openOutputStream()); 049 * // do stuff 050 * } catch (Throwable e) { 051 * // ensure that any checked exception types other than IOException that could be thrown are 052 * // provided here, e.g. throw closer.rethrow(e, CheckedException.class); 053 * throw closer.rethrow(e); 054 * } finally { 055 * closer.close(); 056 * } 057 * }</pre> 058 * 059 * <p>Note that this try-catch-finally block is not equivalent to a try-catch-finally block using 060 * try-with-resources. To get the equivalent of that, you must wrap the above code in <i>another</i> 061 * try block in order to catch any exception that may be thrown (including from the call to {@code 062 * close()}). 063 * 064 * <p>This pattern ensures the following: 065 * 066 * <ul> 067 * <li>Each {@code Closeable} resource that is successfully registered will be closed later. 068 * <li>If a {@code Throwable} is thrown in the try block, no exceptions that occur when attempting 069 * to close resources will be thrown from the finally block. The throwable from the try block 070 * will be thrown. 071 * <li>If no exceptions or errors were thrown in the try block, the <i>first</i> exception thrown 072 * by an attempt to close a resource will be thrown. 073 * <li>Any exception caught when attempting to close a resource that is <i>not</i> thrown (because 074 * another exception is already being thrown) is <i>suppressed</i>. 075 * </ul> 076 * 077 * <p>An exception that is suppressed is not thrown. The method of suppression used depends on the 078 * version of Java the code is running on: 079 * 080 * <ul> 081 * <li><b>Java 7+:</b> Exceptions are suppressed by adding them to the exception that <i>will</i> 082 * be thrown using {@code Throwable.addSuppressed(Throwable)}. 083 * <li><b>Java 6:</b> Exceptions are suppressed by logging them instead. 084 * </ul> 085 * 086 * @author Colin Decker 087 * @since 14.0 088 */ 089// Coffee's for {@link Closer closers} only. 090@Beta 091@GwtIncompatible 092public final class Closer implements Closeable { 093 094 /** The suppressor implementation to use for the current Java version. */ 095 private static final Suppressor SUPPRESSOR = 096 SuppressingSuppressor.isAvailable() 097 ? SuppressingSuppressor.INSTANCE 098 : LoggingSuppressor.INSTANCE; 099 100 /** Creates a new {@link Closer}. */ 101 public static Closer create() { 102 return new Closer(SUPPRESSOR); 103 } 104 105 @VisibleForTesting final Suppressor suppressor; 106 107 // only need space for 2 elements in most cases, so try to use the smallest array possible 108 private final Deque<Closeable> stack = new ArrayDeque<>(4); 109 @MonotonicNonNull private Throwable thrown; 110 111 @VisibleForTesting 112 Closer(Suppressor suppressor) { 113 this.suppressor = checkNotNull(suppressor); // checkNotNull to satisfy null tests 114 } 115 116 /** 117 * Registers the given {@code closeable} to be closed when this {@code Closer} is {@linkplain 118 * #close closed}. 119 * 120 * @return the given {@code closeable} 121 */ 122 // close. this word no longer has any meaning to me. 123 @CanIgnoreReturnValue 124 public <C extends Closeable> C register(@Nullable C closeable) { 125 if (closeable != null) { 126 stack.addFirst(closeable); 127 } 128 129 return closeable; 130 } 131 132 /** 133 * Stores the given throwable and rethrows it. It will be rethrown as is if it is an {@code 134 * IOException}, {@code RuntimeException} or {@code Error}. Otherwise, it will be rethrown wrapped 135 * in a {@code RuntimeException}. <b>Note:</b> Be sure to declare all of the checked exception 136 * types your try block can throw when calling an overload of this method so as to avoid losing 137 * the original exception type. 138 * 139 * <p>This method always throws, and as such should be called as {@code throw closer.rethrow(e);} 140 * to ensure the compiler knows that it will throw. 141 * 142 * @return this method does not return; it always throws 143 * @throws IOException when the given throwable is an IOException 144 */ 145 public RuntimeException rethrow(Throwable e) throws IOException { 146 checkNotNull(e); 147 thrown = e; 148 Throwables.propagateIfPossible(e, IOException.class); 149 throw new RuntimeException(e); 150 } 151 152 /** 153 * Stores the given throwable and rethrows it. It will be rethrown as is if it is an {@code 154 * IOException}, {@code RuntimeException}, {@code Error} or a checked exception of the given type. 155 * Otherwise, it will be rethrown wrapped in a {@code RuntimeException}. <b>Note:</b> Be sure to 156 * declare all of the checked exception types your try block can throw when calling an overload of 157 * this method so as to avoid losing the original exception type. 158 * 159 * <p>This method always throws, and as such should be called as {@code throw closer.rethrow(e, 160 * ...);} to ensure the compiler knows that it will throw. 161 * 162 * @return this method does not return; it always throws 163 * @throws IOException when the given throwable is an IOException 164 * @throws X when the given throwable is of the declared type X 165 */ 166 public <X extends Exception> RuntimeException rethrow(Throwable e, Class<X> declaredType) 167 throws IOException, X { 168 checkNotNull(e); 169 thrown = e; 170 Throwables.propagateIfPossible(e, IOException.class); 171 Throwables.propagateIfPossible(e, declaredType); 172 throw new RuntimeException(e); 173 } 174 175 /** 176 * Stores the given throwable and rethrows it. It will be rethrown as is if it is an {@code 177 * IOException}, {@code RuntimeException}, {@code Error} or a checked exception of either of the 178 * given types. Otherwise, it will be rethrown wrapped in a {@code RuntimeException}. <b>Note:</b> 179 * Be sure to declare all of the checked exception types your try block can throw when calling an 180 * overload of this method so as to avoid losing the original exception type. 181 * 182 * <p>This method always throws, and as such should be called as {@code throw closer.rethrow(e, 183 * ...);} to ensure the compiler knows that it will throw. 184 * 185 * @return this method does not return; it always throws 186 * @throws IOException when the given throwable is an IOException 187 * @throws X1 when the given throwable is of the declared type X1 188 * @throws X2 when the given throwable is of the declared type X2 189 */ 190 public <X1 extends Exception, X2 extends Exception> RuntimeException rethrow( 191 Throwable e, Class<X1> declaredType1, Class<X2> declaredType2) throws IOException, X1, X2 { 192 checkNotNull(e); 193 thrown = e; 194 Throwables.propagateIfPossible(e, IOException.class); 195 Throwables.propagateIfPossible(e, declaredType1, declaredType2); 196 throw new RuntimeException(e); 197 } 198 199 /** 200 * Closes all {@code Closeable} instances that have been added to this {@code Closer}. If an 201 * exception was thrown in the try block and passed to one of the {@code exceptionThrown} methods, 202 * any exceptions thrown when attempting to close a closeable will be suppressed. Otherwise, the 203 * <i>first</i> exception to be thrown from an attempt to close a closeable will be thrown and any 204 * additional exceptions that are thrown after that will be suppressed. 205 */ 206 @Override 207 public void close() throws IOException { 208 Throwable throwable = thrown; 209 210 // close closeables in LIFO order 211 while (!stack.isEmpty()) { 212 Closeable closeable = stack.removeFirst(); 213 try { 214 closeable.close(); 215 } catch (Throwable e) { 216 if (throwable == null) { 217 throwable = e; 218 } else { 219 suppressor.suppress(closeable, throwable, e); 220 } 221 } 222 } 223 224 if (thrown == null && throwable != null) { 225 Throwables.propagateIfPossible(throwable, IOException.class); 226 throw new AssertionError(throwable); // not possible 227 } 228 } 229 230 /** Suppression strategy interface. */ 231 @VisibleForTesting 232 interface Suppressor { 233 /** 234 * Suppresses the given exception ({@code suppressed}) which was thrown when attempting to close 235 * the given closeable. {@code thrown} is the exception that is actually being thrown from the 236 * method. Implementations of this method should not throw under any circumstances. 237 */ 238 void suppress(Closeable closeable, Throwable thrown, Throwable suppressed); 239 } 240 241 /** Suppresses exceptions by logging them. */ 242 @VisibleForTesting 243 static final class LoggingSuppressor implements Suppressor { 244 245 static final LoggingSuppressor INSTANCE = new LoggingSuppressor(); 246 247 @Override 248 public void suppress(Closeable closeable, Throwable thrown, Throwable suppressed) { 249 // log to the same place as Closeables 250 Closeables.logger.log( 251 Level.WARNING, "Suppressing exception thrown when closing " + closeable, suppressed); 252 } 253 } 254 255 /** 256 * Suppresses exceptions by adding them to the exception that will be thrown using JDK7's 257 * addSuppressed(Throwable) mechanism. 258 */ 259 @VisibleForTesting 260 static final class SuppressingSuppressor implements Suppressor { 261 262 static final SuppressingSuppressor INSTANCE = new SuppressingSuppressor(); 263 264 static boolean isAvailable() { 265 return addSuppressed != null; 266 } 267 268 static final Method addSuppressed = getAddSuppressed(); 269 270 private static Method getAddSuppressed() { 271 try { 272 return Throwable.class.getMethod("addSuppressed", Throwable.class); 273 } catch (Throwable e) { 274 return null; 275 } 276 } 277 278 @Override 279 public void suppress(Closeable closeable, Throwable thrown, Throwable suppressed) { 280 // ensure no exceptions from addSuppressed 281 if (thrown == suppressed) { 282 return; 283 } 284 try { 285 addSuppressed.invoke(thrown, suppressed); 286 } catch (Throwable e) { 287 // if, somehow, IllegalAccessException or another exception is thrown, fall back to logging 288 LoggingSuppressor.INSTANCE.suppress(closeable, thrown, suppressed); 289 } 290 } 291 } 292}