INT-3915: Possible Memory Leak in FileChannelCache

JIRA: https://jira.spring.io/browse/INT-3915

Close the redundant `FileChannel` when Map collision occurs.

Author: garyrussell

spring-integration-file/src/main/java/org/springframework/integration/file/locking/FileChannelCache.java

@@ -1,11 +1,11 @@
 /*
- * Copyright 2002-2013 the original author or authors.
+ * Copyright 2002-2015 the original author or 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
+ *	  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,
@@ -19,69 +19,82 @@
 import java.io.File;
 import java.io.IOException;
 import java.io.RandomAccessFile;
+import java.nio.channels.FileChannel;
 import java.nio.channels.FileLock;
 import java.nio.channels.OverlappingFileLockException;
-import java.nio.channels.FileChannel;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentMap;
 
 /**
  * Static cache of FileLocks that can be used to ensure that only a single lock is used inside this ClassLoader.
  *
  * @author Iwein Fuld
+ * @author Gary Russell
  * @since 2.0
  */
 final class FileChannelCache {
 
-    private static ConcurrentMap<File, FileChannel> channelCache = new ConcurrentHashMap<File, FileChannel>();
+	private static ConcurrentMap<File, FileChannel> channelCache = new ConcurrentHashMap<File, FileChannel>();
 
 
-    /**
-     * Try to get a lock for this file while guaranteeing that the same channel will be used for all file locks in this
-     * VM. If the lock could not be acquired this method will return <code>null</code>.
-     * <p>
-     * Locks acquired through this method should be passed back to #closeChannelFor to prevent memory leaks.
-     * <p>
-     * Thread safe.
-     */
-    public static FileLock tryLockFor(File fileToLock) throws IOException {
-        FileChannel channel = channelCache.get(fileToLock);
-        if (channel == null) {
-            FileChannel newChannel = new RandomAccessFile(fileToLock, "rw").getChannel();
-            FileChannel original = channelCache.putIfAbsent(fileToLock, newChannel);
-            channel = (original != null) ? original : newChannel;
-        }
-        FileLock lock = null;
-        if (channel != null) {
-            try {
-                lock = channel.tryLock();
-            }
-            catch (OverlappingFileLockException e) {
-                // File is already locked in this thread or virtual machine
-            }
-        }
-        return lock;
-    }
+	/**
+	 * Try to get a lock for this file while guaranteeing that the same channel will be used for all file locks in this
+	 * VM. If the lock could not be acquired this method will return <code>null</code>.
+	 * <p>
+	 * Locks acquired through this method should be passed back to #closeChannelFor to prevent memory leaks.
+	 * <p>
+	 * Thread safe.
+	 */
+	public static FileLock tryLockFor(File fileToLock) throws IOException {
+		FileChannel channel = channelCache.get(fileToLock);
+		if (channel == null) {
+			@SuppressWarnings("resource")
+			FileChannel newChannel = new RandomAccessFile(fileToLock, "rw").getChannel();
+			FileChannel original = channelCache.putIfAbsent(fileToLock, newChannel);
+			if (original != null) {
+				channel = original;
+				try {
+					newChannel.close();
+				}
+				catch (IOException e) {
+					// ignore
+				}
+			}
+			else {
+				channel = newChannel;
+			}
+		}
+		FileLock lock = null;
+		if (channel != null) {
+			try {
+				lock = channel.tryLock();
+			}
+			catch (OverlappingFileLockException e) {
+				// File is already locked in this thread or virtual machine
+			}
+		}
+		return lock;
+	}
 
-    /**
-     * Close the channel for the file passed in.
-     * <p>
-     * Thread safe.
-     */
-    public static void closeChannelFor(File fileToUnlock) {
-        FileChannel fileChannel = channelCache.remove(fileToUnlock);
-        if (fileChannel != null) {
-        	try {
+	/**
+	 * Close the channel for the file passed in.
+	 * <p>
+	 * Thread safe.
+	 */
+	public static void closeChannelFor(File fileToUnlock) {
+		FileChannel fileChannel = channelCache.remove(fileToUnlock);
+		if (fileChannel != null) {
+			try {
 				fileChannel.close();
 			}
-        	catch (IOException e) {
+			catch (IOException e) {
 				// ignore
 			}
-        }
-    }
+		}
+	}
 
-    public static boolean isLocked(File file) {
-        return channelCache.containsKey(file);
-    }
+	public static boolean isLocked(File file) {
+		return channelCache.containsKey(file);
+	}
 
 }