java - Who is better in performance filechannel or RandomAccessFile for reading and writing?

Question

I recently came across FileChannel, I am a big fan of RandomAccessFile. But I am wondering why would I pick FileChannel over RandomAccessFile for reading from a file and writing that content to another.

Is there any specific performance reason? I dont want to use locking of FileChannel for any purpose as I believe that could be one of the reasons why filechannel can be used. I don't want to use BufferReader or anything like that as suggested in other StackOverflow response.

Answer 1

FileChannel API 说：文件的一个区域可以直接映射到内存中；对于大文件，这通常比调用通常的读取或写入方法更有效。

Answer 2

除非您使用带有直接缓冲区的 a 并且从不自己访问数据，否则它们之间没有任何选择FileChannel，例如您只将其复制到 aSocketChannel.这更快，因为数据永远不必跨越 JNI/JVM 边界。

但我想知道你为什么不选择BufferedReader. 对于逐行读取文件，它肯定会比其中任何一个都快几个数量级。

Answer 3

RandomAccess 文件来源：

看到 RandomAccessFile 实际上是在后台使用 FileChannel ......

public final FileChannel getChannel() {
         synchronized (this) {
             if (channel == null) {
                 channel = FileChannelImpl.open(fd, true, rw, this);

                 /*
                  * FileDescriptor could be shared by FileInputStream or
                  * FileOutputStream.
                  * Ensure that FD is GC'ed only when all the streams/channels
                  * are done using it.
                  * Increment fd's use count. Invoking the channel's close()
                  * method will result in decrementing the use count set for
                  * the channel.
                  */
                 fd.incrementAndGetUseCount();
             }
             return channel;
         }
     }

http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/6-b14/java/io/RandomAccessFile.java

Answer 4

FileChannel可以安全地被多个并发线程使用。

Answer 5

RandomAccessFile 性能好，而且它允许直接读取和写入大多数主要类型。