About the use and instructions of the transferFrom method of FileChannel

FileChanneloftransferFrom()Method is an important method in Java NIO for efficient transfer of data between channels, and is often used in scenarios such as file copying.

The following is a detailed introduction to its usage.

Method signature

FileChanneloftransferFrom()There are two overloaded forms of the method:

public abstract long transferFrom(ReadableByteChannel src, long position, long count) throws IOException;

Parameter description

• src: This is oneReadableByteChannelA parameter of type, indicating the source channel, from which data will be read.FileChannelImplementedReadableByteChannelinterface, so you can pass in directlyFileChannelAs the source channel, the object can also be passed into other implementations.ReadableByteChannelThe channel object of the interface.
• position: This is onelongParameter of type, specify the target channel (calltransferFrom()MethodFileChannelObject) where the data starts to be written. This position is the offset relative to the starting position of the target channel, counting from 0.
• count: This is also onelongA parameter of type that specifies the maximum number of bytes to be transferred from the source channel to the destination channel.

Return value

This method returns the actual number of bytes transferred.

In some cases, the actual number of bytes transmitted may be less thancountSpecified value, such as when there is insufficient available data in the source channel.

Specific usage examples

Here is a usetransferFrom()Sample code for method for file copying:

import ;
import ;
import ;
import ;

public class FileCopyWithTransferFrom {
    public static void main(String[] args) {
        try (FileInputStream fis = new FileInputStream("");
             FileOutputStream fos = new FileOutputStream("");
             FileChannel sourceChannel = ();
             FileChannel targetChannel = ()) {

            long size = ();
            // Start from the start position of the source channel and transfer all data to the start position of the target channel            long transferred = (sourceChannel, 0, size);
            ("Copyed successfully" + transferred + " byte");
        } catch (IOException e) {
            ();
        }
    }
}    

Code explanation

1. Create input and output streams and channels：

• useFileInputStreamRead the source file,FileOutputStreamWrite to the target file.
• passgetChannel()Methods to obtain source and target files respectivelyFileChannelObject.

2. Get the source file size：

Call()Method gets the size of the source file to determine the number of bytes to be transferred.

3. CalltransferFrom()method：

Transfer the source channelsourceChannelThe data in the target channel is transferred to the target channeltargetChannel, from the starting position of the target channel (position0) Start writing, the maximum number of bytes transferred is the size of the source filesize。

4. Process the return value：

WilltransferFrom()The actual number of transmitted bytes returned by the method is stored intransferredvariable and print the output.

5. Exception handling：

usetry-with-resourcesStatements ensure that the resource is automatically closed, while capturing and processing possible occurrencesIOExceptionabnormal.

Things to note

• Performance Advantages：transferFrom()The method uses the operating system's zero copy mechanism at the bottom, avoiding multiple copies of data between user space and kernel space, so it has high performance in scenarios such as file copying.
• Insufficient data: If there is insufficient available data in the source channelcountThe specified number of bytes,transferFrom()The method transfers as much data as possible and returns the actual number of bytes transferred.
• Cross-platform issues:AlthoughtransferFrom()Methods work properly on most operating systems, but some operating systems may have limits on the maximum number of bytes transferred, so you need to pay attention to when handling large files.

Friendly reminder: You need to""and""Replace with the actual file path.

Summarize

The above is personal experience. I hope you can give you a reference and I hope you can support me more.