NIO is an efficient I/O API introduced by Java 1.4. Its core advantages are non-blocking IO and buffer-oriented operation; its key components are Buffers (such as ByteBuffer, CharBuffer) and Channel (such as FileChannel, SocketChannel); the non-blocking mode realizes multi-connection processing through Selector to improve system throughput; it is suitable for scenarios such as high concurrent servers and large file transfers; it is more efficient to copy files using FileChannel; when operating Buffers, you need to pay attention to capacity, position, limit status, flip(), clear() and other methods; NIO is not better than traditional IO in all scenarios, and has high requirements for developers.
NIO (New Input/Output) is a new set of I/O APIs introduced by Java 1.4, located under the java.nio package. Compared with traditional IO (i.e. java.io package), it provides a more efficient and flexible way to handle the read and write operations of files and network data.
Simply put, the core advantage of NIO lies in non-blocking IO and buffer-oriented operations , which are more suitable for scenarios with high concurrency and large data transmission.
Core components: Buffer and Channel
Two key concepts of NIO are Buffer and Channel :
- A Buffer is a container, and all data reading and writing must be buffered. Common Buffer types include
ByteBuffer,CharBuffer,IntBuffer, etc. - Channel is similar to a stream, but has stronger functions, can read and write at the same time, and supports asynchronous operations. Commonly used Channels include
FileChannel,SocketChannel,ServerSocketChannel, etc.
To give a simple example: traditional IO operations are like "You can only wait for the meal after you order food in a restaurant", while NIO is like "You can wait for the meal while browsing your phone."
Non-blocking mode: The key to improving efficiency
In traditional IO, each connection requires a thread to process, which can easily cause waste of resources. NIO supports non-blocking mode , for example, in network programming, a thread can handle multiple connection requests at the same time.
For example, using the Selector mechanism, a thread can listen to events on multiple channels (such as connection, read completion, etc.), thereby greatly reducing the number of threads and improving system throughput.
Application scenarios include:
- High concurrency server development
- Real-time communication system
- Large file transfer optimization
Actual usage in file operations
Using NIO for file operations is usually faster than traditional IO, especially large file processing. For example, use FileChannel to copy files:
try (FileChannel source = new FileInputStream("source.txt").getChannel();
FileChannel dest = new FileOutputStream("dest.txt").getChannel()) {
dest.transferFrom(source, 0, source.size());
} catch (IOException e) {
e.printStackTrace();
} This code utilizes the transferFrom method to directly transfer file content from one Channel to another, which is more efficient and concise.
Notable details
- Buffer has three important states: capacity, position and limit. When operating, pay attention to the order of use of methods such as flip(), clear(), and rewind().
- NIO is not superior to traditional IO in all cases. For small-scale data or simple tasks, the performance difference between the two is not much, and traditional IO is even more intuitive and easy to use.
- Be careful when using Selector to register event types and cancel processed keys, otherwise it may result in duplicate processing or memory leaks.
Basically that's it. NIO provides a more underlying and more efficient IO operation method, but also puts higher understanding requirements for developers. Mastering its basic principles and common techniques will make you more comfortable when dealing with high-performance IO scenarios.
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