Java NIO is a new IO API introduced by Java 1.4, 1) is aimed at buffers and channels, 2) contains core components of Buffer, Channel and Selector, 3) supports non-blocking mode, and 4) handles concurrent connections more efficiently than traditional IO. Its advantages are reflected in: 1) Non-blocking IO reduces thread overhead, 2) Buffer improves data transmission efficiency, 3) Selector realizes multiplexing, and 4) Memory mapping speeds up file reading and writing. Note when using: 1) The flip/clear operation of the Buffer is easy to be confused, 2) Incomplete data needs to be processed manually in non-blocking, 3) Selector registration must be canceled in time, 4) NIO is not suitable for all scenarios.

Java NIO (New Input/Output) was introduced in Java 1.4, which is an important upgrade to traditional IO. It performs better in handling large amounts of concurrent connections and high-performance network communications, and is especially suitable for building high-throughput server-side applications.

What is Java NIO?

Java NIO is not just a simple improvement to IO, but provides a brand new set of APIs for input and output operations. Unlike traditional Stream-Oriented IO, NIO is buffer-oriented and channel-based.

Core components include:

• Buffer : Data reading and writing are completed through Buffer, and are no longer direct operation of streams.
• Channel : Similar to streams, but can be read and written in both directions and supports asynchronous operations.
• Selector : used to listen to events of multiple channels, which is the key to implementing multiplexing.

These designs make NIO more flexible and efficient, especially in non-blocking mode where a thread can manage multiple connections.

What are the advantages of Java NIO?

Compared with traditional IO, Java NIO has the following obvious advantages:

• Non-blocking IO mode : Multiple connection requests can be processed in one thread, reducing thread switching overhead.
• Efficient Buffer Management : Using Buffer improves data transmission efficiency and reduces the number of system calls.
• Selector multiplexing mechanism : Very suitable for handling large number of concurrent connections, such as common scenarios in server-side development.
• Memory mapped file support : MappedByteBuffer can directly map files to memory, greatly improving file read and write speed.

For example, if a web server uses traditional IO, each client connection needs an independent thread to handle; while with NIO, a thread can monitor and process multiple connections at the same time, which consumes less resources and responds faster.

What should I pay attention to in actual use?

Although Java NIO is powerful, there are some details that are easy to get stuck in actual use:

• The flip and clear operations of Buffer are easily confused : remember to call flip() when switching read and write, otherwise the data you just wrote will not be read; after use, use clear() or compact() to clear or retain part of the data.
• Non-blocking mode requires manual processing of incomplete data : for example, when receiving HTTP requests, you may not get the complete request header at one time, and you need to loop through to read until you receive the complete data.
• When registering and canceling Selector, you should pay attention to timely quality : when the connection is closed, you should cancel the registration in time to avoid resource leakage.
• NIO is not omnipotent : traditional IO is more intuitive and easy to use for simple IO operations; only when it is necessary to deal with a large number of concurrent connections can the advantages of NIO be truly reflected.

Let's summarize

Java NIO provides a more underlying and flexible IO operation method, especially in network programming with significant advantages. If your application needs to deal with high concurrency and low latency scenarios, such as chat servers, real-time data push, etc., then NIO is an option worth considering.

Basically that's it. By mastering the three core concepts of Buffer, Channel and Selector, and paying attention to some common usage details, you can use Java NIO to build efficient IO applications well.

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