Netty实战：探索Java NIO与高级特性

5星 · 超过95%的资源需积分: 34 160 浏览量更新于2024-07-23 收藏 5.4MB PDF 举报

"《Netty 实战》是 Manning 出版社出版的一本书，通过 Early Access Program 提供，由 Jinpu Hu 获得许可。本书深入介绍了 Netty 框架，涵盖了从基础到高级的主题，包括 Java NIO API、构建第一个 Netty 应用、传输、缓冲区、ChannelHandler、编码解码器、启动 Netty 应用、单元测试、WebSocket、SPDY、UDP 广播等，并涉及定制编解码器、选择合适的线程模型、与 EventLoop 的注册注销等高级话题。此外，还提到了社区参与方式以及相关的书籍和项目。" 《Netty 实战》是一本详尽介绍 Netty 框架的专著，适合 Java 开发者和网络编程人员阅读。Netty 是一个高性能、异步事件驱动的网络应用程序框架，用于快速开发可维护的协议服务器和客户端。书中首先探讨了 Netty 与 Java NIO API 的关系，解释了 Netty 如何改进了标准的 Java NIO 模型，使得网络编程更为简便。第二部分，读者将学习构建第一个 Netty 应用程序，逐步理解 Netty 的核心组件和设计模式。这包括了解如何设置传输层（例如，TCP 和 UDP）、使用缓冲区高效地处理数据、定义 ChannelHandler 处理网络事件，以及实现编码解码器以转换应用层协议的数据。第三部分“Netty 举例”提供了实际应用案例，如单元测试代码以确保网络服务的健壮性，实现 WebSocket 服务器支持实时通信，以及 SPDY 协议的实现，后者为网页应用提供了更快的加载速度。此外，还有通过 UDP 进行广播的示例，展示了 Netty 在多播场景下的应用。第四部分深入到高级主题，指导读者如何根据需求定制自己的编解码器，选择最适合应用的线程模型以优化性能，以及如何在 EventLoop 中正确地注销和重新注册，确保系统资源的有效管理。最后，书中通过案例研究展示了 Netty 在真实项目中的应用场景，帮助读者将理论知识应用于实践。附录部分提供了 Netty 社区的参与方式，以及推荐的相关书籍和项目，对于希望深入研究或寻求社区支持的读者来说，这部分信息非常有价值。《Netty 实战》是一本全面且实用的指南，能够帮助开发者充分利用 Netty 的强大功能，构建高效、可靠的网络应用。

ServerSocketChannel serverChannel = ServerSocketChannel.open();

ServerSocket ss = serverChannel.socket();

InetSocketAddress address = new InetSocketAddress(port);

ss.bind(address); #1

serverChannel.configureBlocking(false);

Selector selector = Selector.open();

serverChannel.register(selector, SelectionKey.OP_ACCEPT); #2

while (true) {

try {

selector.select(); #3

} catch (IOException ex) {

ex.printStackTrace();

// handle in a proper way

break;

}

Set readyKeys = selector.selectedKeys(); #4

Iterator iterator = readyKeys.iterator();

while (iterator.hasNext()) {

SelectionKey key = (SelectionKey) iterator.next();

iterator.remove(); #5

try {

if (key.isAcceptable()) {

ServerSocketChannel server = (ServerSocketChannel)

key.channel();

SocketChannel client = server.accept(); #6

System.out.println("Accepted connection from " +

client);

client.configureBlocking(false);

client.register(selector, SelectionKey.OP_WRITE |

SelectionKey.OP_READ, ByteBuffer.allocate(100)); #7

}

if (key.isReadable()) { #8

SocketChannel client = (SocketChannel) key.channel();

ByteBuffer output = (ByteBuffer) key.attachment();

client.read(output); #9

}

if (key.isWritable()) { #10

SocketChannel client = (SocketChannel) key.channel();

ByteBuffer output = (ByteBuffer) key.attachment();

output.flip();

client.write(output); #11

output.compact();

}

} catch (IOException ex) {

key.cancel();

try {

key.channel().close();

} catch (IOException cex) {

}

©Manning Publications Co. We welcome reader comments about anything in the manuscript - other than typos and

other simple mistakes. These will be cleaned up during production of the book by copyeditors and proofreaders.

http://www.manning-sandbox.com/forum.jspa?forumID=857

Licensed to Jinpu Hu <hujinpu@gmail.com>

#1 Bind server to port

#2 Register the channel with the selector to be interested in new Client connections that get accepted

#3 Block until something is selected

#4 Get all SelectedKey instances

#5 Remove the SelectedKey from the iterator

#6 Accept the client connection

#7 Register connection to selector and set ByteBuffer

#8 Check for SelectedKey for read

#9 Read data to ByteBuffer

#10 Check for SelectedKey for write

#11 Write data from ByteBuffer to channel

This example is more complex than the previous version of EchoServer. This complexity is a

trade off; asynchronous code is typically more complicated than its synchronous counterpart.

Semantically, the original NIO and the new NIO.2 API are similar, but their implementations

are different. We’ll take a look the differences next, and we’ll implement version 3 of

EchoServer.

1.3.4 EchoServer based on NIO.2

Unlike the original NIO implementation, NIO.2 allows you to issue IO operations and provide

what is called a completion handler (

CompletionHandler class). This completion handler

gets executed after the operation completes. Therefore, execution of the completion handler is

driven by the underlying system and the implementation is hidden from the developer. It also

guarantees that only one

CompletionHandler is executed for channel at the same time. This

approach helps to simplify the code because it removes the complexity that comes with

multithreaded execution.

The major difference between the original NIO and NIO.2 is that you don’t have to check

whether an event accours on the Channel and then trigger some action. In NIO.2 you can just

trigger an IO operation and register a completion handler with it, this handler will then get

notified once the operation complates. This removes the need to create your own application

logic to check for completion, which itself results in unnecessary processing.

Now let’s see how the same asynchronous EchoServer would be implemented with

NIO2,implementation as shown in the next listing.

Listing 1.7 EchoServer v3: NIO.2

public class PlainNio2EchoServer {

public void serve(int port) throws IOException {

System.out.println("Listening for connections on port " + port);

final AsynchronousServerSocketChannel serverChannel =

AsynchronousServerSocketChannel.open();

InetSocketAddress address = new InetSocketAddress(port);

serverChannel.bind(address); #1

final CountDownLatch latch = new CountDownLatch(1);

serverChannel.accept(null, new

CompletionHandler<AsynchronousSocketChannel, Object>() { #2

@Override

public void completed(final AsynchronousSocketChannel channel,

Object attachment) {

©Manning Publications Co. We welcome reader comments about anything in the manuscript - other than typos and

other simple mistakes. These will be cleaned up during production of the book by copyeditors and proofreaders.

http://www.manning-sandbox.com/forum.jspa?forumID=857

Licensed to Jinpu Hu <hujinpu@gmail.com>

serverChannel.accept(null, this); #3

ByteBuffer buffer = ByteBuffer.allocate(100);

channel.read(buffer, buffer,

new EchoCompletionHandler(channel)); #4

}

@Override

public void failed(Throwable throwable, Object attachment) {

try {

serverChannel.close(); #5

} catch (IOException e) {

// ingnore on close

} finally {

latch.countDown();

}

});

try {

latch.await();

} catch (InterruptedException e) {

Thread.currentThread().interrupt();

}

private final class EchoCompletionHandler implements

CompletionHandler<Integer, ByteBuffer> {

private final AsynchronousSocketChannel channel;

EchoCompletionHandler(AsynchronousSocketChannel channel) {

this.channel = channel;

}

@Override

public void completed(Integer result, ByteBuffer buffer) {

buffer.flip();

channel.write(buffer, buffer, new CompletionHandler<Integer,

ByteBuffer>() { #6

@Override

public void completed(Integer result, ByteBuffer buffer) {

if (buffer.hasRemaining()) {

channel.write(buffer, buffer, this); #7

} else {

buffer.compact();

channel.read(buffer, buffer,

EchoCompletionHandler.this); #8

}

@Override

public void failed(Throwable exc, ByteBuffer attachment) {

try {

channel.close();

} catch (IOException e) {

// ingnore on close

}

});

}

©Manning Publications Co. We welcome reader comments about anything in the manuscript - other than typos and

other simple mistakes. These will be cleaned up during production of the book by copyeditors and proofreaders.

http://www.manning-sandbox.com/forum.jspa?forumID=857

Licensed to Jinpu Hu <hujinpu@gmail.com>

@Override

public void failed(Throwable exc, ByteBuffer attachment) {

try {

channel.close();

} catch (IOException e) {

// ingnore on close

}

#1Bind Server to port

#2 Start to accept new Client connections. Once one is accepted the CompletionHandler will get called.

#3 Again accept new Client connections

#4 Trigger a read operation on the Channel, the given CompletionHandler will be notified once

something was read

#5 Close the socket on error

#6 Trigger a write operation on the Channel, the given CompletionHandler will be notified once

something was written

#7 Trigger again a write operation if something is left in the ByteBuffer

#8 Trigger a read operation on the Channel, the given CompletionHandler will be notified once

something was read

At first glance, it may look like more code than what you had when using the previous NIO

implementation. But notice that NIO.2 handles threading and the creation of the so-called

event loop for you. This approach simplifies the code needed to build a multithreaded NIO

application, even though it may not seem to be the case in this example. As the complexity of

the application increases, the gains become more evident because you’ll be producing cleaner

code.

In the next section, we’ll look at some known problems that exist in the JDK’s NIO

implementation.

1.4 NIO problems and how Netty comes to the rescue

In this section, we’ll look at some problems and limitations of the Java NIO APIs and how Netty

addresses these issues. Having the NIO packages of the JDK is a great step in the right

direction, but users are limited in how they can use them. These issues are often the result of

design choices that were made in the past and aren’t easy to change now, others are defects.

1.4.1 Cross-platform and compatibility issues

NIO is low level and depends on how the operating system (OS) handles IO. So fulfilling the

requirement of having a unified API exposed in Java, which works and behaves the same on all

OSs, isn’t trivial.

When using NIO you often find that your code works fine on Linux, for example, but has

problems on Windows. My general advice, even if you’re not using NIO, but it’s more important

if you are, is to test on all the OSs you want to support or use. Even if all the tests pass on

your Linux workstation, be sure to verify it on the other OSs. If you don’t verify, prepare to

have fun later.

other simple mistakes. These will be cleaned up during production of the book by copyeditors and proofreaders.

http://www.manning-sandbox.com/forum.jspa?forumID=857

Licensed to Jinpu Hu <hujinpu@gmail.com>

Ideal as NIO.2 may seem, it’s only supported in Java 7, and if your application runs on Java

6, you may not be able to use it. Also, at the time of writing, there is no NIO.2 API for

datagram channels (for UDP applications), so its usage is limited to TCP applications only.

Netty addresses this problem by providing a unified API, which allows the same semantics

to work seamlessly on either Java 6 or 7. You don’t have to worry about the underlying

version, and you benefit from a simple and consistent API.

1.4.2 Extending ByteBuffer ... or not

As you saw previously, ByteBuffer is used as data container. Unfortunately, the JDK doesn’t

contain a

ByteBuffer implementation that allows wrapping an array of ByteBuffer

instances. This functionality is useful if you want to minimize memory copies. If you ‘rethinking

I’ll implement it myself, don’t waste your time;

ByteBuffer has a private constructor, so it

isn’t possible to extend it.

Netty provides its own

ByteBuffer implementation, which gets around this limitation and

goes further by providing several other means of constructing, using, and manipulating a

ByteBuffer all with a simpler API.

1.4.3 Scattering and gathering may leak

Many channel implementations support scattering and gathering. This feature allows writing to

or reading from many

ByteBuffer instances at the same time with better performance. Here

the kernel/OS handles how these are written/read, which often gives you the best performance

because the kernel/OS, being closer to the hardware, knows how to do it in the most efficient

way.

Scattering/gathering is often used if you want to split data in different

ByteBuffer

instances to handle each buffer separately. For example, you may want to have the header in

one

ByteBuffer and the body in another.

Figure 1.4 shows how a scattering read is performed. You pass an array of

ByteBuffer

instances to the

ScatteringByteChannel and the data gets scattered from the channel to

the buffers.

Figure 1.4 A scattering read from a channel

other simple mistakes. These will be cleaned up during production of the book by copyeditors and proofreaders.

http://www.manning-sandbox.com/forum.jspa?forumID=857

Licensed to Jinpu Hu <hujinpu@gmail.com>

剩余264页未读，继续阅读

gjq5233

粉丝: 2
资源: 29

Netty实战：探索Java NIO与高级特性

netty in action.rar

netty in action中文版

netty in action 中文版

Netty In Action

Netty in Action

Netty in Action合集

Netty in Action mobi

Manning Netty in Action

netty in action源码

Essential Netty In Action

最新资源