Java sockets基础教程：入门与实践

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"Java sockets 101"教程由developerWorks提供，是一份旨在帮助开发者理解和有效地使用Java socket编程的基础指南。这份教程针对的是那些对Java编程有一定基础但希望深入理解socket通信机制的读者，因为尽管Java语言本身支持sockets，但很多Java编程书籍往往对其覆盖不足或讲解不够详尽。本教程首先探讨了为什么要学习这个主题。尽管sockets在早期计算机网络中就已经存在，但随着Java的兴起，它为开发者提供了一种简单易用的方式来处理跨机器通信。通过Java sockets，开发者无需过多关注底层操作系统细节，可以直接在代码中实现高效通信。教程的核心内容包括以下几个部分： 1. 教程提示：这部分会指导读者判断是否应该继续学习，确保这门教程能够满足他们对Java socket技术的实际需求。 2. Socket基础知识：介绍socket的基本概念，如它们是什么、在网络通信中的作用以及在程序架构中的定位。读者可以在这里了解socket通信模型、套接字类型（如TCP/IP）以及连接和数据传输的基本原理。 3. 底层剖析：深入讲解socket工作的原理，包括套接字的创建、连接、读写操作以及错误处理等关键步骤，让读者对socket的内部机制有更深刻的理解。 4. 简单示例：通过一个基础的示例，展示如何在Java中创建和使用socket进行基本的客户端与服务器交互，包括创建套接字、绑定地址、接收和发送数据等。 5. 多线程示例：扩展到多线程环境，介绍如何在并发编程中利用Java socket进行高效的通信，包括线程同步和并发控制。 6. 池化示例：探讨socket连接的复用和池化，以提高性能和资源利用率，减少创建和销毁套接字的开销。 7. 真实生活中的应用：将理论知识与实际场景相结合，讨论socket在Web服务器、数据库连接、游戏服务器等各种应用场景中的具体运用。 8. 总结：回顾整个教程的重要知识点，并为初学者提供进一步学习的资源和建议。 9. 附录：包含相关的参考资料、代码示例、最佳实践和常见问题解答，以帮助读者在实际开发中解决遇到的问题。通过阅读这篇Java sockets 101教程，开发者可以建立起坚实的socket编程基础，更好地构建和优化网络应用程序。无论是对新手还是经验丰富的开发者来说，这都是提升Java编程技能、扩展网络通信能力的一个宝贵资源。

Section 3. An undercover socket

Introduction

The Java platform provides implementations of sockets in the java.net package. In this

tutorial, we'll be working with the following three classes in java.net:

* URLConnection

* Socket

* ServerSocket

There are more classes in java.net, but these are the ones you'll run across the most

often. Let's begin with URLConnection. This class provides a way to use sockets in your

Java code without having to know any of the underlying socket details.

Using sockets without even trying

The URLConnection class is the abstract superclass of all classes that create a

communications link between an application and a URL. URLConnections are most useful

for getting documents on Web servers, but can be used to connect to any resource identified

by a URL. Instances of this class can be used both to read from and to write to the resource.

For example, you could connect to a servlet and send a well-formed XML String to the

server for processing. Concrete subclasses of URLConnection (such as

HttpURLConnection) provide extra features specific to their implementation. For our

example, we're not doing anything special, so we'll make use of the default behaviors

provided by URLConnection itself.

Connecting to a URL involves several steps:

* Create the URLConnection

* Configure it using various setter methods

* Connect to the URL

* Interact with it using various getter methods

Next, we'll look at some sample code that demonstrates how to use a URLConnection to

request a document from a server.

The URLClient class

We'll begin with the structure for the URLClient class.

import java.io.*;

import java.net.*;

public class URLClient {

protected URLConnection connection;

public static void main(String[] args) {

}

public String getDocumentAt(String urlString) {

}

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Java sockets 101 Page 7 of 38

The first order of business is to import java.net and java.io.

We give our class one instance variable to hold a URLConnection.

Our class has a main() method that handles the logic flow of surfing for a document. Our

class also has a getDocumentAt() method that connects to the server and asks it for the

given document. We will go into the details of each of these methods next.

Surfing for a document

The main() method handles the logic flow of surfing for a document:

public static void main(String[] args) {

URLClient client = new URLClient();

String yahoo = client.getDocumentAt("http://www.yahoo.com");

System.out.println(yahoo);

}

Our main() method simply creates a new URLClient and calls getDocumentAt() with a

valid URL String. When that call returns the document, we store it in a String and then

print it out to the console. The real work, though, gets done in the getDocumentAt()

method.

Requesting a document from a server

The getDocumentAt() method handles the real work of getting a document over the Web:

public String getDocumentAt(String urlString) {

StringBuffer document = new StringBuffer();

try {

URL url = new URL(urlString);

URLConnection conn = url.openConnection();

BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));

String line = null;

while ((line = reader.readLine()) != null)

document.append(line + "\n");

reader.close();

} catch (MalformedURLException e) {

System.out.println("Unable to connect to URL: " + urlString);

} catch (IOException e) {

System.out.println("IOException when connecting to URL: " + urlString);

}

return document.toString();

}

The getDocumentAt() method takes a String containing the URL of the document we

want to get. We start by creating a StringBuffer to hold the lines of the document. Next,

we create a new URL with the urlString we passed in. Then we create a URLConnection

and open it:

URLConnection conn = url.openConnection();

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Java sockets 101 Page 8 of 38

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