Binding Sockets to Specific Ports

JDK Tutorials - Herong's Tutorial Examples

∟Socket Network Communication

∟Binding Sockets to Specific Ports

This section describes how to bind a socket to a specific port. Binding multiple client sockets to the same port is not allowed.

As I mentioned previously, I used a special socket constructor to allow the system to bind the socket an un-specified local address and port number. This gives the system the freedom to pickup an un-used port number. If I change SocketClient.java from:

         Socket c = new Socket("localhost",8888);

to:

         Socket c = new Socket();
         c.bind(new InetSocketAddress("localhost",4444));
         c.connect(new InetSocketAddress("localhost",8888));

The first running instance of SocketClient will work, but additional running instances will get the following error:

   java.net.BindException: Address already in use: JVM_Bind

Why? Because, at any given time, only one socket can be bound to a given port.

So, allowing the system to pick up a free local port number is a better idea.

However, the sockets created by the ServerSocket.accept() method seems to be allowed to bind to the same local port. See the output of ReverseEchoServer. When two or more client programs are connected to it, sockets created for the connections are all bound to the same port number, 8888.

Exercise: Can you re-bind a bound socket to new port number?

Table of Contents

About This JDK Tutorial Book

JDK (Java Development Kit)

Java Date-Time API

Date, Time and Calendar Classes

Date and Time Object and String Conversion

Number Object and Numeric String Conversion

Locales, Localization Methods and Resource Bundles

Calling and Importing Classes Defined in Unnamed Packages

HashSet, Vector, HashMap and Collection Classes

Character Set Encoding Classes and Methods

Character Set Encoding Maps

Encoding Conversion Programs for Encoded Text Files

►Socket Network Communication

What Is a Socket?

Establishing a Socket Communication Link

ReverseEchoer.java - A Simple Server Socket Application

SocketClient.java - A Simple Client Socket Application

ReverseEchoServer.java - A Multi-Connection Socket Server

►Binding Sockets to Specific Ports

Datagram Network Communication

DOM (Document Object Model) - API for XML Files

SAX (Simple API for XML)

DTD (Document Type Definition) - XML Validation

XSD (XML Schema Definition) - XML Validation

XSL (Extensible Stylesheet Language)

Message Digest Algorithm Implementations in JDK

Private key and Public Key Pair Generation

PKCS#8/X.509 Private/Public Encoding Standards

Digital Signature Algorithm and Sample Program

"keytool" Commands and "keystore" Files

KeyStore and Certificate Classes

Secret Key Generation and Management

Cipher - Encryption and Decryption

The SSL (Secure Socket Layer) Protocol

SSL Socket Communication Testing Programs

SSL Client Authentication

HTTPS (Hypertext Transfer Protocol Secure)

Outdated Tutorials

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