Access to networks (the Internet in particular) is becoming an important and often necessary feature of applications. Applications frequently need to access and provide services. As the Internet of Things (IoT) connects more and more devices, understanding how to access networks becomes crucial.
The important factors that have been the driving forces for more network applications include the availability of faster networks with greater bandwidth. This has made it possible to transmit wider ranges of data, such as video streams. In recent years, we have seen an increase in connectivity, whether it has been for new services, more extensive social interactions, or games. Knowing how to develop network applications is an important development skill.
In this chapter, we will cover the basics of Network programming:
Why networking is important
The support that Java provides
Simple programs to address basic network operations
Basic networking terminology
A simple server/client application
Using a thread to support a server
Throughout this book, you will be exposed to many network concepts, ideas, patterns, and implementation strategies using both older and newer Java technologies. Network connections occur at a low level using sockets, and at a much higher level using a multitude of protocols. Communications can be synchronous requiring careful coordination of requests and responses, or they can be asynchronous where other activities are performed until the response has been submitted.
These and other concepts are addressed through a series of chapters, each focusing on a specific topic. The chapters complement each other by elaborating on concepts that were previously introduced, whenever possible. Numerous code examples are used whenever possible to further your understanding of the topic.
Central to accessing a service is knowing or discovering its address. This address may be human readable, such as www.packtpub.com, or in the form of an IP address such as 83.166.169.231. Internet Protocol (IP) is a low-level addressing scheme that is used to access information on the Internet. Addressing has long used IPv4 to access resources. However, these addresses are all but gone. The newer IPv6 is available to provide a larger range of addresses. The basics of network addressing and how they can be managed in Java is the focus of Chapter 2, Network Addressing.
The intent of network communication is to transfer information to and from other applications. This is facilitated using buffers and channels. Buffers hold information temporarily until it can be processed by an application. Channels are an abstraction that simplifies communications between applications. The NIO and NIO.2 packages provide much of the support for buffers and channels. We will explore these techniques along with other techniques, such as blocking and non-blocking IO, in Chapter 3, NIO Support for Networking.
Services are provided by servers. An example of this is the simple echo server, which retransmits what it was sent. More sophisticated servers, such as HTTP servers, can support extensive services to meet a wide range of needs. The client/server model and its Java support are covered in Chapter 3, NIO Support for Networking.
Another service model is the peer-to-peer (P2P) model. In this architecture, there is no central server, but rather a network of applications that communicate to provide a service. This model is represented by applications, such as BitTorrent, Skype, and BBC's iPlayer. While much of the support that is required for the development of these types of applications is beyond the scope of this book, Chapter 4, Client/Server Development, explores P2P issues and the support provided by Java and JXTA.
IP is used at a low level to send and receive packets of information across a network. We will also demonstrate the use of User Datagram Protocol (UDP) and Transmission Control Protocol (TCP) communication protocols. These protocols are layered on top of IP. UDP is used to broadcast short packets or messages with no guarantee of reliable delivery. TCP is used more commonly and provides a higher level of service than that of UDP. We will cover the use of these related technologies in Chapter 5, Peer-to-Peer Networks.
A service will often be faced with varying levels of demand placed on it due to a number of factors. Its load may vary by the time of the day. As it becomes more popular, its overall demand will also increase. The server will need to scale to meet increases and decreases in its load. Threads and thread pools have been used to support this effort. These and other technologies are the focus of Chapter 6, UDP and Multicasting.
Increasingly, applications need to be secure against attacks by hackers. When it is connected to a network, this threat increases. In Chapter 7, Network Scalability, we will explore many of the techniques available to support secure Java applications. Among these is the Secure Socket Level (SSL), and how Java supports it.
Applications rarely work in isolation. Hence, they need to use networks to access other applications. However, not all applications are written in Java. Networking with these applications can pose special problems ranging from how the bytes of a data type are organized to the interface supported by the application. It is common to work with specialized protocols, such as HTTP, and WSDL. The last chapter of this book examines these issues from a Java perspective.
We will demonstrate both older and newer Java technologies. Understanding the older technologies may be necessary in order to maintain older code, and it can provide insight into why the newer technologies were developed. We will also complement our examples using many of the Java 8 functional programming techniques. Using Java 8 examples along with pre-Java 8 implementations, we can learn how to use Java 8 and be better informed as to when it can and should be used.
It is not the intent to fully explain the newer Java 8 technologies, such as lambda expressions, and streams. However, the use of Java 8 examples will provide an insight into how they can be used to support networked applications.
The remainder of this chapter touches on many of the network technologies that are explored in this book. You will be introduced to the basics of these techniques, and you should find them easy to understand. However, there are a few places where time does not permit us to fully explore and explain these concepts. These issues will be addressed in subsequent chapters. So, let's begin our exploration with network addressing.