Java Network Programming, Second Edition

Chapter 4. Java I/O

A large part of what network programs do is simple input and output, moving bytes from one system to another. Bytes are bytes; and to a large extent, reading data a server sends you is not all that different from reading a file. Sending text to a client is not all that different from writing a file. However, input and output (I/O) in Java is organized differently than it is in most other languages, such as C, Pascal, and C++. Consequently, I’d like to take one chapter to summarize Java’s unique approach to I/O.

I/O in Java is built on streams. Input streams read data. Output streams write data. Different fundamental stream classes such as java.io.FileInputStream and sun.net.TelnetOutputStream read and write particular sources of data. However, all fundamental output streams have the same basic methods to write data and all fundamental input streams use the same basic methods to read data. After a stream is created, you can often ignore the details of exactly what it is you’re reading or writing.

Filter streams can be chained to either an input stream or an output stream. Filters can modify the data as it’s read or written—for instance, by encrypting or compressing it—or they can simply provide additional methods for converting the data that’s read or written into other formats. For instance, the java.io.DataOutputStream class provides a method that converts an int to four bytes and writes those bytes onto its underlying output stream.

Finally, readers and writers ...