Java Network Programming, Second Edition

Input Streams

Java’s basic input class is java.io.InputStream:

public abstract class InputStream

This class provides the fundamental methods needed to read data as raw bytes. These are:

public abstract int read(  ) throws IOException
public int read(byte[] input) throws IOException
public int read(byte[] input, int offset, int length) throws IOException
public long skip(long n) throws IOException
public int available(  ) throws IOException
public void close(  ) throws IOException

Concrete subclasses of InputStream use these methods to read data from particular media. For instance, a FileInputStream reads data from a file. A TelnetInputStream reads data from a network connection. A ByteArrayInputStream reads data from an array of bytes. But whichever source you’re reading, you mostly use only these same six methods. Sometimes you may not even know exactly what kind of stream you’re reading from. For instance, TelnetInputStream is an undocumented class hidden inside the sun.net package. Instances of it are returned by various methods in the java.net package; for example, the openStream( ) method of java.net.URL. However, these methods are declared to return only InputStream, not the more specific subclass TelnetInputStream. That’s polymorphism at work once again. The instance of the subclass can be used transparently as an instance of its superclass. No specific knowledge of the subclass is required.

The basic method of InputStream is the noargs read( ) method. This method reads a ...