CS 4773 Object Oriented Systems Java IO

• input and output streams
• files
• exceptions
• network I/O

Input and Output Streams The abstract classes InputStream and OutputStream contain the basic I/O interface.
Note: Use the ones from java.io, not Corba.
These have abstract methods to read and write a single byte and implemented methods to close and handle arrays of bytes.

Look at the Java documentation for these.

There are lots of extension to each of these.
Here are the tables from the Core Java book.
This does not even count the Reader and Writer classes.

Figure 12-1: Input and output stream hierarchy, page 623.

Files

The simplest ways to get these streams from file is with the FileInputStream and FileOutputStream.

First create a File. The constructor takes a String parameter.
File f = new File(filename);

If a file exists, you can find its size with the length method.

Then create a stream: FileInputStream fis = new FileInputStream(f);
FileOutputStream fis = new FileOutputStream(f);

Note that write will write all you ask, but read may not read all you ask it to.

If you have a DataInputStream you can use readFully(byte[] b).

General way of figuring out which type of stream to use:
First determine the functionality you need.

Exceptions
Most of the I/O methods and some constructors can throw an exception.

Handle exceptions with try ... catch ... finally.
It is important to close all streams when you are done.
This can be tricky when an error occurs, especially since close can also throw an error.
Note that the finally clause is executed whether an exception occurs or not.

Look at the code for readEntireFile.

Network communication
We will look only at connection-oriented communication.

Server: waits for a connection from a remote client using a given port

• create a new ServerSocket
• call accept to wait for a connection
• accept creates a Socket
• get and input or output stream from the Socket
• communicate as before
• close the stream
• close the Socket returned by accept
• close the ServerSocket

• Create a new Socket
• as above, without the ServerSocket.