The java.io package provides a rich framework and class library for reading and writing any type of data (text, numbers, images) in streams from any type of location (disk, network, memory).
The package provides 2 class hierarchies: one for byte streams, the other for character streams.
Base classes for reading data: InputStream for byte streams, Reader for character streams.
Base classes for writing data: OutputStream for byte streams, Writer for character streams.
Example of copying one file to another.
Reader in = new FileReader("one.txt");
Writer out = new FileWriter("two.txt");
int token = -1;
while( (token != in.read()) != -1 )
{
out.write(token);
}
out.close();
The library uses the decorator pattern to add flexible stream handling. By chaining constructors of various classes, you can change how streams are read or written. Examples:
We need to read some data on disk, and for performance reasons the read operation should be buffered.
Reader bufferedFileIn =
new BufferedReader(new FileReader("datafile"));
Read an in-memory byte array as UTF-8 encoded characters.
byte[] data = ...;
Reader charReader =
new BufferedReader(
new InputStreamReader(
new ByteArrayInputStream(data), "UTF-8"));
