Fast stream reading in Java

To increase the performance of your Java™ application when reading from an InputStream, there are a few key areas to look into. If possible, don't make any reallocations of memory. Allocate the input buffer once. Let the Java™ VM do the bulk of the reading, i.e. read data in big chunks. Some coding examples show a loop that reads data a small amount at a time. Using a too small buffer is inefficient. A much better technique is to use a relatively large buffer.

If you know the maximum content length, the most optimal read would be a single line, like this:

<!---->len = instream.read( buf, 0, MAX_BUFFER_SIZE );

In this case we assume that the buffer has already been allocated with a size set to MAX_BUFFER_SIZE.

If the content is of varying size, we have to make a tradeoff between performance and memory usage. If you keep your buffer size just above the average content length, then the number of reallocations of the data buffer and the number of reads will be kept at a minimum. There is no defined size of what a large buffer is but a good rule of thumb might be to keep the buffer size at most about 0,5 to 1 MB.