BufferedOutputStream

BufferedOutputStream is a Java I/O class that provides buffered output capabilities by wrapping another OutputStream. It adds an internal byte buffer to reduce the number of write operations sent to the underlying stream, which can improve performance when writing small amounts of data frequently.

Internally, BufferedOutputStream maintains a byte array buffer and a count of the number of bytes currently stored in the buffer. When data is written, it is copied into the buffer. If the buffer becomes full, or when flush is invoked, the buffered data is written to the underlying OutputStream in a single operation. The flush method transfers any buffered data to the underlying stream and clears the buffer, while the close method flushes the buffer and then closes the wrapped stream.

Constructors typically used are BufferedOutputStream(OutputStream out) and BufferedOutputStream(OutputStream out, int size). The former uses a default buffer size (commonly 8192 bytes), while the latter allows specifying the buffer size. The buffer size should be chosen based on the expected write patterns and available memory.

Usage patterns include wrapping a FileOutputStream or a network stream to improve efficiency. For example, one might create a buffered stream around a file output stream and use try-with-resources to ensure proper closure. BufferedOutputStream is not inherently thread-safe; if used from multiple threads, external synchronization or separate streams per thread should be employed.

Related classes include FilterOutputStream (from which BufferedOutputStream inherits) and the broader java.io package. BufferedOutputStream is commonly used to optimize sequential writes, particularly when writing small chunks of data repeatedly.