<!DOCTYPE qhelp PUBLIC

"-//Semmle//qhelp//EN"

"qhelp.dtd">

<qhelp>

<overview>

<p>

The classes <code>java.io.OutputStream</code>

and <code>java.io.FilterOutputStream</code> only require

subclasses to implement the method <code>write(byte b)</code>.

Typically, uses of <code>OutputStream</code>s will not write

single bytes, but an array via the <code>write(byte[] b, int off,

int len)</code> method. The default implementation of this method,

which you are not required to override,

calls <code>write(byte b)</code> for each byte in the array. If

this method involves I/O, such as accessing the network or disk,

this is likely to incur significant overhead.

</p>

</overview>

<recommendation>

<p>

Always provide an implementation of the <code>write(byte[] b, int

off, int len)</code> method.

</p>

</recommendation>

<example>

<p>

The following example shows a subclass

of <code>OutputStream</code> that simply wraps

a <code>DigestOutputStream</code> to confirm that the data it

writes to a file has the expected MD5 hash. Without an

implementation of <code>write(byte[] b, int off, int len)</code>

this will be very slow, because it makes a call

to <code>DigestOutputStream.write(byte b)</code>

and <code>FileOutputStream.write(byte b)</code> for each byte

written.

</p>

<sample src="InefficientOutputStreamBad.java" />

<p>

The example can be updated to use a more efficient method. In this

case, calls to <code>write(byte[] b, int off, int len)</code> are

simply forwarded to <code>DigestOutputStream.write(byte[] b, int

off, int len)</code>.

</p>

<sample src="InefficientOutputStreamGood.java" />

</example>

<references>

<li>

Java API Specification:

<a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/io/OutputStream.html#write(byte[],int,int)">OutputStream.write(byte[] b, int off, int len)</a>,

<a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/io/FilterOutputStream.html#write(byte[],int,int)">FilterOutputStream.write(byte[] b, int off, int len)</a>.

</li>

</references>

</qhelp>