FULL PRODUCT VERSION :
java version "1.5.0_04"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0
Java HotSpot(TM) Client VM (build 1.5.0_04-b05, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows XP [Version 5.1.2600]

A DESCRIPTION OF THE PROBLEM :
java.net.URLEncoder consumes a lot of CPU and memory. The main problem for this is that java.net.URLEncoder is not lazy. It always creates instances regardless it will use them or not. This has a great impact on URL fragments with no unsafe characters.

In the beginning of the method block I can see the following statements:
ByteArrayOutputStream buf = new ByteArrayOutputStream(maxBytesPerChar);
OutputStreamWriter writer = new OutputStreamWriter(buf, enc);
Why create them so early in the method? The actual need for them is if there are any characters to encode. Therefore it is better to create these two instances where they are needed.

Another problem is the following statement:
 if (wroteUnencodedChar) { // Fix for 4407610
writer = new OutputStreamWriter(buf, enc);
Why can't we just reuse the first created instance?


Execution time in millis for 100 000 sequential encodings:

Encoding                 "Robert  ���� ���� ����"	"PLEASE_SUN_OPTIMIZE_THIS_CODE"
SUN Orginal                  13547	3547
SUN Optimized	578 	158
Apache commons	360 	453

Memory usage for 10 000 (Not 100 000) sequential encodings:

Implementation	"Robert ���� ���� ����"	"PLEASE_SUN_OPTIMIZE_THIS_CODE"
SUN Orginal	348 322Kb	87 442Kb
SUN Optimized	90329Kb	1040Kb
Apache commons	3844Kb	4564Kb


STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Just encode any sequence of characters in a benchmark:
long tStart = System.currentTimeMillis();
for (int idx = 0; idx < 100000; idx++) {
java.util.URLEncoder.encode("Robert Hoglund")
}
System.out.println("Time in millis : " + (System.currentTimeMillis() - tStart));



REPRODUCIBILITY :
This bug can be reproduced always.