RFR: 8243469: Lazily encode name in ZipFile.getEntryPos

[Claes Redestad]

Hi,

current implementation of ZipFile.getEntryPos takes the encoded byte[]
of the String we're looking up. Which means when looking up entries
across multiple jar files, we allocate the byte[] over and over for each
jar file searched.

If we instead refactor the internal hash table to use a normalized
String-based hash value, we can almost always avoid both the repeated
encoding and (most of) the hash calculation when the entry is not found
in the jar/zip.

This realizes a significant startup improvement on applications with
several or many jar files. A rather typical case. For example I see a
25% speedup of ZipEnty.getEntry calls on a Spring PetClinic, which
reduces total startup time by ~120ms, or ~2.5% of total, on my setup. At
the same time remaining neutral on single-jar apps.

Webrev: http://cr.openjdk.java.net/~redestad/8243469/open.00/
Bug:    https://bugs.openjdk.java.net/browse/JDK-8243469

Testing: tier1-2

Thanks!

/Claes