Use PermGen space or roll-my-own intern method?

Posted by Adamski on Stack Overflow See other posts from Stack Overflow or by Adamski
Published on 2010-05-19T11:29:21Z Indexed on 2010/05/19 11:40 UTC
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I am writing a Codec to process messages sent over TCP using a bespoke wire protocol. During the decode process I create a number of Strings, BigDecimals and dates. The client-server access patterns mean that it is common for the client to issue a request and then decode thousands of response messages, which results in a large number of duplicate Strings, BigDecimals, etc.

Therefore I have created an InternPool<T> class allowing me to intern each class of object. Internally, the pool uses a WeakHashMap<T, WeakReferemce<T>>. For example:

InternPool<BigDecimal> pool = new InternPool<BigDecimal>();

...

// Read BigDecimal from in buffer and then intern.
BigDecimal quantity = pool.intern(readBigDecimal(in));

My question: I am using InternPool for BigDecimal but should I consider also using it for String instead of String's intern() method, which I believe uses PermGen space? What is the advantage of using PermGen space?

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