-1. Unmanaged static caches are bad, especially in an embeddable
framework like Cayenne. This is (a) a potential memory leak and (b) a
potential synchronization nightmare (Expression is not immutable and
can be modified by the caller).
Andrus
On Sep 16, 2008, at 5:24 PM, mgentr..pache.org wrote:
> Author: mgentry
> Date: Tue Sep 16 07:24:11 2008
> New Revision: 695898
>
> URL: http://svn.apache.org/viewvc?rev=695898&view=rev
> Log:
> Updated Expression.fromString to cache the parsed expressions
> instead of re-parsing them every time.
>
> Modified:
> cayenne/main/trunk/framework/cayenne-jdk1.5-unpublished/src/main/
> java/org/apache/cayenne/exp/Expression.java
>
> Modified: cayenne/main/trunk/framework/cayenne-jdk1.5-unpublished/
> src/main/java/org/apache/cayenne/exp/Expression.java
> URL: http://svn.apache.org/viewvc/cayenne/main/trunk/framework/cayenne-jdk1.5-unpublished/src/main/java/org/apache/cayenne/exp/Expression.java?rev=695898&r1=695897&r2=695898&view=diff
> =
> =
> =
> =
> =
> =
> =
> =
> ======================================================================
> --- cayenne/main/trunk/framework/cayenne-jdk1.5-unpublished/src/main/
> java/org/apache/cayenne/exp/Expression.java (original)
> +++ cayenne/main/trunk/framework/cayenne-jdk1.5-unpublished/src/main/
> java/org/apache/cayenne/exp/Expression.java Tue Sep 16 07:24:11 2008
>.. -26,6 +26,7 @@
> import java.io.StringWriter;
> import java.util.Collection;
> import java.util.Collections;
> +import java.util.HashMap;
> import java.util.LinkedList;
> import java.util.List;
> import java.util.Map;
>.. -119,21 +120,36 @@
>
> protected int type;
>
> + private static Map<String, Expression> expressionCache =
> + Collections.synchronizedMap(new HashMap<String,
> Expression>(32));
> +
> /**
> * Parses string, converting it to Expression. If string does
> not represent a
> * semantically correct expression, an ExpressionException is
> thrown.
> *
> *..ince 1.1
> */
> - // TODO: cache expression strings, since this operation is
> pretty slow
> public static Expression fromString(String expressionString) {
> if (expressionString == null) {
> throw new NullPointerException("Null expression string.");
> }
>
> - Reader reader = new StringReader(expressionString);
> + // Retrieve, if possible, the expression from the cache.
> + Expression expression =
> expressionCache.get(expressionString);
> +
> + // If the expression was cached, return it immediately
> without parsing.
> + if (expression != null)
> + return expression;
> +
> + // Couldn't find expression, parse, cache, and return it.
> try {
> - return new ExpressionParser(reader).expression();
> + Reader reader = new StringReader(expressionString);
> +
> + expression = new ExpressionParser(reader).expression();
> +
> + expressionCache.put(expressionString, expression);
> +
> + return expression;
> }
> catch (ParseException ex) {
> throw new ExpressionException(ex.getMessage(), ex);
>
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