Also (c) (related to my "emeddable" note) - in an environment like
J2EE, where there are layers upon layers of explicit and implicit
containers between the VM and the application code, having a static
object storage buried in a framework is a bad practice - it prevents
the container layers from performing their functions of isolating
"contexts" for various users (whatever those contexts might be).
Andrus
On Sep 16, 2008, at 5:30 PM, Andrus Adamchik wrote:
> -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 cayenne/main/trunk/framework/cayenne-jdk1.5-unpublished/src/main/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 Modified: cayenne/main/trunk/framework/cayenne-jdk1.5-unpublished/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 URL: http://svn.apache.org/viewvc/cayenne/main/trunk/framework/cayenne-jdk1.5-unpublished/src/main/java/org/apache/cayenne/exp/Expression.java?rev=695898&r1=695897&r2=695898&view=diff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 --- cayenne/main/trunk/framework/cayenne-jdk1.5-unpublished/src/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 +++ cayenne/main/trunk/framework/cayenne-jdk1.5-unpublished/src/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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