Contains.java
/*
** Module : Contains.java
** Abstract : simplified implementation of the CONTAINS operator for lightweight use
**
** Copyright (c) 2018-2025, Golden Code Development Corporation.
**
** -#- -I- --Date-- --------------------------------Description----------------------------------
** 001 ECF 20180830 Created initial version.
** 002 ECF 20190309 Silently tolerate, but do not match on an empty string expression.
** 003 CA 20190821 Allow a specified set of characters to be used as word delimiters.
** 004 IAS 20201113 Re-worked using Reverse Polish Notation and LogicalExpressionConverter
** 005 GBB 20230512 Logging methods replaced by CentralLogger/ConversionStatus.
** 006 SP 20240612 Improved word split logic using regex Pattern.split().
** 007 SP 20241111 Avoid duplicate call to word.toUpperCase(). Javadoc fixes.
** 008 SP 20250311 Performance improvements for words() method.
*/
/*
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** published by the Free Software Foundation, either version 3 of the
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** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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**
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**
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*/
package com.goldencode.p2j.persist.pl;
import java.util.*;
import java.util.regex.*;
import java.util.concurrent.*;
import com.goldencode.p2j.util.*;
import com.goldencode.p2j.util.LogicalExpressionConverter.*;
import com.goldencode.p2j.util.logging.*;
/**
* Simplified implementation of the CONTAINS operator for lightweight use. Evaluates a data
* string against an expression which uses the CONTAINS operator's right operand expression
* syntax:
* <pre>
* Construct Precedence Description
* -----------------------------------------------------------------------------------------------
* (...) 3 Parentheses to change precedence of a subexpression operation.
* word 3 A full word to match
* prefix 3 A prefix of a word to match, followed by an asterisk (*), indicating
* a wildcard. The asterisk may only be at the end of the word.
* & 2 Logical AND operator.
* | or ! or ^ 1 Logical OR operator.
* </pre>
* <p>
* Subexpressions may be nested arbitrarily deeply. An empty expression is silently tolerated,
* but does not produce a match.
* <p>
* Match tests are performed by constructing an instance of this class and invoking the
* {@link #evaluate(String)} method against it. The match expression is parsed into an AST, and
* the AST is walked to evaluate the expression for the data passed to the {@code evaluate}
* method.
* <p>
* In practice, a separate instance of this class is constructed for every data match. This
* design is necessary because this class will be used from within a database user defined
* function, which is driven statelessly by a database in connection with a query. Thus, we have
* no control over when or how often the feature is used. To amortize the expense of parsing the
* match expression, a cache is used to permit re-use of previously parsed expression ASTs.
* Since ASTs may be shared across threads, they are treated as immutable.
* <p>
* NOTE: since this implementation does not leverage true word break tables and joins, it is not
* suitable for use with large tables nor tables with very large data entries. Since it is used
* with a UDF that will be opaque to a database's query planner, this implementation often will
* result in full table scans, unless other components of a query allow the query planner to
* make a more efficient plan. In addition, each data entry will be scanned for each invocation.
* Thus, this implementation is suitable for lightweight uses where the primary objective is to
* properly honor the syntax of the CONTAINS operator's match expression.
* <p>
* TODO: properly handle match expression characters Progress simply ignores when matching. Do
* these have to do with word break rules?
* <p>
* TODO: at this time, word break rules are not used to delimit words.
*
* @author ecf
*/
public final class Contains
{
/** Logger. */
private static final CentralLogger LOG = CentralLogger.get(Contains.class);
/** Cache of match expressions to parsed ASTs. */
private static final Map<String, List<EToken>> cache = new ConcurrentHashMap<>();
/** Cache for a set of characters considered as delimiters. */
private static final BitSet DELIMITERS = new BitSet(128);
/** Cache for a set of characters not considered as delimiters. */
private static final BitSet NOT_DELIMITERS = new BitSet(128);
/** Regular expression pattern used to identify delimiters for splitting words. */
private final Pattern delimiterPattern;
/** Should matches be checked case-sensitively? */
private final boolean caseSensitive;
/** Parsed match expression RPN, used to evaluate matches with string data */
private final List<EToken> exprRPN;
/**
* Constructor.
*
* @param expr
* Match expression which uses CONTAINS operator syntax.
* @param codePage
* Character encoding used.
*
* @throws ErrorConditionException
* if there is an I/O error parsing the match expression.
*/
public Contains(String expr, String codePage)
{
this(expr, false, codePage);
}
/**
* Constructor.
*
* @param expr
* Match expression which uses CONTAINS operator syntax.
* @param caseSensitive
* {@code true} to perform word match comparisons case-sensitively, {@code false} to
* ignore case.
* @param codePage
* Character encoding used.
*
* @throws ErrorConditionException
* if there is a syntax or an I/O error parsing the match expression.
*/
public Contains(String expr, boolean caseSensitive, String codePage)
{
this.delimiterPattern = I18nOps.getDelimiterPattern(codePage);
this.caseSensitive = caseSensitive;
this.exprRPN = expr == null ? Collections.emptyList() : cache.computeIfAbsent(
expr,
exp -> new LogicalExpressionConverter(exp, caseSensitive, codePage).toRPN(false)
);
}
/**
* Given a data string, evaluate the expression to determine whether the data matches. Only
* read as many words from the data as are needed to determine a result.
*
* @param data
* A data string with words delimited by this object's specified delimiter.
*
* @return {@code true} if the words in the data match this object's expression, else
* {@code false}.
*
* @throws ErrorConditionException
* if there is an I/O error reading words from the data stream.
*/
public boolean evaluate(String data)
{
if (exprRPN.isEmpty())
{
return false;
}
Deque<Boolean> stack = new ArrayDeque<>();
Set<String> words = words(data, !caseSensitive);
try
{
for (EToken token: exprRPN)
{
if (token instanceof Term)
{
stack.push(((Term)token).evaluate(words));
}
else if (token instanceof Op)
{
switch ((Op)token)
{
case NOT:
stack.push(!stack.pop());
break;
case AND:
stack.push(stack.pop() & stack.pop());
break;
case OR:
stack.push(stack.pop() | stack.pop());
break;
}
}
}
return stack.pop();
}
catch (EmptyStackException e)
{
throw new ErrorConditionException(e);
}
}
/**
* Split a string to a set of words.
*
* @param data
* A data string with words delimited by this object's specified delimiter.
* @param forCaseInsensitive
* Return words which are unique in case-insensitive sense.
*
* @return words contained in a string
*/
public Set<String> words(String data, boolean forCaseInsensitive)
{
Map<String, String> words = new HashMap<>();
if (data == null || data.trim().isEmpty())
{
return Collections.emptySet();
}
int length = data.length();
int start = 0;
for (int i = 0; i <= length; i++)
{
if (isDelimiter(data, i, length))
{
if (i > start)
{
String word = data.substring(start, i);
if (!caseSensitive)
{
word = word.toUpperCase();
}
String key = forCaseInsensitive && caseSensitive ? word.toUpperCase() : word;
words.putIfAbsent(key, word);
}
start = i + 1;
}
}
return new HashSet<>(words.values());
}
/**
* Determines whether the character at the given index in the string should be treated as a delimiter.
*
* @param data
* The input string to examine.
* @param index
* The current index in the string being checked.
* @param length
* The total length of the input string.
*
* @return {@code true} if the character at the given index is considered a delimiter,
* or if the index represents end of string; {@code false} otherwise.
*/
private boolean isDelimiter(String data, int index, int length)
{
if (index == length)
{
// end of string, treat as delimiter
return true;
}
char c = data.charAt(index);
if (c == '-' || c == '.' || c == ',')
{
if (index + 1 < length)
{
char nextChar = data.charAt(index + 1);
return nextChar < '0' || nextChar > '9';
}
return true;
}
if (NOT_DELIMITERS.get(c))
{
return false;
}
if (DELIMITERS.get(c))
{
return true;
}
boolean matches = delimiterPattern.matcher(String.valueOf(c)).matches();
if (matches)
{
DELIMITERS.set(c);
}
else
{
NOT_DELIMITERS.set(c);
}
return matches;
}
/**
* Simple test harness for command line testing.
*
* @param args
* Expects the first argument to be the match expression and the second to be the
* data to be matched.
*/
public static void main(String[] args)
{
try
{
String expr = args[0];
// boolean caseSens = args.length > 2 && !"0".equals(args[2]);
Contains contains = new Contains(expr, true, null);
System.out.println(contains.exprRPN);
for (int i = 1; i < args.length; i++)
{
String data = args[i];
boolean match = contains.evaluate(data);
System.out.printf("[%s]: %s\n", data, match);
}
}
catch (Exception e)
{
LOG.severe("", e);
}
}
}