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POPerforming multiple string replacements with metacharacter regex patterns
 

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  1. POPerforming multiple string replacements with metacharacter regex patterns
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    <p>I am trying to perform multiple string replacements using Java's Pattern and Matcher, where the regex pattern may include metacharacters (e.g. \b, (), etc.). For example, for the input string <code>fit i am</code>, I would like to apply the replacements: </p> <pre><code>\bi\b --&gt; EYE i --&gt; I </code></pre> <p>I then followed the coding pattern from two questions (<a href="https://stackoverflow.com/questions/1326682/java-replacing-multiple-different-substring-in-a-string-at-once-or-in-the-most">Java Replacing multiple different substring in a string at once</a>, <a href="https://stackoverflow.com/questions/7532042/replacing-multiple-substrings-in-java-when-replacement-text-overlaps-search-text">Replacing multiple substrings in Java when replacement text overlaps search text</a>). In both, they create an or'ed search pattern (e.g foo|bar) and a Map of (pattern, replacement), and inside the <code>matcher.find()</code> loop, they look up and apply the replacement. </p> <p>The problem I am having is that the <code>matcher.group()</code> function does not contain information on matching metacharacters, so I cannot distinguish between <code>i</code> and <code>\bi\b</code>. Please see the code below. What can I do to fix the problem?</p> <pre><code>import java.util.regex.Matcher; import java.util.regex.Pattern; import java.util.*; public class ReplacementExample { public static void main(String argv[]) { Map&lt;String, String&gt; replacements = new HashMap&lt;String, String&gt;(); replacements.put("\\bi\\b", "EYE"); replacements.put("i", "I"); String input = "fit i am"; String result = doit(input, replacements); System.out.printf("%s\n", result); } public static String doit(String input, Map&lt;String, String&gt; replacements) { String patternString = join(replacements.keySet(), "|"); Pattern pattern = Pattern.compile(patternString); Matcher matcher = pattern.matcher(input); StringBuffer resultStringBuffer = new StringBuffer(); while (matcher.find()) { System.out.printf("match found: %s at start: %d, end: %d\n", matcher.group(), matcher.start(), matcher.end()); String matchedPattern = matcher.group(); String replaceWith = replacements.get(matchedPattern); // Do the replacement here. matcher.appendReplacement(resultStringBuffer, replaceWith); } matcher.appendTail(resultStringBuffer); return resultStringBuffer.toString(); } private static String join(Set&lt;String&gt; set, String delimiter) { StringBuilder sb = new StringBuilder(); int numElements = set.size(); int i = 0; for (String s : set) { sb.append(Pattern.quote(s)); if (i++ &lt; numElements-1) { sb.append(delimiter); } } return sb.toString(); } } </code></pre> <p>This prints out:</p> <pre><code>match found: i at start: 1, end: 2 match found: i at start: 4, end: 5 fIt I am </code></pre> <p>Ideally, it should be <code>fIt EYE am</code>.</p>
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    1. COis performance enough of a problem that you can't just loop through the replacements?
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    2. COThe replacements may overlap with each other. The second linked StackOverflow question I provided addresses this ("Replacing multiple substrings in Java when replacement text overlaps search text"), so I used its solution.
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    3. COIn that case you may have to loop through and use dummy characters. (Replace \\wi\\w with $ then replace \\bi\\b with EYE then replace $ with I)
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