Is there any way to replace a regexp with modified content of capture group?
Example:
Pattern regex = Pattern.compile("(\\d{1,2})");
Matcher regexMatcher = regex.matcher(text);
resultString = regexMatcher.replaceAll("$1"); // *3 ??
And I'd like to replace all occurrence with $1 multiplied by 3.
edit:
Looks like, something's wrong :(
If I use
Pattern regex = Pattern.compile("(\\d{1,2})");
Matcher regexMatcher = regex.matcher("12 54 1 65");
try {
String resultString = regexMatcher.replaceAll(regexMatcher.group(1));
} catch (Exception e) {
e.printStackTrace();
}
It throws an IllegalStateException: No match found
But
Pattern regex = Pattern.compile("(\\d{1,2})");
Matcher regexMatcher = regex.matcher("12 54 1 65");
try {
String resultString = regexMatcher.replaceAll("$1");
} catch (Exception e) {
e.printStackTrace();
}
works fine, but I can't change the $1 :(
edit:
Now, it's working :)
Java 9 offers a Matcher.replaceAll()
that accepts a replacement function:
resultString = regexMatcher.replaceAll(
m -> String.valueOf(Integer.parseInt(m.group()) * 3));
earl's answer gives you the solution, but I thought I'd add what the problem is that's causing your IllegalStateException
. You're calling group(1)
without having first called a matching operation (such as find()
). This isn't needed if you're just using $1
since the replaceAll()
is the matching operation.
Source: java-implementation-of-rubys-gsub
Usage:
// Rewrite an ancient unit of length in SI units.
String result = new Rewriter("([0-9]+(\\.[0-9]+)?)[- ]?(inch(es)?)") {
public String replacement() {
float inches = Float.parseFloat(group(1));
return Float.toString(2.54f * inches) + " cm";
}
}.rewrite("a 17 inch display");
System.out.println(result);
// The "Searching and Replacing with Non-Constant Values Using a
// Regular Expression" example from the Java Almanac.
result = new Rewriter("([a-zA-Z]+[0-9]+)") {
public String replacement() {
return group(1).toUpperCase();
}
}.rewrite("ab12 cd efg34");
System.out.println(result);
Implementation (redesigned):
import static java.lang.String.format;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public abstract class Rewriter {
private Pattern pattern;
private Matcher matcher;
public Rewriter(String regularExpression) {
this.pattern = Pattern.compile(regularExpression);
}
public String group(int i) {
return matcher.group(i);
}
public abstract String replacement() throws Exception;
public String rewrite(CharSequence original) {
return rewrite(original, new StringBuffer(original.length())).toString();
}
public StringBuffer rewrite(CharSequence original, StringBuffer destination) {
try {
this.matcher = pattern.matcher(original);
while (matcher.find()) {
matcher.appendReplacement(destination, "");
destination.append(replacement());
}
matcher.appendTail(destination);
return destination;
} catch (Exception e) {
throw new RuntimeException("Cannot rewrite " + toString(), e);
}
}
@Override
public String toString() {
StringBuilder sb = new StringBuilder();
sb.append(pattern.pattern());
for (int i = 0; i <= matcher.groupCount(); i++)
sb.append(format("\n\t(%s) - %s", i, group(i)));
return sb.toString();
}
}
Source: Stackoverflow.com