regex - How to implement "supplant" in java -

"supplant() variable substitution on string. scans through string looking expressions enclosed in { } braces. if expression found, use key on object, , if key has string value or number value, substituted bracket expression , repeats."

more specifically, trying somethink like:

public static string supplant(charsequence message, map<string,object> params) 

i trying use regex \{([\w]*)\} capture variables , lookup map , replace, couldn't write regex matches...

how implement supplant() in java?

what describe more commonly called templating. there many templating applications , libraries out there, if want quick-and-dirty solution, can implemented regexes.

in many regex flavors use built-in callback or callout mechanism, php's preg_replace_callback function, or perl's /e , /ee modifiers. java doesn't have that, provides api let implement yourself. here's example:

import java.util.*; import java.util.regex.*;  public class test {   public static void main(string[] args) throws exception   {     string s = "lorem ipsum {foo} impedit civibus ei pri, legimus\n" +         "antiopam no {marco}, quo id everti forensibus maiestatis.";     map<string,object> p = new hashmap<string,object>()     {{       put("foo", "bar");       put("marco", "polo!");     }};     system.out.printf("%s%n%n%s%n", s, supplant(s, p));   }    public static charsequence supplant(charsequence message, map<string,object> params)   {     matcher m = pattern.compile("\\{(\\w+)\\}").matcher(message);     stringbuffer sb = new stringbuffer();     while (m.find())     {       m.appendreplacement(sb, "");       string key = m.group(1);       sb.append(params.get(key).tostring());     }     m.appendtail(sb);     return sb.tostring();   } } 

obviously code leaves out essential components (principally exception handling), demonstrates main points of technique:

1. capture content within braces using parentheses, access calling group(1) on matcher.
2. use appendreplacement(sb, "") append whatever text appeared between previous match (if there one) , current one.
3. look replacement , append using stringbuffer's append() method. (you could combine steps 2 , 3 passing replacement string second argument appendreplacement(), have watch out dollar signs , backslashes in string, receive special treatment. way simpler.)
4. use appendtail(sb) append whatever's left after last match.

several people have published helper classes let accomplish sort of task without having write boilerplate code. favorite elliott hughes's rewriter.