java regular expression find and replace

Question

I am trying to find environment variables in input and replace them with values.

The pattern of env variable is ${\\\\.}

Pattern myPatte         


        

Answer 1

This gives you 1sojods23:

String s = "${env1}sojods${env2}${env3}";
final Pattern myPattern = Pattern.compile("\\$\\{[^\\}]*\\}");
Matcher m = myPattern.matcher(s);
int i = 0;
while (m.find()) {
    s = m.replaceFirst(String.valueOf(++i));
    m = myPattern.matcher(s);
}

System.out.println(s);

and this works too:

final String re = "\\$\\{[^\\}]*\\}";
String s = "${env1}sojods${env2}${env3}";
int i = 0;
String t;
while (true) {
    t = s.replaceFirst(re, String.valueOf(++i));
    if (s.equals(t)) {
        break;
    } else {
        s = t;
    }
}

System.out.println(s);

Answer 2

You can use a StringBuffer in combination with the Matcher appendReplacement() method, but if the the pattern does not match, there is no point in creating the StringBuffer.

For example, here is a pattern that matches ${...}. Group 1 is the contents between the braces.

static Pattern rxTemplate = Pattern.compile("\\$\\{([^}\\s]+)\\}");

And here is sample function that uses that pattern.

private static String replaceTemplateString(String text) {
    StringBuffer sb = null;
    Matcher m = rxTemplate.matcher(text);
    while (m.find()) {
        String t = m.group(1);
        t = t.toUpperCase(); // LOOKUP YOUR REPLACEMENT HERE

        if (sb == null) {
            sb = new StringBuffer(text.length());
        }
        m.appendReplacement(sb, t);
    }
    if (sb == null) {
        return text;
    } else {
        m.appendTail(sb);
        return sb.toString();
    }
}

Answer 3

Use groups once it is matched ${env1} will be your first group and then you use regex to replace what is in each group.

Pattern p = Pattern.compile("(${\\.})");
Matcher m = p.matcher(line);
while (m.find())
  for (int j = 0; j <= m.groupCount(); j++)
    //here you do replacement - check on the net how to do it;)

Answer 4

Hopefully you would find this code useful:

    Pattern phone = Pattern.compile("\\$\\{env([0-9]+)\\}");
    String line ="${env1}sojods${env2}${env3}";
    Matcher action = phone.matcher(line);
    StringBuffer sb = new StringBuffer(line.length());
    while (action.find()) {
      String text = action.group(1);
      action.appendReplacement(sb, Matcher.quoteReplacement(text));
    }
    action.appendTail(sb);
    System.out.println(sb.toString());

The output is the expected: 1sojods23.

Answer 5

Strings in Java are immutable, which makes this somewhat tricky if you are talking about an arbitrary number of things you need to find and replace.

Specifically you need to define your replacements in a Map, use a StringBuilder (before Java 9, less performant StringBuffer should have been used) and the appendReplacements() and appendTail() methods from Matcher. The final result will be stored in your StringBuilder (or StringBuffer).

Map<String, String> replacements = new HashMap<String, String>() {{
    put("${env1}", "1");
    put("${env2}", "2");
    put("${env3}", "3");
}};

String line ="${env1}sojods${env2}${env3}";
String rx = "(\\$\\{[^}]+\\})";

StringBuilder sb = new StringBuilder(); //use StringBuffer before Java 9
Pattern p = Pattern.compile(rx);
Matcher m = p.matcher(line);

while (m.find())
{
    // Avoids throwing a NullPointerException in the case that you
    // Don't have a replacement defined in the map for the match
    String repString = replacements.get(m.group(1));
    if (repString != null)    
        m.appendReplacement(sb, repString);
}
m.appendTail(sb);

System.out.println(sb.toString());

Output:

1sojods23

Answer 6

I know this is old, I was myself looking for a, appendReplacement/appendTail example when I found it; However, the OP's question doesn't need those complicated multi-line solutions I saw here.

In this exact case, when the string to replace holds itself the value we want to replace with, then this could be done easily with replaceAll:

String line ="${env1}sojods${env2}${env3}";

System.out.println( line.replaceAll("\\$\\{env([0-9]+)\\}", "$1") );

// Output => 1sojods23

DEMO

When the replacement is random based on some conditions or logic on each match, then you can use appendReplacement/appendTail for example