Simple string templates for java. The template can be in the code or in an external file, and any type of delimiters may be used for the variables. The data is provided in a HashMap.

StringTemplate.java

import java.io.IOException;
import java.lang.StringBuilder;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.HashMap;

public class StringTemplate 
{
  public static String templateReplace (String templateStr, String varStart, String varEnd, HashMap <String, String> paramValues) 
  {
    StringBuilder resultBuilder = new StringBuilder ();

    int paramLocation = 0;
    int paramStart, paramEnd;

    for (;;)
    {
      paramStart = templateStr.indexOf (varStart, paramLocation);   // Look for the start of a variable
      if (paramStart == -1)                                         // Not found. Copy remaining data until template end and quit
      {
        resultBuilder.append (templateStr.substring (paramLocation, templateStr.length ()));
        break;
      }
      paramEnd = templateStr.indexOf (varEnd, paramStart);                                // Look for the end of the variable
      String varName = templateStr.substring (paramStart + varStart.length (), paramEnd); // Extract variable name
      resultBuilder.append (templateStr.substring (paramLocation, paramStart));           // Add text preceding the variable
      resultBuilder.append (paramValues.get (varName));                                   // Replace variable it's value from the map
      paramLocation = paramEnd + varEnd.length ();                                        // Set the current pointer location
    }

    return resultBuilder.toString ();
  }

  public static String readFile (String path, Charset encoding) 
    throws IOException 
  {
    byte[] allBytes = Files.readAllBytes (Paths.get (path));
    return new String (allBytes, encoding);
  }

  // Just for testing
  public static void main (String[] args) throws IOException
  {
    // This is the data
    HashMap <String, String> map = new HashMap <String, String> ();
    map.put ("site", "Canada");
    map.put ("user", "Dude");
    map.put ("summary", "my title");
    map.put ("description", "this is a description");
    map.put ("assignee", "skanga");

    // Try a template with variables in %(varName) format
    System.out.println (templateReplace ("Hello %(user),\n\tWelcome to %(site).", "%(", ")", map));

    // Try another template with variables in <<<varName>>> format
    System.out.println (templateReplace ("Hello <<<assignee>>>,\n\tWelcome to <<<site>>>.", "<<<", ">>>", map));

    // Try a template which is stored in an external file (json in this case) with variables in ${varName} format like bash
    String fileContent = readFile ("template.json.txt", StandardCharsets.UTF_8);
    System.out.println (templateReplace (fileContent, "${", "}", map));
  }
}