A class to format message which contain named parameters like "send an email from {sender} to {recipient}".

Templating.java

package de.devsurf.echo.sync.utils;

import java.util.Collections;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Map.Entry;

import com.google.common.base.Preconditions;

/**
 * TODO
 * 	- add optional filling of missing parameter
 * 	- add optional failing on missing parameter
 * 	- add optional failing on brackets errors
 */
public class Templating {
	public static final String LEFT_DELIMITER = "${";
	public static final String RIGHT_DELIMITER = "}";

	private Map<String, String> replacements;
	private Map<Integer, String> parameters = new LinkedHashMap<>();

	public static String format(String message, Map<String, String> parameters) {
		Templating formatter = new Templating();
		formatter.replacements = parameters;
		return formatter.format(message);
	}

	private Templating() {
	};

	public String format(String message) {
		StringBuilder result = new StringBuilder(message.length());
		String pattern = analyze(message);
		int lastOffset = 0;

		for (Entry<Integer, String> entry : parameters.entrySet()) {
			int index = entry.getKey();
			result.append(pattern.substring(lastOffset, index));
			lastOffset = index;
			String key = entry.getValue();
			if (replacements.containsKey(key)) {
				String value = replacements.get(key);
				if (value != null) {
					result.append(value);
					continue;
				}
			}

			result.append(LEFT_DELIMITER).append(RIGHT_DELIMITER);
		}

		result.append(pattern.substring(lastOffset, pattern.length()));

		return result.toString();
	}

	public String analyze(String message) throws IllegalArgumentException {
		StringBuilder outputBuilder = new StringBuilder(message.length());
		int index = 0;
		for (int leftIndex = 0; leftIndex > -1;) {
			leftIndex = message.indexOf(LEFT_DELIMITER, index);
			int rightIndex;
			if (leftIndex >= 0) {
				rightIndex = message.indexOf(RIGHT_DELIMITER, leftIndex
						+ LEFT_DELIMITER.length());
				// sanity check
				int newLextIndex = message.indexOf(LEFT_DELIMITER, leftIndex
						+ LEFT_DELIMITER.length());
				Preconditions.checkArgument(rightIndex > 0,
						"Right Bracket is missing near position %s", leftIndex);
				Preconditions.checkArgument(rightIndex < newLextIndex
						|| newLextIndex == -1,
						"Right Bracket is missing near position %s", leftIndex);

				outputBuilder.append(message.substring(index, leftIndex));
				parameters.put(outputBuilder.length(), message.substring(
						leftIndex + LEFT_DELIMITER.length(), rightIndex));
				index = rightIndex + RIGHT_DELIMITER.length();
			}
		}

		outputBuilder.append(message.substring(index));

		return outputBuilder.toString();
	}

	public static void main(String[] args) {
		System.out.println(Templating.format(
				"send an email from ${sender} to ${recipient}",
				Collections.singletonMap("sender", "d@d.de")));
		try {
			System.out.println(Templating.format(
					"send an email from ${sender to ${recipient}",
					Collections.singletonMap("sender", "d@d.de")));
		} catch (Throwable e) {
			e.printStackTrace();
		}
		try {
			System.out.println(Templating.format(
					"send an email from ${sender} to ${recipient",
					Collections.singletonMap("sender", "d@d.de")));
		} catch (Throwable e) {
			e.printStackTrace();
		}
		System.out.println(Templating.format(
				"send an email from ${sender} to ${recipient}",
				Collections.singletonMap("bla", "d@d.de")));
		System.out.println(Templating.format(
				"A class to format message which contain named parameters like \"send an email from ${sender} to ${recipient}\".",
				Collections.singletonMap("sender", "d@d.de")));
		
	}
}