String replacement in java, similar to a velocity template

Question

Is there any String replacement mechanism in Java, where I can pass objects with a text, and it replaces the string as it occurs.
For example, the text is :

Answer 1

My preferred way is String.format() because its a oneliner and doesn't require third party libraries:

String message = String.format("Hello! My name is %s, I'm %s.", name, age); 

I use this regularly, e.g. in exception messages like:

throw new Exception(String.format("Unable to login with email: %s", email));

Hint: You can put in as many variables as you like because format() uses Varargs

Answer 2

I threw together a small test implementation of this. The basic idea is to call format and pass in the format string, and a map of objects, and the names that they have locally.

The output of the following is:

My dog is named fido, and Jane Doe owns him.

public class StringFormatter {

    private static final String fieldStart = "\\$\\{";
    private static final String fieldEnd = "\\}";

    private static final String regex = fieldStart + "([^}]+)" + fieldEnd;
    private static final Pattern pattern = Pattern.compile(regex);

    public static String format(String format, Map<String, Object> objects) {
        Matcher m = pattern.matcher(format);
        String result = format;
        while (m.find()) {
            String[] found = m.group(1).split("\\.");
            Object o = objects.get(found[0]);
            Field f = o.getClass().getField(found[1]);
            String newVal = f.get(o).toString();
            result = result.replaceFirst(regex, newVal);
        }
        return result;
    }

    static class Dog {
        public String name;
        public String owner;
        public String gender;
    }

    public static void main(String[] args) {
        Dog d = new Dog();
        d.name = "fido";
        d.owner = "Jane Doe";
        d.gender = "him";
        Map<String, Object> map = new HashMap<String, Object>();
        map.put("d", d);
        System.out.println(
           StringFormatter.format(
                "My dog is named ${d.name}, and ${d.owner} owns ${d.gender}.", 
                map));
    }
}

Note: This doesn't compile due to unhandled exceptions. But it makes the code much easier to read.

Also, I don't like that you have to construct the map yourself in the code, but I don't know how to get the names of the local variables programatically. The best way to do it, is to remember to put the object in the map as soon as you create it.

The following example produces the results that you want from your example:

public static void main(String[] args) {
    Map<String, Object> map = new HashMap<String, Object>();
    Site site = new Site();
    map.put("site", site);
    site.name = "StackOverflow.com";
    User user = new User();
    map.put("user", user);
    user.name = "jjnguy";
    System.out.println(
         format("Hello ${user.name},\n\tWelcome to ${site.name}. ", map));
}

_{I should also mention that I have no idea what Velocity is, so I hope this answer is relevant.}