JSTL/JSP EL (Expression Language) in a non JSP (st

Question

Can anyone recommend a framework for templating/formatting messages in a standalone application along the lines of the JSP EL (Expression Language)?

I would expect to be able to instantiate a an object of some sort, give it a template along the lines of

Dear ${customer.firstName}. You order will be dispatched on ${order.estimatedDispatchDate}

provide it with a context which would include a value dictionary of parameter objects (in this case an object of type Customer with a name 'customer', say, and an object of type Order with a name 'order').

I know there are many template frameworks out there - many of which work outside the web application context, but I do not see this as a big heavyweight templating framework. Just a better version of the basic Message Format functionality Java already provides

For example, I can accomplish the above with java.text.MessageFormat by using a template (or a 'pattern' as they call it) such as

Dear {0}. You order will be dispatched on {1,date,EEE dd MMM yyyy}

and I can pass it an Object array, in my calling Java program

new Object[] { customer.getFirstName(), order.getEstimatedDispatchDate() };

However, in this usage, the code and the pattern are intimately linked. While I could put the pattern in a resource properties file, the code and the pattern need to know intimate details about each other. With an EL-like system, the contract between the code and the pattern would be at a much higher level (e.g. customer and order, rather then customer.firstName and order.estimatedDispatchDate), making it easier to change the structure, order and contents of the message without changing any code.

Answer 1

I would go for the Spring Expression language:

http://docs.spring.io/spring/docs/current/spring-framework-reference/html/expressions.html

A few examples which demonstrate the power (the first two are from the documentation):

int year = (Integer) parser.parseExpression("Birthdate.Year + 1900").getValue(context);

String city = (String) parser.parseExpression("placeOfBirth.City").getValue(context);

// weekday is a String, e.g. "Mon", time is an int, e.g. 1400 or 900
{"Thu", "Fri"}.contains(weekday) and time matches '\d{4}'

Expressions can also use object properties:

public class Data {
    private String name; // getter and setter omitted
}

Data data = new Data();
data.setName("John Doe");

ExpressionParser p = new SpelExpressionParser();
Expression e = p.parseExpression("name == 'John Doe'");
Boolean r = (Boolean) e.getValue(data); // will return true

e = p.parseExpression("Hello " + name + ", how are you ?");
String text = e.getValue(data, String.class); // text will be "Hello John Doe, how are you ?"

Answer 2

You can use Casper very similar to jsp and easy to use : Casper

Answer 3

StringTemplate is a more lightweight alternative to Velocity and Freemarker.

Answer 4

Freemarker would do exactly what you need. This is a template engine with a syntax very similar to JSP :

http://freemarker.org/