Question

I have a class with an attribute and getter method:

public Class MyClass
{
  private String myValue = "foo";

  public String getMyValue();
}

I would like to be able to use the value of foo in a formatted string as such:

String someString = "Your value is {myValue}."
String result = Formatter.format(someString, new MyClass());
// result is now "Your value is foo."

That is, I would like to have some function like .format above which takes a format string specifying properties on some object, and an instance with those properties, and formats the string accordingly.

Is it possible to do accomplish this feat in Java?

Answer 1

you could use JUEL for this. it’s an implementation of the Java Expression Language. the code is rather compact and looks like this:

ExpressionFactory factory = new ExpressionFactoryImpl();

// create a context and add a Person object to the context, this variable will be used
// in the property replacement
// objects of type Person have two fields: firstName and lastName

SimpleContext context = new SimpleContext();
Person person = new Person("John", "Doe");
context.setVariable("person", factory.createValueExpression(person, Person.class));

// create the expression

String expr = "My name is ${person.firstName} ${person.lastName}";
ValueExpression e = factory.createValueExpression(context, expr, String.class);

// evaluate the expression
System.out.println(e.getValue(context));

which prints ‘My name is John Doe’

note that it’s also possible to use an expression like this: ‘${firstName}’ instead of ‘${person.firstName}’, but then you will have to write and provide a custom resolver (javax.el.ELResolver) for the variable and property resolution