Java - Explicit Casting of a Component to a Specific Interface

Java - Explicit Casting of a Component to a Specific Interface

This guide demonstrates how to explicitly cast a component to a specific interface in Lucee.

Implicit Casting

Lucee supports implicit casting by passing a component to a method where the method argument is of a specific type. For example:

cs = new component implementsJava="java.lang.CharSequence" {
  variables.text = "en_us";

public function onMissingMethod(missingMethodName, missingMethodArguments) {
if ("toString" == missingMethodName) return variables.text;
else throw "method #missingMethodName# not supported yet!";
}
};
// setLocale expects a String as argument PageContext.setLocale(java.lang.String)
getPageContext().setLocale(cs);

In this example, Lucee implicitly finds a matching method and converts the component to a class implementing the java.lang.CharSequence interface.

Explicit Casting

Sometimes, implicit casting can be problematic if Lucee cannot make the correct fit, or if a method is overloaded and you need to specify which method to use.

For instance, the PageContext class has two setLocale methods:

  • setLocale(java.lang.String): void
  • setLocale(java.util.Locale): void

To ensure the correct method is called, it is better to use explicit casting. Here's the modified example:

cs = new component implementsJava="java.lang.CharSequence" {
  variables.text = "en_us";

public function onMissingMethod(missingMethodName, missingMethodArguments) {
if ("toString" == missingMethodName) return variables.text;
else throw "method #missingMethodName# not supported yet!";
}
};
// Explicitly cast to java.lang.CharSequence
obj = JavaCast("java.lang.CharSequence", cs);
dump(obj);


// Use the CharSequence object
getPageContext().setLocale(obj);

In this example, we first cast the component to java.lang.CharSequence (the base interface for String), then call setLocale. With this explicit casting, Lucee is able to link the correct method.

See also