JAX-RS Injection - RESTful Java with JAX-RS 2.0 - page 71

ParamConverters

Sometimes a parameter class cannot use the default mechanisms to convert from string val-
ues. Either the class has no String constructor or no valueOf( ) method, or the ones that ex-
ist won't work with your HTTP requests. For this scenario, JAX-RS 2.0 has provided an ad-
ditional component to help with parameter conversions.

package package javax . ws . rs . ext ;

public public interface interface ParamConverter ParamConverter < T > {

public public T fromString ( String value );

public

public String toString ( T value );

}

As you can see from the code, ParamConverter is a pretty simple interface. The
fromString() method takes a String and converts it to the desired Java type. The
toString() method does the opposite. Let's go back to our Color example. It pretty much
requires full uppercase for all Color parameters. Instead, let's write a ParamConverter that
allows a Color string to be any case.

public public class class ColorConverter ColorConverter implements implements ParamConverter < Color > {

public public Color fromString ( String value ) {

iif ( value . equalsIgnoreCase ( BLACK . toString ())) return

return BLACK ;

else else if ( value . equalsIgnoreCase ( BLUE . toString ())) return return BLUE ;

else else if ( value . equalsIgnoreCase ( RED . toString ())) return return RED ;

else else if ( value . equalsIgnoreCase ( WHITE . toString ())) return return WHITE ;

else else if ( value . equalsIgnoreCase ( SILVER . toString ())) return return SILVER ;

throw throw new new IllegalArgumentException ( "Invalid color: " + value );

}

public public String toString ( Color value ) { return return value . toString (); }

}

We're still not done yet. We also have to implement the ParamConverterProvider inter-
face.

package package javax . ws . rs . ext ;

public public interface interface ParamConverterProvider ParamConverterProvider {

public public < T > ParamConverter < T > getConverter ( Class < T > rawType ,

Type genericType ,
Annotation annotations []);

}