Java 8 ReflectionParanamer using compiled parameter names

[mjustin]

Now that this project is being upgraded to Java 8, it occurs to me that a Java 8 reflection-based paranamer could add some value, using the compiled parameters provided per the javac -parameters flag.

I can see a few scenarios where this would be useful, but I think the main one would be for code being run against classes that may or may not have been compiled using -parameters (e.g. third party libraries), and the developer wants to fall back to other strategies if the parameter names were not compiled. This could use an AdaptiveParanamer which wants to fall back to a different strategy if the parameters were not compiled. Note that this is the scenario I personally ran into that is causing me to take a look at Paranamer despite the Java 8 support for parameter names.

The implementation would be dirt simple:

package com.thoughtworks.paranamer;

import com.thoughtworks.paranamer.ParameterNamesNotFoundException;
import com.thoughtworks.paranamer.Paranamer;

import java.lang.reflect.AccessibleObject;
import java.lang.reflect.Executable;
import java.lang.reflect.Parameter;
import java.util.Arrays;

public class ReflectionParanamer implements Paranamer {
    @Override
    public String[] lookupParameterNames(AccessibleObject methodOrConstructor) {
        return lookupParameterNames(methodOrConstructor, true);
    }

    @Override
    public String[] lookupParameterNames(AccessibleObject methodOrConstructor, boolean throwExceptionIfMissing) {
        Executable executable = (Executable) methodOrConstructor;
        Parameter[] parameters = executable.getParameters();
        if (Arrays.stream(parameters).anyMatch(p -> !p.isNamePresent())) {
            if (throwExceptionIfMissing) {
                throw new ParameterNamesNotFoundException("Parameter names not present: " + methodOrConstructor);
            } else {
                return Paranamer.EMPTY_NAMES;
            }
        }

        return Arrays.stream(parameters).map(Parameter::getName).toArray(String[]::new);
    }
}

[paul-hammant]

Pull requests accepted :)