How can you retrieve Java method parameter names using reflection in Java 8?

Obtaining Java Method Parameter Names via Reflection

In Java, method parameter names are not accessible by default, leading to the question of whether it's possible to retrieve them using reflection.

Java 8 Solution with Parameter Reflection

Prior to Java 8, it was not feasible to access parameter names via reflection. However, with the introduction of parameter reflection in Java 8, it became possible. The following code demonstrates how to obtain parameter names:

import java.lang.reflect.Method;
import java.lang.reflect.Parameter;

public class ParameterReflection {

    public static void main(String[] args) {
        Class<?> clazz = Whatever.class;

        Method[] methods = clazz.getDeclaredMethods();
        for (Method method : methods) {
            if (method.getName().equals("aMethod")) {
                Parameter[] parameters = method.getParameters();
                for (Parameter parameter : parameters) {
                    System.out.println(parameter.getName());
                }
                break;
            }
        }
    }
}

In this example, the Whatever class contains a aMethod method with an integer parameter named aParam. By using the method.getParameters() method, you can retrieve an array of Parameter objects representing each parameter of the method, along with their names.

Compiler Flag (-parameters)

It's important to note that Java 8 requires enabling the compiler flag -parameters to make parameter names accessible at runtime. In Maven projects, this flag can be added to the configuration:

<compilerArgument>-parameters</compilerArgument>

Alternatively, in Java 8 versions of the compiler newer than 3.6.2, you can set parameters to true in :

<parameters>true</parameters>

Conclusion

With the introduction of parameter reflection in Java 8, obtaining method parameter names via reflection is now feasible. By using the Parameter class and the -parameters compiler flag, you can access parameter names at runtime.

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