Return the list of a method parameters names

gistfile1.java

/**
 * Based on Stackoverflow answer http://stackoverflow.com/a/2729907/395921
 * 
 * @author Paolo Di Tommaso
 *
 */
public class Names {

	
	/**
	 * Returns a list containing one parameter name for each argument accepted
	 * by the given constructor. If the class was compiled with debugging
	 * symbols, the parameter names will match those provided in the Java source
	 * code. Otherwise, a generic "arg" parameter name is generated ("arg0" for
	 * the first argument, "arg1" for the second...).
	 * 
	 * This method relies on the constructor's class loader to locate the
	 * bytecode resource that defined its class.
	 * 
	 * @param constructor
	 * @return 
	 * @throws IOException
	 */
	public static List<String> getParameterNames(Constructor<?> constructor) throws IOException {
	    Class<?> declaringClass = constructor.getDeclaringClass();
	    ClassLoader declaringClassLoader = declaringClass.getClassLoader();

	    Type declaringType = Type.getType(declaringClass);
	    String constructorDescriptor = Type.getConstructorDescriptor(constructor);
	    String url = declaringType.getInternalName() + ".class";

	    InputStream classFileInputStream = declaringClassLoader.getResourceAsStream(url);
	    if (classFileInputStream == null) {
	        throw new IllegalArgumentException("The constructor's class loader cannot find the bytecode that defined the constructor's class (URL: " + url + ")");
	    }

	    ClassNode classNode = getClassNode(classFileInputStream);

	    return getNames(classNode, "<init>", constructorDescriptor);
	}	
	
	public static List<String> getParameterNames(Method method) throws IOException {
	    Class<?> declaringClass = method.getDeclaringClass();
	    ClassLoader declaringClassLoader = declaringClass.getClassLoader();

	    Type declaringType = Type.getType(declaringClass);
	    String constructorDescriptor = Type.getMethodDescriptor(method);
	    String url = declaringType.getInternalName() + ".class";

	    InputStream classFileInputStream = declaringClassLoader.getResourceAsStream(url);
	    if (classFileInputStream == null) {
	        throw new IllegalArgumentException("The constructor's class loader cannot find the bytecode that defined the constructor's class (URL: " + url + ")");
	    }

	    ClassNode classNode = getClassNode(classFileInputStream);

	    return getNames(classNode, method.getName(), constructorDescriptor);
	}	

	
	private static List<String> getNames( ClassNode classNode, String methodName, String methodSignature ) {
		
	    @SuppressWarnings("unchecked")
	    List<MethodNode> methods = classNode.methods;
	    for (MethodNode method : methods) {
	        if (method.name.equals(methodName) && method.desc.equals(methodSignature)) {
	            Type[] argumentTypes = Type.getArgumentTypes(method.desc);
	            List<String> parameterNames = new ArrayList<String>(argumentTypes.length);

	            @SuppressWarnings("unchecked")
	            List<LocalVariableNode> localVariables = method.localVariables;
	            for (int i = 0; i < argumentTypes.length; i++) {
	                // The first local variable actually represents the "this" object
	                parameterNames.add(localVariables.get(i + 1).name);
	            }

	            return parameterNames;
	        }
	    }

	    return null;		
		
	}
	
	private static ClassNode getClassNode( InputStream classFileInputStream ) throws IOException {
		
		ClassNode classNode = null;
	    try {
	        classNode = new ClassNode();
	        ClassReader classReader = new ClassReader(classFileInputStream);
	        classReader.accept(classNode, 0);
	    } finally {
	        classFileInputStream.close();
	    }
	
	    return classNode;
	}
	
}