Getting the name of a method parameter

java reflection runtime java-6
Tiago Veloso picture Tiago Veloso · Jul 20, 2011 · Viewed 30.4k times · Source

In Java 6, imagine I have the following method signature:

public void makeSandwich(Bread slice1, Bread slice2, List<Filling> fillings, boolean mustard)

I would like to know, at runtime, the value that was passed on to slice2 or any other parameter, the important bit here is that I want to get the value by parameter name.

I know how to get the list of parameter types with getParameterTypes or getGenericParameterTypes.

Ideally I would like to get a list of parameter names instead of types. Is there a way to do so?

Answer

Bozho picture Bozho · Jul 20, 2011

Parameter names are available if you have told the compiler to include them (compile with debug information). Spring has ParameterNameDiscoverer which can help you obtain the names. The default implementation uses asm ClassReader to do so.

With javac you should include the -g argument to include debug information. With Eclipse I think it is there by default; it can be configured using the preferences: Java -> Compiler and then enable "Store information about method parameters (usable via reflection)" (see also this answer).

Some frameworks use this. For example spring-mvc has @RequestParam which defaults to the param name, if resolvable. It also supports explicit naming - @RequestParam("foo") in case no debug information is provided.

Related questions

Detecting the present annotations within the given object passed into a constructor

My question in short: how do I detect if a java annotation is present (and in the right place) for a given user class/object. Details of the "problem" Lets say I have two java classes: public class Line { private …

Read More
Java reflection: How do I override or generate methods at runtime?

It is possible in plain Java to override a method of a class programmatically at runtime (or even create a new method)? I want to be able to do this even if I don't know the classes at compile time. …

Read More
about java: get `String[].class` from `String.class`, what if `String.class` is a "runtime type"?

Here is a variable Class<?> cls, now I want to get another Array Class Object which component type is cls. For example, if cls=String.class , I want to get String[].class; if cls=int.class, I want …

Read More