Getting the name of a method parameter

Question

In Java 6 , imagine that 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 passed to slice2 or any other parameter, the important bit here is that I want to get the value by the parameter name.

I know how to get a list of parameter types using getParameterTypes or getGenericParameterTypes .

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

Answer 1

Parameter names are available if you told the compiler to enable them (compile with debugging information). Spring has a ParameterNameDiscoverer to help you get the names. the default implementation uses asm ClassReader to do therefore.

With javac you must include the -g argument to enable debugging information. With Eclipse, I think it is by default; it can be configured using the settings: Java → Compiler and then enable "Save information about the method parameters (can be used with reflection)" (see also this answer ).

Some structures use this. For example, spring -mvc has @RequestParam , which by default has a parameter name if it is resolvable. It also supports explicit naming - @RequestParam("foo") in the absence of debugging information.

Answer 2

I found another solution after he answered this question. Paranamer Solution.

Example:

  Method method = Foo.class.getMethod(...); Paranamer paranamer = new CachingParanamer(); String[] parameterNames = paranamer.lookupParameterNames(method) // throws ParameterNamesNotFoundException if not found // or ... parameterNames = paranamer.lookupParameterNames(method, false) // will return null if not found 

Answer 3

It's impossible. Class files do not contain argument names, as you can see with IDE completion when the source is unavailable.

Therefore, the reflection API cannot provide parameter names.

Answer 4

In parameter names, Java is not accessible through reflection.

Answer 5

In addition to this, the answer is: “Parameter names are available if you told the compiler to include them”

If you use Eclipse, go to the project -> properties -> Java compiler -> check "Save information about method parameters (can be used with reflection)

Answer 6

You can simply assign a parameter value to another value

 Bread slice2; public void makeSandwich(Bread slice1, Bread slice2, List<Filling> fillings, boolean mustard) { this.slice2 = slice2; System.out.println(this.slice2.getSomething()); } 

Answer 7

Do you have a method code? You could annotate the parameters and pass the names as arguments to @Param("slice1") . You can later get the annotation and extract the parameter name from it.