Expression Language

[Kunal Lakhani]

Hello

I have a following piece of code in my Servlet class

Map music = new HashMap();
		music.put("Bryan", "18 till i die");
		music.put("Taylor S", "Back to December");
		music.put("Akon", "Lonely");
		req.setAttribute("musics", music);
		req.setAttribute("Genre", "Bryan");

And here is my jsp

Music is ${musics[Genre]} 

Why the above mentioned jsp runs successfully, and not this one?

Music is ${musics["Genre"]} 

Similarly,

Music is ${musics["Akon"]}

works

but

Music is ${musics[Akon]}

doesn't. Why?

[Rob Spoor]

Because it will try to find the value of an attribute (page context first, then request, then session, then servlet context) called Akon, and use that value as the index / key.
That's why the first example works the other way around - the map doesn't have a key "Genre", but there is an attribute called "Genre" with a value that is a valid key.

[Kunal Lakhani]

That means, the variable in double quotes represents map key, and those without double quotes represents attribute. Am i right?

[Rob Spoor]

Yes. The main thing to remember - with the bracket notation, anything not in quotes is either a numeric literal (e.g. [0]), boolean literal (e.g. [true]), null or the name of an attribute.

[Kunal Lakhani]

Thanks a lot Rob

[Rob Spoor]

You're welcome.