Constructing java classes from a string containing the class name

[Dave Snowdon]

I need the ability to create one of a number of java classes which have constructors taking a known list of parameters. There are a large enough number of classes that having a set of conditions testing for each class name would be unmanageable. The classes are from a third-party jar file so I cannot modify them either.

The trouble is that new is special form and does not evaluate it's first parameter so if I write an expression like

(new (Class/forName klassname)  param1 param2) it fails because (Class/forName klassname)  is treated as the class name rather than being evaluated first.

The closest I've got so far is to write the following macro

(defmacro make-proxy

  "Build proxy class from name and map"

  [klassname params] (list 'new (Class/forName klassname) '(:hostname params) '(:port params)))

This gets me some of the way, I can now write

(make-proxy "com.example.foo" {:hostname "127.0.0.1 :port 9559})

but it only works for constant strings since the first parameter is evaluated when the macro is expanded.

Can anyone suggest a solution?

thanks

Dave

[dennis zhuang]

You can get the constructor and instance it:

(-> klassname (Class/forName) (.getDeclaredConstructors String int) (.newInstance host port))

2013/3/17 Dave Snowdon <dave.s...@gmail.com>

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[dennis zhuang]

Sorry,it's getDeclaredConstructor:

(-> klassname (Class/forName) (. getDeclaredConstructor String int) (.newInstance host port))

2013/3/17 dennis zhuang <killm...@gmail.com>

[Dave Snowdon]

Great! Many thanks.

Dave