Struts 2 Dynamic Method Invocation

java1I’ve been doing plenty of Sruts2 work lately, and have used wildcard method mapping quite a bit. Wildcard method mapping is one way Struts2 allows a developer to flexibly call methods other than execute() on your action classes. Recently, however, I had reason to check out another flexible method calling feature in Struts – Dynamic Method Invocation.

The struts documentation says this about Dynamic Method Invocation:

Dynamic Method Invocation (DMI) will use the string following a “!” character in an action name as the name of a method to invoke (instead of execute). A reference to “Category!create.action”, says to use the “Category” action mapping, but call the create method instead.

So basically, instead of changing your struts.xml file to support flexible method calling on your actions, you could simply target specific action methods my using the actionname!methodname.action format supported by DMI.

Of course, there are potential security risks with this, and Struts 2.3 adds the ability to restrict the methods that you can use DMI upon. Also, the Apache docs state clearly that wildcard method mapping is preferred over DMI.

If you have a Struts2 application that faces the internet, please consider disabling DMI, or at least providing a set of allowable DMI methods. Be aware that you have to explicitly disable by setting a constant in your struts.xml (or file. Since DMI enabled by default, your application could be at risk if you don’t manage how users access your action methods.  

For example, adding this line to your struts.xml will completely disable DMI:

Given that our usage involved an internal application, we found that DMI helped us solve a problem quickly and cleanly, and its use in our application outweighed the potential for abuse.

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