How do I check if a Class is an instanceof another Class without initializing it?

Illustration: Cathy Wilcox

We had a recent security audit and a question was posed about how to check a Class without doing an instanceof. This turned out to be a great learning experience. There were a couple of issues that needed to be resolved, first we were loading a Class by passing in its name using something similar to the line below:

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1	Class<?> clazz = Class.forName("com.bluelotussoftware.example.assignable.SoilentGreen");

This will load the Class, but from here how do we check that it is an instanceof without instantiating it?
This can be solved by using isAssignableFrom(Class clazz) as shown below. In this case we are checking if SolientGreen is Green. Some of you will find the moral paradox of being "Green" with Soilent Green.

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public static boolean isGreen(Class clazz) {         return Green.class.isAssignableFrom(clazz);     }

The second issue is a more potential security problem. How do we load the Class without initializing it. If the Class has a static initializer, the code is executed when the class is loaded. Alas, this is handled by using a variation of Class.forName(String name, boolean initialize, ClassLoader loader) which takes a boolean to determine if the class should be initialized, and a ClassLoader if you want to specify a specific loader.

Finally, we can check the Class like this:

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public static void main(String[] args) throws ClassNotFoundException,         InstantiationException, IllegalAccessException {       Class<?> clazz = Class.forName("com.bluelotussoftware.example.assignable.StaticInitializerImpl",                                    false, ClassLoader.getSystemClassLoader());     boolean check = isGreen(clazz);     System.out.println("Passed? " + check);     System.out.println("You shouldn't see: \"The static initializer was called.\""); }   public static boolean isGreen(Class clazz) {     return Green.class.isAssignableFrom(clazz); }

When this is run, you will not see the message. Very nice indeed!

So here is the remaining code for education and entertainment:

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package com.bluelotussoftware.example.assignable;   public interface Green {       String getFoodType();   }

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package com.bluelotussoftware.example.assignable;   public class SoilentGreen implements Green {       @Override     public String getFoodType() {         return "people";     }       public boolean isPeople() {         return true;     }   }

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package com.bluelotussoftware.example.assignable;   public class StaticInitializerImpl {       static {         System.out.println("The static initializer was called.");     }   }

The code for the project can be downloaded from Bitbucket here: assignable

Cassandra Ruby Gem Issues on Mac OS X 10.9.5

I was trying to resolve some issues with building the cassandra gem on Mac OS X 10.9.5. The solution was a multipart solution. You first need to build thrift first which has a known issue, and then build cassandra. This technical tip is very simple. I didn't want to lose it, and I am sure that there are other people out there who will need it.
Note: Please make sure you have updated all the gems in your repository before executing these commands.

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1 2	sudo gem install thrift -- --with-cppflags='-D_FORTIFY_SOURCE=0' sudo gem install cassandra -- --with-cppflags='-D_FORTIFY_SOURCE=0'

This will build both required gems.