CyclicDependencyException.java

package org.jboss.seam;

import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.List;

import org.jboss.seam.core.BijectionInterceptor;

/**
 * An exception that is thrown when {@link BijectionInterceptor} detects that a
 * component's dependencies cannot be injected due to a cyclic dependency. As
 * the exception is passed up the stack, the call sequence is recorded so that a
 * useful exception message can be constructed.
 * 
 * @author Matt Drees
 * 
 */
public class CyclicDependencyException extends IllegalStateException
{

   /**
    * stores the invocations in reverse call order
    */
   private final List<String> invocations = new ArrayList<String>();
   private String tailComponentName;
   private boolean cycleComplete;

   /**
    * Records this invocation's component name and method to be displayed in
    * {@link #getMessage()}, unless this invocation is not part of the detected
    * cycle. This method will be successively called as the exception is
    * propagated up the stack.
    * 
    * @param componentName
    * @param method
    */
   public void addInvocation(String componentName, Method method)
   {
      if (cycleComplete)
      {
         return;
      }

      if (invocations.isEmpty())
      {
         tailComponentName = componentName;
      }
      else
      {
         if (tailComponentName.equals(componentName))
         {
            cycleComplete = true;
         }
      }
      invocations.add(createInvocationLabel(componentName, method));
   }

   /**
    * returns e.g. "foo.doSomething()"
    */
   private String createInvocationLabel(String componentName, Method method)
   {
      String invocationLabel = componentName + "." + method.getName() + "(";
      int i = 1;
      for (Class<?> parameterType : method.getParameterTypes())
      {
         invocationLabel += parameterType.getSimpleName();
         if (i < method.getParameterTypes().length)
         {
            invocationLabel += ", ";
         }
         i++;
      }
      invocationLabel += ")";
      return invocationLabel;
   }

   @Override
   public String getMessage()
   {
      if (!cycleComplete)
      {
         return "Cyclic dependency found";
      }
      else
      {
         String message = "Injection into " + tailComponentName + " resulted in a dependency cycle, requiring the invocation of " + invocations.get(0) + ".  The complete cycle: ";
         for (int i = invocations.size() - 1; i >= 0; i--)
         {
            message += invocations.get(i);
            if (i != 0)
               message += " -> ";
         }
         return message;
      }
   }

}