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               <h1>Multiple Business Interface Hazzards</h1>
             </div>
           </div>
         </div>
         <div class="row">

             <div class="col-md-12">
                 <h1 id="_undeclaredthrowableexception" class="sect0">UndeclaredThrowableException</h1>
 <div class="paragraph">
 <p>When two java interfaces are implemented by a proxy and those two
 interfaces declare the <em>same method</em> but with <em>different throws clauses</em>
 some very nasty side effects happen, namely you loose the ability to
 throw any checked exceptions that are not in the throws clause of both
 methods.</p>
 </div>
 <div class="listingblock">
 <div class="content">
 <pre class="highlight"><code class="language-java" data-lang="java">import junit.framework.TestCase;

 import java.lang.reflect.InvocationHandler;
 import java.lang.reflect.Method;
 import java.lang.reflect.UndeclaredThrowableException;

 /**
  * @version $Rev$ $Date$
  */
 public class ExceptionTest extends TestCase {

     public void test() throws Exception {
     ClassLoader classLoader = this.getClass().getClassLoader();
         Class[]</code></pre>
 </div>
 </div>
 <div class="paragraph">
 <p>interfaces = new Class[]\{One.class, Two.class};</p>
 </div>
 <div class="listingblock">
 <div class="content">
 <pre class="highlight"><code class="language-java" data-lang="java">    InvocationHandler h = new TestInvocationHandler();

     Object proxy =</code></pre>
 </div>
 </div>
 <div class="paragraph">
 <p>java.lang.reflect.Proxy.newProxyInstance(classLoader, interfaces, h);</p>
 </div>
 <div class="listingblock">
 <div class="content">
 <pre class="highlight"><code class="language-java" data-lang="java">    One one = (One) proxy;

     try {
         one.run(new CommonException());
     } catch (CommonException e) {
         // this will work
     } catch(UndeclaredThrowableException u) {
         Throwable t = u.getCause();
         fail("Undeclared: "+t);
     } catch(Throwable t){
         fail("Caught: "+t);
     }

     try {
         one.run(new OneException());
     } catch (OneException e) {
     } catch(UndeclaredThrowableException u) {
         Throwable t = u.getCause();
         fail("Undeclared: "+t); // This will always be the code that</code></pre>
 </div>
 </div>
 <div class="paragraph">
 <p>executes } catch(Throwable t)\{ fail("Caught: "+t); }</p>
 </div>
 <div class="listingblock">
 <div class="content">
 <pre class="highlight"><code class="language-java" data-lang="java">    Two two = (Two) proxy;
     try {
         two.run(new CommonException());
     } catch (TwoException e) {
     } catch(UndeclaredThrowableException u) {
         Throwable t = u.getCause();
         fail("Undeclared: "+t); // This will always be the code that</code></pre>
 </div>
 </div>
 <div class="paragraph">
 <p>executes } catch(Throwable t)\{ fail("Caught: "+t); }</p>
 </div>
 <div class="listingblock">
 <div class="content">
 <pre class="highlight"><code class="language-java" data-lang="java">    }

     public static class CommonException extends Exception {
     public CommonException() {
     }
     }

     public static interface One {
     void run(Object o) throws OneException, CommonException;
     }

     public static class OneException extends Exception {
     public OneException() {
     }
     }

     public static interface Two {
     void run(Object o) throws TwoException, CommonException;
     }

     public static class TwoException extends Exception {
     public TwoException() {
     }
     }

     private static class TestInvocationHandler implements InvocationHandler</code></pre>
 </div>
 </div>
 <div class="paragraph">
 <p>\{ public Object invoke(Object proxy, Method method, Object[] args)
 throws Throwable \{ throw (Throwable)args[0] ; } } }</p>
 </div>
 <h1 id="_illegalargumentexception" class="sect0">IllegalArgumentException</h1>
 <div class="paragraph">
 <p>This one is less of a runtime problem as doing this will cause things to
 fail up front. When two java interfaces are implemented by a proxy and
 those two interfaces declare the <em>same method</em> but with <em>different
 return types</em> the VM proxy code will refuse to create a proxy at all.
 Take this code example:</p>
 </div>
 <div class="listingblock">
 <div class="content">
 <pre class="highlight"><code class="language-java" data-lang="java">import junit.framework.TestCase;

 import java.lang.reflect.InvocationHandler;
 import java.lang.reflect.Method;

 /**
  * @version $Rev$ $Date$
  */
 public class ReturnTest extends TestCase {

     public void test() throws Exception {
     ClassLoader classLoader = this.getClass().getClassLoader();
         Class[]</code></pre>
 </div>
 </div>
 <div class="paragraph">
 <p>interfaces = new Class[]\{ReturnTest.One.class, ReturnTest.Two.class};</p>
 </div>
 <div class="listingblock">
 <div class="content">
 <pre class="highlight"><code class="language-java" data-lang="java">    InvocationHandler h = new ReturnTest.TestInvocationHandler();

     Object proxy =</code></pre>
 </div>
 </div>
 <div class="paragraph">
 <p>java.lang.reflect.Proxy.newProxyInstance(classLoader, interfaces, h);</p>
 </div>
 <div class="listingblock">
 <div class="content">
 <pre class="highlight"><code class="language-java" data-lang="java">    One one = (One) proxy;
     try {
         Object object = one.run(new ThingOne());
     } catch (Throwable t) {
         fail("Caught: " + t);
     }

     Two two = (Two) proxy;
     try {
         Object object = two.run(new ThingTwo());
     } catch (Throwable t) {
         fail("Caught: " + t);
     }

     }

     public static interface One {
     ThingOne run(Object o);
     }

     public static class ThingOne {
     }

     public static interface Two {
     ThingTwo run(Object o);
     }

     public static class ThingTwo {
     }

     private static class TestInvocationHandler implements InvocationHandler</code></pre>
 </div>
 </div>
 <div class="paragraph">
 <p>\{ public Object invoke(Object proxy, Method method, Object[] args)
 throws Throwable \{ return args[0] ; } } }</p>
 </div>
 <div class="paragraph">
 <p>Running this code will result in the following exception:</p>
 </div>
 <div class="listingblock">
 <div class="content">
 <pre class="highlight"><code class="language-properties" data-lang="properties">java.lang.IllegalArgumentException: methods with same signature</code></pre>
 </div>
 </div>
 <div class="paragraph">
 <p>run(java.lang.Object) but incompatible return types: [class
 ReturnTest\($ThingOne, class ReturnTest$\)ThingTwo] at
 sun.misc.ProxyGenerator.checkReturnTypes(ProxyGenerator.java:669) at
 sun.misc.ProxyGenerator.generateClassFile(ProxyGenerator.java:420) at
 sun.misc.ProxyGenerator.generateProxyClass(ProxyGenerator.java:306) at
 java.lang.reflect.Proxy.getProxyClass(Proxy.java:501) at
 java.lang.reflect.Proxy.newProxyInstance(Proxy.java:581) at
 ReturnTest.test(ReturnTest.java:36) at
 sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at
 sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
 at
 sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
 at
 com.intellij.rt.execution.junit2.JUnitStarter.main(JUnitStarter.java:32)</p>
 </div>
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	<div id="main-block" class="container main-block">
	<div class="row title">
	<div class="col-md-12">
	<div class='page-header'>

	<h1>Multiple Business Interface Hazzards</h1>
	</div>
	</div>
	</div>
	<div class="row">

	<div class="col-md-12">
	<h1 id="_undeclaredthrowableexception" class="sect0">UndeclaredThrowableException</h1>
	<div class="paragraph">
	<p>When two java interfaces are implemented by a proxy and those two
	interfaces declare the <em>same method</em> but with <em>different throws clauses</em>
	some very nasty side effects happen, namely you loose the ability to
	throw any checked exceptions that are not in the throws clause of both
	methods.</p>
	</div>
	<div class="listingblock">
	<div class="content">
	<pre class="highlight"><code class="language-java" data-lang="java">import junit.framework.TestCase;

	import java.lang.reflect.InvocationHandler;
	import java.lang.reflect.Method;
	import java.lang.reflect.UndeclaredThrowableException;

	/**
	* @version $Rev$ $Date$
	*/
	public class ExceptionTest extends TestCase {

	public void test() throws Exception {
	ClassLoader classLoader = this.getClass().getClassLoader();
	Class[]</code></pre>
	</div>
	</div>
	<div class="paragraph">
	<p>interfaces = new Class[]\{One.class, Two.class};</p>
	</div>
	<div class="listingblock">
	<div class="content">
	<pre class="highlight"><code class="language-java" data-lang="java"> InvocationHandler h = new TestInvocationHandler();

	Object proxy =</code></pre>
	</div>
	</div>
	<div class="paragraph">
	<p>java.lang.reflect.Proxy.newProxyInstance(classLoader, interfaces, h);</p>
	</div>
	<div class="listingblock">
	<div class="content">
	<pre class="highlight"><code class="language-java" data-lang="java"> One one = (One) proxy;

	try {
	one.run(new CommonException());
	} catch (CommonException e) {
	// this will work
	} catch(UndeclaredThrowableException u) {
	Throwable t = u.getCause();
	fail("Undeclared: "+t);
	} catch(Throwable t){
	fail("Caught: "+t);
	}

	try {
	one.run(new OneException());
	} catch (OneException e) {
	} catch(UndeclaredThrowableException u) {
	Throwable t = u.getCause();
	fail("Undeclared: "+t); // This will always be the code that</code></pre>
	</div>
	</div>
	<div class="paragraph">
	<p>executes } catch(Throwable t)\{ fail("Caught: "+t); }</p>
	</div>
	<div class="listingblock">
	<div class="content">
	<pre class="highlight"><code class="language-java" data-lang="java"> Two two = (Two) proxy;
	try {
	two.run(new CommonException());
	} catch (TwoException e) {
	} catch(UndeclaredThrowableException u) {
	Throwable t = u.getCause();
	fail("Undeclared: "+t); // This will always be the code that</code></pre>
	</div>
	</div>
	<div class="paragraph">
	<p>executes } catch(Throwable t)\{ fail("Caught: "+t); }</p>
	</div>
	<div class="listingblock">
	<div class="content">
	<pre class="highlight"><code class="language-java" data-lang="java"> }

	public static class CommonException extends Exception {
	public CommonException() {
	}
	}

	public static interface One {
	void run(Object o) throws OneException, CommonException;
	}

	public static class OneException extends Exception {
	public OneException() {
	}
	}

	public static interface Two {
	void run(Object o) throws TwoException, CommonException;
	}

	public static class TwoException extends Exception {
	public TwoException() {
	}
	}

	private static class TestInvocationHandler implements InvocationHandler</code></pre>
	</div>
	</div>
	<div class="paragraph">
	<p>\{ public Object invoke(Object proxy, Method method, Object[] args)
	throws Throwable \{ throw (Throwable)args[0] ; } } }</p>
	</div>
	<h1 id="_illegalargumentexception" class="sect0">IllegalArgumentException</h1>
	<div class="paragraph">
	<p>This one is less of a runtime problem as doing this will cause things to
	fail up front. When two java interfaces are implemented by a proxy and
	those two interfaces declare the <em>same method</em> but with <em>different
	return types</em> the VM proxy code will refuse to create a proxy at all.
	Take this code example:</p>
	</div>
	<div class="listingblock">
	<div class="content">
	<pre class="highlight"><code class="language-java" data-lang="java">import junit.framework.TestCase;

	import java.lang.reflect.InvocationHandler;
	import java.lang.reflect.Method;

	/**
	* @version $Rev$ $Date$
	*/
	public class ReturnTest extends TestCase {

	public void test() throws Exception {
	ClassLoader classLoader = this.getClass().getClassLoader();
	Class[]</code></pre>
	</div>
	</div>
	<div class="paragraph">
	<p>interfaces = new Class[]\{ReturnTest.One.class, ReturnTest.Two.class};</p>
	</div>
	<div class="listingblock">
	<div class="content">
	<pre class="highlight"><code class="language-java" data-lang="java"> InvocationHandler h = new ReturnTest.TestInvocationHandler();

	Object proxy =</code></pre>
	</div>
	</div>
	<div class="paragraph">
	<p>java.lang.reflect.Proxy.newProxyInstance(classLoader, interfaces, h);</p>
	</div>
	<div class="listingblock">
	<div class="content">
	<pre class="highlight"><code class="language-java" data-lang="java"> One one = (One) proxy;
	try {
	Object object = one.run(new ThingOne());
	} catch (Throwable t) {
	fail("Caught: " + t);
	}

	Two two = (Two) proxy;
	try {
	Object object = two.run(new ThingTwo());
	} catch (Throwable t) {
	fail("Caught: " + t);
	}

	}

	public static interface One {
	ThingOne run(Object o);
	}

	public static class ThingOne {
	}

	public static interface Two {
	ThingTwo run(Object o);
	}

	public static class ThingTwo {
	}

	private static class TestInvocationHandler implements InvocationHandler</code></pre>
	</div>
	</div>
	<div class="paragraph">
	<p>\{ public Object invoke(Object proxy, Method method, Object[] args)
	throws Throwable \{ return args[0] ; } } }</p>
	</div>
	<div class="paragraph">
	<p>Running this code will result in the following exception:</p>
	</div>
	<div class="listingblock">
	<div class="content">
	<pre class="highlight"><code class="language-properties" data-lang="properties">java.lang.IllegalArgumentException: methods with same signature</code></pre>
	</div>
	</div>
	<div class="paragraph">
	<p>run(java.lang.Object) but incompatible return types: [class
	ReturnTest\($ThingOne, class ReturnTest$\)ThingTwo] at
	sun.misc.ProxyGenerator.checkReturnTypes(ProxyGenerator.java:669) at
	sun.misc.ProxyGenerator.generateClassFile(ProxyGenerator.java:420) at
	sun.misc.ProxyGenerator.generateProxyClass(ProxyGenerator.java:306) at
	java.lang.reflect.Proxy.getProxyClass(Proxy.java:501) at
	java.lang.reflect.Proxy.newProxyInstance(Proxy.java:581) at
	ReturnTest.test(ReturnTest.java:36) at
	sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at
	sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	at
	sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at
	com.intellij.rt.execution.junit2.JUnitStarter.main(JUnitStarter.java:32)</p>
	</div>
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