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| Multiple Business Interface Hazzards |
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| <H1><A name="MultipleBusinessInterfaceHazzards-UndeclaredThrowableException"></A>UndeclaredThrowableException</H1> |
| |
| <P>When two java interfaces are implemented by a proxy and those two interfaces declare the <B>same method</B> but with <B>different throws clauses</B> 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 class="code panel" style="border-width: 1px;"><DIV class="codeContent panelContent"> |
| <PRE class="code-java"> |
| <SPAN class="code-keyword">import</SPAN> junit.framework.TestCase; |
| |
| <SPAN class="code-keyword">import</SPAN> java.lang.reflect.InvocationHandler; |
| <SPAN class="code-keyword">import</SPAN> java.lang.reflect.Method; |
| <SPAN class="code-keyword">import</SPAN> java.lang.reflect.UndeclaredThrowableException; |
| |
| /** |
| * @version $Rev$ $Date$ |
| */ |
| <SPAN class="code-keyword">public</SPAN> class ExceptionTest <SPAN class="code-keyword">extends</SPAN> TestCase { |
| |
| <SPAN class="code-keyword">public</SPAN> void test() <SPAN class="code-keyword">throws</SPAN> Exception { |
| <SPAN class="code-object">ClassLoader</SPAN> classLoader = <SPAN class="code-keyword">this</SPAN>.getClass().getClassLoader(); |
| <SPAN class="code-object">Class</SPAN>[] interfaces = <SPAN class="code-keyword">new</SPAN> <SPAN class="code-object">Class</SPAN>[]{One.class, Two.class}; |
| |
| InvocationHandler h = <SPAN class="code-keyword">new</SPAN> TestInvocationHandler(); |
| |
| <SPAN class="code-object">Object</SPAN> proxy = java.lang.reflect.Proxy.newProxyInstance(classLoader, interfaces, h); |
| |
| One one = (One) proxy; |
| |
| <SPAN class="code-keyword">try</SPAN> { |
| one.run(<SPAN class="code-keyword">new</SPAN> CommonException()); |
| } <SPAN class="code-keyword">catch</SPAN> (CommonException e) { |
| <SPAN class="code-comment">// <SPAN class="code-keyword">this</SPAN> will work |
| </SPAN> } <SPAN class="code-keyword">catch</SPAN>(UndeclaredThrowableException u) { |
| Throwable t = u.getCause(); |
| fail(<SPAN class="code-quote">"Undeclared: "</SPAN>+t); |
| } <SPAN class="code-keyword">catch</SPAN>(Throwable t){ |
| fail(<SPAN class="code-quote">"Caught: "</SPAN>+t); |
| } |
| |
| <SPAN class="code-keyword">try</SPAN> { |
| one.run(<SPAN class="code-keyword">new</SPAN> OneException()); |
| } <SPAN class="code-keyword">catch</SPAN> (OneException e) { |
| } <SPAN class="code-keyword">catch</SPAN>(UndeclaredThrowableException u) { |
| Throwable t = u.getCause(); |
| fail(<SPAN class="code-quote">"Undeclared: "</SPAN>+t); <SPAN class="code-comment">// This will always be the code that executes |
| </SPAN> } <SPAN class="code-keyword">catch</SPAN>(Throwable t){ |
| fail(<SPAN class="code-quote">"Caught: "</SPAN>+t); |
| } |
| |
| Two two = (Two) proxy; |
| <SPAN class="code-keyword">try</SPAN> { |
| two.run(<SPAN class="code-keyword">new</SPAN> CommonException()); |
| } <SPAN class="code-keyword">catch</SPAN> (TwoException e) { |
| } <SPAN class="code-keyword">catch</SPAN>(UndeclaredThrowableException u) { |
| Throwable t = u.getCause(); |
| fail(<SPAN class="code-quote">"Undeclared: "</SPAN>+t); <SPAN class="code-comment">// This will always be the code that executes |
| </SPAN> } <SPAN class="code-keyword">catch</SPAN>(Throwable t){ |
| fail(<SPAN class="code-quote">"Caught: "</SPAN>+t); |
| } |
| |
| } |
| |
| <SPAN class="code-keyword">public</SPAN> <SPAN class="code-keyword">static</SPAN> class CommonException <SPAN class="code-keyword">extends</SPAN> Exception { |
| <SPAN class="code-keyword">public</SPAN> CommonException() { |
| } |
| } |
| |
| <SPAN class="code-keyword">public</SPAN> <SPAN class="code-keyword">static</SPAN> <SPAN class="code-keyword">interface</SPAN> One { |
| void run(<SPAN class="code-object">Object</SPAN> o) <SPAN class="code-keyword">throws</SPAN> OneException, CommonException; |
| } |
| |
| <SPAN class="code-keyword">public</SPAN> <SPAN class="code-keyword">static</SPAN> class OneException <SPAN class="code-keyword">extends</SPAN> Exception { |
| <SPAN class="code-keyword">public</SPAN> OneException() { |
| } |
| } |
| |
| <SPAN class="code-keyword">public</SPAN> <SPAN class="code-keyword">static</SPAN> <SPAN class="code-keyword">interface</SPAN> Two { |
| void run(<SPAN class="code-object">Object</SPAN> o) <SPAN class="code-keyword">throws</SPAN> TwoException, CommonException; |
| } |
| |
| <SPAN class="code-keyword">public</SPAN> <SPAN class="code-keyword">static</SPAN> class TwoException <SPAN class="code-keyword">extends</SPAN> Exception { |
| <SPAN class="code-keyword">public</SPAN> TwoException() { |
| } |
| } |
| |
| <SPAN class="code-keyword">private</SPAN> <SPAN class="code-keyword">static</SPAN> class TestInvocationHandler <SPAN class="code-keyword">implements</SPAN> InvocationHandler { |
| <SPAN class="code-keyword">public</SPAN> <SPAN class="code-object">Object</SPAN> invoke(<SPAN class="code-object">Object</SPAN> proxy, Method method, <SPAN class="code-object">Object</SPAN>[] args) <SPAN class="code-keyword">throws</SPAN> Throwable { |
| <SPAN class="code-keyword">throw</SPAN> (Throwable)args[0]; |
| } |
| } |
| } |
| </PRE> |
| </DIV></DIV> |
| |
| |
| <H1><A name="MultipleBusinessInterfaceHazzards-IllegalArgumentException"></A>IllegalArgumentException</H1> |
| |
| <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 <B>same method</B> but with <B>different return types</B> the VM proxy code will refuse to create a proxy at all. Take this code example:</P> |
| |
| <DIV class="code panel" style="border-width: 1px;"><DIV class="codeContent panelContent"> |
| <PRE class="code-java"> |
| |
| <SPAN class="code-keyword">import</SPAN> junit.framework.TestCase; |
| |
| <SPAN class="code-keyword">import</SPAN> java.lang.reflect.InvocationHandler; |
| <SPAN class="code-keyword">import</SPAN> java.lang.reflect.Method; |
| |
| /** |
| * @version $Rev$ $Date$ |
| */ |
| <SPAN class="code-keyword">public</SPAN> class ReturnTest <SPAN class="code-keyword">extends</SPAN> TestCase { |
| |
| <SPAN class="code-keyword">public</SPAN> void test() <SPAN class="code-keyword">throws</SPAN> Exception { |
| <SPAN class="code-object">ClassLoader</SPAN> classLoader = <SPAN class="code-keyword">this</SPAN>.getClass().getClassLoader(); |
| <SPAN class="code-object">Class</SPAN>[] interfaces = <SPAN class="code-keyword">new</SPAN> <SPAN class="code-object">Class</SPAN>[]{ReturnTest.One.class, ReturnTest.Two.class}; |
| |
| InvocationHandler h = <SPAN class="code-keyword">new</SPAN> ReturnTest.TestInvocationHandler(); |
| |
| <SPAN class="code-object">Object</SPAN> proxy = java.lang.reflect.Proxy.newProxyInstance(classLoader, interfaces, h); |
| |
| One one = (One) proxy; |
| <SPAN class="code-keyword">try</SPAN> { |
| <SPAN class="code-object">Object</SPAN> object = one.run(<SPAN class="code-keyword">new</SPAN> ThingOne()); |
| } <SPAN class="code-keyword">catch</SPAN> (Throwable t) { |
| fail(<SPAN class="code-quote">"Caught: "</SPAN> + t); |
| } |
| |
| Two two = (Two) proxy; |
| <SPAN class="code-keyword">try</SPAN> { |
| <SPAN class="code-object">Object</SPAN> object = two.run(<SPAN class="code-keyword">new</SPAN> ThingTwo()); |
| } <SPAN class="code-keyword">catch</SPAN> (Throwable t) { |
| fail(<SPAN class="code-quote">"Caught: "</SPAN> + t); |
| } |
| |
| } |
| |
| <SPAN class="code-keyword">public</SPAN> <SPAN class="code-keyword">static</SPAN> <SPAN class="code-keyword">interface</SPAN> One { |
| ThingOne run(<SPAN class="code-object">Object</SPAN> o); |
| } |
| |
| <SPAN class="code-keyword">public</SPAN> <SPAN class="code-keyword">static</SPAN> class ThingOne { |
| } |
| |
| <SPAN class="code-keyword">public</SPAN> <SPAN class="code-keyword">static</SPAN> <SPAN class="code-keyword">interface</SPAN> Two { |
| ThingTwo run(<SPAN class="code-object">Object</SPAN> o); |
| } |
| |
| <SPAN class="code-keyword">public</SPAN> <SPAN class="code-keyword">static</SPAN> class ThingTwo { |
| } |
| |
| <SPAN class="code-keyword">private</SPAN> <SPAN class="code-keyword">static</SPAN> class TestInvocationHandler <SPAN class="code-keyword">implements</SPAN> InvocationHandler { |
| <SPAN class="code-keyword">public</SPAN> <SPAN class="code-object">Object</SPAN> invoke(<SPAN class="code-object">Object</SPAN> proxy, Method method, <SPAN class="code-object">Object</SPAN>[] args) <SPAN class="code-keyword">throws</SPAN> Throwable { |
| <SPAN class="code-keyword">return</SPAN> args[0]; |
| } |
| } |
| } |
| </PRE> |
| </DIV></DIV> |
| |
| <P>Running this code will result in the following exception:</P> |
| |
| <DIV class="preformatted panel" style="border-width: 1px;"><DIV class="preformattedContent panelContent"> |
| <PRE>java.lang.IllegalArgumentException: methods with same signature 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) |
| |
| </PRE> |
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