I need somehow to intercept Test class constructor to override a behavior. In JUnit, it is done with:
#Override
public <T> T interceptTestClassConstructor(Invocation<T> invocation,
ReflectiveInvocationContext<Constructor<T>> invocationContext,
ExtensionContext extensionContext) throws Throwable {
...
}
How is this achievable in TestNG?
You could override the behavior using IObjectFactory.
public class CustomObjectFactory implements IObjectFactory {
#Override
public Object newInstance(Constructor constructor, Object... params) {
if(constructor.getDeclaringClass().equals(YourTestCalss.class)) {
return yourCustomObject();
}
try {
return constructor.newInstance(params);
} catch(InstantiationException | IllegalAccessException | IllegalArgumentException | InvocationTargetException e) {
// error handling...
}
return null; // or any other object or throw exception
}
}
Now in a test class, add a method as below:
#Test
public class YourTestClass {
// ......
// test methods
// ......
#ObjectFactory
public ITestObjectFactory getObjectFactory() {
return new CustomObjectFactory();
}
}
Please note that even though this method is declared inside YourTestClass, this same object factory would be used for every other test class in your suite. Hence the if condition to check the class is required in CustomObjectFactory.newInstance.
You may also try IObjectFactory2 which has a newInstance method taking Class as the parameter.
TestNG has an implementation for IObjectFactory -> ObjectFactoryImpl.
You could use extends ObjectFactoryImpl instead, in which case the code within the `newInstance could be:
if(constructor.getDeclaringClass().equals(YourTestCalss.class)) {
return yourCustomObject();
}
return super.newInstance(constructor, params);
BUT note that, Since ObjectFactoryImpl is inside the testng.internal package, I assume that extending ObjectFactoryImpl is not recommended.
As discuss in mailing group, #KrishnanMahadevan fixed a bug which will allow to intercept Test class constructor in version 7.5
public class LocalSuiteAlteringListener implements IAlterSuiteListener {
#Override
public void alter(List<XmlSuite> suites) {
suites.forEach(each -> each.setObjectFactoryClass(MyFactory.class));
I have two classes inheriting from java.lang.Exception. They both have a method with the same signature void a(){...}. They both can be thrown in a code block. If I do:
catch (SubException1 | SubException2 e)
{
e.a();
}
Then it won't compile because method a() does not belong to Exception. Is it a Java language flaw? How should I design my code properly to prevent code redundancy?
When you catch multiple exception types in a single catch statement the inferred type of the caught exception is the greatest common denominator of those classes. In your case, the greatest common denominator is Exception, which doesn't have the method void a(). In order to make it accessible to the catch block you could either extract it to a common base class, or (arguably) more elegantly, define it in an interface that both classes implement:
public interface SomeExceptionInterface {
void a();
}
public class SomeException extends Exception implements SomeExceptionInterface {
// Implementation...
}
public class SomeException2 extends Exception implements SomeExceptionInterface {
// Implementation...
}
If you need to access a method called a(), you need a type that provides that method. A simple solution could be:
public class AbstractSubException extends Exception {
public abstract void a();
}
public class SubException1 extends AbstractSubException {
#Override public void a() { ... }
}
public class SubException2 extends AbstractSubException {
#Override public void a() { ... }
}
Then you can catch the way you did or (somewhat simpler):
catch (AbstractSubException e) {
e.a();
}
Maybe the code for the method a is the same in all sub classes. Then you can make it concrete and put the code into the parent class.
I have an interface, lets say it looks like this.
public interface TestObject {
String getString();
Long getLong();
}
I want to actually build a concrete implementation of this object using ByteBuddy.
Here's what I tried.
public class Runme {
public static void main(String[] args) {
ByteBuddy bb = new ByteBuddy();
Class<?> clz = bb
.subclass(TestObject.class)
.method(any()).intercept(MethodDelegation.to(Interceptor.class))
.make()
.load(Object.class.getClassLoader(), ClassLoadingStrategy.Default.WRAPPER)
.getLoaded();
try {
Object test = clz.newInstance();
} catch (InstantiationException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
public class Interceptor {
public Object intercept(#Origin String method, #AllArguments Object[] args) throws Throwable {
System.out.println("I have intercepted a call");
return "Hello";
}
}
}
I get this error
Exception in thread "main" java.lang.IllegalArgumentException: None of [] allows for delegation from public boolean java.lang.Object.equals(java.lang.Object)
at net.bytebuddy.implementation.bind.MethodDelegationBinder$Processor.process(MethodDelegationBinder.java:881)
at net.bytebuddy.implementation.MethodDelegation$Appender.apply(MethodDelegation.java:1218)
at net.bytebuddy.dynamic.scaffold.TypeWriter$MethodPool$Record$ForDefinedMethod$WithBody.applyBody(TypeWriter.java:510)
at net.bytebuddy.dynamic.scaffold.TypeWriter$MethodPool$Record$ForDefinedMethod.apply(TypeWriter.java:444)
at net.bytebuddy.dynamic.scaffold.TypeWriter$Default$ForCreation.create(TypeWriter.java:3193)
at net.bytebuddy.dynamic.scaffold.TypeWriter$Default.make(TypeWriter.java:1481)
at net.bytebuddy.dynamic.scaffold.subclass.SubclassDynamicTypeBuilder.make(SubclassDynamicTypeBuilder.java:234)
at net.bytebuddy.dynamic.DynamicType$Builder$AbstractBase$AbstractDelegatingBuilder.make(DynamicType.java:2177)
at com.meta.testbytebuddy.Runme.main(Runme.java:22)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)
What am I doing wrong ++.. What if I want to implement multiple interfaces?
I am using ByteBuddy for code generation purposes.
The problem is that you are delegating to the interceptor's static methods by MethodDelegation.to(Interceptor.class) while the interceptor class only declared non-static members. You can either declare your interceptor method to be static or you delegate to an instance instead of to the class. I think the former approach would be more suitable.
This alone will however still not work. You are returning an Object type from your interceptor while, at the same time, you are intercepting any() method. This includes the methods of your TestObject interface but also the methods declared by Object, the implicit super class. You could define your interceptor as follows to make your class compile but then Byte Buddy will cast the return type to each method's return type what will result in a ClassCastException:
public class Interceptor {
#RuntimeType
public static Object intercept(#Origin String method, #AllArguments Object[] args) {
System.out.println("I have intercepted a call");
return "Hello";
}
}
Say I have a class with many of public methods:
public class MyClass {
public void method1() {}
public void method2() {}
(...)
public void methodN() {}
}
Now I would like to create a wrapper class which would delegate all the methods to wrapped instance (delegate):
public class WrapperClass extends MyClass {
private final MyClass delegate;
public WrapperClass(MyClass delegate) {
this.delagate = delegate;
}
public void method1() { delegate.method1(); }
public void method2() { delegate.method2(); }
(...)
public void methodN() { delegate.methodN(); }
}
Now if MyClass has a lot of methods I would need to override each of them which is more or less the same code which just "delegates". I was wondering if it is possible to do some magic to automatically call a method in Java (so the Wrapper class would need to say "Hey if you call a method on me just go to delegate object and call this method on it).
BTW: I can not use inheritance because the delegate is not under my control.I just get its instance from elsewhere (another case would be if MyClass was final).
NOTE: I do not want IDE generation. I know I can do it with help of IntelliJ/Eclipse, but I'm curious if this can be done in code.
Any suggestions how to achieve something like this? (NOTE: I would probably be able to do it in some scripting languages like php where I could use php magic functions to intercept the call).
Perhaps the dynamic Proxy of java can help you. It only works if you consequently use interfaces. In this case, I will call the interface MyInterface and set up a default implementation:
public class MyClass implements MyInterface {
#Override
public void method1() {
System.out.println("foo1");
}
#Override
public void method2() {
System.out.println("foo2");
}
#Override
public void methodN() {
System.out.println("fooN");
}
public static void main(String[] args) {
MyClass wrapped = new MyClass();
wrapped.method1();
wrapped.method2();
MyInterface wrapper = WrapperClass.wrap(wrapped);
wrapper.method1();
wrapper.method2();
}
}
The wrapper class implementation would look like:
public class WrapperClass extends MyClass implements MyInterface, InvocationHandler {
private final MyClass delegate;
public WrapperClass(MyClass delegate) {
this.delegate = delegate;
}
public static MyInterface wrap(MyClass wrapped) {
return (MyInterface) Proxy.newProxyInstance(MyClass.class.getClassLoader(), new Class[] { MyInterface.class }, new WrapperClass(wrapped));
}
//you may skip this definition, it is only for demonstration
public void method1() {
System.out.println("bar");
}
#Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
Method m = findMethod(this.getClass(), method);
if (m != null) {
return m.invoke(this, args);
}
m = findMethod(delegate.getClass(), method);
if (m != null) {
return m.invoke(delegate, args);
}
return null;
}
private Method findMethod(Class<?> clazz, Method method) throws Throwable {
try {
return clazz.getDeclaredMethod(method.getName(), method.getParameterTypes());
} catch (NoSuchMethodException e) {
return null;
}
}
}
Note that this class:
extends MyClass, to inherit a default implementation (any other would do)
implements Invocationhandler, to allow the proxy to do reflection
optionally implement MyInterface (to satisfy the decorator pattern)
This solution allows you to override special methods, but to delegate all others. This will even work with sub classes of Wrapper class.
Note that the method findMethod does not yet capture the special cases.
This question is 6 months old already and #CoronA's wonderful answer has satisfied and been accepted by #walkeros, but I thought I would add something here as I think this can be pushed an extra step.
As discussed with #CoronA in the comments to his answer, instead of having to create and maintain a long list of MyClass methods in WrapperClass (i.e. public void methodN() { delegate.methodN(); }), the dynamic proxy solution moves this to the interface. The issue is that you still have to create and maintain a long list of signatures for the MyClass methods in the interface, which is perhaps a bit simpler but doesn't completely solve the problem. This is especially the case if you don't have access to MyClass in order to know all the methods.
According to Three approaches for decorating your code,
For longer classes, a programmer must choose the lesser of two evils:
implement many wrapper methods and keep the type of decorated object
or maintain a simple decorator implementation and sacrifice retaining
the decorated object type.
So perhaps this is an expected limitation of the Decorator Pattern.
#Mark-Bramnik, however, gives an fascinating solution using CGLIB at Interposing on Java Class Methods (without interfaces). I was able to combine this with #CoronaA's solution in order to create a wrapper that can override individual methods but then pass everything else to the wrapped object without requiring an interface.
Here is MyClass.
public class MyClass {
public void method1() { System.out.println("This is method 1 - " + this); }
public void method2() { System.out.println("This is method 2 - " + this); }
public void method3() { System.out.println("This is method 3 - " + this); }
public void methodN() { System.out.println("This is method N - " + this); }
}
Here is WrapperClass which only overrides method2(). As you'll see below, the non-overridden methods are, in fact, not passed to the delegate, which can be a problem.
public class WrapperClass extends MyClass {
private MyClass delagate;
public WrapperClass(MyClass delegate) { this.delagate = delegate; }
#Override
public void method2() {
System.out.println("This is overridden method 2 - " + delagate);
}
}
Here is MyInterceptor which extends MyClass. It employs the proxy solution using CGLIB as described by #Mark-Bramnik. It also employs #CononA's method of determining whether or not to send the method to the wrapper (if it is overridden) or the wrapped object (if it is not).
import java.lang.reflect.Method;
import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;
public class MyInterceptor extends MyClass implements MethodInterceptor {
private Object realObj;
public MyInterceptor(Object obj) { this.realObj = obj; }
#Override
public void method2() {
System.out.println("This is overridden method 2 - " + realObj);
}
#Override
public Object intercept(Object arg0, Method method, Object[] objects,
MethodProxy methodProxy) throws Throwable {
Method m = findMethod(this.getClass(), method);
if (m != null) { return m.invoke(this, objects); }
Object res = method.invoke(realObj, objects);
return res;
}
private Method findMethod(Class<?> clazz, Method method) throws Throwable {
try {
return clazz.getDeclaredMethod(method.getName(), method.getParameterTypes());
} catch (NoSuchMethodException e) {
return null;
}
}
}
Here is Main and the results you get if you run it.
import net.sf.cglib.proxy.Enhancer;
public class Main {
private static MyClass unwrapped;
private static WrapperClass wrapped;
private static MyClass proxified;
public static void main(String[] args) {
unwrapped = new MyClass();
System.out.println(">>> Methods from the unwrapped object:");
unwrapped.method1();
unwrapped.method2();
unwrapped.method3();
wrapped = new WrapperClass(unwrapped);
System.out.println(">>> Methods from the wrapped object:");
wrapped.method1();
wrapped.method2();
wrapped.method3();
proxified = createProxy(unwrapped);
System.out.println(">>> Methods from the proxy object:");
proxified.method1();
proxified.method2();
proxified.method3();
}
#SuppressWarnings("unchecked")
public static <T> T createProxy(T obj) {
Enhancer e = new Enhancer();
e.setSuperclass(obj.getClass());
e.setCallback(new MyInterceptor(obj));
T proxifiedObj = (T) e.create();
return proxifiedObj;
}
}
>>> Methods from the unwrapped object:
This is method 1 - MyClass#e26db62
This is method 2 - MyClass#e26db62
This is method 3 - MyClass#e26db62
>>> Methods from the wrapped object:
This is method 1 - WrapperClass#7b7035c6
This is overridden method 2 - MyClass#e26db62
This is method 3 - WrapperClass#7b7035c6
>>> Methods from the proxy object:
This is method 1 - MyClass#e26db62
This is overridden method 2 - MyClass#e26db62
This is method 3 - MyClass#e26db62
As you can see, when you run the methods on wrapped you get the wrapper for the methods that are not overridden (i.e. method1() and method3()). When you run the methods on proxified, however, all of the methods are run on the wrapped object without the pain of having to delegate them all in WrapperClass or put all of the method signatures in an interface. Thanks to #CoronA and #Mark-Bramnik for what seems like a pretty cool solution to this problem.
Check the #Delegate annotation from Lombok framework:
https://projectlombok.org/features/Delegate.html
Switch to Groovy :-)
#CompileStatic
public class WrapperClass extends MyClass {
#Delegate private final MyClass delegate;
public WrapperClass(MyClass delegate) {
this.delagate = delegate;
}
//Done. That's it.
}
http://mrhaki.blogspot.com/2009/08/groovy-goodness-delegate-to-simplify.html
You don't have to do this -- your Wrapper class is a subclass of the original class, so it inherits all of its publicly accessible methods -- and if you don't implement them, the original method will be called.
You shouldn't have extends Myclass together with a private MyClass object -- that's really really redundant, and I can't think of a design pattern where doing that is right. Your WrapperClass is a MyClass, and hence you can just use its own fields and methods instead of calling delegate.
EDIT: In the case of MyClass being final, you'd be circumventing the willfull declaration to not allow subclassing by "faking" inheritance; I can't think of anyone willing to do that other than you, who is in control of WrapperClass; but, since you're in control of WrapperClass, not wrapping everything you don't need is really more than an option -- it's the right thing to do, because your object is not a MyClass, and should only behave like one in the cases you mentally considered.
EDIT you've just changed your question to mean something completely different by removing the MyClass superclass to your WrapperClass; that's a bit bad, because it invalidates all answers given so far. You should have opened another question.
Credits go to CoronA for Pointing out the Proxy and InvocationHandler classes. I worked out a more reusable utility class based on his solution, using generics:
public class DelegationUtils {
public static <I> I wrap(Class<I> iface, I wrapped) {
return wrapInternally(iface, wrapped, new SimpleDecorator(wrapped));
}
private static <I> I wrapInternally (Class<I> iface, I wrapped, InvocationHandler handler) {
return (I) Proxy.newProxyInstance(wrapped.getClass().getClassLoader(), new Class[] { iface }, handler);
}
private static class SimpleDecorator<T> implements InvocationHandler {
private final T delegate;
private SimpleDecorator(T delegate) {
this.delegate = delegate;
}
#Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
Method m = findMethod(delegate.getClass(), method);
if (m == null) {
throw new NullPointerException("Found no method " + method + " in delegate: " + delegate);
}
return m.invoke(delegate, args);
}
}
private static Method findMethod(Class<?> clazz, Method method) throws Throwable {
try {
return clazz.getDeclaredMethod(method.getName(), method.getParameterTypes());
} catch (NoSuchMethodException e) {
return null;
}
}
}
Test it:
public class Test {
public interface Test {
public void sayHello ();
}
public static class TestImpl implements Test {
#Override
public void sayHello() {
System.out.println("HELLO!");
}
}
public static void main(String[] args) {
Test proxy = DelegationUtils.wrap(Test.class, new TestImpl());
proxy.sayHello();
}
}
I wanted to create an automatic delegation class that executes the delegatee's methods on the EDT. With this class, you just create a new utility method that will use an EDTDecorator, in which the implementation will wrap m.invoke in a SwingUtilities.invokeLater.
However, if I reflect on this, I may want to reconsider making a non-Reflection based proxy per interface that I have - it might be cleaner and faster, and more understandable. But, it's possible.
Define a method in WrapperClass i.e. delegate() that returns the instance of MyClass
OR
You can use reflection to do that but the caller has to pass the method name as an argument to an exposed method. And there will be complications regarding the method arguments/overloaded methods etc.
BTW: I can not use inheritance because the delegate is not under my control.I just get its instance from elsewhere (another case would be if MyClass was final)
The code that you have posted has public class WrapperClass extends MyClass
Actually your current implementation of WrapperClass is actually a decorator on top of MyClass
Let me redefine the problem for a specific case.
I want to override the close method of ResultSet interface in jdbc. My aim is to close the preparedstatement in close method of result set. I could not access to the Class (DelegatingResultSet) that implements in ResultSet interface. There are a lot of methods in ResultSet interface and overriding them one by one and calling the corresponding method from the ResultSet object is one solution. For a dynamic solution I used Dynamic ProxyClasses (https://docs.oracle.com/javase/1.5.0/docs/guide/reflection/proxy.html).
// New ResultSet implementation
public class MyResultSet implements InvocationHandler {
ResultSet rs;
PreparedStatement ps;
private Method closeMethod;
public MyResultSet(ResultSet rs, PreparedStatement ps) {
super();
this.rs = rs;
this.ps = ps;
try {
closeMethod = ResultSet.class.getMethod("close",null);
} catch (NoSuchMethodException | SecurityException e) {
e.printStackTrace();
}
}
public void close() {
try {
rs.close();
ps.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
public static Object newInstance(ResultSet rs, PreparedStatement ps) {
return java.lang.reflect.Proxy.newProxyInstance(rs.getClass().getClassLoader(), rs.getClass().getInterfaces(),
new MyResultSet(rs,ps));
}
public Object invoke(Object proxy, Method m, Object[] args)
throws Throwable {
Object result = null;
try {
Class declaringClass = m.getDeclaringClass();
if (m.getName().compareTo("close")==0) {
close();
} else {
result = m.invoke(rs, args);
}
} catch (InvocationTargetException e) {
throw e.getTargetException();
} catch (Exception e) {
throw new RuntimeException(e.getMessage());
} finally {
}
return result;
}
}
// How to call it:
ResultSet prs = (ResultSet) MyResultSet.newInstance(rs,ps);
I really appreciated #CoronA's answer. I also looked at #Mark Cramer's answer, but, if I'm not missing something, I think that there are always at least two instances of the "proxified" class with a strange relationship beteen the two objects.
This, along with the fact that cglib is now deprecated, pushed me to find a new implementation based on ByteBuddy.
This is what I came up with:
public class MyClass {
public String testMethod() {
return "11111";
}
public String testMethod2() {
return "aaaaa";
}
}
public class MyClassWithDelegate extends MyClass {
private static final Constructor<? extends MyClassWithDelegate> CONSTRUCTOR_WITH_DELEGATE;
static {
Constructor<? extends MyClassWithDelegate> temp = null;
try {
final var instrumentedMyClassWithDelegateType =
new ByteBuddy()
.subclass(MyClassWithDelegate.class)
.method(ElementMatchers.any())
.intercept(MethodDelegation.to(MethodInterceptor.class))
.make()
.load(MyClassWithDelegate.class.getClassLoader())
.getLoaded();
temp = instrumentedMyClassWithDelegateType.getConstructor(MyClass.class);
} catch (final Exception e) {
LOGGER.error("Cannot instrument class {}", MyClassWithDelegate.class, e);
}
CONSTRUCTOR_WITH_DELEGATE = temp;
}
public static MyClassWithDelegate getInstanceWithDelegate(final MyClass myClass) {
try {
return CONSTRUCTOR_WITH_DELEGATE.newInstance(myClass);
} catch (final Exception e) {
LOGGER.error("Cannot get instance of {}", MyClassWithDelegate.class, e);
throw new IllegalStateException();
}
}
private final boolean initialized;
private final MyClass delegate;
public MyClassWithDelegate(final MyClass delegate) {
super();
this.delegate = delegate;
this.initialized = true;
}
public String testMethod() {
return "22222";
}
public static class MethodInterceptor {
#RuntimeType
public static Object intercept(#This final MyClassWithDelegate self,
#Origin final Method method,
#AllArguments final Object[] args,
#SuperMethod final Method superMethod) throws Throwable {
if (!self.initialized || method.getDeclaringClass().equals(MyClassWithDelegate.class)) {
return superMethod.invoke(self, args);
} else {
return method.invoke(self.delegate, args);
}
}
}
}
The initialized field is used to prevent method calls the super constructor from being redirected to the delegate before its assignment (in this case it wouldn't be a problem, but I wanted to create a generic solution).
Every method called on an instance of MyClassWithDelegate will be redirected to the delegate, except from methods declared inside MyClassWithDelegate itself.
In this example, calling testMethod() on an instance of MyClassWithDelegate will return "22222", while testMethod2() will return "aaaaa".
Obviously, the delegation will actually work only if every instance of MyClassWithDelegate is obtained calling the getInstanceWithDelegate factory method.
I am working on an assignment where I am told that I need to create a class (Call it ClassB) that must extend a given class (Call it ClassA). The only problem is that the code inside of the constructor of ClassA may throw an exception, so when I create my constructor for ClassB, I am trying to wrap a try/catch block around the call to super(), but of course, that doesn't work since super has to be the first call.
How can I work around this?
public ClassB extends ClassA {
public ClassB() throws MyClassAException {
super();
}
}
You can add your exception in the throws clause of your sub class constructor: -
class ClassA {
ClassA() throws Exception {
}
}
public class Demo extends ClassA {
Demo() throws Exception {
super();
}
public static void main(String[] args) {
try {
Demo d = new Demo(); // Handle exception here.
} catch (Exception e) {
e.printStackTrace();
}
}
}
ClassB should have a static method
public static ClassB makeClassB() {
try {
return new ClassB();
}
catch(Exception exc) {
// whatever logic you are currently performing to swallow
// presumably you have some default ClassB to return as part of this logic?
}
that will wrap the construction of ClassB with a try/catch. Client code will call makeClassB() and the constructor to ClassB will be private and throwing.