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ClassImposteriser.java

package org.jmock.lib.legacy;

import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.List;

import net.sf.cglib.core.CodeGenerationException;
import net.sf.cglib.core.DefaultNamingPolicy;
import net.sf.cglib.core.NamingPolicy;
import net.sf.cglib.core.Predicate;
import net.sf.cglib.proxy.Callback;
import net.sf.cglib.proxy.CallbackFilter;
import net.sf.cglib.proxy.Enhancer;
import net.sf.cglib.proxy.Factory;
import net.sf.cglib.proxy.InvocationHandler;
import net.sf.cglib.proxy.NoOp;

import org.jmock.api.Imposteriser;
import org.jmock.api.Invocation;
import org.jmock.api.Invokable;
import org.jmock.internal.SearchingClassLoader;
import org.objenesis.Objenesis;
import org.objenesis.ObjenesisStd;

/**
 * This class lets you imposterise abstract and concrete classes 
 * <em>without</em> calling the constructors of the mocked class.
 *   
 * @author npryce
 */
00032 public class ClassImposteriser implements Imposteriser {
    public static final Imposteriser INSTANCE = new ClassImposteriser();
    
    private ClassImposteriser() {}
    
    private static final NamingPolicy NAMING_POLICY_THAT_ALLOWS_IMPOSTERISATION_OF_CLASSES_IN_SIGNED_PACKAGES = new DefaultNamingPolicy() {
        @Override
        public String getClassName(String prefix, String source, Object key, Predicate names) {
            return "org.jmock.codegen." + super.getClassName(prefix, source, key, names);
        }
    };
    
    private static final CallbackFilter IGNORE_BRIDGE_METHODS = new CallbackFilter() {
        public int accept(Method method) {
            return method.isBridge() ? 1 : 0;
        }
    };
    
    private final Objenesis objenesis = new ObjenesisStd();
    
00052     public boolean canImposterise(Class<?> type) {
        return !type.isPrimitive() && 
               !Modifier.isFinal(type.getModifiers()) && 
               (type.isInterface() || !toStringMethodIsFinal(type));
    }
    
    public <T> T imposterise(final Invokable mockObject, Class<T> mockedType, Class<?>... ancilliaryTypes) {
        if (!mockedType.isInterface() && toStringMethodIsFinal(mockedType)) {
            throw new IllegalArgumentException(mockedType.getName() + " has a final toString method");
        }
        
        try {
            setConstructorsAccessible(mockedType, true);
            Class<?> proxyClass = createProxyClass(mockedType, ancilliaryTypes);
            return mockedType.cast(createProxy(proxyClass, mockObject));
        }
        finally {
            setConstructorsAccessible(mockedType, false);
        }
      }
    
    private boolean toStringMethodIsFinal(Class<?> type) {
        try {
            Method toString = type.getMethod("toString");
            return Modifier.isFinal(toString.getModifiers());
            
        }
        catch (SecurityException e) {
            throw new IllegalStateException("not allowed to reflect on toString method", e);
        }
        catch (NoSuchMethodException e) {
            throw new Error("no public toString method found", e);
        }
    }

    private void setConstructorsAccessible(Class<?> mockedType, boolean accessible) {
        for (Constructor<?> constructor : mockedType.getDeclaredConstructors()) {
            constructor.setAccessible(accessible);
        }
    }
    
    private <T> Class<?> createProxyClass(Class<?> mockedType, Class<?>... ancilliaryTypes) {
        if (mockedType == Object.class) {
            mockedType = ClassWithSuperclassToWorkAroundCglibBug.class;
        }
        
        Enhancer enhancer = new Enhancer() {
            @Override
            @SuppressWarnings("unchecked")
            protected void filterConstructors(Class sc, List constructors) {
                // Don't filter
            }
        };
        enhancer.setClassLoader(SearchingClassLoader.combineLoadersOf(mockedType, ancilliaryTypes));
        enhancer.setUseFactory(true);
        if (mockedType.isInterface()) {
            enhancer.setSuperclass(Object.class);
            enhancer.setInterfaces(prepend(mockedType, ancilliaryTypes));
        }
        else {
            enhancer.setSuperclass(mockedType);
            enhancer.setInterfaces(ancilliaryTypes);
        }
        enhancer.setCallbackTypes(new Class[]{InvocationHandler.class, NoOp.class});
        enhancer.setCallbackFilter(IGNORE_BRIDGE_METHODS);
        if (mockedType.getSigners() != null) {
            enhancer.setNamingPolicy(NAMING_POLICY_THAT_ALLOWS_IMPOSTERISATION_OF_CLASSES_IN_SIGNED_PACKAGES);
        }
        
        try {
            return enhancer.createClass();
        }
        catch (CodeGenerationException e) {
            // Note: I've only been able to manually test this.  It exists to help people writing
            //       Eclipse plug-ins or using other environments that have sophisticated class loader
            //       structures.
            throw new IllegalArgumentException("could not imposterise " + mockedType, e);
        }
    }
    
    private Object createProxy(Class<?> proxyClass, final Invokable mockObject) {
        Factory proxy = (Factory)objenesis.newInstance(proxyClass);
        proxy.setCallbacks(new Callback[] {
            new InvocationHandler() {
                public Object invoke(Object receiver, Method method, Object[] args) throws Throwable {
                    return mockObject.invoke(new Invocation(receiver, method, args));
                }
            },
            NoOp.INSTANCE
        });
        return proxy;
    }
    
    private Class<?>[] prepend(Class<?> first, Class<?>... rest) {
        Class<?>[] all = new Class<?>[rest.length+1];
        all[0] = first;
        System.arraycopy(rest, 0, all, 1, rest.length);
        return all;
    }
    
    public static class ClassWithSuperclassToWorkAroundCglibBug {}
}

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