constructorutils.java

APACHE 公司出的java bean 工具包

            NoSuchMethodException,
            IllegalAccessException,
            InvocationTargetException,
            InstantiationException {
        if (null == args) {
            args = EMPTY_OBJECT_ARRAY;
        }
        int arguments = args.length;
        Class parameterTypes[] = new Class[arguments];
        for (int i = 0; i < arguments; i++) {
            parameterTypes[i] = args[i].getClass();
        }
        return invokeExactConstructor(klass, args, parameterTypes);

    }

    /**
     * <p>Returns new instance of <code>klazz</code> created using constructor
     * with signature <code>parameterTypes</code> and actual arguments
     * <code>args</code>.</p>
     *
     * <p>The signatures should match exactly.</p>
     *
     * @param klass the class to be constructed.
     * @param args actual argument array
     * @param parameterTypes parameter types array
     * @return new instance of <code>klazz</code>
     *
     * @throws NoSuchMethodException if matching constructor cannot be found
     * @throws IllegalAccessException thrown on the constructor's invocation
     * @throws InvocationTargetException thrown on the constructor's invocation
     * @throws InstantiationException thrown on the constructor's invocation
     * @see Constructor#newInstance
     */
    public static Object invokeExactConstructor(
        Class klass,
        Object[] args,
        Class[] parameterTypes)
        throws
            NoSuchMethodException,
            IllegalAccessException,
            InvocationTargetException,
            InstantiationException {

        if (args == null) {
            args = EMPTY_OBJECT_ARRAY;
        }

        if (parameterTypes == null) {
            parameterTypes = EMPTY_CLASS_PARAMETERS;
        }

        Constructor ctor = getAccessibleConstructor(klass, parameterTypes);
        if (null == ctor) {
            throw new NoSuchMethodException(
                "No such accessible constructor on object: " + klass.getName());
        }
        return ctor.newInstance(args);

    }

    /**
     * Returns a constructor with single argument.
     * @param klass the class to be constructed
     * @param parameterType The constructor parameter type
     * @return null if matching accessible constructor can not be found.
     * @see Class#getConstructor
     * @see #getAccessibleConstructor(java.lang.reflect.Constructor)
     */
    public static Constructor getAccessibleConstructor(
        Class klass,
        Class parameterType) {

        Class[] parameterTypes = { parameterType };
        return getAccessibleConstructor(klass, parameterTypes);

    }

    /**
     * Returns a constructor given a class and signature.
     * @param klass the class to be constructed
     * @param parameterTypes the parameter array
     * @return null if matching accessible constructor can not be found
     * @see Class#getConstructor
     * @see #getAccessibleConstructor(java.lang.reflect.Constructor)
     */
    public static Constructor getAccessibleConstructor(
        Class klass,
        Class[] parameterTypes) {

        try {
            return getAccessibleConstructor(
                klass.getConstructor(parameterTypes));
        } catch (NoSuchMethodException e) {
            return (null);
        }

    }

    /**
     * Returns accessible version of the given constructor.
     * @param ctor prototype constructor object.
     * @return <code>null</code> if accessible constructor can not be found.
     * @see java.lang.SecurityManager
     */
    public static Constructor getAccessibleConstructor(Constructor ctor) {

        // Make sure we have a method to check
        if (ctor == null) {
            return (null);
        }

        // If the requested method is not public we cannot call it
        if (!Modifier.isPublic(ctor.getModifiers())) {
            return (null);
        }

        // If the declaring class is public, we are done
        Class clazz = ctor.getDeclaringClass();
        if (Modifier.isPublic(clazz.getModifiers())) {
            return (ctor);
        }

        // what else can we do?
        return null;

    }

    // -------------------------------------------------------- Private Methods
    /**
     * <p>Find an accessible constructor with compatible parameters.
     * Compatible parameters mean that every method parameter is assignable from
     * the given parameters. In other words, it finds constructor that will take
     * the parameters given.</p>
     *
     * <p>First it checks if there is constructor matching the exact signature.
     * If no such, all the constructors of the class are tested if their signatures
     * are assignment compatible with the parameter types.
     * The first matching constructor is returned.</p>
     *
     * @param clazz find constructor for this class
     * @param parameterTypes find method with compatible parameters
     * @return a valid Constructor object. If there's no matching constructor, returns <code>null</code>.
     */
    private static Constructor getMatchingAccessibleConstructor(
        Class clazz,
        Class[] parameterTypes) {
        // see if we can find the method directly
        // most of the time this works and it's much faster
        try {
            Constructor ctor = clazz.getConstructor(parameterTypes);
            try {
                //
                // XXX Default access superclass workaround
                //
                // When a public class has a default access superclass
                // with public methods, these methods are accessible.
                // Calling them from compiled code works fine.
                //
                // Unfortunately, using reflection to invoke these methods
                // seems to (wrongly) to prevent access even when the method
                // modifer is public.
                //
                // The following workaround solves the problem but will only
                // work from sufficiently privilages code. 
                //
                // Better workarounds would be greatfully accepted.
                //
                ctor.setAccessible(true);
            } catch (SecurityException se) {
                /* SWALLOW, if workaround fails don't fret. */
            }
            return ctor;

        } catch (NoSuchMethodException e) { /* SWALLOW */
        }

        // search through all methods 
        int paramSize = parameterTypes.length;
        Constructor[] ctors = clazz.getConstructors();
        for (int i = 0, size = ctors.length; i < size; i++) {
            // compare parameters
            Class[] ctorParams = ctors[i].getParameterTypes();
            int ctorParamSize = ctorParams.length;
            if (ctorParamSize == paramSize) {
                boolean match = true;
                for (int n = 0; n < ctorParamSize; n++) {
                    if (!MethodUtils
                        .isAssignmentCompatible(
                            ctorParams[n],
                            parameterTypes[n])) {
                        match = false;
                        break;
                    }
                }

                if (match) {
                    // get accessible version of method
                    Constructor ctor = getAccessibleConstructor(ctors[i]);
                    if (ctor != null) {
                        try {
                            ctor.setAccessible(true);
                        } catch (SecurityException se) {
                            /* Swallow SecurityException
                             * TODO: Why?
                             */
                        }
                        return ctor;
                    }
                }
            }
        }

        return null;
    }

}