driver-mapping/src/main/java/com/datastax/driver/mapping/AccessorInvocationHandler.java

/*
 *      Copyright (C) 2012-2015 DataStax Inc.
 *
 *   Licensed under the Apache License, Version 2.0 (the "License");
 *   you may not use this file except in compliance with the License.
 *   You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *   Unless required by applicable law or agreed to in writing, software
 *   distributed under the License is distributed on an "AS IS" BASIS,
 *   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *   See the License for the specific language governing permissions and
 *   limitations under the License.
 */
package com.datastax.driver.mapping;

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

class AccessorInvocationHandler<T> implements InvocationHandler {

    private static final Object[] NO_ARGS = new Object[0];

    private static final Method TO_STRING;
    private static final Method EQUALS;
    private static final Method HASH_CODE;
    static {
        try {
            TO_STRING = Object.class.getMethod("toString");
            EQUALS = Object.class.getMethod("equals", Object.class);
            HASH_CODE = Object.class.getMethod("hashCode");
        } catch (NoSuchMethodException e) {
            throw new AssertionError(e); // Can't happen
        }
    }

    private final AccessorMapper<T> mapper;

    private final Map<Method, MethodMapper> methodMap = new HashMap<Method, MethodMapper>();

    AccessorInvocationHandler(AccessorMapper<T> mapper) {
        this.mapper = mapper;

        for (MethodMapper method : mapper.methods)
            methodMap.put(method.method, method);
    }

    public Object invoke(Object proxy, Method m, Object[] args) throws Throwable {
        if (m.equals(TO_STRING))
            return mapper.daoClass.getSimpleName() + " implementation generated by the Cassandra driver mapper";

        // It's unlikely that equals and hashCode will be used on accessor implementations, but better safe than sorry.
        // Identity equality is enough, given that the mapper always returns the same instance for a given accessor.
        if (m.equals(EQUALS))
            return proxy == args[0];

        if (m.equals(HASH_CODE))
            return System.identityHashCode(proxy);

        MethodMapper method = methodMap.get(m);
        if (method == null)
            throw new UnsupportedOperationException();
        return method.invoke(args == null ? NO_ARGS : args);
    }
}