net.hydromatic.optiq.impl.ReflectiveFunctionBase.java Source code

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Here is the source code for net.hydromatic.optiq.impl.ReflectiveFunctionBase.java

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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to you 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 net.hydromatic.optiq.impl;

import net.hydromatic.optiq.Function;
import net.hydromatic.optiq.FunctionParameter;

import org.eigenbase.reltype.RelDataType;
import org.eigenbase.reltype.RelDataTypeFactory;

import com.google.common.collect.ImmutableList;

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

/**
 * Implementation of a function that is based on a method.
 * This class mainly solves conversion of method parameter types to {@code
 * List<FunctionParameter>} form.
 */
public abstract class ReflectiveFunctionBase implements Function {
    /** Method that implements the function. */
    public final Method method;
    /** Types of parameter for the function call. */
    public final List<FunctionParameter> parameters;

    /**
     * {@code ReflectiveFunctionBase} constructor
     * @param method method that is used to get type information from
     */
    public ReflectiveFunctionBase(Method method) {
        this.method = method;
        this.parameters = toFunctionParameters(method.getParameterTypes());
    }

    /**
     * Returns the parameters of this function.
     *
     * @return Parameters; never null
     */
    public List<FunctionParameter> getParameters() {
        return parameters;
    }

    public static ImmutableList<FunctionParameter> toFunctionParameters(Class... types) {
        return toFunctionParameters(Arrays.asList(types));
    }

    public static ImmutableList<FunctionParameter> toFunctionParameters(Iterable<? extends Class> types) {
        final ImmutableList.Builder<FunctionParameter> res = ImmutableList.builder();
        int i = 0;
        for (final Class type : types) {
            final int ordinal = i;
            res.add(new FunctionParameter() {
                public int getOrdinal() {
                    return ordinal;
                }

                public String getName() {
                    return "arg" + ordinal;
                }

                public RelDataType getType(RelDataTypeFactory typeFactory) {
                    return typeFactory.createJavaType(type);
                }
            });
            i++;
        }
        return res.build();
    }

    /**
     * Verifies if given class has public constructor with zero arguments.
     * @param clazz class to verify
     * @return true if given class has public constructor with zero arguments
     */
    static boolean classHasPublicZeroArgsConstructor(Class<?> clazz) {
        for (Constructor<?> constructor : clazz.getConstructors()) {
            if (constructor.getParameterTypes().length == 0 && Modifier.isPublic(constructor.getModifiers())) {
                return true;
            }
        }
        return false;
    }

    /**
     * Finds a method in a given class by name.
     * @param clazz class to search method in
     * @param name name of the method to find
     * @return the first method with matching name or null when no method found
     */
    static Method findMethod(Class<?> clazz, String name) {
        for (Method method : clazz.getMethods()) {
            if (method.getName().equals(name)) {
                return method;
            }
        }
        return null;
    }
}

// End ReflectiveFunctionBase.java