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Apache Commons Lang, a package of Java utility classes for the
classes that are in java.lang's hierarchy, or are considered to be so
standard as to justify existence in java.lang.
/*
* 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 org.apache.commons.lang3.function;
import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandleProxies;
import java.lang.invoke.MethodHandles;
import java.lang.reflect.Method;
import java.util.Objects;
import java.util.function.BiConsumer;
import java.util.function.BiFunction;
import java.util.function.Function;
import java.util.function.Supplier;
import org.apache.commons.lang3.exception.UncheckedIllegalAccessException;
/**
* Converts {@link Method} objects to lambdas.
*
* More specifically, produces instances of single-method interfaces which redirect calls to methods; see
* {@link #asInterfaceInstance(Class, Method)}.
*
* Calling supplier methods with no arguments
*
* If the interface's single-method defines no arguments, use {@link #asFunction(Method)} and then apply the function
* passing in the object to receive the method call.
*
*
* For example to invoke {@link String#length()}:
*
*
*
* final Method method = String.class.getMethod("length");
* final Function<String, Integer> function = MethodInvokers.asFunction(method);
* assertEquals(3, function.apply("ABC"));
*
*
* Calling function methods with one argument
*
* If the interface's single-method defines one argument, use {@link #asBiFunction(Method)} and then apply the function
* passing in the object to receive the method call. The second argument to the function is the only argument to the
* method.
*
*
* For example to invoke {@link String#charAt(int)}:
*
*
*
* final Method method = String.class.getMethod("charAt", int.class);
* final BiFunction<String, Integer, Character> function = MethodInvokers.asBiFunction(method);
* assertEquals('C', function.apply("ABC", 2));
*
*
* @since 3.13.0
*/
public final class MethodInvokers {
/**
* Produces a {@link BiConsumer} for a given consumer Method. For example, a classic setter method (as opposed
* to a fluent setter). You call the BiConsumer with two arguments: (1) the object receiving the method call, and (2)
* the method argument.
*
* @param the type of the first argument to the operation: The type containing the Method.
* @param the type of the second argument to the operation: The type of the method argument.
* @param method the method to invoke.
* @return a correctly-typed wrapper for the given target.
*/
@SuppressWarnings("unchecked")
public static BiConsumer asBiConsumer(final Method method) {
return asInterfaceInstance(BiConsumer.class, method);
}
/**
* Produces a {@link BiFunction} for a given a function Method. You call the BiFunction with two arguments: (1)
* the object receiving the method call, and (2) the method argument. The BiFunction return type must match the method's
* return type.
*
* For example to invoke {@link String#charAt(int)}:
*
*
*
* final Method method = String.class.getMethod("charAt", int.class);
* final BiFunction<String, Integer, Character> function = MethodInvokers.asBiFunction(method);
* assertEquals('C', function.apply("ABC", 2));
*
*
* @param the type of the first argument to the function: The type containing the method.
* @param the type of the second argument to the function: the method argument type.
* @param the type of the result of the function: The method return type.
* @param method the method to invoke.
* @return a correctly-typed wrapper for the given target.
*/
@SuppressWarnings("unchecked")
public static BiFunction asBiFunction(final Method method) {
return asInterfaceInstance(BiFunction.class, method);
}
/**
* Produces a {@link FailableBiConsumer} for a given consumer Method. For example, a classic setter method (as
* opposed to a fluent setter). You call the FailableBiConsumer with two arguments: (1) the object receiving the method
* call, and (2) the method argument.
*
* @param the type of the first argument to the operation: The type containing the Method.
* @param the type of the second argument to the operation: The type of the method argument.
* @param method the method to invoke.
* @return a correctly-typed wrapper for the given target.
*/
@SuppressWarnings("unchecked")
public static FailableBiConsumer asFailableBiConsumer(final Method method) {
return asInterfaceInstance(FailableBiConsumer.class, method);
}
/**
* Produces a {@link FailableBiFunction} for a given a function Method. You call the FailableBiFunction with
* two arguments: (1) the object receiving the method call, and (2) the method argument. The BiFunction return type must
* match the method's return type.
*
* @param the type of the first argument to the function: The type containing the method.
* @param the type of the second argument to the function: the method argument type.
* @param the type of the result of the function: The method return type.
* @param method the method to invoke.
* @return a correctly-typed wrapper for the given target.
*/
@SuppressWarnings("unchecked")
public static FailableBiFunction asFailableBiFunction(final Method method) {
return asInterfaceInstance(FailableBiFunction.class, method);
}
/**
* Produces a {@link FailableFunction} for a given a supplier Method. You call the Function with one argument:
* the object receiving the method call. The FailableFunction return type must match the method's return type.
*
* @param the type of the first argument to the function: The type containing the method.
* @param the type of the result of the function: The method return type.
* @param method the method to invoke.
* @return a correctly-typed wrapper for the given target.
*/
@SuppressWarnings("unchecked")
public static FailableFunction asFailableFunction(final Method method) {
return asInterfaceInstance(FailableFunction.class, method);
}
/**
* Produces a {@link FailableSupplier} for a given a supplier Method. The FailableSupplier return type must
* match the method's return type.
*
* Only works with static methods.
*
*
* @param The Method return type.
* @param method the method to invoke.
* @return a correctly-typed wrapper for the given target.
*/
@SuppressWarnings("unchecked")
public static FailableSupplier asFailableSupplier(final Method method) {
return asInterfaceInstance(FailableSupplier.class, method);
}
/**
* Produces a {@link Function} for a given a supplier Method. You call the Function with one argument: the
* object receiving the method call. The Function return type must match the method's return type.
*
* For example to invoke {@link String#length()}:
*
*
*
* final Method method = String.class.getMethod("length");
* final Function<String, Integer> function = MethodInvokers.asFunction(method);
* assertEquals(3, function.apply("ABC"));
*
*
* @param the type of the first argument to the function: The type containing the method.
* @param the type of the result of the function: The method return type.
* @param method the method to invoke.
* @return a correctly-typed wrapper for the given target.
*/
@SuppressWarnings("unchecked")
public static Function asFunction(final Method method) {
return asInterfaceInstance(Function.class, method);
}
/**
* Produces an instance of the given single-method interface which redirects its calls to the given method.
*
* For the definition of "single-method", see {@linkplain MethodHandleProxies#asInterfaceInstance(Class, MethodHandle)}.
*
*
* @param The interface type.
* @param interfaceClass a class object representing {@code T}.
* @param method the method to invoke.
* @return a correctly-typed wrapper for the given target.
* @see MethodHandleProxies#asInterfaceInstance(Class, MethodHandle)
*/
public static T asInterfaceInstance(final Class interfaceClass, final Method method) {
return MethodHandleProxies.asInterfaceInstance(Objects.requireNonNull(interfaceClass, "interfaceClass"), unreflectUnchecked(method));
}
/**
* Produces a {@link Supplier} for a given a supplier Method. The Supplier return type must match the method's
* return type.
*
* Only works with static methods.
*
*
* @param The Method return type.
* @param method the method to invoke.
* @return a correctly-typed wrapper for the given target.
*/
@SuppressWarnings("unchecked")
public static Supplier asSupplier(final Method method) {
return asInterfaceInstance(Supplier.class, method);
}
/**
* Throws NullPointerException if {@code method} is {@code null}.
*
* @param method The method to test.
* @return The given method.
* @throws NullPointerException if {@code method} is {@code null}.
*/
private static Method requireMethod(final Method method) {
return Objects.requireNonNull(method, "method");
}
private static MethodHandle unreflect(final Method method) throws IllegalAccessException {
return MethodHandles.lookup().unreflect(requireMethod(method));
}
private static MethodHandle unreflectUnchecked(final Method method) {
try {
return unreflect(method);
} catch (final IllegalAccessException e) {
throw new UncheckedIllegalAccessException(e);
}
}
/**
* No need to create instances.
*/
private MethodInvokers() {
// noop
}
}