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From StephanEwen <...@git.apache.org>
Subject [GitHub] flink pull request #2621: [FLINK-4793] [types] Improve lambda constructor re...
Date Tue, 11 Oct 2016 14:39:55 GMT
Github user StephanEwen commented on a diff in the pull request:

    https://github.com/apache/flink/pull/2621#discussion_r82807840
  
    --- Diff: flink-core/src/main/java/org/apache/flink/api/java/typeutils/TypeExtractionUtils.java
---
    @@ -0,0 +1,167 @@
    +/*
    + * 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.flink.api.java.typeutils;
    +
    +import java.lang.reflect.Constructor;
    +import java.lang.reflect.Method;
    +import java.lang.reflect.Type;
    +import java.util.ArrayList;
    +import java.util.List;
    +import org.apache.flink.annotation.Internal;
    +import org.apache.flink.api.common.functions.Function;
    +import static org.objectweb.asm.Type.getConstructorDescriptor;
    +import static org.objectweb.asm.Type.getMethodDescriptor;
    +
    +@Internal
    +public class TypeExtractionUtils {
    +
    +	private TypeExtractionUtils() {
    +		// do not allow instantiation
    +	}
    +
    +	/**
    +	 * Similar to a Java 8 Executable but with a return type.
    +	 */
    +	public static class LambdaExecutable {
    +
    +		private Type[] parameterTypes;
    +		private Type returnType;
    +		private String name;
    +		private Object executable;
    +
    +		public LambdaExecutable(Constructor<?> constructor) {
    +			this.parameterTypes = constructor.getGenericParameterTypes();
    +			this.returnType = constructor.getDeclaringClass();
    +			this.name = constructor.getName();
    +			this.executable = constructor;
    +		}
    +
    +		public LambdaExecutable(Method method) {
    +			this.parameterTypes = method.getGenericParameterTypes();
    +			this.returnType = method.getGenericReturnType();
    +			this.name = method.getName();
    +			this.executable = method;
    +		}
    +
    +		public Type[] getParameterTypes() {
    +			return parameterTypes;
    +		}
    +
    +		public Type getReturnType() {
    +			return returnType;
    +		}
    +
    +		public String getName() {
    +			return name;
    +		}
    +
    +		public boolean executablesEquals(Method m) {
    +			return executable.equals(m);
    +		}
    +
    +		public boolean executablesEquals(Constructor<?> c) {
    +			return executable.equals(c);
    +		}
    +	}
    +
    +	public static LambdaExecutable checkAndExtractLambda(Function function) {
    +		try {
    +			// get serialized lambda
    +			Object serializedLambda = null;
    +			for (Class<?> clazz = function.getClass(); clazz != null; clazz = clazz.getSuperclass())
{
    +				try {
    +					Method replaceMethod = clazz.getDeclaredMethod("writeReplace");
    +					replaceMethod.setAccessible(true);
    +					Object serialVersion = replaceMethod.invoke(function);
    +
    +					// check if class is a lambda function
    +					if (serialVersion.getClass().getName().equals("java.lang.invoke.SerializedLambda"))
{
    +
    +						// check if SerializedLambda class is present
    +						try {
    +							Class.forName("java.lang.invoke.SerializedLambda");
    +						}
    +						catch (Exception e) {
    +							throw new UnsupportedOperationException("User code tries to use lambdas, but framework
is running with a Java version < 8");
    +						}
    +						serializedLambda = serialVersion;
    +						break;
    +					}
    +				}
    +				catch (NoSuchMethodException e) {
    +					// thrown if the method is not there. fall through the loop
    +				}
    +			}
    +
    +			// not a lambda method -> return null
    +			if (serializedLambda == null) {
    +				return null;
    +			}
    +
    +			// find lambda method
    +			Method implClassMethod = serializedLambda.getClass().getDeclaredMethod("getImplClass");
    +			Method implMethodNameMethod = serializedLambda.getClass().getDeclaredMethod("getImplMethodName");
    +			Method implMethodSig = serializedLambda.getClass().getDeclaredMethod("getImplMethodSignature");
    +
    +			String className = (String) implClassMethod.invoke(serializedLambda);
    +			String methodName = (String) implMethodNameMethod.invoke(serializedLambda);
    +			String methodSig = (String) implMethodSig.invoke(serializedLambda);
    +
    +			Class<?> implClass = Class.forName(className.replace('/', '.'), true, Thread.currentThread().getContextClassLoader());
    +
    +			// find constructor
    +			if (methodName.equals("<init>")) {
    +				Constructor<?>[] constructors = implClass.getDeclaredConstructors();
    +				for (Constructor<?> constructor : constructors) {
    +					if(getConstructorDescriptor(constructor).equals(methodSig)) {
    +						return new LambdaExecutable(constructor);
    +					}
    +				}
    +			}
    +			// find method
    +			else {
    +				List<Method> methods = getAllDeclaredMethods(implClass);
    +				for (Method method : methods) {
    +					if(method.getName().equals(methodName) && getMethodDescriptor(method).equals(methodSig))
{
    +						return new LambdaExecutable(method);
    +					}
    +				}
    +			}
    +			throw new Exception("No lambda method found.");
    +		}
    +		catch (Exception e) {
    +			throw new RuntimeException("Could not extract lambda method out of function: " + e.getClass().getSimpleName()
+ " - " + e.getMessage(), e);
    --- End diff --
    
    RuntimeException is usually used for programming errors (wrong arguments, null divisions,
...).
    Something that is expected to fail sometimes beyond the programmers control (I/O, code
analysis, etc) should use checked exceptions.


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