Java tutorial
/* * 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. */ // Build example in default package // package org.apache.giraph.examples; import org.apache.giraph.graph.BasicComputation; import org.apache.giraph.conf.LongConfOption; import org.apache.giraph.edge.Edge; import org.apache.giraph.graph.Vertex; import org.apache.hadoop.io.DoubleWritable; import org.apache.hadoop.io.FloatWritable; import org.apache.hadoop.io.LongWritable; import org.apache.log4j.Logger; import java.io.IOException; /** * Demonstrates the basic Pregel shortest paths implementation. */ //@Algorithm( // name = "Shortest paths", // description = "Finds all shortest paths from a selected vertex" //) public class LongestPathDAG extends BasicComputation<LongWritable, DoubleWritable, FloatWritable, DoubleWritable> { /** The shortest paths id */ public static final LongConfOption SOURCE_ID = new LongConfOption("SimpleLongestPathsVertex.sourceId", 1, "The longest paths id"); /** Class logger */ private static final Logger LOG = Logger.getLogger(LongestPathDAG.class); /** * Is this vertex the source id? * * @param vertex Vertex * @return True if the source id */ private boolean isSource(Vertex<LongWritable, ?, ?> vertex) { return vertex.getId().get() == SOURCE_ID.get(getConf()); } @Override public void compute(Vertex<LongWritable, DoubleWritable, FloatWritable> vertex, Iterable<DoubleWritable> messages) throws IOException { if (getSuperstep() == 0) { vertex.setValue(new DoubleWritable(0)); } double maxDist = 0; for (DoubleWritable message : messages) { maxDist = Math.max(maxDist, message.get()); } LOG.info("Vertex " + vertex.getId() + " got maxDist = " + maxDist + " vertex value = " + vertex.getValue()); if (maxDist >= vertex.getValue().get()) { vertex.setValue(new DoubleWritable(maxDist)); for (Edge<LongWritable, FloatWritable> edge : vertex.getEdges()) { double distance = maxDist + edge.getValue().get(); LOG.info("Vertex " + vertex.getId() + " sent to " + edge.getTargetVertexId() + " = " + distance); sendMessage(edge.getTargetVertexId(), new DoubleWritable(distance)); } } vertex.voteToHalt(); } }