12.12图计算选购

import org.apache.giraph.graph.BasicComputation;
import org.apache.giraph.graph.Vertex;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.NullWritable;

public class SimpleShortestPathsComputation extends BasicComputation<
    LongWritable, IntWritable, NullWritable, IntWritable> {

  @Override
  public void compute(Vertex<LongWritable, IntWritable, NullWritable> vertex,
                      Iterable<IntWritable> messages) {
    int minDist = isSource(vertex) ? 0 : Integer.MAX_VALUE;
    for (IntWritable msg : messages) {
      minDist = Math.min(minDist, msg.get());
    }
    if (minDist < vertex.getValue().get()) {
      vertex.setValue(new IntWritable(minDist));
      for (Edge<LongWritable, NullWritable> edge : vertex.getEdges()) {
        sendMessage(edge.getTargetVertexId(), new IntWritable(minDist + 1));
      }
    }
    vertex.voteToHalt();
  }

  private boolean isSource(Vertex<LongWritable, IntWritable, NullWritable> vertex) {
    return vertex.getId().get() == getSourceId();
  }
}