嗨，我在为吉拉夫编写自己的代码。
我成功地构建了eclipse环境。然后我粘贴了simpleshortestpathsco计算代码，制作jar并成功运行它（输出与giraph示例相同）。
所以现在我想更深入地理解。为此，我在代码中插入了system.out.println（），但它不起作用。。。是不是正常的system.out.prinln（）不能显示给我？
然后我从尝试system.out.println（）转到尝试使用log4j。但是我找不到日志！！
这是密码

package code1;

import org.apache.giraph.Algorithm;
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;

@Algorithm(
    name = "Shortest paths",
    description = "Finds all shortest paths from a selected vertex"
)
public class MySimpleShortpath extends BasicComputation<
    LongWritable, DoubleWritable, FloatWritable, DoubleWritable> {
  /**The shortest paths id */
  public static final LongConfOption SOURCE_ID =
      new LongConfOption("SimpleShortestPathsVertex.sourceId", 1,
          "The shortest paths id");
  /**Class logger */
  private static final Logger LOG =
      Logger.getLogger(MySimpleShortpath.class);

  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(Double.MAX_VALUE));
    }
    double minDist = isSource(vertex) ? 0d : Double.MAX_VALUE;
    for (DoubleWritable message : messages) {
      minDist = Math.min(minDist, message.get());
    }
    if (LOG.isDebugEnabled()) {
      LOG.debug("Vertex " + vertex.getId() + " got minDist = " + minDist +
          " vertex value = " + vertex.getValue());
    }
    if (minDist < vertex.getValue().get()) {
      vertex.setValue(new DoubleWritable(minDist));
      for (Edge<LongWritable, FloatWritable> edge : vertex.getEdges()) {
        double distance = minDist + edge.getValue().get();
        // ============== Here is the code for Log4j & System.out.println() ==========
        if (LOG.isDebugEnabled()) {
          LOG.debug("Vertex " + vertex.getId() + " sent to " +
              edge.getTargetVertexId() + " = " + distance);
          System.out.println("Here");
        }
        sendMessage(edge.getTargetVertexId(), new DoubleWritable(distance));
      }
    }
    vertex.voteToHalt();
  }
}