如何在 Hadoop 中序列化 Java 对象？

对象应该实现Writable接口以便在 Hadoop 中传输时序列化。采取卢森ScoreDoc以类为例：

public class ScoreDoc implements java.io.Serializable {

  /** The score of this document for the query. */
  public float score;

  /** Expert: A hit document's number.
   * @see Searcher#doc(int) */
  public int doc;

  /** Only set by {@link TopDocs#merge} */
  public int shardIndex;

  /** Constructs a ScoreDoc. */
  public ScoreDoc(int doc, float score) {
    this(doc, score, -1);
  }

  /** Constructs a ScoreDoc. */
  public ScoreDoc(int doc, float score, int shardIndex) {
    this.doc = doc;
    this.score = score;
    this.shardIndex = shardIndex;
  }

  // A convenience method for debugging.
  @Override
  public String toString() {
    return "doc=" + doc + " score=" + score + " shardIndex=" + shardIndex;
  }
}

我应该如何序列化它Writable界面？之间有什么联系Writable and java.io.serializable界面？

我认为篡改内置的 Lucene 类并不是一个好主意。相反，拥有您自己的类，该类可以包含 ScoreDoc 类型的字段，并在接口中实现 Hadoop 可写。它会是这样的：

public class MyScoreDoc implements Writable  {      

  private ScoreDoc sd;

  public void write(DataOutput out) throws IOException {
      String [] splits = sd.toString().split(" ");

      // get the score value from the string
      Float score = Float.parseFloat((splits[0].split("="))[1]);

      // do the same for doc and shardIndex fields
      // ....    

      out.writeInt(score);
      out.writeInt(doc);
      out.writeInt(shardIndex);
  }

  public void readFields(DataInput in) throws IOException {
      float score = in.readInt();
      int doc = in.readInt();
      int shardIndex = in.readInt();

      sd = new ScoreDoc (score, doc, shardIndex);
  }

  //String toString()
}