Hive UDF文本到数组

Question

我正在尝试为Hive创建一些UDF,它给了我比已经提供的split()功能更多的功能.

import org.apache.hadoop.hive.ql.exec.UDF;
import org.apache.hadoop.io.Text;

public class LowerCase extends UDF {

  public Text evaluate(final Text text) {
    return new Text(stemWord(text.toString()));
  }

  /**
   * Stems words to normal form.
   * 
   * @param word
   * @return Stemmed word.
   */
  private String stemWord(String word) {
    word = word.toLowerCase();
    // Remove special characters
    // Porter stemmer
    // ...
    return word;
  }
}

这在Hive中有效.我将这个类导出到一个jar文件中.然后我将它加载到Hive中

add jar /path/to/myJar.jar;

并使用创建一个函数

create temporary function lower_case as 'LowerCase';

我有一个带有String字段的表.声明是:

select lower_case(text) from documents;

但是现在我想创建一个返回数组的函数(例如split split).

import java.util.ArrayList;
import java.util.List;
import java.util.StringTokenizer;

import org.apache.hadoop.hive.ql.exec.UDF;
import org.apache.hadoop.io.Text;

public class WordSplit extends UDF {

  public Text[] evaluate(final Text text) {
    List<Text> splitList = new ArrayList<>();

    StringTokenizer tokenizer = new StringTokenizer(text.toString());

    while (tokenizer.hasMoreElements()) {
      Text word = new Text(stemWord((String) tokenizer.nextElement()));

      splitList.add(word);
    }

    return splitList.toArray(new Text[splitList.size()]);
  }

  /**
   * Stems words to normal form.
   * 
   * @param word
   * @return Stemmed word.
   */
  private String stemWord(String word) {
    word = word.toLowerCase();
    // Remove special characters
    // Porter stemmer
    // ...
    return word;
  }
}

不幸的是,如果我执行上面提到的完全相同的加载过程,则此功能不起作用.我收到以下错误:

FAILED: SemanticException java.lang.IllegalArgumentException: Error: name expected at the position 7 of 'struct<>' but '>' is found.

由于我没有找到任何提及这种转变的文件,我希望你能给我一些建议!

Answer 1

实际上'UDF'接口确实支持返回一个数组.

返回ArrayList<Text>甚至ArrayList<String>代替Text[]

您的代码应如下所示:

import java.util.ArrayList;
import java.util.List;
import java.util.StringTokenizer;

import org.apache.hadoop.hive.ql.exec.UDF;
import org.apache.hadoop.io.Text;

public class WordSplit extends UDF {

  public ArrayList<String> evaluate(final Text text) {
    ArrayList<String> splitList = new ArrayList<String>();

    StringTokenizer tokenizer = new StringTokenizer(text.toString());

    while (tokenizer.hasMoreElements()) {
      String word = stemWord((String) tokenizer.nextElement());
      splitList.add(word);
    }
    return splitList;
  }

  /**
   * Stems words to normal form.
   *
   * @param word
   * @return Stemmed word.
   */
  private String stemWord(String word) {
    word = word.toLowerCase();
    return word;
  }
}