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利用Scan和Scroll处理大结果集

Elasticsearch在处理大结果集时可以使用scan和scroll。在Spring Data Elasticsearch中，可以向下面那样使用ElasticsearchTemplate来使用scan和scroll处理大结果集。

Example 39. Using Scan and Scroll(使用scan和scroll)

  1. SearchQuery searchQuery = new NativeSearchQueryBuilder()
  2.     .withQuery(matchAllQuery())
  3.     .withIndices("test-index")
  4.     .withTypes("test-type")
  5.     .withPageable(new PageRequest(0,1))
  6.     .build();
  7. String scrollId = elasticsearchTemplate.scan(searchQuery,1000,false);
  8. List<SampleEntity> sampleEntities = new ArrayList<SampleEntity>();
  9. boolean hasRecords = true;
  10. while (hasRecords){
  11.     Page<SampleEntity> page = elasticsearchTemplate.scroll(scrollId, 5000L , new ResultsMapper<SampleEntity>()
  12.     {
  13.         @Override
  14.         public Page<SampleEntity> mapResults(SearchResponse response) {
  15.             List<SampleEntity> chunk = new ArrayList<SampleEntity>();
  16.             for(SearchHit searchHit : response.getHits()){
  17.                 if(response.getHits().getHits().length <= 0) {
  18.                     return null;
  19.                 }
  20.                 SampleEntity user = new SampleEntity();
  21.                 user.setId(searchHit.getId());
  22.                 user.setMessage((String)searchHit.getSource().get("message"));
  23.                 chunk.add(user);
  24.             }
  25.             return new PageImpl<SampleEntity>(chunk);
  26.         }
  27.     });
  28.     if(page != null) {
  29.         sampleEntities.addAll(page.getContent());
  30.         hasRecords = page.hasNextPage();
  31.     }
  32.     else{
  33.         hasRecords = false;
  34.     }
  35.     }
  36. }