http://service_host:8080/search?q=purple%20rain&limit=5&skip=0&project=title,genres,plot,year&search=title,plot&filter=genres:Music

{
  "request": {
    "q": "purple rain",
    "skip": 0,
    "limit": 5,
    "search": "title,plot",
    "project": "title,genres,plot,year",
    "filter": [
      "genres:Music"
    ]
  },
  "docs": [
    {
      "plot": "A young musician, tormented by an abusive situation at home, must contend with a rival singer, a burgeoning romance and his own dissatisfied band as his star begins to rise.",
      "genres": [
        "Drama",
        "Music",
        "Musical"
      ],
      "title": "Purple Rain",
      "year": 1984
    },
    {
      "plot": "Graffiti Bridge is the unofficial sequel to Purple Rain. In this movie, The Kid and Morris Day are still competitors and each runs a club of his own. They make a bet about who writes the ...",
      "genres": [
        "Drama",
        "Music",
        "Musical"
      ],
      "title": "Graffiti Bridge",
      "year": 1990
    }
  ],
  "meta": [
    {
      "count": {
        "total": 2
      }
    }
  ]
}
```## 搜索服务实现

代码！这才是关键所在。为了尽可能保持简单，以便我们的实现能适用于所有前端技术，我们正在实现一个使用标准 GET 请求参数并返回易于消化的 JSON 的 HTTP 服务。Java 是我们选择的语言，让我们开始吧。编程是一项带有主观色彩的工作，所以我们承认在 Java 和其他语言中有多种方法可以实现这一点——这里提供一种主观的（且经验丰富的）方法。

要运行此处展示的配置，一个很好的起点是运行文章《[Using Atlas Search from Java](https://www.mongodb.com/developer/products/atlas/atlas-search-java/?utm_campaign=devrel&utm_source=third-party-content&utm_medium=cta&utm_content=search-service-foojay&utm_term=erik.hatcher)》中的示例。一旦运行起来，创建一个名为 `movies_index` 的新索引，并使用以下 JSON 中指定的自定义索引配置：

```json
{
  "analyzer": "lucene.english",
  "searchAnalyzer": "lucene.english",
  "mappings": {
    "dynamic": true,
    "fields": {
      "cast": [
        { "type": "token" },
        { "type": "string" }
      ],
      "genres": [
        { "type": "token" },
        { "type": "string" }
      ]
    }
  }
}

public class SearchServlet extends HttpServlet {
    private MongoCollection<Document> collection;
    private String index_name;
    private Logger logger;

    // ...
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
        String q = request.getParameter("q");
        String search_fields_value = request.getParameter("search");
        String limit_value = request.getParameter("limit");
        String skip_value = request.getParameter("skip");
        String project_fields_value = request.getParameter("project");
        String debug_value = request.getParameter("debug");
        String[] filters = request.getParameterMap().get("filter");
        // ...
    }
}

@Override
public void init(ServletConfig config) throws ServletException {
    super.init(config);
    logger = Logger.getLogger(config.getServletName());
    String uri = System.getenv("ATLAS_URI");
    if (uri == null) {
        throw new ServletException("ATLAS_URI must be specified");
    }
    String database_name = config.getInitParameter("database");
    String collection_name = config.getInitParameter("collection");
    index_name = config.getInitParameter("index");
    // ... log the details ...
    MongoClient mongo_client = MongoClients.create(uri);
    MongoDatabase database = mongo_client.getDatabase(database_name);
    collection = database.getCollection(collection_name);
}

<web-app>
  <servlet>
    <servlet-name>SearchServlet</servlet-name>
    <servlet-class>com.mongodb.atlas.SearchServlet</servlet-class>
    <load-on-startup>1</load-on-startup>
    <!-- The connection string must be defined in the `ATLAS_URI` environment variable -->
    <init-param>
      <param-name>database</param-name>
      <param-value>sample_mflix</param-value>
    </init-param>
    <init-param>
      <param-name>collection</param-name>
      <param-value>movies</param-value>
    </init-param>
    <init-param>
      <param-name>index</param-name>
      <param-value>movies_index</param-value>
    </init-param>
  </servlet>
  <servlet-mapping>
    <servlet-name>SearchServlet</servlet-name>
    <url-pattern>/search</url-pattern>
  </servlet-mapping>
</web-app>

[
  {
    "$search": {
      "compound": {
        "must": [
          {
            "text": {
              "query": "purple rain",
              "path": [
                "title",
                "plot"
              ]
            }
          }
        ],
        "filter": [
          {
            "equals": {
              "path": "genres",
              "value": "Music"
            }
          }
        ]
      },
      "index": "movies_index",
      "count": {
        "type": "total"
      }
    }
  },
  {
    "$facet": {
      "docs": [
        {
          "$skip": 0
        },
        {
          "$limit": 5
        },
        {
          "$project": {
            "title": 1,
            "genres": 1,
            "plot": 1,
            "year": 1,
            "_id": 0
          }
        }
      ],
      "meta": [
        {
          "$replaceWith": "$$SEARCH_META"
        },
        {
          "$limit": 1
        }
      ]
    }
  }
]

// $search
List<SearchPath> search_path = new ArrayList<>();
for (String search_field : search_fields) {
    search_path.add(SearchPath.fieldPath(search_field));
}

CompoundSearchOperator operator = SearchOperator.compound()
    .must(List.of(SearchOperator.text(search_path, List.of(q))));

if (filter_operators.size() > 0)
    operator = operator.filter(filter_operators);

Bson searchStage = search(
    operator,
    searchOptions()
        .option("scoreDetails", debug)
        .index(index_name)
        .count(SearchCount.total())
);

List<String> project_fields = new ArrayList<>();
if (project_fields_value != null) {
    project_fields.addAll(List.of(project_fields_value.split(",")));
}

boolean include_id = false;
if (project_fields.contains("_id")) {
    include_id = true;
    project_fields.remove("_id");
}

boolean include_score = false;
if (project_fields.contains("_score")) {
    include_score = true;
    project_fields.remove("_score");
}

// $project
List<Bson> projections = new ArrayList<>();
projections.add(include(project_fields));

if (include_id) {
    projections.add(include("_id"));
} else {
    projections.add(excludeId());
}

if (debug) {
    projections.add(meta("_scoreDetails", "searchScoreDetails"));
}

if (include_score) {
    projections.add(metaSearchScore("_score"));
}

Bson projection = fields(projections);

AggregateIterable<Document> aggregation_results = collection.aggregate(List.of(
    searchStage, facet_stage
));

Document response_doc = new Document();
response_doc.put("request", new Document()
    .append("q", q)
    .append("skip", skip)
    .append("limit", limit)
    .append("search", search_fields_value)
    .append("project", project_fields_value)
    .append("filter", filters==null ? Collections.EMPTY_LIST : List.of(filters)));

if (debug) {
    response_doc.put("debug", aggregation_results.explain().toBsonDocument());
}

// When using $facet stage, only one "document" is returned,
// containing the keys specified above: "docs" and "meta"
Document results = aggregation_results.first();
for (String s : results.keySet()) {
    response_doc.put(s,results.get(s));
}

response.setContentType("text/json");
PrintWriter writer = response.getWriter();
writer.println(response_doc.toJson());
writer.close();

./gradlew buildProduct