java 运行mongo runcommand mapReduce例子

好的，你可以参考以下代码：

MongoClient mongoClient = new MongoClient("localhost:27017");
DB database = mongoClient.getDB("your_database_name");
DBCollection collection = database.getCollection("your_collection_name");

String map = "function() { " +
             "    emit(this.field_to_emit_on, 1); " +
             "}";

String reduce = "function(key, values) { " +
                "    var count = 0; " +
                "    for (var i in values) { " +
                "        count += values[i]; " +
                "    } " +
                "    return count; " +
                "}";

MapReduceOutput output = collection.mapReduce(map, reduce, "output_collection_name", null);

请注意替换 "your_database_name"、"your_collection_name" 和 "output_collection_name" 为实际的数据库名称、集合名称和输出集合名称。此外，请确保您已经导入了要处理的数据到集合中。