如何使用Java在MongoDB中创建索引？
在MongoDB中创建索引，您需要使用createIndex()方法。
语法
db.COLLECTION_NAME.createIndex({KEY:1})其中的键是要在其上创建索引的文件的名称，而1是升序。要以降序创建索引，您需要使用-1。
在Java中，您可以使用 createIndex()方法创建索引，该方法需要传递索引的类型（升序或降序）和要在其上创建索引的字段名称，例如-
createIndex(Indexes.descinding("name"));示例
import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;
import com.mongodb.client.model.Indexes;
import org.bson.Document;
import com.mongodb.MongoClient;
public class CreatingIndex {
public static void main( String args[] ) {
//Creating a MongoDB client
MongoClient mongo = new MongoClient( "localhost" , 27017 );
//Accessing the database
MongoDatabase database = mongo.getDatabase("myDatabase");
//Creating a collection
database.createCollection("sampleCollection");
//Retrieving the collection on which you want to create the index
MongoCollection<Document> coll = database.getCollection("sampleCollection");
//Creating an index
coll.createIndex(Indexes.ascending("age"));
System.out.println("Index created successfully");
//Printing the list of indices in the collection
for (Document index : coll.listIndexes()) {
System.out.println(index.toJson());
}
}
}输出结果
Index created successfully
{"v": 2, "key": {"_id": 1}, "name": "_id_", "ns": "myDatabase.sampleCollection"}
{"v": 2, "key": {"age": 1}, "name": "age_1", "ns": "myDatabase.sampleCollection"}