无法遍历 MongoDB 集合

问题描述

作为熟悉 MongoDB 的一步，我开始创建简单的 Java 类来在 MongoDB 中执行 CRUD。我能够与 MongoDB 建立连接。然而，当我尝试遍历 MongoDB 集合时，我遇到了错误。已实现的 Java 类在此共享。

import com.mongodb.client.FindIterable;
import com.mongodb.client.MongoClients;
import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;
import java.util.Iterator;
import org.bson.Document;
public class ReadMongo {
    public static void main( String args[] ) {
        //Creating a MongoDB client
        com.mongodb.client.MongoClient mongo = MongoClients.create("mongodb://localhost:27017");
        //Connecting to the database
        MongoDatabase database = mongo.getDatabase("myDB");
        //Creating a collection object
        MongoCollection<Document> collection = database.getCollection("myGrid");
        //Retrieving the documents
        FindIterable<Document> iterDoc = collection.find();
        Iterator it = iterDoc.iterator();
        while (it.hasNext()) {
            System.out.println(it.next());
        }
    }
}

下面我分享了错误日志。

INFO: Cluster created with settings {hosts=[localhost:27017],mode=SINGLE,requiredClusterType=UNKNowN,serverSelectionTimeout='30000 ms',maxWaitQueueSize=500}
Exception in thread "main" java.lang.NoSuchMethodError: com.mongodb.internal.operation.Syncoperations.<init>(Lcom/mongodb/MongoNamespace;Ljava/lang/Class;Lcom/mongodb/ReadPreference;Lorg/bson/codecs/configuration/CodecRegistry;Lcom/mongodb/WriteConcern;Z)V
    at com.mongodb.client.internal.MongoCollectionImpl.<init>(MongoCollectionImpl.java:106)
    at com.mongodb.client.internal.MongoDatabaseImpl.getCollection(MongoDatabaseImpl.java:132)
    at com.mongodb.client.internal.MongoDatabaseImpl.getCollection(MongoDatabaseImpl.java:127)
    at ReadMongo.main(ReadMongo.java:14)

第 14 行对应于 MongoCollection<Document> collection = database.getCollection("myGrid"); 行。

解决方法

我还是不知道上面的代码有什么问题。尽管如此，我还是能够通过以下资源解决这个问题：(i) resource 1 和 (ii) resource 2。最终的工作解决方案如下。

import com.mongodb.MongoClient;
import com.mongodb.MongoClientURI;
import com.mongodb.client.FindIterable;
import com.mongodb.client.MongoCursor;
import com.mongodb.client.MongoDatabase;
import org.bson.Document;

public class MongoDB {
    
    public static MongoClient mongoClient;
    public static MongoDatabase database;
    
    public static void main(String[] args) {
        mongoClient = new MongoClient(new MongoClientURI("mongodb://localhost:27017"));
        database = mongoClient.getDatabase("myDB");
      
        FindIterable<Document> mydatabaserecords = database.getCollection("myGrid").find();
        MongoCursor<Document> iterator = mydatabaserecords.iterator();
        while (iterator.hasNext()) {
            Document doc = iterator.next();
            System.out.println(iterator.next());
        }
    }
}