无法从java连接到本地mongoDB

Question

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public static void main(String[] args) {
        // connect to the local database server,default:127.0.0.1:27017
        MongoClient mongoClient = MongoClients.create();
        // get handle to "testDB" database
        MongoDatabase database = (MongoDatabase) mongoClient.getDatabase("testDB");
        SingleResultCallback<Void> callbackWhenFinished = new SingleResultCallback<Void>() {
            @Override
            public void onResult(final Void result, final Throwable t) {
                System.out.println("Operation Finished!");
            }
        };
        // get a handle to the "test" collection
        MongoCollection<Document> collection = database.getCollection("test");
        collection.insertOne(new Document("lala","hehe"),callbackWhenFinished);
    }

我确信我已经在127.0.0.1:27017启动了数据库服务，并且可以用shell和非异步方法连接。错误：

PrimaryServerSelector没有从群集描述中选择服务器ClusterDescription{type=unknown,connectionmode=single,all=[ServerDescription{address=localhost:27017,type=unknown,state=connecting}]}。超时前等待30000毫秒

Answer 1

我在自己的（正在运行的）MongoDB服务器上运行您的代码，可以看到相同的错误。但令我震惊的是，错误显示“在超时前等待30000ms”，但代码在不到30秒的时间内完成。这给出了一个问题的暗示。

请记住，这是异步的--因此，您不能期望所有操作都在同一线程上顺序运行。实际发生的情况是，main方法在对数据库的调用完成之前就已经完成了。

如果在终止之前更改代码以等待结果返回，则会得到更合理的结果。

public static void main(String[] args) throws InterruptedException {
    CountDownLatch latch = new CountDownLatch(1);
    // connect to the local database server,default:127.0.0.1:27017
    MongoClient mongoClient = MongoClients.create();
    // get handle to "testDB" database
    MongoDatabase database = (MongoDatabase) mongoClient.getDatabase("testDB");
    SingleResultCallback<Void> callbackWhenFinished = new SingleResultCallback<Void>() {
        @Override
        public void onResult(final Void result, final Throwable t) {
            System.out.println("Operation Finished!");
            latch.countDown();
        }
    };
    // get a handle to the "test" collection
    MongoCollection<Document> collection = database.getCollection("test");
    collection.insertOne(new Document("lala", "hehe"), callbackWhenFinished);

    latch.await();
}

Aug 11, 2015 9:31:34 AM com.mongodb.diagnostics.logging.JULLogger log
INFO: Cluster created with settings {hosts=[localhost:27017], mode=SINGLE, requiredClusterType=UNKNOWN, serverSelectionTimeout='30000 ms', maxWaitQueueSize=500}
Aug 11, 2015 9:31:35 AM com.mongodb.diagnostics.logging.JULLogger log
INFO: No server chosen by PrimaryServerSelector from cluster description ClusterDescription{type=UNKNOWN, connectionMode=SINGLE, all=[ServerDescription{address=localhost:27017, type=UNKNOWN, state=CONNECTING}]}. Waiting for 30000 ms before timing out
Aug 11, 2015 9:31:35 AM com.mongodb.diagnostics.logging.JULLogger log
INFO: Opened connection [connectionId{localValue:1, serverValue:4}] to localhost:27017
Aug 11, 2015 9:31:35 AM com.mongodb.diagnostics.logging.JULLogger log
INFO: Monitor thread successfully connected to server with description ServerDescription{address=localhost:27017, type=STANDALONE, state=CONNECTED, ok=true, version=ServerVersion{versionList=[3, 0, 2]}, minWireVersion=0, maxWireVersion=3, electionId=null, maxDocumentSize=16777216, roundTripTimeNanos=1281647}
Aug 11, 2015 9:31:35 AM com.mongodb.diagnostics.logging.JULLogger log
INFO: Opened connection [connectionId{localValue:2, serverValue:5}] to localhost:27017
Operation Finished!

public static void main(String[] args) throws InterruptedException {
    CountDownLatch latch = new CountDownLatch(1);
    // connect to the local database server,default:127.0.0.1:27017
    MongoClient mongoClient = MongoClients.create();
    // get handle to "testDB" database
    MongoDatabase database = mongoClient.getDatabase("testDB");
    // get a handle to the "test" collection
    MongoCollection<Document> collection = database.getCollection("test");

    collection.insertOne(new Document("lala", "hehe"),
                         (result, t) -> {
                             System.out.println("Operation Finished!");
                             latch.countDown();
                         });

    latch.await();
}