Timed out after 30000 ms while waiting to connect

今天使用mongo-java-drive写连接mongo的客户端，着实被上面那个错坑了一把。回顾一下解决过程：

报错：

 com.mongodb.MongoTimeoutException: Timed out after  ms while waiting to connect. Client view of cluster state is {type=UNKNOWN, servers=[{address=localhost:, type=UNKNOWN, state=CONNECTING, exception={com.mongodb.MongoSocketWriteException: Exception sending message}, caused by {javax.net.ssl.SSLHandshakeException: Remote host closed connection during handshake}, caused by {java.io.EOFException: SSL peer shut down incorrectly}}]
     at com.mongodb.connection.BaseCluster.getDescription(BaseCluster.java:)
     at com.mongodb.client.internal.MongoClientDelegate.getConnectedClusterDescription(MongoClientDelegate.java:)
     at com.mongodb.client.internal.MongoClientDelegate.createClientSession(MongoClientDelegate.java:)
     at com.mongodb.client.internal.MongoClientDelegate$DelegateOperationExecutor.getClientSession(MongoClientDelegate.java:)
     at com.mongodb.client.internal.MongoClientDelegate$DelegateOperationExecutor.execute(MongoClientDelegate.java:)
     at com.mongodb.client.internal.MongoCollectionImpl.executeSingleWriteRequest(MongoCollectionImpl.java:)
     at com.mongodb.client.internal.MongoCollectionImpl.executeInsertOne(MongoCollectionImpl.java:)
     at com.mongodb.client.internal.MongoCollectionImpl.insertOne(MongoCollectionImpl.java:)
     at com.mongodb.client.internal.MongoCollectionImpl.insertOne(MongoCollectionImpl.java:)
     at com.czb.chargepile.core.MongeTemplate.insert(MongeTemplate.java:)
     at com.czb.chargepile.manage.X01Manager.insert(X01Manager.java:)
     at manage.X01ManagerTest.main(X01ManagerTest.java:)

分析：mongodb数据库连接超时，也就是客户端连不上mongo

代码：

 MongoCredential credential = MongoCredential.createCredential(user, databaseName, password);

 mongoClient = MongoClients.create(

 MongoClientSettings.builder()

 .applyToSslSettings(builder -> builder.enabled(true))

 .applyToClusterSettings(builder ->

 builder.hosts(Arrays.asList(new ServerAddress("localhost", 27017))))

 .credential(credential)

 .build());

 MongoDatabase database = mongoClient.getDatabase(databaseName);

解决：

1、看到错误，首先想到的是用户名密码不对，为了确保密码无误，重新设置了mongo的密码，然而并未好使

2、检查用户所属数据库是否正确，经过检查，发现完全匹配

3、通过：https://docs.mongodb.com/ecosystem/drivers/driver-compatibility-reference/#reference-compatibility-mongodb-java

检查mongo-java-drive版本是否和mongo版本匹配，发现完全匹配

4、最后开始怀疑上面的代码有问题，找官方文档https://mongodb.github.io/mongo-java-driver/3.8/driver/tutorials/authentication/，从这里找到了新的写法，先无脑拷贝，然后运行，发现这里写法是成功的，与自己的代码对比，发现我的代码多了一行

 .applyToSslSettings(builder -> builder.enabled(true))

回到我代码，去掉，发现成功了。又回去看官方文档，找到端倪

如果使用那个选项，传输过程会使用TLS/SSL对传输层进行加密，但是我的mongo服务是没有对应设置的，所以导致连接不上。