今天使用mongo-java-drive寫連線mongo的客戶端，著實被上面那個錯坑了一把。回顧一下解決過程：

報錯：

 1 com.mongodb.MongoTimeoutException: Timed out after 30000 ms while waiting to connect. Client view of cluster state is {type=UNKNOWN, servers=[{address=localhost:27017, 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}}]
 2     at com.mongodb.connection.BaseCluster.getDescription(BaseCluster.java:167)
 3     at com.mongodb.client.internal.MongoClientDelegate.getConnectedClusterDescription(MongoClientDelegate.java:106)
 4     at com.mongodb.client.internal.MongoClientDelegate.createClientSession(MongoClientDelegate.java:77)
 5     at com.mongodb.client.internal.MongoClientDelegate$DelegateOperationExecutor.getClientSession(MongoClientDelegate.java:185)
 6     at com.mongodb.client.internal.MongoClientDelegate$DelegateOperationExecutor.execute(MongoClientDelegate.java:152)
 7     at com.mongodb.client.internal.MongoCollectionImpl.executeSingleWriteRequest(MongoCollectionImpl.java:894)
 8     at com.mongodb.client.internal.MongoCollectionImpl.executeInsertOne(MongoCollectionImpl.java:443)
 9     at com.mongodb.client.internal.MongoCollectionImpl.insertOne(MongoCollectionImpl.java:427)
10     at com.mongodb.client.internal.MongoCollectionImpl.insertOne(MongoCollectionImpl.java:421)
11     at com.czb.chargepile.core.MongeTemplate.insert(MongeTemplate.java:59)
12     at com.czb.chargepile.manage.X01Manager.insert(X01Manager.java:17)
13     at manage.X01ManagerTest.main(X01ManagerTest.java:21)

分析：mongodb資料庫連線超時，也就是客戶端連不上mongo

程式碼：

 1 MongoCredential credential = MongoCredential.createCredential(user, databaseName, password);
 2 
 3 mongoClient = MongoClients.create(
 4 
 5 MongoClientSettings.builder()
 6 
 7 .applyToSslSettings(builder -> builder.enabled(true))
 8 
 9 .applyToClusterSettings(builder ->
10 
11 builder.hosts(Arrays.asList(new ServerAddress("localhost", 27017))))
12 
13 .credential(credential)
14 
15 .build());
16 
17 MongoDatabase database = mongoClient.getDatabase(databaseName);

解決：

1、看到錯誤，首先想到的是使用者名稱密碼不對，為了確保密碼無誤，重新設定了mongo的密碼，然而並未好使

2、檢查使用者所屬資料庫是否正確，經過檢查，發現完全匹配

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

檢查mongo-java-drive版本是否和mongo版本匹配，發現完全匹配

4、最後開始懷疑上面的程式碼有問題，找官方文件https://mongodb.github.io/mongo-java-driver/3.8/driver/tutorials/authentication/，從這裡找到了新的寫法，先無腦拷貝，然後執行，發現這裡寫法是成功的，與自己的程式碼對比，發現我的程式碼多了一行

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

回到我程式碼，去掉，發現成功了。又回去看官方文件，找到端倪

如果使用那個選項，傳輸過程會使用TLS/SSL對傳輸層進行加密，但是我的mongo服務是沒有對應設定的，所以導致連線不