创建 MongoClient 实例时如何捕获异常

Question

我正在使用 Mongo DB java 驱动程序连接到 mongo 实例。下面是我用来创建 MongoClient 实例的代码。

try {
            new MongoClient("localhost", 1111);

        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

如果主机名或端口号不正确，我会得到以下异常。我徘徊如何捕捉异常。 MongoDB 连接发生在客户端代码无法捕获的内部线程中。我想知道 MongoClient 是否连接正确。我怎样才能获得这些信息？

INFO: Exception in monitor thread while connecting to server localhost:0
com.mongodb.MongoSocketOpenException: Exception opening socket
    at com.mongodb.connection.SocketStream.open(SocketStream.java:63)
    at com.mongodb.connection.InternalStreamConnection.open(InternalStreamConnection.java:115)
    at com.mongodb.connection.DefaultServerMonitor$ServerMonitorRunnable.run(DefaultServerMonitor.java:116)
    at java.lang.Thread.run(Thread.java:745)
Caused by: java.net.ConnectException: Can't assign requested address (connect failed)
    at java.net.PlainSocketImpl.socketConnect(Native Method)
    at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350)
    at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)
    at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)
    at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
    at java.net.Socket.connect(Socket.java:589)
    at com.mongodb.connection.SocketStreamHelper.initialize(SocketStreamHelper.java:50)
    at com.mongodb.connection.SocketStream.open(SocketStream.java:58)
    ... 3 more

EDIT1

上面显示的异常没有被我的代码捕获。它可能会被 Mongo 代码捕获。所以不知道实例是否创建正确。

Answer 1

服务器连接是在守护线程上创建的。长话短说，您将无法在创建 Mongo 客户端时检查与连接相关的错误。

当您创建第一个涉及读取或写入的真实数据库时，您将不得不延迟连接检查。

仅用于演示目的，让您了解一下。

MongoClient mongoClient = new MongoClient("127.0.34.1", 89);
DB db = mongoClient.getDB("test");
try {
   db.addUser("user", new char[] {'p', 'a', 's', 's'});
} catch(Exception e) { MongoTimeoutException exception}

来自 Deamon 线程的 MongoSocketOpenException

INFO: Exception in monitor thread while connecting to server 127.0.34.1:89
com.mongodb.MongoSocketOpenException: Exception opening socket
at com.mongodb.connection.SocketStream.open(SocketStream.java:63)
at com.mongodb.connection.InternalStreamConnection.open(InternalStreamConnection.java:115)
at com.mongodb.connection.DefaultServerMonitor$ServerMonitorRunnable.run(DefaultServerMonitor.java:116)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.net.ConnectException: Connection refused: connect

来自主线程的 MongoTimeoutException

Exception in thread "main" com.mongodb.MongoTimeoutException: Timed out after 30000 ms while waiting for a server that matches ReadPreferenceServerSelector{readPreference=primary}. Client view of cluster state is {type=UNKNOWN, servers=[{address=127.0.34.1:89, type=UNKNOWN, state=CONNECTING, exception={com.mongodb.MongoSocketOpenException: Exception opening socket}, 
caused by {java.net.ConnectException: Connection refused: connect}}]
at com.mongodb.connection.BaseCluster.createTimeoutException(BaseCluster.java:375)

因此，使用MongoTimeoutException 将代码包装在try catch 块中，它可以正常检查与连接相关的错误。

Answer 2

它非常简单优雅：

1. 将System.err 重定向到一个文件：

   ByteArrayOutputStream file=new ByteArrayOutputStream();
   System.setErr(new PrintStream(file));
   

2. 使用您的MongoClient 和您的MongoCredentials 连接到服务器：

   MongoCredential credenciales=MongoCredential.createCredential("root", "admin", "root".toCharArray());
   MongoClient client = new MongoClient(new ServerAddress("localhost"), Arrays.asList(credenciales));
   

3. 读取错误输出，在ByteArrayOutputStream对象中：

   String texto=new String(file.toByteArray());
   

4. 检查Autentication failed字符串是否存在：

   if (texto.contains("'Authentication failed.'"))
      // do something;
   else
     ...
   

Answer 3

对于现在偶然发现这一点的任何人。我遇到了同样的问题并尝试使用 Macario 的答案，但运气不佳。然后意识到监视连接的线程不是将其发送到 System.err，而是将其发送到 System.out，所以不要使用 System.err，而是像这样使用 System.out：

PrintStream out = System.out;  // Save the original out stream to reset later

// Set out to a buffer
ByteArrayOutputStream file=new ByteArrayOutputStream();
System.setOut(new PrintStream(file));

mongoClient = new MongoClient(new MongoClientURI("<connection_string>")));

// Found this to be important as we need to wait for the thread to dump to out
// 1000 millis was too fast for me but 2000 did the trick
Thread.sleep(2000);

// Convert buffer to a string
String texto=new String(file.toByteArray());

System.setOut(out); // Reset out

// Check if saved out contins the error (I was looking for MongoSocketException)
if(texto.contains("MongoSocketException")){
    // Do Stuff
}

Answer 4

  new MongoClient("localhost", 1111);

        } catch (MongoSocketOpenException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

您只需在 catch 块中命名适当的异​​常。这适用于任何例外。您可以为每个唯一异常添加尽可能多的 catch 块