我目前正在使用 MongoDB Java API 开发一个项目。我在这个项目上工作了一段时间，但最近遇到了一个我无法解决的问题。我正在尝试制作一个容错的数据库系统。为了模拟数据库崩溃，我让我的程序连接到我制作的 Mongodb 服务器，执行简单的读取或写入，然后关闭数据库服务器。我最初认为这会导致我调用的某些方法抛出一个MongoException我可以捕获然后从数据库崩溃中恢复的方法。但是，我得到一个奇怪的堆栈跟踪，上面说我正在抛出 EOFException 等等。下面是堆栈跟踪本身。
Mar 04, 2013 8:06:15 PM com.mongodb.DBPortPool gotError
WARNING: emptying DBPortPool to polaris.cs.wcu.edu/152.30.5.5:12345 b/c of error
java.io.EOFException
at org.bson.io.Bits.readFully(Bits.java:48)
at org.bson.io.Bits.readFully(Bits.java:33)
at org.bson.io.Bits.readFully(Bits.java:28)
at com.mongodb.Response.<init>(Response.java:40)
at com.mongodb.DBPort.go(DBPort.java:124)
at com.mongodb.DBPort.call(DBPort.java:74)
at com.mongodb.DBTCPConnector.innerCall(DBTCPConnector.java:282)
at com.mongodb.DBTCPConnector.call(DBTCPConnector.java:256)
at com.mongodb.DBApiLayer$MyCollection.__find(DBApiLayer.java:289)
at com.mongodb.DBApiLayer$MyCollection.__find(DBApiLayer.java:274)
at com.mongodb.DBCursor._check(DBCursor.java:368)
at com.mongodb.DBCursor._hasNext(DBCursor.java:459)
at com.mongodb.DBCursor.hasNext(DBCursor.java:484)
at edu.wcu.cs.capstone.view.AbstractViewEngine.getView(AbstractViewEngine.java:57)
at edu.wcu.cs.capstone.transaction.ServerTransactionManager.getView(ServerTransactionManager.java:52)
at edu.wcu.cs.capstone.transaction.ServerTransactionManager.run(ServerTransactionManager.java:183)
at java.lang.Thread.run(Thread.java:722)
Caught exception
Mar 04, 2013 8:06:15 PM com.mongodb.DBPortPool gotError
WARNING: emptying DBPortPool to polaris.cs.wcu.edu/152.30.5.5:12345 b/c of error
java.io.IOException: couldn't connect to [polaris.cs.wcu.edu/152.30.5.5:12345] bc:java.net.ConnectException: Connec
at com.mongodb.DBPort._open(DBPort.java:214)
at com.mongodb.DBPort.go(DBPort.java:107)
at com.mongodb.DBPort.call(DBPort.java:74)
at com.mongodb.DBTCPConnector.innerCall(DBTCPConnector.java:282)
at com.mongodb.DBTCPConnector.call(DBTCPConnector.java:256)
at com.mongodb.DBApiLayer$MyCollection.__find(DBApiLayer.java:289)
at com.mongodb.DBApiLayer$MyCollection.__find(DBApiLayer.java:274)
at com.mongodb.DBCursor._check(DBCursor.java:368)
at com.mongodb.DBCursor._hasNext(DBCursor.java:459)
at com.mongodb.DBCursor.hasNext(DBCursor.java:484)
at edu.wcu.cs.capstone.view.AbstractViewEngine.getView(AbstractViewEngine.java:61)
at edu.wcu.cs.capstone.transaction.ServerTransactionManager.getView(ServerTransactionManager.java:52)
at edu.wcu.cs.capstone.transaction.ServerTransactionManager.run(ServerTransactionManager.java:183)
at java.lang.Thread.run(Thread.java:722)
DB is down.
Exception in thread "Thread-3" java.lang.NullPointerException
at edu.wcu.cs.capstone.transaction.ServerTransactionManager.run(ServerTransactionManager.java:184)
at java.lang.Thread.run(Thread.java:722)
Caught ExceptionandDB is down.是我用来验证是否捕获某些异常的打印语句。以下是相关代码：
public View getView(Mongo mongo, Query query) throws MongoException,
EOFException {
String connected = "";
try {
connected = mongo.getConnectPoint();
} catch (Exception e) {
throw new MongoException("Error.");
}
System.out.println("Connected: " + connected);
DB db = mongo.getDB(query.getServer());
List<DBObject> viewList = new ArrayList<DBObject>();
DBCollection collection = db.getCollection(query.getCollection());
DBCursor cursor = collection.find(query.getQuery(), excludeID);
try {
cursor.hasNext();
} catch (Exception e) {
System.out.println("Caught exception");
}
while (cursor.hasNext()) {
viewList.add(cursor.next());
}
return new View(viewList);
}
如您所见，当我调用cursor.hasNext(). 实际上，我仍然在捕获由于Caught exception. 但是，我仍然得到一个堆栈跟踪，就好像它没有被捕获一样。我怀疑这与该DBPortPoolgotError()方法有关，但我查看了该方法的代码，无法确定它实际上在做什么，甚至无法确定它是如何被调用的。（GrepCode 链接）
如上所述，我认为这种类型的代码的行为应该是MongoException在对该特定Mongo对象的调用失败时抛出一个，因为数据库不再处于活动状态。任何人都可以提供的任何帮助将不胜感激！