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Connection closed when trying to read an oracle Clob returned from procedure

I have an Oracle procedure with an input Clob and returns an output Clob.
When i'm trying to recover the value, i reach the object, if i try to read the toString fro the object, i take the "oracle.sql.CLOB#625a8a83" . But when i want to read the object, in anyways i tryed, allways get a connection closed exception.
in my code:
MapSqlParameterSource parametros = new MapSqlParameterSource();
// setting input parameter
parametros.addValue("PE_IN", new SqlLobValue("IN DATA CLOB", new DefaultLobHandler()),
Types.CLOB);
// Executing call
Map<String, Object> out = jdbcCall.execute(parametros);
salida.setDatosRespuesta(out.get("PS_OUT").toString());
if i change the last line for this:
Clob clob = (Clob) out.get("PS_OUT");
long len = clob.length();
String rtnXml = clob.getSubString(1, (int) len);
i get the connection close error. I tryed in several ways and i can't solve this problem. Any ideas?

I think yo are using the SimpleJdbcCall of the spring framework. If so the database configuration are the default configurations for the oracle driver, you need to increase the time out for the reading of the values for the connection. Check the DatabaseMetaData documentation, also check the OracleConnection properies CONNECTION_PROPERTY_THIN_READ_TIMEOUT_DEFAULT. This happends because you are reading a large data from the database remember that de CLOB can have until 4gb of data
You need to keep in mind that is this process is very common in your application you need to consider the quantity of the connections to the database in order to have always enable connections to your database to guarantee your application availability
Regarding the out.get("PS_OUT").toString() this basically only show the hash that represents your object that the reason beacause why that line works fine

Get Collections in Java from MongoDB

I have a local MongoDB instance running via shell on windows 10.
University provided a Java Project for us to learn about queries.
Now, I have a database ("imdb") and want to get two collections from it ("movies","tweets").
The problem is, one the one hand
List<String> test = mongo.getDatabaseNames();
System.out.println(test); //prints [admin,config,imdb,local]
...
db = mongo.getDB("imdb");
System.out.println(db.getCollectionNames()); //prints []
There seem to be no collections on imdb but
db.createCollection("movies", new BasicDBObject());
Returns a com.mongodb.CommandFailureException, stating that a collection 'imdb.movies' already exists.
So how do I ensure that Java actually "loads" the Collections?
For Clarification: My goal is to have
System.out.println(db.getCollectionNames());
to print [movies,tweets] instead of []

You could try
Set<String> colls = db.getCollectionNames();
for (String s : colls) {
System.out.println(s);
}
ref: code examples

Which version of mongodb shell you're using
If it's before 3.0, it will return no data for db.getCollectionNames() command
ref: mongodb docs

Since version 3.0 you should use MongoDatabase.listCollectionNames() method.
http://mongodb.github.io/mongo-java-driver/3.8/driver/tutorials/databases-collections/#get-a-list-of-collections
MongoDatabase db = client.getDatabase(dbName);
MongoIterable<String> names = db.listCollectionNames();

You can do like this:
//If you don't need connection's configures. i.e. your mongo is in you localhost at 127.0.0.1:27017
MongoClient cliente = new MongoClient(); //to connect into a mongo DB
MongoDatabase mongoDb = client.getDatabase("imdb"); //get database
MongoCollection<Document> robosCollection = mongoDb.getCollection("movies"); //get the name of the collection that you want
MongoCursor<Document> cursor = robosCollection.find().cursor();//Mongo Cursor interface implementing the iterator protocol
cursor.forEachRemaining(System.out::println); //print all documents in Collection using method reference

List all MongoDB Databases and their details from Java

I am developing a Java/MongoDB application and require a list of all existing MongoDB Databases.
I know I can use this code:-
final MongoClient mongoClient = DatabaseManager.getMongoclient();
final ListDatabasesIterable<Document> databasesDocument = mongoClient.listDatabases();
final MongoCursor<Document> mongoCursor = databasesDocument.iterator();
while (mongoCursor.hasNext()) {
final Document databaseDocument = mongoCursor.next();
Assert.assertNotNull(databaseDocument);
}
However the details only include the Database Name, its size on disk, and whether or not the database is empty.
I need to know when the database was created, when = Date & Time.
Is there anyway I can retrieve this information from within a Java application?

As far as I know, MongoDB doesn't keep track of database creation dates.
One possible workaround if you are creator of databases is tracking it by yourself. Create meta collection in meta database and insert new record db_name=time when you create database.

Mongo insert $currentDate in Java Driver

I've got a question about $currentDate
What is the best way to insert a document in mongo db so that it contains the "server time" (like ''now()'' in some RDBMSs) using the Java Driver?
For example, lest say I have a document like:
{
name : "John",
birthday : <$currentDate_goes_here>
}
What I want is to insert the document so that the evaluation of the date would be done by mongo server at the time of insertion on the server side.
This is critical because our servers might not be totally synchronized and there is a need to have the time we can rely on (for example the time on mongo server).
I'm using a standard java driver for mongo, so any code snippet in Java will be more than welcome.
This is what I've tried so far
MongoClient mongoClient = new MongoClient();
DB sampleDB = mongoClient.getDB("sampleDB");
BasicDBObject update =
new BasicDBObject("$set", new BasicDBObject("name","john")
.append("$currentDate", new BasicDBObject("birthday",true)));
sampleDB.getCollection("col1").insert(update);
This thing fails on the following exception:
java.lang.IllegalArgumentException: Document field names can't start with '$' (Bad Key: '$set')
at com.mongodb.DBCollection.validateKey(DBCollection.java:1845)
at com.mongodb.DBCollection._checkKeys(DBCollection.java:1803)
at com.mongodb.DBCollection._checkObject(DBCollection.java:1790)
at com.mongodb.DBCollectionImpl.applyRulesForInsert(DBCollectionImpl.java:392)
at com.mongodb.DBCollectionImpl.insertWithCommandProtocol(DBCollectionImpl.java:381)
at com.mongodb.DBCollectionImpl.insert(DBCollectionImpl.java:186)
at com.mongodb.DBCollectionImpl.insert(DBCollectionImpl.java:165)
at com.mongodb.DBCollection.insert(DBCollection.java:93)
at com.mongodb.DBCollection.insert(DBCollection.java:78)
at com.mongodb.DBCollection.insert(DBCollection.java:120)

In which case the answer is fairly simple. It is really about serializing from java BasicDBObject classes to the basic MongoDB interpretation. Without respect to your actual "query" document the "update" document part of your statement should be:
BasicDBObject update = new BasicDBObject("$set", new BasicDBObject("name","john")
.append("$currentDate", new BasicDBObject("birthrhday",true))
;
Which will indeed use the "server time" at the point of "update insertion" or "modification" with respect to the $currentDate modifier as used.
Just to be clear here, you don't use the .insert() method but an "upsert"operation with .insert(). The "query" and "update" syntax applies. Also see the $setOnInsert operator for specifically not modifying existing documents.

You can also use aggregation variable "$$NOW" if you are using an aggregation pipeline with update method.
MongoClient mongoClient = new MongoClient();
DB sampleDB = mongoClient.getDB("sampleDB");
BasicDBObject update =
new BasicDBObject("$set", new BasicDBObject("name","john")
.append("birthday", new BsonString("$$NOW")));
sampleDB.getCollection("col1").updateOne(query, List.of(update));
You can also use "$$NOW" with aggregation operators such as $add, $subtract, and many more, to compute more specific values (including dates) on the database side.

If you want to pass the Application Server's time instead of Database time, use the following code to send the current time. You should decide whether to use this in case if the Application Server time differs from Database Server time.
new BsonDateTime(Instant.now().toEpochMilli())
Sample Code:
MongoClient mongoClient = new MongoClient();
DB sampleDB = mongoClient.getDB("sampleDB");
BasicDBObject update =
new BasicDBObject("$set", new BasicDBObject("name","john")
.append("birthday", new BsonDateTime(Instant.now().toEpochMilli())));
sampleDB.getCollection("col1").updateOne(query, update);

how to Create if not exists a new Java DB?

conn = DriverManager.getConnection("jdbc:derby:mydatabase;create=true",props);
will this line make my DB get overwritten everytime i execute it? if it will how do i create the DB once and just use it ever since?

What you are doing will work with Derby. It will create the database if it doesn't exist and do nothing if it already does exist.