Connection Management

/**
 * Factory for MongoClient instances
 */
public final class MongoClients {
    /**
     * Creates a client with default connection string "mongodb://localhost:27017"
     * @return the MongoDB client
     */
    public static MongoClient create();
    
    /**
     * Creates a client with the given connection string
     * @param connectionString the MongoDB connection string
     * @return the MongoDB client
     */
    public static MongoClient create(String connectionString);
    
    /**
     * Creates a client with the given connection string object
     * @param connectionString the MongoDB ConnectionString object
     * @return the MongoDB client
     */
    public static MongoClient create(ConnectionString connectionString);
    
    /**
     * Creates a client with detailed settings
     * @param settings the MongoDB client settings
     * @return the MongoDB client
     */
    public static MongoClient create(MongoClientSettings settings);
    
    /**
     * Creates a client with connection string and driver information
     * @param connectionString the MongoDB connection string
     * @param mongoDriverInformation optional driver metadata
     * @return the MongoDB client
     */
    public static MongoClient create(ConnectionString connectionString, 
                                     MongoDriverInformation mongoDriverInformation);
    
    /**
     * Creates a client with settings and driver information
     * @param settings the MongoDB client settings
     * @param mongoDriverInformation optional driver metadata
     * @return the MongoDB client
     */
    public static MongoClient create(MongoClientSettings settings, 
                                     MongoDriverInformation mongoDriverInformation);
}

import com.mongodb.client.MongoClient;
import com.mongodb.client.MongoClients;
import com.mongodb.MongoClientSettings;
import com.mongodb.ConnectionString;

// Default localhost connection
MongoClient client1 = MongoClients.create();

// Connection string
MongoClient client2 = MongoClients.create("mongodb://user:pass@host:27017/mydb");

// ConnectionString object with options
ConnectionString connString = new ConnectionString("mongodb://host:27017");
MongoClient client3 = MongoClients.create(connString);

// Detailed settings
MongoClientSettings settings = MongoClientSettings.builder()
    .applyConnectionString(new ConnectionString("mongodb://host:27017"))
    .readPreference(ReadPreference.secondary())
    .writeConcern(WriteConcern.MAJORITY)
    .build();
MongoClient client4 = MongoClients.create(settings);

/**
 * Main MongoDB client interface for connection management
 */
public interface MongoClient extends MongoCluster, AutoCloseable {
    /**
     * Releases all resources associated with this client
     */
    void close();
    
    /**
     * Gets information about the cluster this client is connected to
     * @return cluster description containing server information
     */
    ClusterDescription getClusterDescription();
}

import com.mongodb.client.MongoClient;
import com.mongodb.client.MongoClients;
import com.mongodb.connection.ClusterDescription;

// Create and use client
try (MongoClient client = MongoClients.create("mongodb://localhost:27017")) {
    // Get cluster information
    ClusterDescription cluster = client.getClusterDescription();
    System.out.println("Connected to: " + cluster.getServerDescriptions());
    
    // Use client for operations...
    MongoDatabase db = client.getDatabase("mydb");
    
} // Automatically closes connection

/**
 * Interface for cluster-level MongoDB operations
 */
public interface MongoCluster {
    /**
     * Gets a database instance for the given name
     * @param databaseName the name of the database
     * @return MongoDatabase instance
     */
    MongoDatabase getDatabase(String databaseName);
    
    /**
     * Starts a new client session with default options
     * @return ClientSession for transaction and consistency support
     */
    ClientSession startSession();
    
    /**
     * Starts a new client session with specific options
     * @param options session configuration options
     * @return ClientSession for transaction and consistency support
     */
    ClientSession startSession(ClientSessionOptions options);
    
    /**
     * Lists all database names
     * @return iterable of database names
     */
    MongoIterable<String> listDatabaseNames();
    
    /**
     * Lists databases with detailed information
     * @return iterable of database documents with metadata
     */
    ListDatabasesIterable<Document> listDatabases();
    
    /**
     * Lists databases with detailed information as specified type
     * @param clazz the class to decode each database document to
     * @return iterable of database information objects
     */
    <TResult> ListDatabasesIterable<TResult> listDatabases(Class<TResult> clazz);
    
    /**
     * Creates a change stream to monitor cluster-level changes
     * @return change stream iterable for all databases
     */
    ChangeStreamIterable<Document> watch();
    
    /**
     * Creates a change stream with aggregation pipeline
     * @param pipeline aggregation pipeline to filter changes
     * @return change stream iterable with filtering
     */
    ChangeStreamIterable<Document> watch(List<? extends Bson> pipeline);
    
    /**
     * Creates a change stream with specific result type
     * @param pipeline aggregation pipeline to filter changes
     * @param clazz the class to decode each change document to
     * @return change stream iterable with custom type
     */
    <TResult> ChangeStreamIterable<TResult> watch(List<? extends Bson> pipeline, Class<TResult> clazz);
}

import com.mongodb.client.MongoClient;
import com.mongodb.client.MongoClients;
import com.mongodb.client.MongoDatabase;
import com.mongodb.client.ClientSession;

try (MongoClient client = MongoClients.create()) {
    // Get database
    MongoDatabase database = client.getDatabase("myapp");
    
    // List all databases
    for (String dbName : client.listDatabaseNames()) {
        System.out.println("Database: " + dbName);
    }
    
    // Start session for transactions
    try (ClientSession session = client.startSession()) {
        // Use session for transactional operations...
    }
    
    // Monitor cluster-wide changes
    try (var cursor = client.watch().cursor()) {
        while (cursor.hasNext()) {
            System.out.println("Change detected: " + cursor.next());
        }
    }
}

// Configuration with MongoClientSettings
MongoClientSettings settings = MongoClientSettings.builder()
    .applyConnectionString(new ConnectionString("mongodb://host:27017"))
    .readPreference(ReadPreference.primaryPreferred())
    .writeConcern(WriteConcern.MAJORITY)
    .readConcern(ReadConcern.SNAPSHOT)
    .codecRegistry(CodecRegistries.fromProviders(PojoCodecProvider.builder().automatic(true).build()))
    .build();

// Configuration with connection string options
String connStr = "mongodb://host:27017/mydb?" +
    "readPreference=secondary&" +
    "writeConcern=majority&" +
    "readConcernLevel=snapshot&" +
    "maxPoolSize=50";

/**
 * ObjectFactory for creating MongoClient instances in DI containers
 */
public class MongoClientFactory implements ObjectFactory<MongoClient> {
    /**
     * Creates a MongoClient instance for dependency injection
     * @return MongoClient instance
     */
    @Override
    public MongoClient getObject();
}