Structural Design Pattern: Proxy

In software design, efficiency and control are often paramount concerns. The Proxy Pattern emerges as a versatile solution, offering a means to manage object access and resource allocation effectively. Imagine a scenario where a resource-intensive object requires frequent access. Here, the Proxy Pattern acts as a surrogate, intercepting requests and controlling access to optimize resource usage and enhance system efficiency. One significant usage scenario for the Proxy Pattern is lazy initialization, where the creation of resource-intensive objects is deferred until they are needed. By serving as intermediaries, proxies facilitate lazy initialization by instantiating the real object only when necessary, thus optimizing system performance and avoiding unnecessary initialization overhead.

Unveiling Common Usage Scenarios:

Proxy patterns encompass a range of implementations, each serving distinct purposes and addressing specific needs. Let’s embark on a journey to explore various types of proxy patterns, their applications, and their significance in different domains:

1. Virtual Proxies: Used for lazy initialization of objects, delaying their creation until they are actually needed. This is particularly useful for large or complex objects, where deferred instantiation can improve application startup time and conserve memory.
2. Remote Proxies: Facilitate communication with objects located in remote systems or networks. By serving as local representatives for remote objects, proxies handle communication details such as serialization, deserialization, and network interactions, shielding clients from the complexities of remote access.
3. Protection Proxies: Control access to sensitive or critical resources by implementing authentication and authorization mechanisms. Protection proxies enforce security policies, ensuring that only authorized users or clients can interact with the underlying object.
4. Logging Proxies: Capture and log method invocations, enabling monitoring and analysis of system behavior. Logging proxies provide insights into the sequence of operations performed on objects, facilitating debugging, performance optimization, and auditing.
5. Cache Proxies: Cache frequently accessed or expensive-to-create objects, reducing the overhead of repeated instantiation or computation. Cache proxies store previously computed results and serve them directly to clients, minimizing latency and improving overall system responsiveness.
6. Counting Proxies: Track the number of times a method is invoked on an object, enabling usage statistics and performance monitoring. Counting proxies maintain counters for method invocations and expose metrics for analysis and optimization purposes.
7. Synchronization Proxies: Implement thread safety mechanisms to ensure concurrent access to shared resources. Synchronization proxies serialize access to critical sections of code, preventing race conditions and data corruption in multi-threaded environments.

Common Implementation Steps:

Implementing the Proxy Pattern typically involves the following steps:

1. Define Interface: Define an interface that represents the subject or the real object, specifying the operations that clients can perform.
2. Implement Real Subject: Create a class that implements the interface, representing the actual object whose behavior needs to be controlled or augmented.
3. Implement Proxy: Create a proxy class that also implements the interface, acting as a surrogate for the real object. The proxy intercepts client requests and delegates them to the real object, optionally adding additional functionality such as access control, logging, or lazy initialization.

Example Implementation in C# (Virtual Proxy):

Let’s consider an example where we have a DatabaseConnection class that represents a connection to a database. Establishing a database connection can be resource-intensive, so we want to delay its creation until the connection is actually required. We can use a proxy to achieve this lazy initialization:

// Interface representing the database connection
public interface IDatabaseConnection
{
    void ExecuteQuery(string query);
}

// Real database connection
public class DatabaseConnection : IDatabaseConnection
{
    private readonly string _connectionString;

    public DatabaseConnection(string connectionString)
    {
        _connectionString = connectionString;
        // Simulate establishing a database connection
        Console.WriteLine("Establishing database connection...");
    }

    public void ExecuteQuery(string query)
    {
        // Simulate executing a query on the database
        Console.WriteLine($"Executing query: {query}");
    }
}

// Proxy for lazy initialization of the database connection
public class DatabaseConnectionProxy(string connectionString) : IDatabaseConnection
{
    private readonly string _connectionString = connectionString;
    private DatabaseConnection? _realConnection;


    public void ExecuteQuery(string query)
    {
        // Lazily initialize the real database connection
        if (_realConnection == null)
        {
            _realConnection = new DatabaseConnection(_connectionString);
        }

        // Delegate the query execution to the real connection
        _realConnection.ExecuteQuery(query);
    }
}

class Program
{
    static void Main(string[] args)
    {
        // Create a proxy for the database connection
        IDatabaseConnection connection = new DatabaseConnectionProxy("db_connection_string");

        // Execute queries using the proxy (connection will be lazily initialized)
        connection.ExecuteQuery("SELECT * FROM table1");
        connection.ExecuteQuery("SELECT * FROM table2");
    }
}

Link to the GitHub repo: design-patterns/06-ProxyPattern at master · antonespo/design-patterns · GitHub

In this example:

• We have an IDatabaseConnection interface that defines the contract for interacting with the database connection.
• The DatabaseConnection class is the implementation of the real database connection, which is instantiated with a connection string and performs database operations.
• The DatabaseConnectionProxy class is a proxy that wraps around the real database connection. It lazily initializes the real connection when a query is executed for the first time.
• In the Main method, we create a proxy for the database connection and execute queries using the proxy. The real connection is lazily initialized only when needed.

The output presented in the console window is:

Establishing database connection...
Executing query: SELECT * FROM table1
Executing query: SELECT * FROM table2

In conclusion, the Proxy Pattern offers a powerful mechanism for optimizing resource usage, enhancing security, and improving system performance. By providing a flexible way to control access to objects and add additional functionality, the Proxy Pattern empowers developers to design robust, efficient, and scalable software solutions.