Proxies in Spring

Proxies are a powerful tool in Spring that allows developers to add functionality to beans without modifying their original code, leading to more robust and maintainable applications.

Proxies in Spring are objects that act as intermediaries or wrappers around other objects, often referred to as target objects. They are a fundamental mechanism used by Spring to add extra behavior to beans without modifying their original code. This is particularly useful for implementing cross-cutting concerns such as transaction management, security, and logging.

They are a fundamental part of Spring’s Aspect-Oriented Programming (AOP) capabilities, enabling cross-cutting concerns like transaction management, security, and logging to be applied declaratively.

Proxies are a powerful tool for implementing aspect-oriented programming (AOP) in Spring. AOP allows developers to define cross-cutting concerns as aspects, which can then be applied to beans using proxies. This makes it possible to keep business logic separate from cross-cutting concerns, resulting in cleaner and more maintainable code.

Types of Proxies

Spring uses two main types of proxies:

1. JDK Dynamic Proxies:
   1. These proxies are created using the java.lang.reflect.Proxy class and can only be used for interfaces. If a bean implements an interface, Spring will typically use a JDK dynamic proxy.
   2. These proxies are created at runtime using Java’s built-in proxy mechanism. They require the target class to implement at least one interface.
2. CGLIB Proxies
   1. These proxies are created using the CGLIB library and can be used for classes, regardless of whether they implement an interface. If a bean does not implement an interface, Spring will use a CGLIB proxy.

How Proxies Work

Proxies work by intercepting method calls to the target object. When a method is called on a proxied bean, the proxy intercepts the call and can perform additional actions before or after invoking the method on the target object. This allows Spring to add functionality such as transaction management or security checks without modifying the original code of the bean.

1. Interception:
   1. When a method is called on a bean that requires additional behavior (e.g., a method annotated with @Transactional), Spring creates a proxy for that bean.
2. Delegation:
   1. The proxy intercepts the method call and performs the necessary actions, such as starting a transaction or logging the call.
3. Forwarding:
   1. After the additional behavior is applied, the proxy delegates the call to the actual method implementation of the bean.

Benefits of Using Proxies

1. Separation of Concerns: Allows for the separation of cross-cutting concerns from business logic, leading to cleaner and more maintainable code.
2. Code Reusability: Enables the reuse of common functionalities across multiple beans.
3. Flexibility: Provides a flexible way to add or modify behavior without changing the original code.

Use Cases

1. Transaction Management: Applying transactional behavior to methods.
2. Security: Implementing security checks before method execution.
3. Logging: Logging method calls for auditing or debugging purposes.
4. Caching: Caching method results to improve performance.
5. Asynchronous processing: Executing methods asynchronously.

TODO

1. https://codingnomads.com/spring-proxies-aop
2. https://docs.spring.io/spring-framework/reference/core/aop/proxying.html
3. https://docs.spring.io/spring-framework/reference/core/aop/introduction-proxies.html
4. https://medium.com/@nitheeshhs/understanding-the-spring-proxy-and-its-pitfalls-1b8cc121f5d3
5. https://stackoverflow.com/questions/2227836/what-is-the-meaning-of-using-proxy-dynamic-proxy-in-spring-framework

Dynamic Proxies in Java

1. https://docs.oracle.com/javase/8/docs/technotes/guides/reflection/proxy.html
2. https://stackoverflow.com/questions/933993/what-are-dynamic-proxy-classes-and-why-would-i-use-one
3. https://stackoverflow.com/questions/19519787/when-do-we-use-static-and-dynamic-class-loading
4. https://web.archive.org/web/20150226062232/http://userpages.umbc.edu/~tarr/dp/lectures/DynProxies-2pp.pdf

Dynamic Class loading

1. https://naveen-metta.medium.com/java-dynamic-class-loading-unleashing-the-power-of-runtime-flexibility-7ae4a2193b4f

Tags

1. Spring Data JPA - transactions