Behavioral Patterns - Memento Pattern Exercise

behavioral-patterns-memento-pattern-exercise

The Memento Pattern is used to record the internal state of an object. It is used to create a state machine and also makes undo or redo operation very easy with this pattern. In this exercise, we will use a scenario of account and account manager to understand the components of this pattern.

Reading Materials

  1. https://en.wikipedia.org/wiki/Memento_pattern (15 minutes reading)

Practice Materials

  1. Use the Memento Pattern to support an account manager to do save and roll back operations for his managed accounts.

Components:

  1. Originator (The object whose state will be saved as a memento) - Account
  2. Memento (The object that represent the saved state from its originator) - AccountMemento
  3. Caretaker (The object that keep the immutable state of mementos) - AccountManager
  4. Client (The entry point of the application that will run the given scenario) - App

Tip

  • Not all states of the originator have to be saved to a memento object.
  • To implement rollback or revert in the AccountManager, a stack could be used to keep track of the entire memento history.
  • Account.deposit or Account.withdraw could be created to change the Account.balance

Solution

Account Manager Example

Questions to discuss

  1. What are the common use cases to apply a Memento Pattern?
  2. What are the similarities and differences of the Memento Pattern and the Command Pattern?

Comments

Post a Comment

Popular posts from this blog

Creating a Library Project for Spring Boot

creating-a-library-project-for-spring-boot This article introduces the key points when creating a library for spring boot project. It could be common that over the years you have created a number of services that could be reused by other spring projects. It then makes sense to make the reusable modules such as a library and install it in your local repository for later use. Here are the key points to consider when building a spring boot library. release version build plugin dependency injection autoconfigurations Release Version To guarantee spring boot works the way you expect, it is recommended to keep update the release versions of the library so that it supports some versions of the spring boot minor version. A good practice is to monitor change spring boot changelog and see if there are any conflicting dependencies that are used in the library project. If there is, introduce a new version to resolve the conflict. Build Plugin If the projects refere
Read more

Spring Data Repository Query Precedence Tricks

spring-data-repository-query-precedence-tricks Spring Data repository method is very handy but it also comes with its limitation, especially when composed with condition precedence. This article shows one way to work with it and its caveats. Use Case Given the following type: @Entity public class Book { @Id private Long id ; private String title ; private String edition ; // Getters and Setters ... } 1. check if there is any book whose title or edition matches the specified. This one is easy to come up with. We could simply use the keyword Or to compose the query: boolean existsByTitleOrEdition ( String title , String edition ) ; 2. check if there is any book whose title or edition matches the specified and is not itself. This one looks just as easy as the first one, we could have just added another condition and compose with the keyword And : boolean existsByTitleOrEditionAndIdIsNot ( String title , String edi
Read more

Distributed Transaction Management with REST and Try Confirm/Cancel Pattern

distributed-transaction-management-with-rest-and-try-confirm-cancel-pattern This article introduces how to manage transactions effectively in distributed REST services with Try Confirm/Cancel (TCC) pattern. It also provides a repository that is a simplified Java implementation for anyone who is interested in learning the TCC pattern. This repository attempts to trim the most of the common boilerplate, but only preserve the minimal that could be most straightforward to observe this pattern. It could be adapted to use any backend stack. Try Confirm/Cancel (TCC) Pattern TCC is a distributed transactions pattern that fits in the stateless REST services. It is originally proposed by Guy Pardon, the creator of Atomikos. Useful References Conference Speech By Guy Pardon TCC for REST API (API specification) Spring Cloud TCC Example By Chris About This Repository This repository is a simplified Java implementation for anyone who is interested in learning the TCC p
Read more