Skip to main content

Command Pattern

Command Pattern

Enclose your request under an object as a command and pass it to the object which can invoke the appropriate behavior by using appropriate object which will handle the passed command and execute it.

Its an Action

Advantage 

  • It separates the invoker and the executor based on command operation.
    • for example an invoker will invoke the relevant object for command execution.
  • New command can be easily added.
It command pattern, have 4 actors.
  1. Command Request : Encapsulates command and its parameters.
  2. Receiver : who knows how to perform the requested action.
  3. Invoker : Sends the command request
  4. Client : create and configure the command and the invoker.

Usage
  • When parametrized object is required as per required action
  • creation and execution of request at different times
  • when logging , transaction, rollback is required
  • Its often used in a scenarios where you want to decouple the sender (client) of the request from the receiver (the object that performs the action) and provide a level of abstraction for invoking action

There are following participant in command design pattern

Command : an Interface for executing an operation.
ConcreteCommand : It extends the Command interface to execute the method. This class creates the binding between the action and the receiver.
Invoker : This class asks the command to carry out the request
Receiver : This class knows the operation.

Labels:

Comments

Post a Comment

Popular posts from this blog

How to create Annotation in Spring boot

 To create Custom Annotation in JAVA, @interface keyword is used. The annotation contains :  1. Retention :  @Retention ( RetentionPolicy . RUNTIME ) It specifies that annotation should be available at runtime. 2. Target :  @Target ({ ElementType . METHOD }) It specifies that the annotation can only be applied to method. The target cane be modified to:   @Target ({ ElementType . TYPE }) for class level annotation @Target ({ ElementType . FIELD }) for field level annotation @Retention ( RetentionPolicy . RUNTIME ) @Target ({ ElementType . FIELD }) public @ interface CustomAnnotation { String value () default "default value" ; } value attribute is defined with @ CustomAnnotation annotation. If you want to use the attribute in annotation. A single attribute value. Example : public class Books {           @CustomAnnotation(value = "myBook")     public void updateBookDetail() {         ...
Post a Comment
Read more

Kafka And Zookeeper SetUp

 Kafka And Zookeeper SetUp zookeeper download Link : https://www.apache.org/dyn/closer.lua/zookeeper/zookeeper-3.8.3/apache-zookeeper-3.8.3-bin.tar.gz Configuration: zoo.conf # The number of milliseconds of each tick tickTime =2000 # The number of ticks that the initial # synchronization phase can take initLimit =10 # The number of ticks that can pass between # sending a request and getting an acknowledgement syncLimit =5 # the directory where the snapshot is stored. # do not use /tmp for storage, /tmp here is just # example sakes. dataDir =/tmp/zookeeper # the port at which the clients will connect clientPort =2181 4 char whitelist in command arguments 4lw.commands.whitelist =* Start ZooKeeper Server $ bin/zkServer.sh start Check zookeeper status dheeraj.kumar@Dheeraj-Kumar bin % echo stat | nc localhost 2181 stat is 4 character whitelisted argument  Check Kafka running status : echo dump | nc localhost 2181 | grep broker Responsibility of Leader in Zookeeper: 1. Distrib...
Post a Comment
Read more

Auto retries in REST API clients On Java On Ease

  Writing REST clients to consume API endpoints has become commonplace. While consuming REST endpoints, we sometimes end up in a situation where a downstream service throws some kind of transient error that goes away when the API call is retried. In such situations, we ask ourselves — “What if my API client was smart enough that knew how to retry a failed call?” Some of us go the extra mile to implement our own custom code that can retry API calls on error. But mind you, it is not only about knowing how to retry. The client also has to know when to retry and when not to. If the error is irrecoverable such as 400 — Bad Request, there is no point in retrying. It might also have to know how to back off and how to recover from the error. Implementing all this by hand, and then repeating it over and over again in every API client is cumbersome. It also adds a lot of boilerplate code and makes things even worse. But if you are a Spring/Spring Boot developer, you will be surprised to know...
Post a Comment
Read more