Spring structure diagram

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Structures of JAVA

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JAVA Features of Java  Everything is a class in Java - Java is a pure Object Oriented Language  The way how Java executes in the first place(without creating an object) is by defining a static function (usually we call it main) that will run even without creating an object.   A package in java is a collections of classes  Java is interpreted language (compiler + interpreter)  Java can run on many different operating systems without modifying the source code  This is why Java is called platform independent language unlike C/C++  Java is platform independent thanks to the JVM(Java Virtual Machine)  Java generates .class files (C/C++ will generate .exe files) Java has garbage collection which handles automatic memory allocation and de-allocation by counting reference to an object.  There are 3 interrelated components for developing and running Java programs  JVM  JRE JVM https://www.javatpoint.com/difference-between-jdk-jre-and-jvm JVM (Java Virtual Machine)  Before moving on, let's b
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What is URI(URN, URL)

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URI (Uniform Resource Identifier)  URI is an identifier of a specific resource. Like a page, or book, or a document.  For example, if you request a specific resource via https://www.google.com/resource/sample/1, you will retrieve resources such as sample.pdf, sample.docx etc.  URL and URN are sub-types of URI.  URL (Uniform Resource Locator)  URL is a special type of identifier which tells you the location of specific resource on the server.   If the location of resource changes in the server, you will not be able to access the resource via the previous URL URN (Uniform Resource Name)  URN is the name of specific resource.  Unlike the URL, even if the location of the resource changes on the server, you will still be able to access the resource using URN because URN points to the specified resource. 
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Spring Boot JPA - Pagination

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Pagination  Pagination is a mechanism to separate a bit result set into smaller chunks. Providing a fluent pagination navigator could increase both the value of your website for search engines and enhance user experience through minimizing the response time.  Static pagination with Spring Boot  Let's first define ExampleEntity and a repository for ExampleEntity @Entity @Table (name = "Example" ) @Getter @Builder @AllArgsConstructor @NoArgsConstructor @ToString public class ExampleEntity { @Id @GeneratedValue (strategy = GenerationType . IDENTITY ) private Long id ; @Column (length = 100 , nullable = false ) private String content ; } @Repository public interface ExampleRepository extends JpaRepository < ExampleEntity , Long > { } Now's let's insert dummy data's that will be used for pagination.  @Test public void testInsert () { LongStream . rangeClosed ( 1 , 300 ).forEach(i -> {
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Java Data Structures VS Python, C/C++ Data Structures

 Data Structures (JAVA, PYTHON, C/C++) Arrays Arrays(fixed size)  As for python, we use list to store series of data, and by default it's size can be dynamically adjusted. But arrays in JAVA and C/C++ have fixed size.  Arrays(dynamic size)  We can use dynamically adjustable arrays by using importing java.util.ArrayList in Java.  In C/C++, we can #include <vectors>.  Linked List  In java.util.LinkedList, we can use LinkedList data structure (which is doubly linked list).  In python doesn't have built in linked list data type. We will have to make it by ourselves (and it is pretty easy)  In C/C++, we can use list to implement doubly linked list.  Stack There is built libraries for stack in Java and C/C++. But there is no stack for python. We can just use the list for stack operation.  Queue In Java, a Queue is an int
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Spring Boot JPA - What is JPA, Entity, Repository

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 Database  Spring Boot uses JPA (Java Persistence API) to map Java objects to tables in the database. Mapping an object to a table in a database is called ORM(Object Relational Mapping) and JPA is one of Java's way of achieving ORM. JPA is not dependent on specified database language, so that users can associate many different databases using JPA.  JPA Data persistence is the ability to maintain data between application executions.  Persistence is vital for  applications that are developed for enterprises. JPA is a collection of classes and methods to persistently store the vast amounts of data into a database which is provided by the Oracle corporation. To reduce the burden of writing codes for relational object management, a programmer follows the JPA framework, which allows easy interaction with the database instance. JPA standardizes the task of object-relational mapping by using annotations or XML to map objects into one or more tables of a dat
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Design Pattern - Proxy

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Proxy  Definition  A Proxy pattern is a software design that works as an interface to something else. The proxy can interface to anything, a network connection, a large object in memory, a file, or some other resource that is expensive or impossible to duplicate. In short, a proxy is a wrapper or agent object that is being called by the client to access the real serving object behind the scenes. Proxy can add extra functionality like caching.  Types of Proxy pattern  Remote proxy : Responsible for representing the object located remotely. Talking to real object might involve marshalling and unmarshalling of data and talking to the remote object. All the logic is encapsulated in these proxies and the client application need not worry about them.  Virtual proxy : These proxies will provide some default and instant results if the real object is supposed to take some time to produce results. These proxies initiate the operation on rea
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