Prerequisites

1. Development Environment
   Angular 12, Spring Boot 2.2.12.RELEASE

2. Frontend Variable Declaration

preUrl: string = "http://127.0.0.1:8080/user";
user: any = { username: "Lingnian", age: 6, classname: "Class One" };

1. Development Environment:

Spring Boot 2.2.12.RELEASE, MySQL 8.0.2, PostgreSQL 13.2

2. Install Maven Dependencies

1. MySQL Dependency

        <dependency>
			<groupId>mysql</groupId>
			<artifactId>mysql-connector-java</artifactId>
			<scope>runtime</scope>
		</dependency>