Refactoring to resolve security issues by low-version of the dependency libraries.

[TaehoonK]

Refactoring to resolve security issues by low-version of the dependency libraries.

• Update dependency libraries version to stable latest version.
  <spring.version>5.2.10.RELEASE</spring.version>
<jetty.version>9.4.34.v20201102</jetty.version>
<slf4j.version>1.7.30</slf4j.version>
<fasterxml.jackson.version>2.11.2</fasterxml.jackson.version>
<jaxb-api.version>2.3.1</jaxb-api.version>
<jaxb-core.version>2.3.0.1</jaxb-core.version>
<junit.version>4.13.1</junit.version>
• Reformatting all source code to UTF-8 encoding.
• Delete unnecessary codes and libraries.
• Update the JDK version to 11.