Understanding Spring Cloud Config Client with Example

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1- The objective of the lesson

OK, we are in the  serial of guiding for programming a distributed application using Spring Cloud. A Taxi Management Application. In the previous lesson, I showed you how to create a Config-Server application, which manages configuration information for other services.
See previous lesson:
In this lesson, we are going to create an "About Company" application. It is independent of " Passenger Management"  and " Diver Management" applications. For a big taxi company, for example, Uber, the number of users visiting their website is huge, it is a good idea to have an application to introduce the company separate from other functions.
The " About Company" application will use an independent database. Database configuration information will be managed on the Config-Server. In the Microservice architecture, this application is not simply a company introduction website; it can be a service that provides information for other applications, for example, provision of information on hotline, feedback email, etc. In brief, it is part of the Microservice system.
Note: The main objective of this lesson is to discuss and practise an example of " How an application can get its configuration information being managed on a Config-Server."

2- Create Spring Boot project

  • Name: ConfigClientAboutCompany
  • Group: org.o7planning
  • Artifact: ConfigClientAboutCompany
  • Description: Spring Cloud Config Client (About Company App)
  • Package: org.o7planning.aboutcompany
pom.xml
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
    http://maven.apache.org/xsd/maven-4.0.0.xsd">
    
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.o7planning</groupId>
    <artifactId>ConfigClientAboutCompany</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>ConfigClientAboutCompany</name>
    <description>Spring Cloud Config Config Client (About Company App)</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.9.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
        <spring-cloud.version>Edgware.RELEASE</spring-cloud.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-config</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-jdbc</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.postgresql</groupId>
            <artifactId>postgresql</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>com.microsoft.sqlserver</groupId>
            <artifactId>mssql-jdbc</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>${spring-cloud.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>


</project>
ConfigClientAboutCompanyApplication.java
package org.o7planning.aboutcompany;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class ConfigClientAboutCompanyApplication {

    public static void main(String[] args) {
        SpringApplication.run(ConfigClientAboutCompanyApplication.class, args);
    }
    
}

3- Configure Spring Cloud Config Client

This application needs to read its configurations stored on the Config-Server; therefore,  you need to tell it the information on the  Config-Server. This information is configured on the bootstrap.properties (or bootstrap.yml) file . This file is used very early by the application during the application startup.
There is a slight difference in the format of the * .properties file and the * .yml file, and you can learn more in the following:
  • TODO Link!
bootstrap.properties
# Read file on Config-Server:
# app-about-company.properties or app-about-company.yml
spring.application.name=app-about-company

# This is the default:
spring.cloud.config.uri=http://localhost:8888
management.security.enabled=false
Configure so that this application runs on port 7777:
application.properties
server.port=7777
Configuration file for this application (see on GitHub):

4- Controller

MainController.java
package org.o7planning.aboutcompany.controller;

import javax.sql.DataSource;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.cloud.context.config.annotation.RefreshScope;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.RestController;

@RefreshScope
@RestController
public class MainController {

    // https://github.com/o7planning/spring-cloud-config-git-repo-example
    // See: app-about-company.properties
    @Value("${text.copyright: Default Copyright}")
    private String copyright;

    @Value("${spring.datasource.driver-class-name}")
    private String driverClassName;

    @Value("${spring.datasource.url}")
    private String url;

    @Value("${spring.datasource.username}")
    private String userName;

    @Value("${spring.datasource.password}")
    private String password;

    @Autowired
    private DataSource dataSource;

    @RequestMapping("/showConfig")
    @ResponseBody
    public String showConfig() {
        String configInfo = "Copy Right: " + copyright //
                + "<br/>spring.datasource.driver-class-name=" + driverClassName //
                + "<br/>spring.datasource.url=" + url //
                + "<br/>spring.datasource.username=" + userName //
                + "<br/>spring.datasource.password=" + password;

        return configInfo;
    }

    @RequestMapping("/pingDataSource")
    @ResponseBody
    public String pingDataSource() {
        try {
            return this.dataSource.toString();
        } catch (Exception e) {
            e.printStackTrace();
            return "Error: " + e.getMessage();
        }
    }

}

@RefreshScope:

Any Spring Bean annotated by @RefreshScope will be refreshed at runtime. And any components that are using them will get a new instance on the next method call, fully initialized and injected with all dependencies.

5- Run Application

First of all, you need to run the Config-Server application. This application will run on port 8888.
Test it with the following URL:
After that, run the ConfigClientAboutCompany application, which will run on port 7777:
Test it with the following URL:

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