Spring boot application.json properties example

In this article, we will show you how to use JSON instead of the properties file or the yml file in Spring Boot by custom configuration.

Before moving to the example first you must be familiar with the following components.

1.spring.factories file

The file is located in src/java/resources/META-INF/spring.factories. The spring.factories file is a file that spring automatically loads when booting up. It contains references to many configuration classes.

For example,

org.springframework.boot.env.PropertySourceLoader=com.example.demo.JsonPropertySourceLoader

Here we registered our custom Json property source loader

2. YamlPropertySourceLoader

Load the resource into one or more property sources. Implementations may either return a list containing a single source or in the case of a multi-document format such as YAML a source for each document in the resource. Refer

import org.springframework.boot.env.YamlPropertySourceLoader;
public class JsonPropertySourceLoader 
               extends YamlPropertySourceLoader {
                   
    @Override
    public String[] getFileExtensions() {
        return new String[] { "json" };
    }
}

getFileExtensions() returns the file extensions that the loader supports.Refer

3. @Value

@Value annotation provides a convenient way to inject property values into components.

    @Value("${testdata1}")
    private String testData1;
    @Value("#{${valuesMap}}")
    private Map<String, Integer> valuesMap;

Spring boot application.json properties demo

Project Directory

JsonPropertySourceLoader

package com.example.demo;
import org.springframework.boot.env.YamlPropertySourceLoader;
public class JsonPropertySourceLoader 
               extends YamlPropertySourceLoader {
                   
    @Override
    public String[] getFileExtensions() {
        return new String[] { "json" };
    }
}

spring.factories

org.springframework.boot.env.PropertySourceLoader=com.example.demo.JsonPropertySourceLoader

application.json

{
"server.port":9080,
"testdata1":"testing",
"valuesMap":"{key1: '1', key2: '2', key3: '3'}"
}

DemoApplication.java

package com.example.demo;

import java.util.Map;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@SpringBootApplication
public class DemoApplication {

    @Value("${testdata1}")
    private String testData1;

    @Value("#{${valuesMap}}")
    private Map<String, Integer> valuesMap;

    @GetMapping
    public String echo() {

        System.out.println("Iterating the map....");
        for (Map.Entry<String, Integer> entry : valuesMap.entrySet()) {
            System.out.println("Key = " + entry.getKey() 
                        + ", Value = " + entry.getValue());
        }
        return testData1;
    }

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

Run, Test and Verify the application

Step1: Download or clone the source code to a local machine. - Click here

Step2: mvn clean install

Step3: Run the Spring Boot application - mvn spring-boot:run

Step4: Access the URL - http://localhost:9080/

Step5: Verify the output

Download the source code