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Spring Boot @ConfigurationProperties

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Spring Boot @ConfigurationProperties

Get a crash course by example of Spring Boot's neat little feature for loading the configuration properties of an application.

· Java Zone ·
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How do you break a Monolith into Microservices at Scale? This ebook shows strategies and techniques for building scalable and resilient microservices.

Spring Boot provides a very neat way to load properties for an application. Consider a set of properties described using YAML format:

    stringProp1: propValue1
    stringProp2: propValue2
    intProp1: 10
        - listValue1
        - listValue2
        key1: mapValue1
        key2: mapValue2

These entries can also be described in a traditional application.properties file the following way:


It has taken me a little while, but I do like the hierarchical look of the properties described in a YAML format.

So now, given this property file, a traditional Spring application would have loaded up the properties in the following way:

public class SamplePropertyLoadingTest {
    private String stringProp1;

Note the placeholder for "prefix.stringProp" key.

This however is not ideal for loading a family of related properties, say in this specific case namespaced by the prefix conveniently named "prefix".

The approach Spring boot takes is to define a bean that can hold all the families of related properties this way:

@ConfigurationProperties(prefix = "prefix")
public class SampleProperty {
    private String stringProp1;
    private String stringProp2;
    private Integer intProp1;
    private List<String> listProp;
    private Map<String, String> mapProp;


At runtime, all the fields would be bound to the related properties cleanly.

Additionally note the JSR-303 annotations on top of the "intProp1" field that validates that the value of the field is between 0 and 99. @ConfigurationProperties will call the validator to ensure that the bound bean is validated.

An integration test using this feature is shown here:

package prop;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.test.SpringApplicationConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.Matchers.*;

@SpringApplicationConfiguration(classes = SampleWebApplication.class)
public class SamplePropertyLoadingTest {
    private SampleProperty sampleProperty;

    private String stringProp1;

    public void testLoadingOfProperties() {
        System.out.println("stringProp1 = " + stringProp1);
        assertThat(sampleProperty.getStringProp1(), equalTo("propValue1"));
        assertThat(sampleProperty.getStringProp2(), equalTo("propValue2"));
        assertThat(sampleProperty.getIntProp1(), equalTo(10));
        assertThat(sampleProperty.getListProp(), hasItems("listValue1", "listValue2"));
        assertThat(sampleProperty.getMapProp(), allOf(hasEntry("key1", "mapValue1"),
                hasEntry("key2", "mapValue2")));

If you are interested in exploring this sample further, I have a github repo with the code checked in here.

How do you break a Monolith into Microservices at Scale? This ebook shows strategies and techniques for building scalable and resilient microservices.

spring ,spring boot ,java

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