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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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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.

The Java Zone is brought to you in partnership with ZeroTurnaround. Check out this 8-step guide to see how you can increase your productivity by skipping slow application redeploys and by implementing application profiling, as you code!

spring ,spring boot ,java

Published at DZone with permission of Biju Kunjummen, DZone MVB. See the original article here.

Opinions expressed by DZone contributors are their own.

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