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  4. Spring Boot @ConfigurationProperties

Spring Boot @ConfigurationProperties

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

Biju Kunjummen user avatar by
Biju Kunjummen
·
Aug. 03, 15 · Tutorial
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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:

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


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

prefix.stringProp1=propValue1
prefix.stringProp2=propValue2
prefix.intProp1=10
prefix.listProp[0]=listValue1
prefix.listProp[1]=listValue2
prefix.mapProp.key1=mapValue1
prefix.mapProp.key2=mapValue2


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 {
    @Value("${prefix.stringProp1}")
    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")
@Component
public class SampleProperty {
    private String stringProp1;
    private String stringProp2;
    @Max(99)
    @Min(0)
    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.*;

@RunWith(SpringJUnit4ClassRunner.class)
@SpringApplicationConfiguration(classes = SampleWebApplication.class)
public class SamplePropertyLoadingTest {
    @Autowired
    private SampleProperty sampleProperty;

    @Value("${prefix.stringProp1}")
    private String stringProp1;

    @Test
    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.

Spring Framework Spring Boot Property (programming)

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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