Binding to a Map with EnumSet values fails with "Cannot create EnumSet for unknown element type"

[olideakin]

When binding properties to type EnumSet, there is a failure with "Cannot create EnumSet for unknown element type" as the cause. Stack trace is as follows:

Caused by: java.lang.IllegalArgumentException: Cannot create EnumSet for unknown element type
	at org.springframework.util.Assert.notNull(Assert.java:193)
	at org.springframework.core.CollectionFactory.createCollection(CollectionFactory.java:195)
	at org.springframework.core.CollectionFactory.createCollection(CollectionFactory.java:151)
	at org.springframework.boot.context.properties.bind.CollectionBinder.lambda$bindAggregate$0(CollectionBinder.java:49)
	at org.springframework.boot.context.properties.bind.AggregateBinder$AggregateSupplier.get(AggregateBinder.java:109)
	at org.springframework.boot.context.properties.bind.IndexedElementsBinder.bindIndexed(IndexedElementsBinder.java:85)
	at org.springframework.boot.context.properties.bind.IndexedElementsBinder.bindIndexed(IndexedElementsBinder.java:71)
	at org.springframework.boot.context.properties.bind.CollectionBinder.bindAggregate(CollectionBinder.java:50)
	at org.springframework.boot.context.properties.bind.AggregateBinder.bind(AggregateBinder.java:58)
	at org.springframework.boot.context.properties.bind.Binder.lambda$bindAggregate$2(Binder.java:305)
	at org.springframework.boot.context.properties.bind.Binder$Context.withIncreasedDepth(Binder.java:441)
	at org.springframework.boot.context.properties.bind.Binder$Context.access$100(Binder.java:381)
	at org.springframework.boot.context.properties.bind.Binder.bindAggregate(Binder.java:304)
	at org.springframework.boot.context.properties.bind.Binder.bindObject(Binder.java:262)
	at org.springframework.boot.context.properties.bind.Binder.bind(Binder.java:221)
	... 57 common frames omitted

Debugging into the code, it appears this may be caused by a bug.

Stepping into CollectionBinder.bindAggregate(CollectionBinder.java), I can see that aggregateType is set to EnumSet and elementType is set to MyObject, which is expected. However the next lines are:

IndexedCollectionSupplier result = new IndexedCollectionSupplier(
				() -> CollectionFactory.createCollection(collectionType, 0));

which does not pass in the elementType.
The next line (bindAggregate) is then invoked which eventually results in a call to the IndexedCollectionSupplier created above, which ends up in CollectionFactory.createCollection():

        } else if (EnumSet.class == collectionType) {
            Assert.notNull(elementType, "Cannot create EnumSet for unknown element type");

which of course does not have an elementType set because it was not passed into the earlier call, which then results in the assertion stack trace.

Perhaps the CollectionFactory.createCollection(collectionType, 0)) should actually be CollectionFactory.createCollection(collectionType, elementType, 0));?

[wilkinsona]

Thanks for the report, but I can't reproduce the behaviour that you have described. Consider the following application:

package com.example.demo;

import java.util.EnumSet;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.boot.context.properties.EnableConfigurationProperties;

@SpringBootApplication
@EnableConfigurationProperties(ExampleProperties.class)
public class Gh15539Application {

	public static void main(String[] args) {
		ExampleProperties properties = SpringApplication.run(Gh15539Application.class,
				"--example.directions=north,south").getBean(ExampleProperties.class);
		System.out.println(properties.getDirections());
	}

}

@ConfigurationProperties("example")
class ExampleProperties {

	private EnumSet<Direction> directions;

	public EnumSet<Direction> getDirections() {
		return directions;
	}

	public void setDirections(EnumSet<Direction> directions) {
		this.directions = directions;
	}

}

enum Direction {

	NORTH, SOUTH, EAST, WEST

}

It produces the following output when run:

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.1.1.RELEASE)

2018-12-20 16:58:58.146  INFO 61268 --- [           main] com.example.demo.Gh15539Application      : Starting Gh15539Application on Andys-MacBook-Pro.local with PID 61268 (/Users/awilkinson/dev/workspaces/spring-projects/spring-boot/master/gh-15539/target/classes started by awilkinson in /Users/awilkinson/dev/workspaces/spring-projects/spring-boot/master/gh-15539)
2018-12-20 16:58:58.149  INFO 61268 --- [           main] com.example.demo.Gh15539Application      : No active profile set, falling back to default profiles: default
2018-12-20 16:58:58.514  INFO 61268 --- [           main] com.example.demo.Gh15539Application      : Started Gh15539Application in 0.578 seconds (JVM running for 0.868)
[NORTH, SOUTH]

If you'd like us to spend some more time investigating, can you please provide a minimal sample (something that we can unzip or git clone) that reproduces the behaviour you have described?

[olideakin]

Thanks for the quick response - here's a recreator for how I'm getting the error. I'm rebinding properties from a YAML file myself using code similar to the following. This for me gives the "Cannot create EnumSet for unknown element type" IllegalArgumentException:

import java.io.FileInputStream;
import java.util.EnumSet;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;

import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.boot.context.properties.bind.Bindable;
import org.springframework.boot.context.properties.bind.Binder;
import org.springframework.boot.env.YamlPropertySourceLoader;
import org.springframework.core.env.MutablePropertySources;
import org.springframework.core.env.PropertySource;
import org.springframework.core.env.StandardEnvironment;
import org.springframework.core.io.InputStreamResource;

public class Test {

    public static void main(String[] args) throws Exception {
        final StandardEnvironment environment = new StandardEnvironment();
        final YamlPropertySourceLoader propertySourceLoader = new YamlPropertySourceLoader();
        final MutablePropertySources propertySources = environment.getPropertySources();
        final List<PropertySource<?>> load = propertySourceLoader.load("test.yaml", new InputStreamResource(new FileInputStream("test.yaml")));
        load.forEach(propertySources::addFirst);
        final ExampleProperties props = Binder.get(environment).bind("example", Bindable.of(ExampleProperties.class)).orElse(new ExampleProperties());
        System.out.println(props.getDirectionsMap());
    }

    @ConfigurationProperties("example")
    static class ExampleProperties {
        private Map<String, EnumSet<Direction>> directionsMap = new LinkedHashMap<>();

        public Map<String, EnumSet<Direction>> getDirectionsMap() {
            return directionsMap;
        }

        public void setDirectionsMap(Map<String, EnumSet<Direction>> directionsMap) {
            this.directionsMap = directionsMap;
        }

    }

    enum Direction {
        NORTH, SOUTH, EAST, WEST
    }
}

with test.yaml:

example:
  directions-map:
    DIRECTIONS: NORTH, SOUTH

[mbhave]

Thanks for the sample @olideakin. It looks like a bug and this should actually be CollectionFactory.createCollection(collectionType, elementType, 0));, as you suggested.