Using Jackson + Hibernate Validation to load YAML or Java config files and validate configuration key/val pairs are valid.

ConfigLoader.java

package default;

import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.dataformat.yaml.YAMLFactory;
import com.google.common.base.Objects;
import com.google.common.collect.Lists;
import org.hibernate.validator.constraints.NotEmpty;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import javax.validation.ConstraintViolation;
import javax.validation.Validation;
import javax.validation.Validator;
import javax.validation.ValidatorFactory;
import javax.validation.constraints.NotNull;
import java.io.IOException;
import java.util.List;
import java.util.Set;

public class ConfigLoader {
    private static final Logger logger = LoggerFactory.getLogger(ConfigLoader.class);

    public static void main(String[] args) throws IOException {
        ValidatorFactory factory = Validation.buildDefaultValidatorFactory();
        Validator validator = factory.getValidator();
        final ObjectMapper objectMapper = new ObjectMapper(new YAMLFactory());

        List<String> testYamls = Lists.newArrayList(
                "name: Kevin\nage: 34\n",
                "age: 34\n",
                "{\"name\": \"Kevin\", \"age\": 34}"
        );
        testYamls.forEach(yaml -> {
            System.out.println("raw YAML:\n" + yaml);
            User user = null;
            try {
                user = objectMapper.readValue(yaml, User.class);
            } catch (IOException e) {
                logger.error("Exception caught:", e);
            }

            if (user != null) {
                final Set<ConstraintViolation<User>> violations = validator.validate(user);
                if (violations.size() > 0) {
                    System.out.println("YAML config contains errors:");
                    violations.forEach(u -> System.out.println("  \"" + u.getPropertyPath().toString() + "\"" + " " + u.getMessage()));
                } else {
                    System.out.println("YAML successfully decoded: " + user);
                }
                System.out.println("****************************************");
            }
        });

    }

    public static class User {
        @NotEmpty
        @NotNull
        private String name;

        @NotEmpty
        @NotNull
        private String age;

        public User() {
        }

        @JsonProperty
        public String getAge() {
            return age;
        }

        @JsonProperty
        public void setAge(String age) {
            this.age = age;
        }

        @JsonProperty
        public String getName() {
            return name;
        }

        @JsonProperty
        public void setName(String name) {
            this.name = name;
        }

        @Override
        public String toString() {
            return Objects.toStringHelper(this)
                          .add("age", age)
                          .add("name", name)
                          .toString();
        }
    }
}