ObjectBuilder & EntityBuilder

EntityBuilder.java

import ...BaseEntity;
import org.apache.commons.lang.math.RandomUtils;
import org.hibernate.Session;

public class EntityBuilder<T extends BaseEntity> extends ObjectBuilder<T> {

    @Override
    public EntityBuilder<T> set(String fieldName, Object value) {
        return (EntityBuilder<T>) super.set(fieldName, value);
    }

    public EntityBuilder<T> id(Long id) {
        set("id", id);
        return this;
    }

    public EntityBuilder<T> randomId() {
        return id(RandomUtils.nextLong());
    }

    public EntityBuilder<T> deleted(boolean deleted) {
        set("deleted", deleted);
        return this;
    }

    public T save(Session session, Class<T> clazz) {
        T instance = build(clazz);
        return (T) session.merge(instance);
    }

}

ObjectBuilder.java

import org.springframework.test.util.ReflectionTestUtils;

import java.util.HashMap;
import java.util.Map;

public class ObjectBuilder<T> {

    private Map<String, Object> fieldsAndValues = new HashMap<>();

    public ObjectBuilder<T> set(String fieldName, Object value) {
        fieldsAndValues.put(fieldName, value);
        return this;
    }

    public T build(Class<T> clazz) {
        try {
            T instance = clazz.newInstance();
            for (Map.Entry<String, Object> entry : fieldsAndValues.entrySet()) {
                ReflectionTestUtils.setField(instance, entry.getKey(), entry.getValue());
            }
            return instance;
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

}

ObjectBuilderTest.java

import org.junit.Test;

import java.util.Arrays;
import java.util.List;

import static org.hamcrest.Matchers.equalTo;
import static org.junit.Assert.assertThat;

public class ObjectBuilderTest {

    @Test
    public void shouldInitiateAndSetFields() {
        TestClass testClass = new ObjectBuilder<TestClass>()
                .set("integerField", 471989)
                .set("stringField", "Ufuk")
                .set("listField", Arrays.asList(10L, 71L))
                .build(TestClass.class);

        assertThat(testClass.getIntegerField(), equalTo(471989));
        assertThat(testClass.getStringField(), equalTo("Ufuk"));
        assertThat(testClass.getListField(), equalTo(Arrays.asList(10L, 71L)));
    }

    static class TestClass {

        private int integerField;

        private String stringField;

        private List<Long> listField;

        public int getIntegerField() {
            return integerField;
        }

        public void setIntegerField(int integerField) {
            this.integerField = integerField;
        }

        public String getStringField() {
            return stringField;
        }

        public void setStringField(String stringField) {
            this.stringField = stringField;
        }

        public List<Long> getListField() {
            return listField;
        }

        public void setListField(List<Long> listField) {
            this.listField = listField;
        }

    }

}