GuiceSingletonProviderTest.java

package com.github.jangalinski;

import com.google.inject.AbstractModule;
import com.google.inject.Guice;
import com.google.inject.Injector;
import org.junit.Test;

import javax.inject.Provider;
import javax.inject.Singleton;

import static org.assertj.core.api.Assertions.assertThat;

public class GuiceSingletonProviderTest {

    @Test
    public void execute() {
        Injector injector = Guice.createInjector(new AbstractModule() {
            @Override
            protected void configure() {
                bind(GlobalSettings.class).toProvider(GlobalSettingsProvider.class).in(Singleton.class);
            }
        });

        GlobalSettings g1 = injector.getInstance(GlobalSettings.class);
        GlobalSettings g2 = injector.getInstance(GlobalSettings.class);

        assertThat(g1).isSameAs(g2);
    }

    public static class GlobalSettingsProvider implements Provider<GlobalSettings> {

        @Override
        public GlobalSettings get() {

            GlobalSettings globalSettings = new GlobalSettings();
            globalSettings.isDummyRun = Boolean.parseBoolean(System.getProperty("isDummyRun", "false"));
            globalSettings.inputFlavor = System.getProperty("input_flavor", "none");

            return globalSettings;
        }
    }

    private static class GlobalSettings {
        public boolean isDummyRun;
        public String inputFlavor;
    }
}