Spring Boot GenericApplicationContext

last modified July 28, 2023

Spring Boot GenericApplicationContext tutorial shows how to use the GenericApplicationContext in a Spring application. In the example, we create a Spring Boot console application.

Spring is a popular Java application framework and Spring Boot is an evolution of Spring that helps create stand-alone, production-grade Spring based applications easily.

GenericApplicationContext

GenericApplicationContext is an implementation of the ApplicationContext, which does not assume a specific bean definition format; e.g. XML or annotations.

Spring Boot GenericApplicationContext example

In the following application we create a GenericApplicationContext and register a new bean with the context's registerBean method. Later we retrieve the bean from the application context with getBean.

plugins {
    id 'org.springframework.boot' version '3.1.1'
    id 'io.spring.dependency-management' version '1.1.0'
    id 'java'
}

group = 'com.zetcode'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = '17'

repositories {
    mavenCentral()
}

dependencies {
    implementation 'org.springframework.boot:spring-boot-starter'
    testImplementation 'org.springframework.boot:spring-boot-starter-test'
}

test {
    useJUnitPlatform()
}

This is the Gradle build file. The spring-boot-starter is a core starter, including auto-configuration support, logging, and YAML. The spring-boot-starter-test adds testing support in Spring.

spring.main.banner-mode=off
logging.level.root=ERROR
logging.pattern.console=%d{dd-MM-yyyy HH:mm:ss} %magenta([%thread]) %highlight(%-5level) %logger.%M - %msg%n

The application.properties is the main configuration file in Spring Boot. We turn off the Spring banner, reduce the amount of logging to errors only, and set the console logging pattern.

package com.zetcode.service;

import java.time.Instant;

public class TimeService {

    public Instant getNow() {

        return Instant.now();
    }
}

TimeService contains a simple method which returns current date and time. This service class is going to be registered in our generic application context.

package com.zetcode;

import com.zetcode.service.TimeService;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.support.GenericApplicationContext;

@SpringBootApplication
public class Application implements CommandLineRunner {

    private final GenericApplicationContext context;

    public Application(GenericApplicationContext context) {
        this.context = context;
    }

    public static void main(String[] args) {

        SpringApplication.run(Application.class, args);
    }

    @Override
    public void run(String... args) throws Exception {

        context.registerBean("com.zetcode.Service.TimeService",
                TimeService.class, TimeService::new);

        var timeService = (TimeService) context.getBean(TimeService.class);

        System.out.println(timeService.getNow());

        context.registerShutdownHook();
    }
}

Application is the entry point which sets up Spring Boot application. The @SpringBootApplication annotation enables auto-configuration and component scanning. It is a convenience annotation for @Configuration, @EnableAutoConfiguration, and @ComponentScan annotations.

private final GenericApplicationContext context;

public Application(GenericApplicationContext context) {
    this.context = context;
}

We inject the GenericApplicationContext.

context.registerBean("com.zetcode.Service.TimeService",
    TimeService.class, TimeService::new);

A new TimeService bean is registered with the registerBean method.

var timeService = (TimeService) context.getBean(TimeService.class);

We retrieve the bean with getBean.

System.out.println(timeService.getNow());

Finally, we call the bean's getNow method.

package com.zetcode;

import com.zetcode.service.TimeService;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.context.support.GenericApplicationContext;

import java.time.Instant;

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

@SpringBootTest
public class ApplicationTests {

    @Autowired
    private GenericApplicationContext context;

    @Test
    public void testNow() {

        var timeService = (TimeService) context.getBean("com.zetcode.service.TimeService");
        var now = timeService.getNow();

        assertThat(now.isBefore(Instant.now()));
    }
}

We have a simple test that uses the TimeService's getNow method.

var timeService = (TimeService) context.getBean("com.zetcode.service.TimeService");

This time we refer to the bean by its given name.

$ ./gradlew bootRun
...
... INFO  Application MyApp

We run the application.

In this article we have shown how to use GenericApplicationContext in a Spring application.

Author

My name is Jan Bodnar and I am a passionate programmer with many years of programming experience. I have been writing programming articles since 2007. So far, I have written over 1400 articles and 8 e-books. I have over eight years of experience in teaching programming.

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