SpringApplicationBuilder
last modified August 2, 2023
In this article we show how to use SpringApplicationBuilder to create a simple Spring Boot application.
Spring is a popular Java application framework for creating enterprise applications. Spring Boot is an evolution of Spring framework which helps create stand-alone, production-grade Spring based applications with minimal effort.
SpringApplication
SpringApplication is a class to bootstrap a Spring application from a
Java main method. It creates an appropriate ApplicationContext
instance (depending on the classpath), registers a
CommandLinePropertySource to expose command line arguments as
Spring properties, refreshes the application context, loading all singleton
beans, and triggers any CommandLineRunner beans.
SpringApplicationBuilder
SpringApplicationBuilder is a builder for
SpringApplication and ApplicationContext instances
with convenient fluent API and context hierarchy support.
Spring Boot example
The following application is a simple Spring Boot console application
which uses SpringApplicationBuilder to set up a Spring Boot
application.
The application takes an argument from the user; it expects a full URL of a website and returns its title.
build.gradle
...
src
├── main
│ ├── java
│ │ └── com
│ │ └── zetcode
│ │ ├── Application.java
│ │ └── MyRunner.java
│ └── resources
└── test
└── java
This is the project structure.
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'
implementation 'org.jsoup:jsoup:1.16.1'
}
Spring Boot starters are a set of convenient dependency descriptors which
greatly simplify the configuration. The spring-boot-starter is the
core Spring starter. The jsoup dependency is for the JSoup library.
package com.zetcode;
import java.util.List;
import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;
import org.springframework.boot.ApplicationArguments;
import org.springframework.boot.ApplicationRunner;
import org.springframework.stereotype.Component;
@Component
public class MyRunner implements ApplicationRunner {
@Override
public void run(ApplicationArguments args) throws Exception {
if (!args.containsOption("website")) {
System.err.println("no website specified");
} else {
List<String> vals = args.getOptionValues("website");
String url = vals.get(0);
Document doc = Jsoup.connect(url).get();
String title = doc.title();
System.out.printf("The title is: %s%n", title);
}
}
}
After the Spring application is loaded, any bean that implements ApplicationRunner
is executed.
if (!args.containsOption("website")) {
We check if there is a --website option specified on the command line.
List<String> vals = args.getOptionValues("website");
String url = vals.get(0);
We get the value of the option.
Document doc = Jsoup.connect(url).get();
String title = doc.title();
System.out.printf("The title is: %s%n", title);
With JSoup, we get the title of the specified website.
package com.zetcode;
import org.springframework.boot.Banner;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.builder.SpringApplicationBuilder;
@SpringBootApplication
public class Application {
public static void main(String[] args) {
new SpringApplicationBuilder(Application.class)
.bannerMode(Banner.Mode.OFF)
.logStartupInfo(false)
.build()
.run(args);
}
}
Application is the entry point which sets up Spring Boot
application. The @SpringBootApplication annotation enables
auto-configuration and component scanning.
new SpringApplicationBuilder(Application.class)
.bannerMode(Banner.Mode.OFF)
.logStartupInfo(false)
.build()
.run(args);
The SpringApplicationBuilder is used to build the Spring application. We turn
off the banner and the startup information.
$ ./gradlew bootRun -q --args=--website=http://webcode.me The title is: My html page
The command line arguments are passed with the --args. The
-q (for quiet) is a Gradle option that turns of Gradle messages.
In this article we have covered SpringApplicationBuilder.
