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What is Embedded Server Support in Spring Boot?

Spring Boot enhances Java web development by offering embedded server support, allowing applications to run independently without needing an external application server (like Tomcat or Jetty installed separately). This simplifies development, testing, and deployment, making Spring Boot ideal for microservices and cloud-native applications.

🔧 1. Embedded Server Options in Spring Boot

Spring Boot supports multiple embedded servlet containers:

• Apache Tomcat (default): High-performance, widely-used.
• Jetty: Lightweight and scalable.
• Undertow: Fast, non-blocking, and flexible.

✅ To switch servers:

Use Maven or Gradle to exclude Tomcat and include your preferred server:

Example: Use Jetty

xml

<!-- Exclude default Tomcat -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <exclusions>
        <exclusion>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-tomcat</artifactId>
        </exclusion>
    </exclusions>
</dependency>

<!-- Include Jetty -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-jetty</artifactId>
</dependency>

⚙️ 2. Embedded Server Configuration

You can configure the embedded server using application.properties or application.yml.

Common Properties:

properties

# Set port
server.port=8081

# Set context path
server.servlet.context-path=/myapp

# Bind to IP
server.address=0.0.0.0

# Session timeout
server.servlet.session.timeout=15m

🛠️ 3. Customizing Embedded Servers

Customize embedded server behavior using Java configuration classes.

a) Custom Tomcat Configuration

java

@Configuration
public class TomcatConfig {
    @Bean
    public WebServerFactoryCustomizer<TomcatServletWebServerFactory> customizer() {
        return factory -> factory.addContextCustomizers(context -> {
            // Customize Tomcat context
        });
    }
}

b) Custom Jetty Configuration

java

@Configuration
public class JettyConfig {
    @Bean
    public WebServerFactoryCustomizer<JettyServletWebServerFactory> customizer() {
        return factory -> factory.addServerCustomizers(server -> {
            // Customize Jetty server
        });
    }
}

c) Custom Undertow Configuration

java

@Configuration
public class UndertowConfig {
    @Bean
    public WebServerFactoryCustomizer<UndertowServletWebServerFactory> customizer() {
        return factory -> factory.addBuilderCustomizers(builder -> {
            // Customize Undertow builder
        });
    }
}

📦 4. Packaging and Running Applications

Spring Boot applications can be packaged as executable JARs or WARs.

✅ Run as a standalone JAR:

bash

mvn clean package
java -jar target/myapp.jar

✅ WAR Deployment:

For traditional WAR packaging, you can deploy to external servers or still run as a standalone if the embedded server is included.

🌟 5. Benefits of Embedded Server in Spring Boot

FeatureBenefitStand-alone ExecutionNo need for separate server installationSimplified DeploymentPackage once, run anywhere with java -jarReduced ConfigurationAuto-configured ports, contexts, and threadsFaster DevelopmentInstant startup, better for rapid prototyping and microservice design

🚫 6. Disabling the Embedded Server

In cases like non-web apps or traditional WAR deployments, you might want to disable the embedded server.

Option A: Disable via properties

properties

spring.main.web-application-type=none

Option B: Use provided scope for web starter

xml

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <scope>provided</scope>
</dependency>

📝 Summary

Spring Boot’s embedded server support is a game changer for modern Java development. It lets you:

• Skip external servers
• Simplify deployment
• Configure with ease
• Launch apps with a single command

Whether you're building microservices, REST APIs, or full-stack applications, embedded server support in Spring Boot provides the speed, simplicity, and flexibility today's developers need.