Spring Boot @Lazy
last modified July 23, 2023
In this article we show how to lazily intialize beans with Spring @Lazy annotation.
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.
@Lazy
@Lazy annotation indicates whether a bean is to be
lazily initialized. It can be used on @Component and
@Bean definitions. A @Lazy bean is not
initialized until referenced by another bean or explicitly retrieved
from BeanFactory. Beans that are not annotated with @Lazy
are initialized eagerly.
Spring Boot @Lazy example
In the following example we create beans that are initialized lazily and eagerly. It demostrates the difference between the two types of beans. The application is a simple Spring Boot web application, which runs on embedded Tomcat server. We use Freemarker template engine.
build.gradle
...
src
├── main
│ ├── java
│ │ └── com
│ │ └── zetcode
│ │ ├── Application.java
│ │ ├── bean
│ │ │ ├── MyBean.java
│ │ │ ├── MyLazyBean.java
│ │ │ └── StartUpBean.java
│ │ └── controller
│ │ └── MyController.java
│ └── resources
│ ├── application.properties
│ ├── static
│ │ └── index.html
│ └── templates
│ └── showMessages.ftlh
└── 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.example'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = '17'
repositories {
mavenCentral()
}
dependencies {
implementation 'org.springframework.boot:spring-boot-starter-web'
implementation 'org.springframework.boot:spring-boot-starter-freemarker'
}
This is the build.gradle file.
spring.main.banner-mode=off logging.level.org.springframework=ERROR
In the application.properties we turn off the banner and set
the logging level.
package com.zetcode.bean;
import org.springframework.stereotype.Component;
import java.util.logging.Logger;
@Component
public class MyBean {
static Logger log = Logger.getLogger(MyBean.class.getName());
public MyBean() {
log.info("MyBean initialized");
}
public String getMessage() {
return "Message from MyBean";
}
}
This is MyBean. This bean is initialized eagerly, that is,
at the start of the Spring framework.
package com.zetcode.bean;
import org.springframework.context.annotation.Lazy;
import org.springframework.stereotype.Component;
import java.util.logging.Logger;
@Component
@Lazy
public class MyLazyBean {
static Logger log = Logger.getLogger(MyLazyBean.class.getName());
public MyLazyBean() {
log.info("MyLazyBean initialized");
}
public String getMessage() {
return "Message from MyLazyBean";
}
}
MyLazyBean contains the @Lazy annotation. It is
initialized lazily, when first requested. It is requested from the controller.
package com.zetcode.bean;
import org.springframework.boot.context.event.ApplicationReadyEvent;
import org.springframework.context.ApplicationListener;
import org.springframework.stereotype.Component;
import java.util.logging.Logger;
@Component
public class StartUpBean implements
ApplicationListener<ApplicationReadyEvent> {
static Logger log = Logger.getLogger(StartUpBean.class.getName());
@Override
public void onApplicationEvent(ApplicationReadyEvent applicationReadyEvent) {
log.info("Application is ready");
}
}
StartUpBean implements an application listener; it logs a message
when the application is ready.
package com.zetcode.controller;
import com.zetcode.bean.MyBean;
import com.zetcode.bean.MyLazyBean;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.GetMapping;
@Controller
public class MyController {
private final BeanFactory factory;
@Autowired
public MyController(BeanFactory factory) {
this.factory = factory;
}
@GetMapping(path="/messages")
public String getMessages(Model model) {
MyLazyBean myLazyBean = factory.getBean(MyLazyBean.class);
MyBean myBean = factory.getBean(MyBean.class);
model.addAttribute("mybean", myBean.getMessage());
model.addAttribute("mylazybean", myLazyBean.getMessage());
return "showMessages";
}
}
This is a controller class. It creates the two beans and receives their messages. The messages are displayd in a Freemarker template.
private final BeanFactory factory;
@Autowired
public MyController(BeanFactory factory) {
this.factory = factory;
}
We inject the BeanFactory. The factory is used for accessing
Spring beans.
MyLazyBean myLazyBean = factory.getBean(MyLazyBean.class);
This is the moment when the MyLazyBean is initialized.
MyBean myBean = factory.getBean(MyBean.class);
We get the MyBean from the factory; MyBean
was initialized at Spring's startup.
<!DOCTYPE html>
<html>
<head>
<title>Show data</title>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
</head>
<body>
<p>
MyBean: ${mybean}
</p>
<p>
MyLazyBean: ${mylazybean}
</p>
</body>
</html>
The Freemarker template displays the messages from the two beans.
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Home page</title>
</head>
<body>
<a href="messages">Get messages</a>
</body>
</html>
In the index.html there is a link to get the messages from
beans.
package com.zetcode;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
@SpringBootApplication
public class Application {
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
}
The Application sets up the Spring Boot application.
The @SpringBootApplication enables auto-configuration and
component scanning.
$ ./gradlew bootRun
We start the application.
Initializing Spring embedded WebApplicationContext com.zetcode.bean.MyBean : MyBean initialized com.zetcode.Application : Started Application in 2.483 seconds (JVM running for 2.854) com.zetcode.bean.StartUpBean : Application is ready
We can see these log messages when Spring Boot starts. Notice that MyBean
was initialized at startup.
com.zetcode.bean.MyLazyBean : MyLazyBean initialized
When the controller is called, the MyLazyBean is initialized.
In this article we have showed how to use Spring @Lazy annotation.
