Spring @DependsOn Annotation Example
November 15, 2021
@DependsOn annotation example.
1. The
@DependsOn annotation specifies the beans on which the current bean depends.
2. All beans specified by the
@DependsOn annotation are guaranteed to be created by container before this bean.
3. The
@DependsOn is used by a bean to avoid the side effects of another bean initialization.
4. Using
@DependsOn we control initialization-time dependency. For singleton beans, the destruction-time dependency is also controlled. The bean which uses @DependsOn is destroyed first, prior to the specified beans. In this way, shutdown order can also be controlled by @DependsOn annotation.
5. The
@DependsOn annotation is used with @Bean, @Component and @Service annotations.
6. The
@DependsOn annotation is equivalent to <bean> element's depends-on attribute in XML configuration.
7. The
@DependsOn annotation is introduced in Spring 3.0.
Contents
Using @DependsOn with @Bean
Find the code to use@DependsOn with @Bean annotation.
AppConfig.java
@Configuration
public class AppConfig {
@Bean(name = "city")
public City getCity() {
return new City("Varanasi");
}
@Bean(name = "company")
public Company getCompany() {
return new Company("ABC LTD");
}
@DependsOn("city")
@Bean(name = "college")
public College getCollege() {
return new College("SSIC");
}
@DependsOn("college")
@Bean(name = "student")
public Student getStudent() {
return new Student(getCollege());
}
@DependsOn({ "city", "company" })
@Bean(name = "employee")
public Employee getEmployee() {
return new Employee(getCity(), getCompany());
}
}
public class City {
String name;
public City(String name) {
System.out.println("-- City Initialized --");
this.name = name;
}
}
public class Company {
String name;
public Company(String name) {
System.out.println("-- Company Initialized --");
this.name = name;
}
}
public class College {
String name;
public College(String name) {
System.out.println("-- College Initialized --");
this.name = name;
}
}
public class Student {
College college;
public Student(College college) {
System.out.println("-- Student Initialized --");
}
}
public class Employee {
City city;
Company company;
public Employee(City city, Company company) {
System.out.println("-- Employee Initialized --");
this.city = city;
this.company = company;
}
}
public class SpringDemo {
public static void main(String[] args) {
AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
ctx.register(AppConfig.class);
ctx.refresh();
}
}
15:14:15.926 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'city' -- City Initialized -- 15:14:15.951 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'company' -- Company Initialized -- 15:14:15.952 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'college' -- College Initialized -- 15:14:15.953 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'student' -- Student Initialized -- 15:14:15.954 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'employee' -- Employee Initialized --
Using @DependsOn with @Component
Find the code to use@DependsOn with @Component annotation.
Student.java
@DependsOn("college")
@Component
public class Student {
College college;
public Student(College college) {
System.out.println("-- Student Initialized --");
}
}
@DependsOn({ "city", "company" })
@Component
public class Employee {
City city;
Company company;
public Employee(City city, Company company) {
System.out.println("-- Employee Initialized --");
this.city = city;
this.company = company;
}
}
@ComponentScan("com.concretepage")
@Configuration
public class AppConfig {
@Bean(name = "city")
public City getCity() {
return new City("Varanasi");
}
@Bean(name = "company")
public Company getCompany() {
return new Company("ABC LTD");
}
@DependsOn("city")
@Bean(name = "college")
public College getCollege() {
return new College("SSIC");
}
}
Circular Dependency
In circular dependency, Spring throwsBeanCreationException. Find the code with circular dependency.
AppConfig.java
@Configuration
public class AppConfig {
@DependsOn("college")
@Bean(name = "city")
public City getCity() {
return new City("Varanasi");
}
@DependsOn("city")
@Bean(name = "college")
public College getCollege() {
return new College("SSIC");
}
------
}
Exception in thread "main" org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'college' defined in com.concretepage.AppConfig: Circular depends-on relationship between 'college' and 'city'
