Spring dependency checking with Custom @Required Annotation | Spring Tutorial

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Overview: Custom @Required Annotation in Spring

In the Spring Framework, dependency validation ensures that mandatory bean properties are populated at configuration time rather than failing at runtime with a NullPointerException. While Spring provides the built-in @Required annotation, developers can also create and register their own custom @Required annotations. This allows teams to enforce custom validation semantics, follow organizational naming standards, or integrate seamlessly with custom bean post-processors.

In this guide, you will learn how to define a custom required annotation, configure Spring's RequiredAnnotationBeanPostProcessor to recognize it, and enforce strict dependency checking during bean initialization.

How Custom Dependency Checking Works

Spring's dependency checking framework is highly modular and customizable:

• Custom Annotation Declaration: You can define a standard Java retention annotation (e.g., @Mandatory) targeted at methods.
• Post-Processor Configuration: The RequiredAnnotationBeanPostProcessor supports setting custom annotation types via its setCustomAnnotationType() property.
• Fail-Fast Property Enforcement: If any setter method annotated with your custom annotation does not receive a property value during bean configuration, Spring raises a BeanInitializationException immediately during application startup.
• Cleaner Architecture: Enforces architectural contracts across your service layer without coupling your domain code strictly to Spring's package namespaces.

Step-by-Step Implementation

1. Create the Custom Annotation: Define a retention annotation applicable to methods:
   @Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface Mandatory { }
2. Configure RequiredAnnotationBeanPostProcessor: Register the processor in Spring XML and specify your custom annotation type:
   <bean class="org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcessor">
  <property name="customAnnotationType" value="com.example.Mandatory"/>
</bean>
3. Annotate Setter Methods: Place your custom annotation on setter methods that require dependencies:
   @Mandatory
public void setDataSource(DataSource dataSource) {
  this.dataSource = dataSource;
}

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---

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Spring dependency checking with Custom @Required Annotation | Spring Tutorial

Spring dependency checking with Custom @Required Annotation | Spring Tutorial

Spring dependency checking with Custom @Required Annotation | Spring Tutorial

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0%20http://maven.apache.org/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.ram.core</groupId>
    <artifactId>SpringDemo</artifactId>
    <packaging>jar</packaging>
    <version>1.0-SNAPSHOT</version>
    <name>SpringDemo</name>
    <url>http://maven.apache.org</url>

    <properties>
        <spring.version>5.0.2.RELEASE</spring.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>3.8.1</version>
            <scope>test</scope>
        </dependency>

        <!-- Spring 5 dependencies -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-core</artifactId>
            <version>${spring.version}</version>
        </dependency>

        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>${spring.version}</version>
        </dependency>
    </dependencies>
</project>

Mandatory.java

package com.ram.custom;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface Mandatory
{
}

Address.java

package com.ram.model;

public class Address
{
    private String city;
    private String state;

    public String getCity()
    {
        return city;
    }

    public void setCity(String city)
    {
        this.city = city;
    }

    public String getState()
    {
        return state;
    }

    public void setState(String state)
    {
        this.state = state;
    }

    @Override
    public String toString()
    {
        return "Address [city=" + city + ", state=" + state + "]";
    }

}

Employee.java

package com.ram.model;

import com.ram.custom.Mandatory;

public class Employee
{
    private int id;
    private String name;
    private Address address;

    public int getId()
    {
        return id;
    }

    public void setId(int id)
    {
        this.id = id;
    }

    public String getName()
    {
        return name;
    }

    public void setName(String name)
    {
        this.name = name;
    }

    public Address getAddress()
    {
        return address;
    }
   
    @Mandatory
    public void setAddress(Address address)
    {
        this.address = address;
    }

    @Override
    public String toString()
    {
        return "Employee [id=" + id + ", name=" + name + ", address=" + address
                + "]";
    }

}

applicationContext.xml

<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-4.3.xsd
    http://www.springframework.org/schema/context
    http://www.springframework.org/schema/context/spring-context-4.3.xsd">

    <bean id="address" class="com.ram.model.Address">
        <property name="city" value="TamilNadu"></property>
        <property name="state" value="Chennai"></property>
    </bean>


    <bean id="employee" class="com.ram.model.Employee">
        <property name="id" value="100"></property>
        <property name="name" value="Peter"></property>
        <!-- <property name="address" ref="address"></property> -->
    </bean>

    <bean
        class="org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcessor">
        <property name="requiredAnnotationType" value="com.ram.custom.Mandatory" />
    </bean>

</beans>

App.java

package com.ram.core;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.ram.model.Employee;

public class App
{
    public static void main(String[] args)
    {
        ApplicationContext context = new ClassPathXmlApplicationContext(
                "applicationContext.xml");

        System.out.println("---------------------------------------");

        Employee employee = context.getBean("employee", Employee.class);
        System.out.println(
                "Got employee object from the ApplicationContext(Spring Container)");

        System.out.println(employee);

    }

}

Output

Aug 06, 2018 9:47:19 AM org.springframework.context.support.AbstractApplicationContext prepareRefresh
INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@5b37e0d2: startup date [Mon Aug 06 09:47:19 IST 2018]; root of context hierarchy
Aug 06, 2018 9:47:19 AM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
INFO: Loading XML bean definitions from class path resource [applicationContext.xml]
Aug 06, 2018 9:47:20 AM org.springframework.context.support.AbstractApplicationContext refresh
WARNING: Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'employee' defined in class path resource [applicationContext.xml]: Initialization of bean failed; nested exception is org.springframework.beans.factory.BeanInitializationException: Property 'address' is required for bean 'employee'
Exception in thread "main" org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'employee' defined in class path resource [applicationContext.xml]: Initialization of bean failed; nested exception is org.springframework.beans.factory.BeanInitializationException: Property 'address' is required for bean 'employee'
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:591)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:502)
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:312)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:228)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:310)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:200)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:758)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:868)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:549)
    at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:144)
    at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:85)
    at com.ram.core.App.main(App.java:12)
Caused by: org.springframework.beans.factory.BeanInitializationException: Property 'address' is required for bean 'employee'
    at org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcessor.postProcessPropertyValues(RequiredAnnotationBeanPostProcessor.java:156)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1344)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:582)
    ... 11 more

Click the below link to download the code:
https://sites.google.com/site/ramj2eev2/java_basics/SpringDemo_custom_required_annotation.zip?attredirects=0&d=1

Github Link:
https://github.com/ramram43210/javaee/tree/master/Spring_2018/SpringDemo_custom_required_annotation

Bitbucket Link:
https://bitbucket.org/ramram43210/spring/src/476437cc0ec4e46c307e790b2c10c4099b1c066b/Spring_2018/SpringDemo_custom_required_annotation/?at=master

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Spring dependency checking with @Required Annotation v2 | Spring Tutorial

Master Spring & Java Development!

Subscribe to Ram N Java for clean, beginner-friendly coding guides!

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Overview: Dependency Checking with @Required

In the Spring Framework, ensuring that all critical dependencies and configuration properties are set is crucial for preventing unexpected NullPointerException errors during runtime. Spring provides the @Required annotation to enforce mandatory bean property population at configuration time.

In this guide, you will learn how the @Required annotation works, how to enable it in your Spring configuration, and how it enforces fail-fast validation during bean initialization.

Understanding the @Required Annotation

The @Required annotation provides declarative property checking with the following characteristics:

• Applied to Setter Methods: It is placed directly above setter methods to signify that the associated bean property must be populated in XML configuration.
• Fail-Fast Behavior: If an annotated property is not configured, Spring immediately throws a BeanInitializationException during container startup rather than failing at runtime.
• Managed by Post-Processor: The dependency checking is performed by the RequiredAnnotationBeanPostProcessor, which inspects bean definitions before initialization.
• Explicit Dependency Contracts: It clearly documents and enforces which properties are non-negotiable for a bean's functionality.

Step-by-Step Implementation

1. Annotate the Setter Method: Add @Required on setter methods in your Java bean:
   @Required
public void setMessage(String message) {
  this.message = message;
}
2. Enable RequiredAnnotationBeanPostProcessor: Register the processor in your XML configuration or include <context:annotation-config />:
   <bean class="org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcessor"/>
3. Verify Property Wiring: Provide the property in your XML definition. If omitted, Spring halts initialization with a descriptive error.

Recommended Next Videos from Ram N Java

• 👉 Spring dependency checking with Custom @Required Annotation | Spring Tutorial
• 👉 Enabling and Disabling Dependency Checking with @Autowired Annotation | Spring Tutorial
• 👉 Simplifying Dependency Injection with @Autowired Annotation | Spring Tutorial

---

Click here to watch on Youtube:
https://www.youtube.com/watch?v=BtmpN7TgoxM&list=UUhwKlOVR041tngjerWxVccw

Click the below Image to Enlarge:

Spring dependency checking with @Required Annotation v2 | Spring Tutorial

Spring dependency checking with @Required Annotation v2 | Spring Tutorial

Spring dependency checking with @Required Annotation v2 | Spring Tutorial

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0%20http://maven.apache.org/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.ram.core</groupId>
    <artifactId>SpringDemo</artifactId>
    <packaging>jar</packaging>
    <version>1.0-SNAPSHOT</version>
    <name>SpringDemo</name>
    <url>http://maven.apache.org</url>

    <properties>
        <spring.version>5.0.2.RELEASE</spring.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>3.8.1</version>
            <scope>test</scope>
        </dependency>

        <!-- Spring 5 dependencies -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-core</artifactId>
            <version>${spring.version}</version>
        </dependency>

        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>${spring.version}</version>
        </dependency>
    </dependencies>
</project>

Address.java

package com.ram.model;

public class Address
{
    private String city;
    private String state;

    public String getCity()
    {
        return city;
    }

    public void setCity(String city)
    {
        this.city = city;
    }

    public String getState()
    {
        return state;
    }

    public void setState(String state)
    {
        this.state = state;
    }

    @Override
    public String toString()
    {
        return "Address [city=" + city + ", state=" + state + "]";
    }

}

Employee.java

package com.ram.model;

import org.springframework.beans.factory.annotation.Required;

public class Employee
{
    private int id;
    private String name;
    private Address address;

    public int getId()
    {
        return id;
    }

    public void setId(int id)
    {
        this.id = id;
    }

    public String getName()
    {
        return name;
    }

    public void setName(String name)
    {
        this.name = name;
    }

    public Address getAddress()
    {
        return address;
    }
   
    @Required
    public void setAddress(Address address)
    {
        this.address = address;
    }

    @Override
    public String toString()
    {
        return "Employee [id=" + id + ", name=" + name + ", address=" + address
                + "]";
    }

}

applicationContext.xml

<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-4.3.xsd
    http://www.springframework.org/schema/context
    http://www.springframework.org/schema/context/spring-context-4.3.xsd">

    <bean id="address" class="com.ram.model.Address">
        <property name="city" value="TamilNadu"></property>
        <property name="state" value="Chennai"></property>
    </bean>


    <bean id="employee" class="com.ram.model.Employee">
        <property name="id" value="100"></property>
        <property name="name" value="Peter"></property>
        <!-- <property name="address" ref="address"></property> -->
    </bean>

    <bean
        class="org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcessor" />

</beans>

App.java

package com.ram.core;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.ram.model.Employee;

public class App
{
    public static void main(String[] args)
    {
        ApplicationContext context = new ClassPathXmlApplicationContext(
                "applicationContext.xml");

        System.out.println("---------------------------------------");

        Employee employee = context.getBean("employee", Employee.class);
        System.out.println(
                "Got employee object from the ApplicationContext(Spring Container)");

        System.out.println(employee);

    }

}

Output

Aug 05, 2018 9:29:58 AM org.springframework.context.support.AbstractApplicationContext prepareRefresh
INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@5b37e0d2: startup date [Sun Aug 05 09:29:58 IST 2018]; root of context hierarchy
Aug 05, 2018 9:29:59 AM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
INFO: Loading XML bean definitions from class path resource [applicationContext.xml]
Aug 05, 2018 9:29:59 AM org.springframework.context.support.AbstractApplicationContext refresh
WARNING: Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'employee' defined in class path resource [applicationContext.xml]: Initialization of bean failed; nested exception is org.springframework.beans.factory.BeanInitializationException: Property 'address' is required for bean 'employee'
Exception in thread "main" org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'employee' defined in class path resource [applicationContext.xml]: Initialization of bean failed; nested exception is org.springframework.beans.factory.BeanInitializationException: Property 'address' is required for bean 'employee'
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:591)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:502)
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:312)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:228)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:310)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:200)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:758)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:868)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:549)
    at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:144)
    at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:85)
    at com.ram.core.App.main(App.java:12)
Caused by: org.springframework.beans.factory.BeanInitializationException: Property 'address' is required for bean 'employee'
    at org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcessor.postProcessPropertyValues(RequiredAnnotationBeanPostProcessor.java:156)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1344)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:582)
    ... 11 more

Click the below link to download the code:
https://sites.google.com/site/ramj2eev2/java_basics/SpringDemo_Required_Annotation_V2.zip?attredirects=0&d=1

Github Link:
https://github.com/ramram43210/javaee/tree/master/Spring_2018/SpringDemo_Required_Annotation_V2

Bitbucket Link:
https://bitbucket.org/ramram43210/spring/src/476437cc0ec4e46c307e790b2c10c4099b1c066b/Spring_2018/SpringDemo_Required_Annotation_V2/?at=master

See also:

All JavaEE Videos Playlist

All JavaEE Videos

All JAVA EE Links

Spring Tutorial

Servlets Tutorial

All Design Patterns Links

JDBC Tutorial

Java Collection Framework Tutorial

JAVA Tutorial

Kids Tutorial

Cooking Tutorial