Spring - Constructor Injection with Dependent Object

Spring - Constructor Injection with Dependent Object

Constructor injection with a dependent object in Spring is a common scenario. When one bean has a dependency on another bean, you can inject the dependent bean using constructor injection.

Let's look at an example of how you can inject a dependent object through constructor injection.

Domain Objects:

Address.java:

public class Address { private String city; private String country; // Constructors, getters, setters... public Address(String city, String country) { this.city = city; this.country = country; } }

Person.java:

public class Person { private String name; private Address address; // Constructors, getters, setters... public Person(String name, Address address) { this.name = name; this.address = address; } }

In this example, the Person class has a dependency on the Address class.

XML Configuration:

To set up constructor injection using XML, you'll use the <constructor-arg> element:

spring-config.xml:

<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd"> <bean id="address" class="com.example.Address"> <constructor-arg value="New York" /> <constructor-arg value="USA" /> </bean> <bean id="person" class="com.example.Person"> <constructor-arg value="John" /> <constructor-arg ref="address" /> </bean> </beans>

The address bean is injected into the person bean through the constructor.

Java-based Configuration:

Using Java configuration, you'd set it up like this:

package com.example; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; @Configuration public class AppConfig { @Bean public Address address() { return new Address("New York", "USA"); } @Bean public Person person() { return new Person("John", address()); } }

Here, the address() method creates an Address bean, and it's passed as an argument to create the Person bean.

Annotations-based Autowiring:

If you're using component scanning and annotations:

Address.java (Updated):

import org.springframework.stereotype.Component; @Component public class Address { //... }

Person.java (Updated):

import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Component; @Component public class Person { @Autowired public Person(String name, Address address) { this.name = name; this.address = address; } //... }

In the annotated configuration, Spring automatically wires the Address bean into the Person bean using the @Autowired annotation on the constructor.

Examples

  1. Constructor injection with nested objects in Spring framework:

    • Use constructor injection with nested objects for creating hierarchical dependencies.
    // MyService.java public class MyService { private final MyDependency myDependency; public MyService(MyDependency myDependency) { this.myDependency = myDependency; } }

  2. Injecting dependent objects in Spring constructor using annotations:

    • Inject dependent objects in the constructor using annotations for cleaner configuration.
    // MyService.java import org.springframework.beans.factory.annotation.Autowired; public class MyService { private final MyDependency myDependency; @Autowired public MyService(MyDependency myDependency) { this.myDependency = myDependency; } }

  3. Spring constructor injection with object dependencies example:

    • Demonstrate constructor injection with object dependencies in a Spring project.
    // AppConfig.java import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; @Configuration public class AppConfig { @Bean public MyService myService(MyDependency myDependency) { return new MyService(myDependency); } // Other configuration... }

  4. How to pass dependent objects to a constructor in Spring:

    • Pass dependent objects to a constructor by configuring them in the Spring configuration.
    // AppConfig.java import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; @Configuration public class AppConfig { @Bean public MyDependency myDependency() { return new MyDependency(); } @Bean public MyService myService(MyDependency myDependency) { return new MyService(myDependency); } // Other configuration... }

  5. Constructor-based dependency injection with dependent objects in Spring:

    • Configure constructor-based dependency injection with dependent objects in a Spring project.
    // AppConfig.java import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; @Configuration public class AppConfig { @Bean public MyDependency myDependency() { return new MyDependency(); } @Bean public MyService myService(MyDependency myDependency) { return new MyService(myDependency); } // Other configuration... }

  6. Injecting a hierarchy of dependent objects using Spring IoC container:

    • Utilize the Spring IoC container to inject a hierarchy of dependent objects into the constructor.
    // AppConfig.java import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; @Configuration public class AppConfig { @Bean public MyDependency myDependency() { return new MyDependency(); } @Bean public AnotherDependency anotherDependency() { return new AnotherDependency(); } @Bean public MyService myService(MyDependency myDependency, AnotherDependency anotherDependency) { return new MyService(myDependency, anotherDependency); } // Other configuration... }

More Tags

custom-element axios-cookiejar-support angular2-components rack bag oauth-2.0 android-recyclerview lwc android-file psql

More Programming Guides

Other Guides

More Programming Examples