What will happen in byType Auto wiring mode, multiple bean of one type is there?

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Introduction

In the Spring Framework, byType autowiring allows the container to automatically inject a dependency into a setter method if exactly one bean matches the property's data type. But what happens if multiple beans of that same data type are defined in your XML configuration? Let us explore how the Spring container responds and how to resolve the resulting ambiguity.

What Happens When Multiple Beans of the Same Type Exist?

• Fatal Exception Thrown: If more than one candidate bean of the expected type is present in the ApplicationContext, Spring cannot choose which one to inject.
• NoUniqueBeanDefinitionException: Spring throws a fatal NoUniqueBeanDefinitionException (or UnsatisfiedDependencyException), preventing application context initialization.
• Resolution Techniques: You can resolve this issue by marking one bean as primary (primary="true"), excluding beans with autowire-candidate="false", switching to byName autowiring, or using explicit wiring.

The Ambiguity Scenario Illustrated

Consider two Address beans configured in applicationContext.xml, while an Employee bean uses autowire="byType":

1. Problematic Configuration

<!-- Multiple beans of the same type (Address) -->
<bean id="address1" class="com.ram.model.Address">
    <property name="city" value="Bangalore" />
</bean>

<bean id="address2" class="com.ram.model.Address">
    <property name="city" value="Hyderabad" />
</bean>

<!-- byType autowiring encounters ambiguity here -->
<bean id="employee" 
      class="com.ram.model.Employee" 
      autowire="byType" />

2. Container Exception Result

org.springframework.beans.factory.NoUniqueBeanDefinitionException: 
No qualifying bean of type 'com.ram.model.Address' available: 
expected single matching bean but found 2: address1,address2

Key Takeaway

When using autowire="byType", Spring guarantees type safety only when exactly one qualifying bean is present. To avoid fatal runtime exceptions when multiple beans share the same type, make sure to designate a primary candidate, use qualifier annotations, or switch to explicit bean references.

Recommended Auto-Wiring Tutorials from Ram N Java

• byType Auto-Wiring in Spring: How Does It Work? | Spring Framework Tutorial | Spring Tutorial
• byName Auto-Wiring in Spring: How Does It Work? | Spring Framework Tutorial | Spring Tutorial
• Constructor Auto-Wiring in Spring: How Does It Work? | Spring Framework Tutorial | Spring Tutorial

---

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What will happen in byType Auto wiring mode, multiple bean of one type is there?

What will happen in byType Auto wiring mode, multiple bean of one type is there?

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;
    private String country;

    public Address(String city, String state, String country)
    {
        this.city = city;
        this.state = state;
        this.country = country;
    }

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

}

Employee.java

package com.ram.model;

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;
    }

    public void setAddress(Address address)
    {
        this.address = address;
    }

    public void displayEmployeeDetails()
    {
        System.out.println("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"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-4.3.xsd">

    <bean id="address1" class="com.ram.model.Address">
        <constructor-arg value="Chennai"></constructor-arg>
        <constructor-arg value="Tamil Nadu"></constructor-arg>
        <constructor-arg value="India"></constructor-arg>
    </bean>

    <bean id="address2" class="com.ram.model.Address">
        <constructor-arg value="Bangalore"></constructor-arg>
        <constructor-arg value="Karnataka"></constructor-arg>
        <constructor-arg value="India"></constructor-arg>
    </bean>

    <bean id="employee" class="com.ram.model.Employee" autowire="byType">
        <property name="id" value="100"></property>
        <property name="name" value="Peter"></property>
    </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 = (Employee) context.getBean("employee");
        System.out.println(
                "Got employee object from the ApplicationContext[Spring Container]");
        employee.displayEmployeeDetails();

    }

}

Output

Jun 30, 2018 8:41:53 AM org.springframework.context.support.AbstractApplicationContext prepareRefresh
INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@5b37e0d2: startup date [Sat Jun 30 08:41:53 IST 2018]; root of context hierarchy
Jun 30, 2018 8:41:53 AM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
INFO: Loading XML bean definitions from class path resource [applicationContext.xml]
Jun 30, 2018 8:41:53 AM org.springframework.context.support.AbstractApplicationContext refresh
WARNING: Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'employee' defined in class path resource [applicationContext.xml]: Unsatisfied dependency expressed through bean property 'address'; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'com.ram.model.Address' available: expected single matching bean but found 2: address1,address2
Exception in thread "main" org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'employee' defined in class path resource [applicationContext.xml]: Unsatisfied dependency expressed through bean property 'address'; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'com.ram.model.Address' available: expected single matching bean but found 2: address1,address2
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireByType(AbstractAutowireCapableBeanFactory.java:1439)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1326)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:582)
    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.NoUniqueBeanDefinitionException: No qualifying bean of type 'com.ram.model.Address' available: expected single matching bean but found 2: address1,address2
    at org.springframework.beans.factory.config.DependencyDescriptor.resolveNotUnique(DependencyDescriptor.java:215)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1113)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1062)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireByType(AbstractAutowireCapableBeanFactory.java:1424)
    ... 13 more

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

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

Bitbucket Link:
https://bitbucket.org/ramram43210/spring/src/a2a3948db9c8932cede027a3aaf7ba5a87170ed8/Spring_2018/SpringDemo_byType_Autowiring_multiplebean/?at=master

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What is byType Auto-wiring mode in Spring?

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Introduction

Spring's dependency injection container can automatically wire collaborating beans through autowiring modes. One of the most commonly used approaches is byType autowiring (autowire="byType"). In this mode, Spring inspects the property types of a bean and searches the application context for another bean matching that exact class or interface type to inject.

How Does byType Auto-Wiring Work?

• Type-Based Inspection: Spring inspects each setter method in the bean. If a setter accepts an object of type Address, Spring searches the XML context for a bean of type Address.
• Bean Name Independence: Unlike byName autowiring, the ID or name of the candidate bean does not need to match the property name—only the data type matters.
• Uniqueness Requirement: Exactly one bean of the expected type must exist in the context. If multiple matching beans are found, Spring throws a fatal NoUniqueBeanDefinitionException.
• Optional Injection: If no bean matches the type, Spring leaves the property un-set (null) without throwing an error.

Step-by-Step Configuration Example

Consider an Employee bean that has an Address property with setter methods:

1. The Java Model Classes

package com.ram.model;

public class Employee {
    private Address address;

    public void setAddress(Address address) {
        this.address = address;
    }

    public void display() {
        System.out.println("Employee Address: " + address);
    }
}

2. Configuring autowire="byType" in applicationContext.xml

Notice that the bean ID userAddress does not match the property name address, yet Spring wires it successfully because of matching types:

<!-- Dependent Bean with an arbitrary ID -->
<bean id="userAddress" class="com.ram.model.Address">
    <property name="city" value="Bangalore" />
    <property name="state" value="Karnataka" />
</bean>

<!-- Employee Bean configured with byType autowiring -->
<bean id="employee" 
      class="com.ram.model.Employee" 
      autowire="byType" />

3. Loading the Application Context

ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");

Employee emp = (Employee) context.getBean("employee");
emp.display();

Key Takeaway

autowire="byType" provides seamless dependency wiring decoupled from bean naming conventions. As long as only one unique bean matches the property's type, Spring takes care of dependency injection automatically.

Recommended Auto-Wiring Tutorials from Ram N Java

• What will happen in byType Auto wiring mode, multiple bean of one type is there?
• byName Auto-Wiring in Spring: How Does It Work? | Spring Framework Tutorial | Spring Tutorial
• Constructor Auto-Wiring in Spring: How Does It Work? | Spring Framework Tutorial | Spring Tutorial

---

Click here to watch on Youtube:
https://www.youtube.com/watch?v=SQ8SHmiEeEQ&list=UUhwKlOVR041tngjerWxVccw

Click the below Image to Enlarge:

What is byType Auto-wiring mode in Spring?

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;
    private String country;

    public Address(String city, String state, String country)
    {
        this.city = city;
        this.state = state;
        this.country = country;
    }

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

}

Employee.java

package com.ram.model;

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;
    }

    public void setAddress(Address address)
    {
        this.address = address;
    }

    public void displayEmployeeDetails()
    {
        System.out.println("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"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-4.3.xsd">

    <bean id="address1" class="com.ram.model.Address">
        <constructor-arg value="Chennai"></constructor-arg>
        <constructor-arg value="Tamil Nadu"></constructor-arg>
        <constructor-arg value="India"></constructor-arg>
    </bean>

    <bean id="employee" class="com.ram.model.Employee" autowire="byType">
        <property name="id" value="100"></property>
        <property name="name" value="Peter"></property>
    </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 = (Employee) context.getBean("employee");
        System.out.println(
                "Got employee object from the ApplicationContext[Spring Container]");
        employee.displayEmployeeDetails();

    }

}

Output

Jun 29, 2018 9:15:43 AM org.springframework.context.support.AbstractApplicationContext prepareRefresh
INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@5b37e0d2: startup date [Fri Jun 29 09:15:43 IST 2018]; root of context hierarchy
Jun 29, 2018 9:15:43 AM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
INFO: Loading XML bean definitions from class path resource [applicationContext.xml]
---------------------------------------
Got employee object from the ApplicationContext[Spring Container]
Employee [id=100, name=Peter, address=Address [city=Chennai, state=Tamil Nadu, country=India]]

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

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

Bitbucket Link:
https://bitbucket.org/ramram43210/spring/src/a2a3948db9c8932cede027a3aaf7ba5a87170ed8/Spring_2018/SpringDemo_byType_Autowiring/?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