Spring : @Autowired annotation - where to view the actual changes?

Question

Based on the example being followed here : https://dzone.com/articles/autowiring-in-spring

import org.springframework.stereotype.Component;

@Component
public class Department {
    private String deptName;
    public String getDeptName() {
        return deptName;
    }
    public void setDeptName(String deptName) {
        this.deptName = deptName;
    }
}

The @Autowired annotation is placed on the Department.

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

public class Employee {
    private int eid;
    private String ename;
    @Autowired
    private Department department; //<----------------------
    public int getEid() {
        return eid;
    }
    public void setEid(int eid) {
        this.eid = eid;
    }
    public String getEname() {
        return ename;
    }
    public void setEname(String ename) {
        this.ename = ename;
    }
    public Department getDepartment() {
        return department;
    }
    public void setDepartment(Department department) {
        this.department = department;
    }
    public void showEmployeeDetails(){
        System.out.println("Employee Id : " + eid);
        System.out.println("Employee Name : " + ename);
        System.out.println("Department : " + department.getDeptName());
    }
}

This runs the program.

public class RunThis {
    public static void main(String[] args) 
    {
        System.out.println("Hello World");
        Employee emp = new Employee();
        emp.showEmployeeDetails();
    }
}

Running the program results in a NULL exception which is expected, but per the provided URL, it reads :

@Autowired on Properties
In the below example, when the annotation is directly used on properties, Spring looks for and injects Department when Employee is created.

As a result, I interpreted to mean that the Department object would implicitly be instantiated behind the scenes at the time the Employee object is instantiated, but apparently that is wrong.

1 - How can this sample be modified to view the actual benefits of the @Autowired annotation?

Many other examples discuss the @Autowired annotation affecting what is written to some XML file in my project.

I searched my project for all files and don't see any reference toward the object (Department) other than Employee and Department.

2 - Where is the XML file located that one can view the changes affected by the use of the @Autowired annotation?

score 1 · Accepted Answer · answered Mar 13 '20 at 14:26

I think you're missing the bigger picture. You annotate classes so that they're managed by Spring. In order to use Spring you'll have to adapt your main.

@SpringBootApplication
public class RunThis {
    public static void main(String[] args) 
    {
        SpringApplication.run(RunThis.class, args);
        System.out.println("Hello World");
        Employee emp = new Employee();
        emp.showEmployeeDetails();
    }
}

Now our project is managed in Spring but our Employee isn't as we make this. We should let Spring handle this by creating a bean for our employee and fetching that bean. The creation of beans we do in classes annotated in @Configuration or via a ComponentScan.

Also all your changes when it comes to annotating won't be vissible in any .xml file.

Thanks for the post. From reading it seemed to indicate the annotations affected the XML file, but I guess it affects what the developer as to write to the XML file???? — Unhandled Exception, Mar 13 '20 at 14:49
No problem, the annotations have no impact on the XML file. There are 2 ways to setup your Spring configuration, via xml or via annotations. In the documentation you shared you can see both xml and annotations but they're the same configuration. — SanderDR, Mar 13 '20 at 15:36

score 1 · Answer 2 · answered Mar 13 '20 at 14:27

1

You haven't set department to be anything, as department is a pojo, to benefit from autowired you'd be better to do something like the following in a configuration class that gets loaded by spring boot

@Bean
public Department department () {
  Department department = new Department ();
  department.setDeptName("foo");
  return department;
}

Although the link you provided, you haven't even followed it I am guessing as it shows them configuring the beans using XML, which you haven't done so autowiring will not work.

answered Mar 13 '20 at 14:27

Thomas__

320
3
13

Thanks. I was thinking the XML files were generated as part of the project in the IDE or it was auto-generated based on the annotations being used. Is there a specific location within the Project the XML file needs to be located? – Unhandled Exception Mar 13 '20 at 14:47
https://docs.spring.io/spring/docs/4.2.x/spring-framework-reference/html/xsd-configuration.html personally never done xml configuration, I usually go with the Java configuration, similar to my answer. – Thomas__ Mar 13 '20 at 15:04

Spring : @Autowired annotation - where to view the actual changes?

2 Answers2