How @Autowired Work using Reflection and how invoke appropriate Setter Method

Question

My Main Problem is that i can use Reflection API and i can invoke the setter method in my User bean class.But I have Only have UserBean objects. I does not know which setter method to invoke.i want extract all information in my User bean Object and the invoke appropriate Method using Reflection.

//-->This My User Bean Class

public class User {

 private String name;
 private int age;

private String getName() {
    return name;
}
private void setName(String name) {
    this.name = name;
}
private int getAge() {
    return age;
}
private void setAge(int age) {
    this.age = age;
}

 void callMethod() { System.out.println("Name :- "+name+" Age :-"+age); }

 @Override
  public String toString() { return "User [name=" + name + ", age=" + age + "]";}
}

//--->This My Main Method

public class TestCase {

public static Object getBean(String beanClassName) throws Exception
{
    Class klass = Class.forName(beanClassName);
    Object obj = klass.newInstance();            
    Method[] b = klass.getDeclaredMethods();

    String MethodName1 = "setName";
    String MethodName2 = "setAge";
    String name ="sanket";
    int age = 21;

    for(int i=0;i<b.length;i++)
    {
        if(b[i].getParameterTypes().toString().equals(MethodName1))
        {
             b[i].setAccessible(true);
             b[i].invoke(obj,name); 
        }
        if(b[i].getName().equals(MethodName2))
        {
             b[i].setAccessible(true);
             b[i].invoke(obj,age);  
        }
    }


    return obj;
}

public static void main(String ars[]) throws Exception
{
    Object obj1 = getBean("www.Fouth.User");

    System.out.println(obj1.toString());
}
}

I my case I can invoke the setter method manually because i can invoke the setter method bases of method name.

I want Extract information in User Bean Class, and identify on the bases of value which setter to invoked.

In spring @AutoWired is does that.How they will identify which setter to invoke and inject dependency.

Answer 1

The Spring identifies which setters to inject dependencies by figuring out which setters are annotated with @Autowired , @Inject , @Resources etc.

Then it figures out which value to inject into the setter by checking the type of the setter arguments and injects the bean that has the same type.

If multiple beans have the same type, it then check the bean name. It will inject the bean that has the same name as configured in the injection point using @Qaulifer or @Resources.

If there are still multiple beans that satisfy to inject , NoUniqueBeanDefinitionException happens.

If there are no beans that satisfy to inject, NoSuchBeanDefinitionException happens.