How does @Value annotation inject values when passed in parameters of a method?-CodePudding

I am new to Spring, I was working with @Value annotation and found out that it can be applied to fields or constructor/method parameters, but as I was trying to inject value using parameters it was not injecting the value for my parameters and I was getting values as null .

I have used @Value in the parameter of the method below

public void setName(@Value("Adventure of War") String name) {
        System.out.println("Setting Company Name");
        this.name = name;
}

Complete code(Company.java)

package gd.rf.anuragsaini.stereotype;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

@Component
public class Company {
    String name;
    String motive;

    public void setName(@Value("Adventure of War") String name) {
        System.out.println("Setting Company Name");
        this.name = name;
    }

    public void setMotive(@Value("A place for War") String motive) {
        System.out.println("Setting Company Motive");
        this.motive = motive;
    }

    @Override
    public String toString() {
        return "Company{"  
                "name='"   name   '\''  
                ", motive='"   motive   '\''  
                '}';
    }
}

Main File(App.java)

package gd.rf.anuragsaini.stereotype;

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

public class App {
    public static void main(String[] args) {
        ApplicationContext IOC = new ClassPathXmlApplicationContext("config.xml");
        Company c1 = IOC.getBean("company", Company.class);
        System.out.println(c1);
    }
}

Output

Company{name='null', motive='null'}

CodePudding user response：

Like that the setters will not be invoked.When constructing the bean of type Company, the frameWork use by default the default constructor of the class Company.

So you should use @Autowired for the setters to garantee that the setters will be invoked by the frameWork when constructing those beans :

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

@Component
public class Company {
    String name;
    String motive;

    @Autowired
    public void setName(@Value("Adventure of War") String name) {
        System.out.println("Setting Company Name");
        this.name = name;
    }

    @Autowired
    public void setMotive(@Value("A place for War") String motive) {
        System.out.println("Setting Company Motive");
        this.motive = motive;
    }

    @Override
    public String toString() {
        return "Company{"   "name='"   name   '\''   ", motive='"   motive   '\''   '}';
    }
}

Output :

Company{name='Adventure of War', motive='A place for War'}

CodePudding user response：

When using @Value you need to pass a placeholder ${} that contains the key of a property that will be resolved against PropertySource. What you try to do here is to pass the value Adventure of War. You should change it to: ${adventure.value} and add the key in your properties file (application.properties / application.yaml / ...).