in spring boot, why i did`t get returned value of a service class to another service class

Question

I'm building a Spring Boot application. I will have 2 service classes A and B, B.getStringNextValue() return a value which called in A.getStringValue() but value of b.getStringNextValue() in A.getStringValue() class have nothin/null.

I already tried below code and also search some questions in StackOverflow but no ane Answer was solved this.

@Service
public class A{

    @Autowired
    private B b;

    public String getStringValue(){
        StringBuilder str = new StringBuilder("Hello ");
        str.append(b.getStringNextValue());
        System.out.println(b.getStringNextValue()); //here nothing as output but expectation is ' World'
        System.out.println(str); //here i only get 'Hello ' But expectation is 'Hello World'
        return str.toString();
    }
}

And B.java,

@Service
public class B {

    public StringBuilder getStringNextValue() {
        StringBuilder str = new StringBuilder();
        str.append(" World");
        System.out.println(str.toString()); //Here i get ' World'
        return str;
    }
}

I don`t know why I get this type of output. can anyone describe it and suggest me some solution? Thanks.

Answer 1

I tested you code and did not obtain the same print results as you. How do you test you code? Here is my unit test with comments in code after 'zp:' . Note that b.getStringNextValue() sends ' World' everytime. And also i obtain 'Hello World' on the last System.out.println(str) . Hope it will help you.

Class A :

package test;

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

@Service
public class A {

    @Autowired
    private B b;

    public String getStringValue() {
        StringBuilder str = new StringBuilder("Hello ");
        str.append(b.getStringNextValue()); // zp: This line prints ' World' AND make str = 'Hello World'
        System.out.println(b.getStringNextValue()); // here nothing as output but expectation is ' World' -> zp: Prints ' World'
        System.out.println(str); // here i only get 'Hello ' But expectation is 'Hello World' -> zp: 'Hello World' is printed
        return str.toString();
    }
}

Class B :

package test;

import org.springframework.stereotype.Service;

@Service
public class B {

    public StringBuilder getStringNextValue() {
        StringBuilder str = new StringBuilder();
        str.append(" World");
        System.out.println(str.toString()); // Here i get ' World' -> zp: Yes, 2 times
        return str;
    }
}

My test here :

import test.A;
import test.B;

@RunWith(SpringRunner.class)
public class MyTest {

    @Configuration
    @ComponentScan("test")
    static class Config {}

    @Autowired
    private A a;

    @Autowired
    private B b;

    @Test
    public void test() {
        a.getStringValue();
    }
}

The output is :

 World
 World
 World
Hello  World