Autowire working in unit test but not in main java class - spring

Question

I've a domain class that I want to auto-populate from external config. Here is my domain class:
#Data
#Configuration
#PropertySource("classpath:application.properties")
public class StudioVo {
#Value("${studio.code}")
private code;
#Bean
public static PropertySourcesPlaceholderConfigurer propertySourcesPlaceholderConfigurer() {
return new PropertySourcesPlaceholderConfigurer();
}
}
Here is my context xml:
<bean class="org.springframework.batch.core.scope.StepScope" />
<bean id="ItemReader" class="com.sdm.studio.reader.StudioReader" scope="step">
<property name="studioVo" ref="StudioVo" />
</bean>
<bean id="StudioConfigVo" class="com.sdm.studio.domain.StudioVo" />
</bean>
Here is the class where I want to use the vo:
#Slf4j
#Data
public class StudioReader implements ItemReader<List<Studio>> {
private StudioVo studioVo;
public List<Studio> read() throws Exception {
System.out.println("getCode: " + studioVo.getCode()); //code is null here
return null;
}
}
However when I run it via unit test by autowiring, it runs fine. Like this:
#RunWith(SpringRunner.class)
#SpringBootTest
public class StudioTest {
#Autowired
private StudioVo studioVo;
#Test
public void testAutoPopulationOfStudio(){
System.out.println("getCode: "+ studioVo.getCode()); // works!
// Assert.assertTrue(studioVo.getCode().equals("102"));
}
}
Not sure what's going on here - I'm working with an old Spring Batch application wrapped in Spring Boot (so there is a mix of XML based and Java based config - and may be that is the cause of this issue). What am I missing?

Answer 1

In your StudioTest, you are autowiring StudioReader where as you missed the #Autowired in your StudioReader code, so add it as shown below:
#Slf4j
#Data
public class StudioReader implements ItemReader<List<Studio>> {
#Autowired //add this so that studioVo can be injected
private StudioVo studioVo;
//add other code
}

Answer 2

Please be certain to note that using #Autowire requires a chain of Spring-managed beans below it from wherever you are using it including the class in which you are using #Autowire. That is because Spring needs the precedent references to match up the object-reference hierarchy. I.e., in business logic layer ClassA, you want to #Autowire a field. ClassA itself needs to be a managed bean. Further, if the field you want to #Autowire holds an object that has referential dependencies to other objects (and most do), these also must be Spring-managed.
For example, the following will work:
package com.example.demo;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
public class MessageRunner {
private static SetterMessage setterMessage;
public static void main(String[] args) {
setterMessage = (SetterMessage) (new AnnotationConfigApplicationContext(DemoConfiguration.class)).getBean("setterMessage");
setterMessage.setMessage("Finally it works.");
p(setterMessage.getMessage());
}
private static void p(String s) {
System.out.println(s);
}
}
DemoConfiguration.java looks like this:
package com.example.demo;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
#Configuration
#ComponentScan(basePackages = "com.example.demo")
public class DemoConfiguration {
}
SetterMessage.java, this:
package com.example.demo;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Scope;
import org.springframework.stereotype.Service;
#Service
#Scope("prototype")
public class SetterMessage {
private String message = null;
#Autowired
private SetterMessage2 setterMessage2;
public String getMessage(){
return message+setterMessage2.getSubMessage();
}
public void setMessage(String message) {
this.message = message;
setterMessage2.setSubMessage("("+message+")");
}
}
SetterMessage2.java:
package com.example.demo;
import org.springframework.context.annotation.Scope;
import org.springframework.stereotype.Service;
#Service
#Scope("prototype")
public class SetterMessage2 {
private String subMsg = "";
public void setSubMessage(String msg) {
subMsg = msg;
}
public String getSubMessage() {
return subMsg;
}
}
Note that SetterMessage2.java is annotated as a Component (#Service) but no field in it is autowired. That is because it's the end of the object reference chain. But because it is a Component, it can be autowired into SetterMessage.java. However look at MessageRunner.java's main() method and field declarations. Note that the class field SetterMessage is NOT autowired. If it were annotated as #Autowired, main() would fail at runtime, throwing an NPE with the reference to setterMessage in main(). This is because MessageRunner.java is not marked as some kind of component. So we need to grab a valid instance of MessageSetter from the application context and use it.
To emphasize, the following version of MessageRunner.java's main() method WILL FAIL, throwing an NPE, if MessageRunner.java looked like this:
...
public class MessageRunner {
#Autowired // <-- This will not do the job for us
private static SetterMessage setterMessage;
public static void main(String[] args) {
setterMessage.setMessage("Finally it works."); // NPE here on ref to setterMessage
p(setterMessage.getMessage());
}
...
This is a real gotchya for people new to Spring. In fact, I'd place it among the Top Five Spring Newbie Discouragers and a really evil, pernicious detail that has caused new Spring programmers countless hours in aggravation and Google searches. So I do hope that noting this phenom here will save at least some newbies time and high blood pressure spikes.
Note: If you go to create the above classes in your IDE, bear in mind these were developed with Spring Boot enabled.