自动装配注释在自定义推土机转换器中不起作用

Question

I am using next dozer custom converter

public class MyCustomDozerConverter extends DozerConverter<MyObject, String> {

    @Autowired
    private AppConfig appConfig;

    public MyCustomDozerConverter() {
        super(MyObject.class, String.class);
    }

    @Override
    public String convertTo(MyObject source, String destination) {      
        String myProperty = appConfig.getWhatever();
        // business logic
        return destination;
    }

    @Override
    public MyObject convertFrom(String source, MyObject destination) {
        // business logic
        return null;
    }
}

My problem is when it goes through convertTo method inside the converter, I always got appConfig instance with null value which of course cause a null pointer exception

Note: my spring boot class have these annotations above:

@SpringBootApplication
@EnableAutoConfiguration
@ComponentScan({"com.xxx"})
@EntityScan("com.xxx")
@EnableJpaRepositories("com.xxx")

Answer 1

I solved this by next trick:

1- Using static with appConfig property.

2- instantiate it by spring so when dozer use default empty constructor it will find appConfig have a value already (which assigned before to it by spring)

And here are the code i used for this:

@Component //import org.springframework.stereotype.Component;
public class MyCustomDozerConverter extends DozerConverter<MyObject, String> {

    private static AppConfig appConfig;

    // dozer needs this constructor to create an instance of converter (so it's a mandatory constructor)
    public MyCustomDozerConverter() {
        super(MyObject.class, String.class);
    }

    @Autowired // Spring will pass appConfig to constructor
    public MyCustomDozerConverter(AppConfig appConfig) {
        this();
        this.appConfig = appConfig;
    }

    @Override
    public String convertTo(MyObject source, String destination) {      
        String myProperty = appConfig.getWhatever();
        // business logic
        return destination;
    }

    @Override
    public MyObject convertFrom(String source, MyObject destination) {
        // business logic
        return null;
    }
}

UPDATE: Another solution

Another trick is using Spring ApplicationContextAware to get a singleton object from getBean method:

import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Component;

@Component
public class ApplicationContextHolder implements ApplicationContextAware {
    private static ApplicationContext context;

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        context = applicationContext;
    }

    public static ApplicationContext getContext() {
        return context;
    }
}

Then create a static method inside AppConfig class and return an instance of the single bean matching the required type:

import org.springframework.context.annotation.Configuration;
import com.tripbru.ms.experiences.ApplicationContextHolder;

@Configuration
public class AppConfig {

    // Static method used to return an instatnce
    public static AppConfig getInstance() {
        return ApplicationContextHolder.getContext().getBean(AppConfig.class);
    }

    // Properties
}

Then calling it direct inside the dozer converter by AppConfig.getInstance();

public class MyCustomDozerConverter extends DozerConverter<MyObject, String> {

    private static AppConfig appConfig;

    public MyCustomDozerConverter() {
        super(MyObject.class, String.class);
        appConfig = AppConfig.getInstance(); // Here are we intializing it by calling the static method we created.
    }

    @Override
    public String convertTo(MyObject source, String destination) {      
        String myProperty = appConfig.getWhatever();
        // business logic
        return destination;
    }

    @Override
    public MyObject convertFrom(String source, MyObject destination) {
        // business logic
        return null;
    }
}

Answer 2

Try constructor dependency injection

private AppConfig appConfig;
@Autowired
MyCustomerDozerConverter(AppConfig appConfig)
{
    this.appConfig = appConfig;
}

Answer 3

You can put following line in the CustomConverter so that Spring will autowire it.

public class MyCustomDozerConverter extends DozerConverter<MyObject, String> {

@Autowired
private AppConfig appConfig;

public MyCustomDozerConverter() {
    super(MyObject.class, String.class);
    SpringBeanAutowiringSupport.processInjectionBasedOnCurrentContext(this);
}
...
}