java - Autowiring 注释在自定义推土机转换器中不起作用

我正在使用下一个推土机自定义转换器

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;
    }
}

我的问题是，当它通过转换器内部的convertTo方法时，我总是得到具有null值的appConfig实例，这当然会导致null指针异常

注意：我的spring boot类上面有这些注释：

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

最佳答案

我通过下一个技巧解决了这个问题：


  1-使用带有appConfig属性的static。
  
  2-在春季之前实例化它，因此当推土机使用默认的空构造函数时，它将发现appConfig具有
  已经有一个值（在春季之前分配给它）


这是我用于此的代码：

@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;
    }
}

更新：另一个解决方案

另一个技巧是使用Spring ApplicationContextAware从getBean方法获取单例对象：

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;
    }
}

然后在AppConfig类内创建一个静态方法，并返回与所需类型匹配的单个bean的实例：

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
}

然后通过AppConfig.getInstance（）在推土机转换器内部直接调用它；

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;
    }
}

关于java - Autowiring 注释在自定义推土机转换器中不起作用，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/47488944/