自动装配注释在自定义推土机转换器中不起作用

Question

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，我总是得到具有空值的 appConfig 实例，这当然会导致空指针异常

注意：我的 spring 引导 class 上面有这些注释：

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

Answer 1

尝试构造函数依赖注入

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

Answer 2

我用下一个技巧解决了这个问题：

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)

这是我为此使用的代码：

@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 中创建静态方法 class 和 return 匹配所需类型的单个 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;
    }
}

Answer 3

您可以在 CustomConverter 中放置以下行，以便 Spring 自动装配它。

public class MyCustomDozerConverter extends DozerConverter<MyObject, String> {

@Autowired
private AppConfig appConfig;

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

自动装配注释在自定义推土机转换器中不起作用

Autowired annotation doesn't work inside custom dozer converter

java

spring

dozer

spring-boot