Spring无法连接泛型bean-没有符合类型的bean

Question

import java.util.List;

public interface Process<E> {

    List<E> determineChanges(List<Integer> approvalIds);

    void applyChanges(List<E> changeCto);
}

接下来，我将读取器和写入器实现定义如下：

import org.springframework.batch.core.configuration.annotation.StepScope;
import org.springframework.batch.item.ItemReader;
import org.springframework.batch.item.NonTransientResourceException;
import org.springframework.batch.item.ParseException;
import org.springframework.batch.item.UnexpectedInputException;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

import java.util.List;

@Component
@StepScope
public class GenericApprovalReader<T extends Process<U>, U> implements ItemReader<List<U>> {

    private final SomeOtherBeanStepScopedBean otherBean;

    private final T processor;

    @Autowired
    public GenericApprovalReader(SomeOtherBeanStepScopedBean otherBean,
                                 T processor) {
        this.SomeOtherBean = otherBean;
        this.processor= processor;
    }

    @Override
    public List<U> read() throws Exception, UnexpectedInputException, ParseException, NonTransientResourceException {
        List<Integer> items = this.someOtherBean.read();

        if(items != null) {
            return processor.determineChanges(items );
        } else {
            return null;
        }
    }
}

同样，我也有一个作家：

import org.springframework.batch.core.configuration.annotation.StepScope;
import org.springframework.batch.item.ItemWriter;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

import java.util.List;

@Component
@StepScope
// Note that second type parameter is necessary only due to necessity to parametrize the ItermWriter<List<U>> with the
// same type as is used for parametrization of Approval<U>
public class GenericApprovalWriter<T extends Process<U>, U> implements ItemWriter<List<U>> {

    private final T processor;

    @Autowired
    public GenericApprovalWriter(T processor) {
        this.approvalProcessor = processor;
    }

    @Override
    public void write(List<? extends List<U>> items) throws Exception {
        for(List<U> item: items) {
            this.processor.applyChanges(item);
        }
    }
}

现在，当我尝试将步骤中的读取器和写入器连接到某个@configuration类中时，如下所示：

    @Bean(name="firstProcessingStep")
    Step firstProcessingStep(GenericApprovalReader<FirstProcessor, Item> reader,
                                   GenericApprovalWriter<FirstProcessor, Item> writer) {
        return stepBuilderFactory.get("firstProcessingStep")
                .<List<Item>,List<Item>>chunk(CHUNK_SIZE)
                .reader(reader)
                .writer(writer)
                .allowStartIfComplete(false)
                .build();
    }

根据另一篇关于Spring中泛型bean的Autowiring的文章，这种行为在Spring4.0之后应该是可能的，我正在使用Spring4.0。

Answer 1

在spring boot应用程序上下文中匹配两个或多个已加载bean的bean是自动连接的时候，会出现预期的单个匹配bean。当bean在Spring Boot中自动连接时，在上下文中会发现两个或多个bean。因此，该bean无法自动布线。考虑将其中一个bean标记为@primary，更新消费者以接受多个bean，或者使用@qualifier来标识应该使用的bean预期为单个匹配bean但找到n。

该类应该用@primary注释。带注释的@Primary类被认为是自动连线中的默认类。@Autowired注释加载@primary bean并向其添加接口或抽象变量。

像这样更改代码。

@Component
@Primary    
@StepScope
public class GenericApprovalReader<T extends Process<U>, U> implements ItemReader<List<U>> {
//content

@Component
@Primary    
@StepScope
 GenericApprovalWriter<T extends Process<U>, U> implements ItemWriter<List<U>> {

//content