java - 使用 spring-data-jpa 自定义 ItemReader

Question

我正在使用现有实体和存储库创建一个 Spring 批处理项目。我需要为使用现有 jpa 存储库读取数据的作业使用自定义 ItemReader。

自定义阅读器

public class InMemoryReader implements ItemReader<Product> {

    @Autowired
    private ProductService productService;


    private int nextStudentIndex;
    private List<Product> studentData;

    public InMemoryReader() {
        initialize();
    }

    private void initialize() {
        studentData = new ArrayList<Product>();
        studentData.add(new Product("hi"));

        for (Product p : productService.get())
            studentData.add(p);
        nextStudentIndex = 0;
    }

    @Override
    public Product read() throws Exception {
        Product nextStudent = null;

        if (nextStudentIndex < studentData.size()) {
            nextStudent = studentData.get(nextStudentIndex);
            nextStudentIndex++;
        }

        return nextStudent;
    }
}

但我无法在 itemreader 中 Autowiring ProductService。它抛出如下错误:

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'reader' defined in class path resource [wariyum/sb/emailNotifier/BatchConfiguration.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.batch.item.ItemReader]: Factory method 'reader' threw exception; nested exception is java.lang.NullPointerException
    at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:599)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1123)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1018)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:510)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:482)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:305)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:301)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:196)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:772)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:834)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:537)
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:689)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:321)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:969)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:958)
    at wariyum.sb.emailNotifier.Application.main(Application.java:15)
Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.batch.item.ItemReader]: Factory method 'reader' threw exception; nested exception is java.lang.NullPointerException
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:189)
    at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:588)
    ... 16 common frames omitted
Caused by: java.lang.NullPointerException: null
    at wariyum.sb.emailNotifier.service.InMemoryReader.initialize(InMemoryReader.java:31)
    at wariyum.sb.emailNotifier.service.InMemoryReader.<init>(InMemoryReader.java:24)
    at wariyum.sb.emailNotifier.BatchConfiguration.reader(BatchConfiguration.java:41)
    at wariyum.sb.emailNotifier.BatchConfiguration$$EnhancerBySpringCGLIB$$df186b4e.CGLIB$reader$0(<generated>)
    at wariyum.sb.emailNotifier.BatchConfiguration$$EnhancerBySpringCGLIB$$df186b4e$$FastClassBySpringCGLIB$$724d6a16.invoke(<generated>)
    at org.springframework.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:228)
    at org.springframework.context.annotation.ConfigurationClassEnhancer$BeanMethodInterceptor.intercept(ConfigurationClassEnhancer.java:318)
    at wariyum.sb.emailNotifier.BatchConfiguration$$EnhancerBySpringCGLIB$$df186b4e.reader(<generated>)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:162)
    ... 17 common frames omitted

批量配置文件

@Configuration
@EnableBatchProcessing
public class BatchConfiguration {


    @Autowired
    public JobBuilderFactory jobBuilderFactory;

    @Autowired
    private DataSource dataSource;

    @Autowired
    public StepBuilderFactory stepBuilderFactory;

    @Bean
    public ItemReader<Product> reader() throws Exception {
        return new InMemoryReader();
    }


    @Bean
    public ProductItemProcessor processor() {
        return new ProductItemProcessor();
    }

    @Bean
    public ItemWriter<Product> writer() {
        return new ItemWriter<Product>() {
            @Override
            public void write(List<? extends Product> items) throws Exception {

            }
        };
    }
    // end::readerwriterprocessor[]

    // tag::listener[]

    @Bean
    public JobExecutionListener listener() {
        return null;
    }

    // end::listener[]

    // tag::jobstep[]

    @Bean
    public Job importPerson(JobBuilderFactory jobs, Step s1) {

        return jobs.get("import")
                .incrementer(new RunIdIncrementer()) // because a spring config bug, this incrementer is not really useful
                .flow(s1)
                .end()
                .build();
    }

    @Bean
    public Step step1() throws Exception {
        return stepBuilderFactory.get("step1")
                .<Product, Product>chunk(10)
                .reader(reader())
                .processor(processor())
                .writer(writer())
                .build();
    }
}

产品服务实现

@Service("productService")
public class ProductServiceImpl implements ProductService {

    private ProductRepository repository;

    @Autowired
    public ProductServiceImpl(ProductRepository repository) {
        this.repository = repository;
    }

    @Override
    public List<Product> get() {
        List<Product> list = new ArrayList<Product>();
        for (Product p : repository.findAll())
            list.add(p);
        return list;
    }
}

Answer 1

您正在从构造函数调用 initialize()，即在连接 ProductService 依赖项之前。

从构造函数中删除对 initialize() 的调用，而是让 Spring 在通过使用 @PostConstruct 注释或使用以下方法之一连接依赖关系后调用它此处概述的其他方法:

How to call a method after bean initialization is complete?