例子

@SpringBootApplication
//可選引數預先初始化還是延遲初始化
@EnableBatchProcessing(modular = true)
public class SpringBatchDemoApplication {
    public static void main(String[] args) {
        SpringApplication.run(SpringBatchDemoApplication.class, args);
    }
}

我們使用spring batch 使用了 @EnableBatchProcessing 此註解

@EnableBatchProcessing作用

我們開啟原始碼可以發現使用Import註解 import註解使用可以檢視https://www.cnblogs.com/LQBlog/p/15410425.html

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(BatchConfigurationSelector.class)//<1>
public @interface EnableBatchProcessing {

    /**
     * Indicate whether the configuration is going to be modularized into multiple application contexts. If true then
     * you should not create any &#64;Bean Job definitions in this context, but rather supply them in separate (child)
     * contexts through an {
 
@link ApplicationContextFactory}.
     *
     * @return boolean indicating whether the configuration is going to be
     * modularized into multiple application contexts.  Defaults to false.
     */
    boolean modular() default false;

}

<1>

 public class BatchConfigurationSelector implements
 
 ImportSelector {
            @Override
            public String[] selectImports(AnnotationMetadata importingClassMetadata) {
                Class<?> annotationType = EnableBatchProcessing.class;
                //獲取註解元資料
                AnnotationAttributes attributes = AnnotationAttributes.fromMap(importingClassMetadata.getAnnotationAttributes(
                        annotationType.getName(), false));
                Assert.notNull(attributes, String.format("@%s is not present on importing class '%s' as expected",
                        annotationType.getSimpleName(), importingClassMetadata.getClassName()));
                String[] imports;
                //是實時初始化 延時延遲初始化 
                if (attributes.containsKey("modular") && attributes.getBoolean("modular")) {
                    //<2> 匯入ModularBatchConfiguration類
                    imports = new String[] { ModularBatchConfiguration.class.getName() };
                }
                else {
                    //是延遲初始化 點進去看程式碼可以看到get相關物件都是建立代理
                    imports = new String[] { SimpleBatchConfiguration.class.getName() };
                }

                return imports;
            }

<2>

//proxyBeanMethods = false @Bean建立的物件將不使用代理
@Configuration(proxyBeanMethods = false)
public class ModularBatchConfiguration extends AbstractBatchConfiguration {

    @Autowired
    private ApplicationContext context;

    @Autowired(required = false)
    private Collection<BatchConfigurer> configurers;

    private AutomaticJobRegistrar registrar = new AutomaticJobRegistrar();

    /**
     * 獲得jobRepository  主要是用來管理 job執行期間相關元資料的
     * 比如redis,檔案，h2庫 預設我們都是用的mysql
     * 可參考:org.springframework.batch.core.repository.support.SimpleJobRepository
     * @return
     * @throws Exception
     */
    @Override
    @Bean
    public JobRepository jobRepository() throws Exception {
        return getConfigurer(configurers).getJobRepository();
    }

    /**
     * 獲得JobLauncher
     * JobLauncher主要job的容器 主要是管理job的啟動
     * @return
     * @throws Exception
     */
    @Override
    @Bean
    public JobLauncher jobLauncher() throws Exception {
        return getConfigurer(configurers).getJobLauncher();
    }

    /**
     * job 執行期間的提交和關閉事物使用的事物管理器
     * @return
     * @throws Exception
     */
    @Override
    @Bean
    public PlatformTransactionManager transactionManager() throws Exception {
        return getConfigurer(configurers).getTransactionManager();
    }

    /**
     * 與JobRepository 後續看原始碼再看具體用來做啥
     * @return
     * @throws Exception
     */
    @Override
    @Bean
    public JobExplorer jobExplorer() throws Exception {
        return getConfigurer(configurers).getJobExplorer();
    }

    /**
     * JobRepository的容器
     * 內部可以通過star方法  在spring容器裡面查詢job並註冊到JobRegistry
     * 通過stop清空 主要是委託給JobLoader 預設實現是在spring 容器查詢
     * 比如我們可以實現從mysql查詢
     * @return
     * @throws Exception
     */
    @Bean
    public AutomaticJobRegistrar jobRegistrar() throws Exception {
        registrar.setJobLoader(new DefaultJobLoader(jobRegistry()));
        for (ApplicationContextFactory factory : context.getBeansOfType(ApplicationContextFactory.class).values()) {
            registrar.addApplicationContextFactory(factory);
        }
        return registrar;
    }

}