给我一个spring batch双数据源的例子，H2与DB2，并且在application.yml中 指定默认数据源为h2

好的，下面是一个简单的 Spring Batch 双数据源配置的例子：

首先，我们需要在 pom.xml 文件中添加 H2 和 DB2 的依赖:

<dependencies>
    <!-- H2 Database -->
    <dependency>
        <groupId>com.h2database</groupId>
        <artifactId>h2</artifactId>
        <version>1.4.200</version>
    </dependency>

    <!-- DB2 Database -->
    <dependency>
        <groupId>com.ibm.db2</groupId>
        <artifactId>db2jcc4</artifactId>
        <version>11.5.0.0</version>
    </dependency>

    <!-- Spring Batch -->
    <dependency>
        <groupId>org.springframework.batch</groupId>
        <artifactId>spring-batch-core</artifactId>
        <version>4.2.4.RELEASE</version>
    </dependency>
</dependencies>

接着，在 application.yml 配置文件中，我们可以指定默认数据源为 H2 数据库。

spring:
  datasource:
    url: jdbc:h2:mem:testdb
    username: sa
    password:
    driver-class-name: org.h2.Driver
  jpa:
    database-platform: org.hibernate.dialect.H2Dialect

# Second Datasource
myapp:
  datasource:
    url: jdbc:db2://localhost:50000/mydb
    username: db2admin
    password: password
    driver-class-name: com.ibm.db2.jcc.DB2Driver

接下来，我们需要配置两个数据源的 Bean，这里使用 `@Primary` 和 `@Qualifier` 注解来指定默认数据源和第二个数据源。

@Configuration
@EnableBatchProcessing
public class BatchConfig {

    @Primary
    @Bean(name = "h2DataSource")
    @ConfigurationProperties(prefix = "spring.datasource")
    public DataSource h2DataSource() {
        return DataSourceBuilder.create().build();
    }

    @Bean(name = "db2DataSource")
    @ConfigurationProperties(prefix = "myapp.datasource")
    public DataSource db2DataSource() {
        return DataSourceBuilder.create().build();
    }

    @Bean(name = "jobRepository")
    public JobRepository jobRepository(@Qualifier("h2DataSource") DataSource dataSource,
                                        PlatformTransactionManager transactionManager) throws Exception {
        JobRepositoryFactoryBean jobRepositoryFactoryBean = new JobRepositoryFactoryBean();
        jobRepositoryFactoryBean.setDataSource(dataSource);
        jobRepositoryFactoryBean.setTransactionManager(transactionManager);
        jobRepositoryFactoryBean.afterPropertiesSet();
        return jobRepositoryFactoryBean.getObject();
    }

    @Bean(name = "jobLauncher")
    public JobLauncher jobLauncher(@Qualifier("h2DataSource") DataSource dataSource,
                                    PlatformTransactionManager transactionManager) throws Exception {
        SimpleJobLauncher jobLauncher = new SimpleJobLauncher();
        jobLauncher.setJobRepository(jobRepository(dataSource, transactionManager));
        jobLauncher.setTaskExecutor(new SimpleAsyncTaskExecutor());
        jobLauncher.afterPropertiesSet();
        return jobLauncher;
    }

    @Bean(name = "transactionManager")
    public PlatformTransactionManager transactionManager(@Qualifier("h2DataSource") DataSource dataSource) {
        return new DataSourceTransactionManager(dataSource);
    }

}

现在，我们已经配置好了双数据源的 Spring Batch，可以在 Job 中使用 `@Qualifier` 注解来选择使用哪个数据源。

@Configuration
public class MyJobConfig {

    @Autowired
    private JobBuilderFactory jobBuilderFactory;

    @Autowired
    private StepBuilderFactory stepBuilderFactory;

    @Autowired
    private DataSource db2DataSource;

    @Autowired
    private DataSource h2DataSource;

    @Bean
    public Job myJob() {
        return jobBuilderFactory.get("myJob")
                .incrementer(new RunIdIncrementer())
                .start(step1())
                .build();
    }

    @Bean
    public Step step1() {
        return stepBuilderFactory.get("step1")
                .<Person, Person>chunk(10)
                .reader(personReader(db2DataSource))
                .processor(personProcessor())
                .writer(personWriter(h2DataSource))
                .build();
    }

    @Bean
    @StepScope
    public JdbcCursorItemReader<Person> personReader(@Qualifier("db2DataSource") DataSource dataSource) {
        return new JdbcCursorItemReaderBuilder<Person>()
                .name("personReader")
                .dataSource(dataSource)
                .sql("SELECT * FROM PERSON")
                .rowMapper(new PersonRowMapper())
                .build();
    }

    @Bean
    public ItemProcessor<Person, Person> personProcessor() {
        return item -> {
            item.setAge(item.getAge() + 1);
            return item;
        };
    }

    @Bean
    public JdbcBatchItemWriter<Person> personWriter(@Qualifier("h2DataSource") DataSource dataSource) {
        return new JdbcBatchItemWriterBuilder<Person>()
                .dataSource(dataSource)
                .sql("INSERT INTO PERSON (ID, NAME, AGE) VALUES (:id, :name, :age)")
                .beanMapped()
                .build();
    }

}

在这个例子中，我们使用了 `@Qualifier` 注解来选择数据源，`personReader()` 方法使用了 DB2 数据源，`personWriter()` 方法使用了 H2 数据源。

希望这个例子能帮助你理解 Spring Batch 双数据源的配置和使用。