所有作业的itemreader在启动时初始化。

以下是一个示例代码，展示了如何在Spring Batch中初始化所有作业的ItemReader：

import org.springframework.batch.core.configuration.annotation.JobBuilderFactory;
import org.springframework.batch.core.configuration.annotation.StepBuilderFactory;
import org.springframework.batch.item.ItemReader;
import org.springframework.batch.item.ItemWriter;
import org.springframework.batch.item.file.FlatFileItemReader;
import org.springframework.batch.item.file.mapping.DefaultLineMapper;
import org.springframework.batch.item.file.mapping.FieldSetMapper;
import org.springframework.batch.item.file.transform.DelimitedLineTokenizer;
import org.springframework.batch.item.file.transform.FieldSet;
import org.springframework.batch.item.file.transform.LineTokenizer;
import org.springframework.batch.item.file.transform.Range;
import org.springframework.batch.item.file.transform.RangeArrayPropertyEditor;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.io.FileSystemResource;
import org.springframework.validation.BindException;

@Configuration
public class BatchConfig {

    @Autowired
    private JobBuilderFactory jobBuilderFactory;

    @Autowired
    private StepBuilderFactory stepBuilderFactory;

    @Bean
    public ItemReader<Employee> employeeItemReader() {
        FlatFileItemReader<Employee> reader = new FlatFileItemReader<Employee>();
        reader.setResource(new FileSystemResource("employees.csv"));
        reader.setLineMapper(new DefaultLineMapper<Employee>() {{
            setLineTokenizer(new DelimitedLineTokenizer() {{
                setNames(new String[]{"id", "name", "age"});
            }});
            setFieldSetMapper(new FieldSetMapper<Employee>() {
                @Override
                public Employee mapFieldSet(FieldSet fieldSet) throws BindException {
                    Employee employee = new Employee();
                    employee.setId(fieldSet.readInt("id"));
                    employee.setName(fieldSet.readString("name"));
                    employee.setAge(fieldSet.readInt("age"));
                    return employee;
                }
            });
        }});
        return reader;
    }

    @Bean
    public ItemWriter<Employee> employeeItemWriter() {
        return new ItemWriter<Employee>() {
            @Override
            public void write(List<? extends Employee> items) throws Exception {
                // 写入逻辑
            }
        };
    }
}

在这个示例中，我们使用了Spring Batch的FlatFileItemReader作为ItemReader的实现，并将它配置为读取名为“employees.csv”的文件。我们还为ItemReader指定了DefaultLineMapper，并为其设置了DelimitedLineTokenizer和FieldSetMapper。

要在启动时初始化所有作业的ItemReader，您可以在配置类中创建和配置所有的ItemReader bean。当Spring Batch启动时，这些bean将被实例化和初始化，以便在作业执行期间使用。

请注意，这只是一个示例，您可以根据您的实际需求进行调整和扩展。