如何使用Spring批量編寫帶空體的csv文件

Question

使用spring boot編寫我的出站批處理需要發送的文件之一，並且只有在沒有找到記錄的情況下清空標頭文件時才使用。

即時通訊使用BeanPropertyRowMapper來映射我的JdbcCursorItemReader ...爲什麼我使用BeanPropertyRowMapper因爲有很多列映射。如果即時通訊使用rowmapper它將是我的地獄哈哈。如此配置：

@Bean 
public Step RawDataOutBoundSteps() throws IOException { 

    return stepBuilderFactory.get("step1").<RawDataExtractionDTO, RawDataExtractionDTO>chunk(1000)//.faultTolerant() 
      //.skip(Exception.class) 
      //.skipLimit(1000) 
      .reader(myDBReader()).processor(myProcessor()) 
      .writer(myWriter()).build(); 
} 

的問題是，如果myDBreader（）查詢返回空結果，我的代碼不會去myProcessor因此myWriter也。

myProcessor：

public class RawDataJobProcessor implements 
ItemProcessor<RawDataExtractionDTO, RawDataExtractionDTO>{ 

@Override 
public RawDataExtractionDTO process(RawDataExtractionDTO item) throws Exception { 
    System.out.println(" Raw DAta Process"); 

    if(item == null) 
    return null; 

    return item; 
}} 

我DB讀者：

@Bean 
ItemReader<RawDataExtractionDTO> rawDataDBReader() { 

    String jobName = Application.jobName; 
    String sql_query = ""; 

    if("RawDataOutBoundweekly".equalsIgnoreCase(jobName)){ 
     log.info("=========RawDataOutBoundweekly========="); 

     sql_query = "select * from vw_rawdata_weekly"; 

    }else if("RawDataOutBoundmonthly".equalsIgnoreCase(jobName)){ 
     log.info("================RawDataOutBoundmonthly============="); 

     sql_query = "select * from vw_rawdata_monthly"; 
    } 
    log.info("ENTERING rawDataDBReader ==================="); 


    JdbcCursorItemReader<RawDataExtractionDTO> datareader = new 
    JdbcCursorItemReader<>(); 
    datareader.setSql(sql_query); 
    datareader.setDataSource(dataSource); 
    datareader.setRowMapper(new BeanPropertyRowMapper<> 
    (RawDataExtractionDTO.class)); 
    return datareader; 
} 

沒有錯誤拋出，但是如果我把調試點我的讀者後，它不會去我的處理器的話，那只是關閉工作。

Answer 1

您可以執行FlatFileHeaderCallback來寫入文件頭。

http://docs.spring.io/spring-batch/apidocs/org/springframework/batch/item/file/FlatFileHeaderCallback.html

一些示例代碼來配置FlatFileHeaderCallback。即使讀者沒有閱讀任何記錄FlatFileHeaderCallback將被調用，並將寫入標題。最終文件將頭只

@Bean 
    public FlatFileItemWriter<Person> myWriter() 
    { 
     System.out.println("FlatFileItemWriter*******************"); 
     FlatFileItemWriter<Person> writer = new FlatFileItemWriter<Person>(); 
     writer.setResource(new FileSystemResource("output.csv")); 
     DelimitedLineAggregator<Person> delLineAgg = new DelimitedLineAggregator<Person>(); 
     delLineAgg.setDelimiter(","); 
     BeanWrapperFieldExtractor<Person> fieldExtractor = new BeanWrapperFieldExtractor<Person>(); 
     fieldExtractor.setNames(new String[] {"firstName", "lastName"}); 
     delLineAgg.setFieldExtractor(fieldExtractor); 
     writer.setLineAggregator(delLineAgg); 

    writer.setHeaderCallback(myFlatFileHeaderCallback);  


     return writer; 
    } 


@Component 
public class MyFlatFileHeaderCallback implements FlatFileHeaderCallback { 

    @Override 
    public void writeHeader(Writer writer) throws IOException { 
     System.out.println("Header called"); 

    } 

}