NullPointerException if I dont supply FieldSetMapper

[trant]

First time using Spring Batch, seems pretty cool. Just one thing kind of confused me.

I setup a quick test to parse a tab-delimitted file and I used the Generics to supply the classname and thought by doing so I would not need to supply a FieldSetMapper.

However as I tested the code I kept getting NullPointerException and had trouble figuring out why, until I tried supplying a FieldSetMapper and then it worked.

Here is the code:

public void handleFile () throws Exception {

		File file = new File("D:/input/input.in");
		
		DelimitedLineTokenizer tokenizer = new DelimitedLineTokenizer();
		tokenizer.setDelimiter(DelimitedLineTokenizer.DELIMITER_TAB);
		tokenizer.setNames(new String[] { "address1", "address2", "address3", "city", "state" });
		
		BeanWrapperFieldSetMapper<AddressVO> wrapper = new BeanWrapperFieldSetMapper();
		wrapper.setTargetType(AddressVO.class);
		
		DefaultLineMapper<AddressVO> mapper = new DefaultLineMapper<AddressVO>();
		mapper.setLineTokenizer(tokenizer);
		mapper.setFieldSetMapper(wrapper);
		
		FlatFileItemReader<AddressVO> reader = new FlatFileItemReader<AddressVO>();
		reader.setLineMapper(mapper);
		reader.setResource(new FileSystemResource(file));
		reader.open(new ExecutionContext());
		
		AddressVO vo = null;
		while ((vo = reader.read()) != null) {
			System.out.println("Read next item: "+vo.getAddress1()+", "+vo.getCity()+", "+vo.getState());
		}
		
		reader.close();
	}

So this code works fine, however if you comment out the "mapper.setFieldSetMapper(wrapper);" the operation throws a NullPointerException which I thought was odd because I thought by instantiating the FlatFileItemReader with <AddressVO> that it would not need the FieldSetMapper, that would be a redundant step, no?

[arno]

So this code works fine, however if you comment out the "mapper.setFieldSetMapper(wrapper);" the operation throws a NullPointerException which I thought was odd because I thought by instantiating the FlatFileItemReader with <AddressVO> that it would not need the FieldSetMapper, that would be a redundant step, no?

the type parameter of the FlatFileItemReader doesn't tell Spring Batch how to create an object from a FieldSet. So the FieldSetMapper is a mandatory dependency.