如何在Spring批处理中使用FlatFileItemWriter写入stdout？

Question

I have the following writer configured in my beans definition file of a spring batch project :

<bean id="writer" class="org.springframework.batch.item.file.FlatFileItemWriter">
    <property name="resource" value="file:/path/to/somefile"/>
    <property name="lineAggregator">
        <bean class="MyCustomLineAggregator"/>
    </property>
</bean>

Now, instead of writing to /path/to/somefile, I want the output to go to the stdout, reason being that I want to launch this job through the command-line launcher and pipe the output to another unix program.

I tried by setting the resource property to "file:/dev/stdout", but then I get the exception : org.springframework.batch.item.ItemStreamException: Unable to create file: [/dev/stdout]

I tried to see if there was an out of the box resource that could handle this, but I'm a bit clueless on which one could do the job...

Thanks for your help.

EDIT : Below is the solution I came up with, following your advise :

import java.util.List;
import org.springframework.batch.item.ItemWriter;
import org.springframework.batch.item.file.transform.LineAggregator;

public class StdoutWriter<T> implements ItemWriter<T> {

LineAggregator<T> lineAggregator;

public void setLineAggregator(LineAggregator<T> lineAggregator) {
    this.lineAggregator = lineAggregator;
}

@Override
public void write(List<? extends T> items) throws Exception {
    for (T item : items) {
        System.out.println(lineAggregator.aggregate(item));
    }
}

}

Answer 1

I don't think there is anything out of the box that does what you are looking for. It is simple enough to create your own ItemWriter that does a simple System.out.println() . You can then use the CompositeItemWriter to tie the two together if you still want the file.

Alternately, you can throw on a custom ItemWriterListener and do the printing there.

Answer 2

There's another hack you can use to write to stdout. Essentially, you can specify /dev/stdout as the output file resource. Be sure to set shouldDeleteIfExists to false and appendAllowed to true within the writer or you'll get runtime errors.