FlatFileHeaderCallback

[luigi.toziani]

Hi all,

I've a callback class for printing header on file:

public class HeaderCallback implements FlatFileHeaderCallback{

	private String header = null;
		
	public void writeHeader(Writer writer) throws IOException {
		if( header != null &&  (! header.isEmpty()) )
			writer.write(header);
	}

	public void setHeader(String header) {
		this.header = header;
	}

	public String getHeader() {
		return header;
	}

}

The private property is the header line I want to print (specified in an external job properties file used in the xml file: ${header.line} ) .

The problem is that a "line.separator" is always generated when registering a FlatFileHeaderCallback onto corresponding FlatFileItemWriter.

The only way for not printing "line.separator" is letting inject a null object in headerCallback property of FlatFileItemWriter. But I get a NullPointerException during context start up phase.

I just need something like:

<bean id="csvWriter" class="org....FlatFileItemWriter">
	....some other stuff.....	
    <property name="headerCallback" >
	<bean factory-bean="headerFactory" >
    </bean>
</property>
		
</bean>

where headerFactory returns null if no ${header.line} is specified in properties file.

How can I allow Spring to inject null object into bean properties?
Otherwise, how can I provide a kind of conditional injection?

Thanks,
Luigi

[Dave Syer]

I didn't really understand the question yet. You want a header callback, but you don't want to emit the line separator between the header and the main fail, or you don't want to emit the line separator at all ever? I don't think there are any restrictions on the value of the line separator, so I assume you want the former? If so it sounds a bit strange - it doesn't really fit the definition of a header. But I didn't understand the bit about "conditional injection" so I'm probably missing something. There is nothing to stop you injecting null into a bean definition, but I don't understand why you want to do that.

[luigi.toziani]

Thank you for reply! Well I try to explain better.

I would configure my header line from a properties file without add and remove the header callback property in the FlatFileItemWriter of my XML configuration.

header.line=MY CUSTOM HEADER LINE

I would have no header line in case of empty property ( header.line= ). I don't want a blank line with the carriage return to be printed on top.

Below the snippet of FlatFileItemWriter where checking headerCallback. So I would header callback to be null on demand (with a FactoryBean). But Spring gives me NullPointerException when trying to inject a null FlatFileHeaderCallback

if (headerCallback != null) {	
try { 
    headerCallback.writeHeader(outputState.outputBufferedWriter);
    outputState.write(lineSeparator);
}

I hope is more clear

thanks again

[Dave Syer]

I'm not sure why you wouldn't be able to inject null. If that's the issue how are you doing it and what is the error?

[luigi.toziani]

Well that's all:

<property name="headerCallback"> //Property of FlatFileItemWriter
    <bean class="com.primeur.listener.HeaderCallback" 
         factory-method="createHeaderCallback">
               <constructor-arg value=""></constructor-arg>
   </bean>
</property>

where createHeaderCallback is a static method that returns null in case of empty parameter or a new HeaderCallback otherwise.

This is the stacktrace:

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'lazyBindingProxy.csvWriter#sysinit' defined in class path resource [job-datatimerec-diff.xml]: Initialization of bean failed; nested exception is java.lang.NullPointerException
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:480)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory$1.run(AbstractAutowireCapableBeanFactory.java:409)
	at java.security.AccessController.doPrivileged(Native Method)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:380)
	at org.springframework.beans.factory.support.AbstractBeanFactory$2.getObject(AbstractBeanFactory.java:302)
	at org.springframework.batch.core.scope.StepScope.get(StepScope.java:150)
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:298)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:185)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:164)
	at org.springframework.batch.core.scope.util.PlaceholderTargetSource.getTarget(PlaceholderTargetSource.java:185)
	at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:184)
	at $Proxy17.open(Unknown Source)
	at org.springframework.batch.item.support.CompositeItemStream.open(CompositeItemStream.java:98)
	at org.springframework.batch.core.step.tasklet.TaskletStep.open(TaskletStep.java:288)
	at org.springframework.batch.core.step.AbstractStep.execute(AbstractStep.java:193)
	at org.springframework.batch.core.job.SimpleStepHandler.handleStep(SimpleStepHandler.java:135)
	at org.springframework.batch.core.job.flow.JobFlowExecutor.executeStep(JobFlowExecutor.java:61)
	at org.springframework.batch.core.job.flow.support.state.StepState.handle(StepState.java:60)
	at org.springframework.batch.core.job.flow.support.SimpleFlow.resume(SimpleFlow.java:144)
	at org.springframework.batch.core.job.flow.support.SimpleFlow.start(SimpleFlow.java:124)
	at org.springframework.batch.core.job.flow.FlowJob.doExecute(FlowJob.java:135)
	at org.springframework.batch.core.job.AbstractJob.execute(AbstractJob.java:281)
	at org.springframework.batch.core.launch.support.SimpleJobLauncher$1.run(SimpleJobLauncher.java:120)
	at java.lang.Thread.run(Thread.java:619)
Caused by: java.lang.NullPointerException
	at org.springframework.batch.core.scope.util.PlaceholderTargetSource$1.convertIfNecessary(PlaceholderTargetSource.java:148)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.convertForProperty(AbstractAutowireCapableBeanFactory.java:1294)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1250)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1010)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:472)
	... 23 more

[Dave Syer]

Interesting. Looks like a corner case bug in Spring Batch PlaceholderTargetSource. This component isn't used if you use Spring 3, so you could try that (and raise a ticket in JIRA), or if you could remove the scope="step" from the enclosing bean definition that would work too.

[luigi.toziani]

Well, thanks.

Anyway I tried removing scope step from writer but nothing happened. I will try to use Spring 3.0. (Actually using 2.5.6)