How to pass List to Spring Batch ItemReader via REST call

Question

I'm working on a REST method that will perform a job using Spring Batch.

I have a simple job defined,

<job id="myIndexJob" xmlns="http://www.springframework.org/schema/batch">
    <step id="step1">
        <tasklet>
            <chunk reader="myIndexItemReader" processor="myIndexItemProcessor" writer="myIndexItemWriter" commit-interval="1" />
        </tasklet>
    </step>
</job>

This job mimics a question I posted earlier,

Spring Batch ItemReader list processed only once

But this time, instead of executing the job on a schedule, I want to manually execute it via a REST call.

The problem I'm having is passing a List to the myIndexItemReader . My REST call will generate a List based on some query string. The previous question I posted got it's List handed to it via the spring bean in the XML each time the step ran.

I'd like to do something like this,

@RequestMapping(value="/rest/{regex}", method=RequestMethod.GET)
public void run(@PathVariable String regex) {

    List<String> myList = new ArrayList<>();
    myList.add("something");

    long nanoBits = System.nanoTime() % 1000000L;
    if (nanoBits < 0) {
        nanoBits *= -1;
    }
    String dateParam = new Date().toString() + System.currentTimeMillis() 
            + "." + nanoBits;
    JobParameters param = new JobParametersBuilder()
            .addString("date", dateParam)
            .toJobParameters();
    JobExecution execution = jobLauncher.run(job, param);

}

but I just don't know how to pass myList to the myIndexItemReader .

As of now I can do this by creating a RepeatTemplate and calling iterate on a callback, but the job chunk seems more clean.

Anyone have any ideas or suggestions? Thanks /w

Answer 1

I took an alternate approach and stored information in a database table based on the REST criteria. Then the ItemReader read the table and cleared it after each run.

Answer 2

You can pass queries as job parameters, but you have to be carefully because string job parameter has a finite lenght (250) (look Metadata schema ).
If this can be a limit you can precompile a property file like that:

queries.properties

query1=<query string 1>
query2=<query string 2>
query3=<query string 3>
queryn=<query string n>

As job parameters you can pass:

queriesIdsCount (integer): number of queries (0..n)
queryId0 (string): identifier of query in queries.properties file (ex: query2)
queryId1 (string): (ex. query3)
queryIdn (string): (ex. query1)

and so on so you can select queries from your list.
With a Tasklet or a usual Reader/Process/Writer (as first step) you can process your job parameters and create List<> using REST.
Job parameters are available using spEL look about late-binding .

I hope I was clear, English is not my native language.