# Spring Batch : The Main Concepts

By

Paul Tomoiu

●

In 

Examples, 

Spring, 

Batch, 

Concepts

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Published 2023-09-30

The tutorial will explain what are the main concepts in Spring Batch.

With Spring Batch, you can define and run jobs. The job may have a step or many steps. During a step, the job do something, a particular task, named tasklet. When you define a step you can define the next step you have to execute.

1 job ---(has)--- > 1..n steps / 1..n flows

1 flow ---(has)--- > 1..n steps

1 step could : --> run a single task(named tasklet)

                        --> follow the READ(in)-PROCESS(in/out)-WRITE(out) pattern

This pattern is implemented when we define the steps:

step.<String, String> chunk(2)
    .reader(itemReader)
    .processor(itemProcessor)
    .writer(itemWriter)

Typically, Batch Jobs are long-running, non-interactive and process large volumes of data, more than fits in memory or a single transaction.

A job could execute steps in a defined order. We can have sequential steps and parallel steps. We can execute some tasks (steps) when a condition is true or false. Because of these things, you can create workflows using Spring Batch.

Sometimes, you need a step to be executed by chunks: you want to insert 100.000 rows ten times instead 1.000.000 one time. This can be done using Spring Batch. For this reason one tasklet could have 0 .. 1 chunk.

All the information about the job executions are stored in a Database Repository. This is named JobRepository.

You can take a look at the following picture:

In this picture you can see that:

• all the information related to the jobs are stored in a JobRepository;
• a typical step include a read sequence (ItemReader), a process which can test/ do something with the data read before (ItemProcessor) and an write sequence (ItemWriter) which write initial/modified or other information to another source of data (to a database for instance).

The jobs are started by JobLauncher. JobLauncher starts a job for a given Job & JobParameters.

The combination Job + JobParameters = JobInstance.

During the execution of a job, a context bean is created automatically: the JobExecution. The JobExecution bean is created each time a job run. When you rerun a job, a new JobExecution Bean is created.

You can use in addition a JobOperator which is an interface that provides operations for inspecting and controlling jobs, mainly for a command-line client or a remote launcher like a JMX console.