Update doc for reader-processor

doc/en/step/item-stream-flux-reader-processor-writer.md

@@ -6,9 +6,12 @@
 - [Create a tasklet without a processor](#create-a-tasklet-without-a-processor)
   - [Java](#java-1)
   - [Kotlin](#kotlin-1)
-- [Use a callback](#use-a-callback)
+- [Create a tasklet without a writer](#create-a-tasklet-without-a-writer)
   - [Java](#java-2)
   - [Kotlin](#kotlin-2)
+- [Use a callback](#use-a-callback)
+  - [Java](#java-3)
+  - [Kotlin](#kotlin-3)
 
 Spring uses a reactive library called [Reactor](https://projectreactor.io/), which provides streams for various types of data using `Flux`. For `ItemReader` in Spring Batch to use the data read using `Flux`, you need to extract each item from `Flux` and return it.
 
@@ -326,9 +329,156 @@ open class TestJobConfig(
 }
 ```
 
+## Create a tasklet without a writer
+
+If you need only `ItemStreamReader` and `ItemProcessor` without a writer, you can inherit `ItemStreamFluxReaderProcessor` to define `ItemStreamReader` and `ItemProcessor` in a single class.
+
+### Java
+
+In Java, you can convert a tasklet defined using `AdapterFactory` to `ItemStreamReader` and `ItemProcessor`.
+
+```java
+@Component
+@StepScope
+class SampleTasklet implements ItemStreamFluxReaderProcessor<Integer, String> {
+
+	@Value("#{jobParameters['totalCount']}")
+	private long totalCount;
+
+	private int count = 0;
+
+	@NonNull
+	@Override
+	public Flux<? extends Integer> readFlux(@NonNull ExecutionContext executionContext) {
+		System.out.println("totalCount: " + totalCount);
+		return Flux.generate(sink -> {
+			if (count < totalCount) {
+				sink.next(count);
+				++count;
+			} else {
+				sink.complete();
+			}
+		});
+	}
+
+	@Override
+	public String process(@NonNull Integer item) {
+		return "'" + item.toString() + "'";
+	}
+}
+```
+
+```java
+@Configuration
+public class TestJobConfig {
+
+	@Bean
+	public Job testJob(
+		SampleTasklet sampleTasklet,
+		JobRepository jobRepository,
+		PlatformTransactionManager transactionManager
+	) {
+		return new JobBuilder("testJob", jobRepository)
+			.start(
+				new StepBuilder("testStep", jobRepository)
+					.<Integer, String>chunk(3, transactionManager)
+					.reader(AdapterFactory.itemStreamReader(sampleTasklet))
+					.processor(AdapterFactory.itemProcessor(sampleTasklet))
+					.writer(chunk -> System.out.println(chunk.getItems()))
+					.build()
+			)
+			.build();
+	}
+}
+```
+
+You can statically import the method of `AdapterFactory` for better readability.
+
+```java
+import static com.navercorp.spring.batch.plus.step.AdapterFactory.itemStreamReader;
+import static com.navercorp.spring.batch.plus.step.AdapterFactory.itemStreamWriter;
+
+...
+
+@Configuration
+public class TestJobConfig {
+
+	@Bean
+	public Job testJob(
+		SampleTasklet sampleTasklet,
+		JobRepository jobRepository,
+		PlatformTransactionManager transactionManager
+	) {
+		return new JobBuilder("testJob", jobRepository)
+			.start(
+				new StepBuilder("testStep", jobRepository)
+					.<Integer, String>chunk(3, transactionManager)
+					.reader(itemStreamReader(sampleTasklet))
+					.processor(itemProcessor(sampleTasklet))
+					.writer(chunk -> System.out.println(chunk.getItems()))
+					.build()
+			)
+			.build();
+	}
+}
+```
+
+### Kotlin
+
+In Kotlin, you can easily convert a tasklet defined using an extension function in Spring Batch Plus to `ItemStreamReader` and `ItemProcessor`.
+
+```Kotlin
+@Component
+@StepScope
+open class SampleTasklet(
+    @Value("#{jobParameters['totalCount']}") private var totalCount: Long,
+) : ItemStreamFluxReaderProcessor<Int, String> {
+    private var count = 0
+
+    override fun readFlux(executionContext: ExecutionContext): Flux<out Int> {
+        println("totalCount: $totalCount")
+        return Flux.generate { sink ->
+            if (count < totalCount) {
+                sink.next(count)
+                ++count
+            } else {
+                sink.complete()
+            }
+        }
+    }
+
+    override fun process(item: Int): String? {
+        return "'$item'"
+    }
+}
+```
+
+```Kotlin
+@Configuration
+open class TestJobConfig(
+    private val batch: BatchDsl,
+    private val transactionManager: PlatformTransactionManager,
+) {
+    @Bean
+    open fun testJob(
+        sampleTasklet: SampleTasklet,
+    ): Job = batch {
+        job("testJob") {
+            step("testStep") {
+                chunk<Int, String>(3, transactionManager) {
+                    reader(sampleTasklet.asItemStreamReader())
+                    processor(sampleTasklet.asItemProcessor())
+                    writer { chunk -> println(chunk.items) }
+                }
+            }
+        }
+    }
+}
+```
+
 ## Use a callback
 
-You can define a callback method for `ItemStream` of `ItemStreamWriter` in `ItemStreamFluxReaderProcessorWriter` and `ItemStreamFluxReaderWriter`. You can selectively define a callback method.
+You can define a callback method for `ItemStream`. You can selectively define a callback method.
 
 ### Java
 

doc/en/step/item-stream-iterable-reader-processor-writer.md

@@ -6,9 +6,12 @@
 - [Create a tasklet without a processor](#create-a-tasklet-without-a-processor)
   - [Java](#java-1)
   - [Kotlin](#kotlin-1)
-- [Use a callback](#use-a-callback)
+- [Create a tasklet without a writer](#create-a-tasklet-without-a-writer)
   - [Java](#java-2)
   - [Kotlin](#kotlin-2)
+- [Use a callback](#use-a-callback)
+  - [Java](#java-3)
+  - [Kotlin](#kotlin-3)
 
 A chunk-oriented step in Spring Batch consists of `ItemReader`, `ItemProcessor`, and `ItemWriter`, which are usually defined separately and then assembled to define a step. However, there are some issues with this approach: it is difficult to share data between `ItemReader`, `ItemProcessor`, and `ItemWriter`, and you need to see each respective file to understand the batch flow. Also, if the classes are not reused, they can make the elements of a job less coherent.
 
@@ -328,9 +331,162 @@ open class TestJobConfig(
 }
 ```
 
+## Create a tasklet without a writer
+
+If you need only `ItemStreamReader` and `ItemProcessor` without a writer, you can inherit `ItemStreamIterableReaderProcessor` to define `ItemStreamReader` and `ItemProcessor` in a single class.
+
+### Java
+
+In Java, you can convert a tasklet defined using `AdapterFactory` to `ItemStreamReader` and `ItemProcessor`.
+
+```java
+@Component
+@StepScope
+class SampleTasklet implements ItemStreamIterableReaderProcessor<Integer, String> {
+
+	@Value("#{jobParameters['totalCount']}")
+	private long totalCount;
+
+	private int count = 0;
+
+	@NonNull
+	@Override
+	public Iterable<? extends Integer> readIterable(@NonNull ExecutionContext executionContext) {
+		System.out.println("totalCount: " + totalCount);
+		return () -> new Iterator<>() {
+			@Override
+			public boolean hasNext() {
+				return count < totalCount;
+			}
+
+			@Override
+			public Integer next() {
+				return count++;
+			}
+		};
+	}
+
+	@Override
+	public String process(@NonNull Integer item) {
+		return "'" + item.toString() + "'";
+	}
+}
+```
+
+```java
+@Configuration
+public class TestJobConfig {
+
+	@Bean
+	public Job testJob(
+		SampleTasklet sampleTasklet,
+		JobRepository jobRepository,
+		PlatformTransactionManager transactionManager
+	) {
+		return new JobBuilder("testJob", jobRepository)
+			.start(
+				new StepBuilder("testStep", jobRepository)
+					.<Integer, String>chunk(3, transactionManager)
+					.reader(AdapterFactory.itemStreamReader(sampleTasklet))
+					.processor(AdapterFactory.itemProcessor(sampleTasklet))
+					.writer(chunk -> System.out.println(chunk.getItems()))
+					.build()
+			)
+			.build();
+	}
+}
+```
+
+You can statically import the method of `AdapterFactory` for better readability.
+
+```java
+import static com.navercorp.spring.batch.plus.step.AdapterFactory.itemStreamReader;
+import static com.navercorp.spring.batch.plus.step.AdapterFactory.itemStreamWriter;
+
+...
+
+@Configuration
+public class TestJobConfig {
+
+	@Bean
+	public Job testJob(
+		SampleTasklet sampleTasklet,
+		JobRepository jobRepository,
+		PlatformTransactionManager transactionManager
+	) {
+		return new JobBuilder("testJob", jobRepository)
+			.start(
+				new StepBuilder("testStep", jobRepository)
+					.<Integer, String>chunk(3, transactionManager)
+					.reader(itemStreamReader(sampleTasklet))
+					.processor(itemProcessor(sampleTasklet))
+					.writer(chunk -> System.out.println(chunk.getItems()))
+					.build()
+			)
+			.build();
+	}
+}
+```
+
+### Kotlin
+
+In Kotlin, you can easily convert a tasklet defined using an extension function in Spring Batch Plus to `ItemStreamReader` and `ItemProcessor`.
+
+```Kotlin
+@Component
+@StepScope
+open class SampleTasklet(
+    @Value("#{jobParameters['totalCount']}") private var totalCount: Long,
+) : ItemStreamIterableReaderProcessor<Int, String> {
+    private var count = 0
+
+    override fun readIterable(executionContext: ExecutionContext): Iterable<Int> {
+        println("totalCount: $totalCount")
+        return Iterable {
+            object : Iterator<Int> {
+                override fun hasNext(): Boolean {
+                    return count < totalCount
+                }
+
+                override fun next(): Int {
+                    return count++
+                }
+            }
+        }
+    }
+
+    override fun process(item: Int): String? {
+        return "'$item'"
+    }
+}
+```
+
+```Kotlin
+@Configuration
+open class TestJobConfig(
+    private val batch: BatchDsl,
+    private val transactionManager: PlatformTransactionManager,
+) {
+    @Bean
+    open fun testJob(
+        sampleTasklet: SampleTasklet,
+    ): Job = batch {
+        job("testJob") {
+            step("testStep") {
+                chunk<Int, String>(3, transactionManager) {
+                    reader(sampleTasklet.asItemStreamReader())
+                    processor(sampleTasklet.asItemProcessor())
+                    writer { chunk -> println(chunk.items) }
+                }
+            }
+        }
+    }
+}
+```
+
 ## Use a callback
 
-You can define a callback method for `ItemStream` of `ItemStreamWriter` in `ItemStreamIterableReaderProcessorWriter` and `ItemStreamIterableReaderWriter`. You can selectively define a callback method.
+You can define a callback method for `ItemStream`. You can selectively define a callback method.
 
 ### Java