Use the Chunk API consistently

This commit replaces the usage of List with Chunk
where appropriate. Summary of changes:

- The Chunk class was moved from the `org.springframework.batch.core.step.item` package to the `org.springframework.batch.item` package
- The signature of the method `ItemWriter#write(List)` was changed to `ItemWriter#write(Chunk)`
- All implementations of `ItemWriter` were updated to use the Chunk API instead of List
- All methods in the `ItemWriteListener` interface were updated to use the Chunk API instead of List
- All implementations of `ItemWriteListener` were updated to use the Chunk API instead of List
- The constructor of `ChunkRequest` was changed to accept a Chunk instead of a Collection of items
- The return type of `ChunkRequest#getItems()` was changed from List to Chunk

Resolves #3954

spring-batch-docs/src/main/asciidoc/common-patterns.adoc

@@ -277,7 +277,7 @@ public class TradeItemWriter implements ItemWriter<Trade>,
 
     private BigDecimal totalAmount = BigDecimal.ZERO;
 
-    public void write(List<? extends Trade> items) throws Exception {
+    public void write(Chunk<? extends Trade> items) throws Exception {
         BigDecimal chunkTotal = BigDecimal.ZERO;
         for (Trade trade : items) {
             chunkTotal = chunkTotal.add(trade.getAmount());
@@ -665,7 +665,7 @@ then it is not persisted during `Step` execution. If the `Step` fails, that data
 public class SavingItemWriter implements ItemWriter<Object> {
     private StepExecution stepExecution;
 
-    public void write(List<? extends Object> items) throws Exception {
+    public void write(Chunk<? extends Object> items) throws Exception {
         // ...
 
         ExecutionContext stepContext = this.stepExecution.getExecutionContext();
@@ -759,7 +759,7 @@ in the following example:
 public class RetrievingItemWriter implements ItemWriter<Object> {
     private Object someObject;
 
-    public void write(List<? extends Object> items) throws Exception {
+    public void write(Chunk<? extends Object> items) throws Exception {
         // ...
     }
 

spring-batch-docs/src/main/asciidoc/processor.adoc

@@ -25,7 +25,7 @@ public class CompositeItemWriter<T> implements ItemWriter<T> {
         this.itemWriter = itemWriter;
     }
 
-    public void write(List<? extends T> items) throws Exception {
+    public void write(Chunk<? extends T> items) throws Exception {
         //Add business logic here
        itemWriter.write(items);
     }
@@ -77,7 +77,7 @@ public class FooProcessor implements ItemProcessor<Foo, Bar> {
 }
 
 public class BarWriter implements ItemWriter<Bar> {
-    public void write(List<? extends Bar> bars) throws Exception {
+    public void write(Chunk<? extends Bar> bars) throws Exception {
         //write bars
     }
 }
@@ -162,7 +162,7 @@ public class BarProcessor implements ItemProcessor<Bar, Foobar> {
 }
 
 public class FoobarWriter implements ItemWriter<Foobar>{
-    public void write(List<? extends Foobar> items) throws Exception {
+    public void write(Chunk<? extends Foobar> items) throws Exception {
         //write items
     }
 }

spring-batch-docs/src/main/asciidoc/readersAndWriters.adoc

@@ -78,7 +78,7 @@ As with `ItemReader`,
 ----
 public interface ItemWriter<T> {
 
-    void write(List<? extends T> items) throws Exception;
+    void write(Chunk<? extends T> items) throws Exception;
 
 }
 ----
@@ -2732,7 +2732,7 @@ public class CustomItemWriter<T> implements ItemWriter<T> {
 
     List<T> output = TransactionAwareProxyFactory.createTransactionalList();
 
-    public void write(List<? extends T> items) throws Exception {
+    public void write(Chunk<? extends T> items) throws Exception {
         output.addAll(items);
     }