Implement jumpToItem in JsonItemReader

Issue #4557

Author: jpraet

spring-batch-infrastructure/src/main/java/org/springframework/batch/item/json/GsonJsonObjectReader.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2018-2021 the original author or authors.
+ * Copyright 2018-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -37,6 +37,7 @@
  *
  * @param <T> type of the target object
  * @author Mahmoud Ben Hassine
+ * @author Jimmy Praet
  * @since 4.1
  */
 public class GsonJsonObjectReader<T> implements JsonObjectReader<T> {
@@ -102,4 +103,11 @@ public void close() throws Exception {
 		this.jsonReader.close();
 	}
 
+	@Override
+	public void jumpToItem(int itemIndex) throws Exception {
+		for (int i = 0; i < itemIndex; i++) {
+			this.jsonReader.skipValue();
+		}
+	}
+
 }

spring-batch-infrastructure/src/main/java/org/springframework/batch/item/json/JacksonJsonObjectReader.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2018-2021 the original author or authors.
+ * Copyright 2018-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -34,6 +34,7 @@
  *
  * @param <T> type of the target object
  * @author Mahmoud Ben Hassine
+ * @author Jimmy Praet
  * @since 4.1
  */
 public class JacksonJsonObjectReader<T> implements JsonObjectReader<T> {
@@ -98,4 +99,13 @@ public void close() throws Exception {
 		this.jsonParser.close();
 	}
 
+	@Override
+	public void jumpToItem(int itemIndex) throws Exception {
+		for (int i = 0; i < itemIndex; i++) {
+			if (this.jsonParser.nextToken() == JsonToken.START_OBJECT) {
+				this.jsonParser.skipChildren();
+			}
+		}
+	}
+
 }

spring-batch-infrastructure/src/main/java/org/springframework/batch/item/json/JsonItemReader.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2018-2020 the original author or authors.
+ * Copyright 2018-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -47,6 +47,7 @@
  *
  * @param <T> the type of json objects to read
  * @author Mahmoud Ben Hassine
+ * @author Jimmy Praet
  * @since 4.1
  */
 public class JsonItemReader<T> extends AbstractItemCountingItemStreamItemReader<T>
@@ -136,4 +137,9 @@ protected void doClose() throws Exception {
 		this.jsonObjectReader.close();
 	}
 
+	@Override
+	protected void jumpToItem(int itemIndex) throws Exception {
+		this.jsonObjectReader.jumpToItem(itemIndex);
+	}
+
 }

spring-batch-infrastructure/src/main/java/org/springframework/batch/item/json/JsonObjectReader.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2018 the original author or authors.
+ * Copyright 2018-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -25,6 +25,7 @@
  *
  * @param <T> type of the target object
  * @author Mahmoud Ben Hassine
+ * @author Jimmy Praet
  * @since 4.1
  */
 public interface JsonObjectReader<T> {
@@ -54,4 +55,19 @@ default void close() throws Exception {
 
 	}
 
+	/**
+	 * Move to the given item index. Implementations should override this method if there
+	 * is a more efficient way of moving to given index than re-reading the input using
+	 * {@link #read()}.
+	 * @param itemIndex index of item (0 based) to jump to.
+	 * @throws Exception Allows implementations to throw checked exceptions for
+	 * interpretation by the framework
+	 * @since 5.2
+	 */
+	default void jumpToItem(int itemIndex) throws Exception {
+		for (int i = 0; i < itemIndex; i++) {
+			read();
+		}
+	}
+
 }

spring-batch-infrastructure/src/test/java/org/springframework/batch/item/json/JsonItemReaderFunctionalTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2018-2022 the original author or authors.
+ * Copyright 2018-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -130,4 +130,25 @@ void testInvalidResourceContent() {
 		assertTrue(getJsonParsingException().isInstance(expectedException.getCause()));
 	}
 
+	@Test
+	void testJumpToItem() throws Exception {
+		// given
+		JsonItemReader<Trade> itemReader = new JsonItemReaderBuilder<Trade>().jsonObjectReader(getJsonObjectReader())
+			.resource(new ClassPathResource("org/springframework/batch/item/json/trades.json"))
+			.name("tradeJsonItemReader")
+			.build();
+		itemReader.open(new ExecutionContext());
+
+		// when
+		itemReader.jumpToItem(3);
+
+		// then
+		Trade trade = itemReader.read();
+		assertNotNull(trade);
+		assertEquals("100", trade.getIsin());
+		assertEquals("barfoo", trade.getCustomer());
+		assertEquals(new BigDecimal("1.8"), trade.getPrice());
+		assertEquals(4, trade.getQuantity());
+	}
+
 }