Allow StaxEventItemReader to auto-detect the input file encoding

Before this commit, it was not possible to pass a null encoding
to the StaxEventItemReader, which prevents the XML event reader
to auto-detect the file encoding.

This commits makes the encoding setter more lenient by accepting
a null value.

Resolves #4101

spring-batch-infrastructure/src/main/java/org/springframework/batch/item/xml/StaxEventItemReader.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2020 the original author or authors.
+ * Copyright 2006-2023 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.
@@ -49,13 +49,13 @@ import org.springframework.util.xml.StaxUtils;
 
 /**
  * Item reader for reading XML input based on StAX.
- * 
+ *
  * It extracts fragments from the input XML document which correspond to records for processing. The fragments are
  * wrapped with StartDocument and EndDocument events so that the fragments can be further processed like standalone XML
  * documents.
- * 
+ *
  * The implementation is <b>not</b> thread-safe.
- * 
+ *
  * @author Robert Kasanicky
  * @author Mahmoud Ben Hassine
  */
@@ -140,16 +140,16 @@ ResourceAwareItemReaderItemStream<T>, InitializingBean {
 	/**
 	 * Set encoding to be used for the input file. Defaults to {@link #DEFAULT_ENCODING}.
 	 *
-	 * @param encoding the encoding to be used
+	 * @param encoding the encoding to be used. Can be {@code null}, in which case, the
+	 * XML event reader will attempt to auto-detect the encoding from the input file.
 	 */
-	public void setEncoding(String encoding) {
-		Assert.notNull(encoding, "The encoding must not be null");
+	public void setEncoding(@Nullable String encoding) {
 		this.encoding = encoding;
 	}
 
 	/**
 	 * Ensure that all required dependencies for the ItemReader to run are provided after all properties have been set.
-	 * 
+	 *
 	 * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet()
 	 * @throws IllegalArgumentException if the Resource, FragmentDeserializer or FragmentRootElementName is null, or if
 	 * the root element is empty.
@@ -161,19 +161,19 @@ ResourceAwareItemReaderItemStream<T>, InitializingBean {
 		Assert.notEmpty(fragmentRootElementNames, "The FragmentRootElementNames must not be empty");
 		for (QName fragmentRootElementName : fragmentRootElementNames) {
 			Assert.hasText(fragmentRootElementName.getLocalPart(), "The FragmentRootElementNames must not contain empty elements");
-		}		
+		}
 	}
 
 	/**
 	 * Responsible for moving the cursor before the StartElement of the fragment root.
-	 * 
+	 *
 	 * This implementation simply looks for the next corresponding element, it does not care about element nesting. You
 	 * will need to override this method to correctly handle composite fragments.
 	 *
 	 * @param reader the {@link XMLEventReader} to be used to find next fragment.
-	 * 
+	 *
 	 * @return <code>true</code> if next fragment was found, <code>false</code> otherwise.
-	 * 
+	 *
 	 * @throws NonTransientResourceException if the cursor could not be moved. This will be treated as fatal and
 	 * subsequent calls to read will return null.
 	 */
@@ -237,7 +237,8 @@ ResourceAwareItemReaderItemStream<T>, InitializingBean {
 		}
 
 		inputStream = resource.getInputStream();
-		eventReader = xmlInputFactory.createXMLEventReader(inputStream, this.encoding);
+		eventReader = this.encoding != null ? xmlInputFactory.createXMLEventReader(inputStream, this.encoding)
+				: xmlInputFactory.createXMLEventReader(inputStream);
 		fragmentReader = new DefaultFragmentEventReader(eventReader);
 		noInput = false;
 
@@ -332,19 +333,19 @@ ResourceAwareItemReaderItemStream<T>, InitializingBean {
 			}
 		}
 	}
-	
+
 	protected boolean isFragmentRootElementName(QName name) {
 		for (QName fragmentRootElementName : fragmentRootElementNames) {
 			if (fragmentRootElementName.getLocalPart().equals(name.getLocalPart())) {
 				if (!StringUtils.hasText(fragmentRootElementName.getNamespaceURI())
-						|| fragmentRootElementName.getNamespaceURI().equals(name.getNamespaceURI())) {					
+						|| fragmentRootElementName.getNamespaceURI().equals(name.getNamespaceURI())) {
 					return true;
 				}
 			}
 		}
 		return false;
-	}	
-	
+	}
+
 	private QName parseFragmentRootElementName(String fragmentRootElementName) {
 		String name = fragmentRootElementName;
 		String nameSpace = null;
@@ -354,5 +355,5 @@ ResourceAwareItemReaderItemStream<T>, InitializingBean {
 		}
 		return new QName(nameSpace, name, "");
 	}
-	
+
 }

spring-batch-infrastructure/src/main/java/org/springframework/batch/item/xml/builder/StaxEventItemReaderBuilder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2017-2020 the original author or authors.
+ * Copyright 2017-2023 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.
@@ -26,6 +26,7 @@ import org.apache.commons.logging.LogFactory;
 
 import org.springframework.batch.item.xml.StaxEventItemReader;
 import org.springframework.core.io.Resource;
+import org.springframework.lang.Nullable;
 import org.springframework.oxm.Unmarshaller;
 import org.springframework.util.Assert;
 import org.springframework.util.StringUtils;
@@ -203,13 +204,14 @@ public class StaxEventItemReaderBuilder<T> {
 	}
 
 	/**
-	 * Encoding for the input file. Defaults to {@link StaxEventItemReader#DEFAULT_ENCODING}.
-	 *
+	 * Encoding for the input file. Defaults to
+	 * {@link StaxEventItemReader#DEFAULT_ENCODING}. Can be {@code null}, in which case
+	 * the XML event reader will attempt to auto-detect the encoding from the input file.
 	 * @param encoding String encoding algorithm
 	 * @return the current instance of the builder
 	 * @see StaxEventItemReader#setEncoding(String)
 	 */
-	public StaxEventItemReaderBuilder<T> encoding(String encoding) {
+	public StaxEventItemReaderBuilder<T> encoding(@Nullable String encoding) {
 		this.encoding = encoding;
 
 		return this;

spring-batch-infrastructure/src/test/java/org/springframework/batch/item/xml/StaxEventItemReaderTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2008-2020 the original author or authors.
+ * Copyright 2008-2023 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.
@@ -36,8 +36,10 @@ import org.springframework.util.xml.StaxUtils;
 import javax.xml.namespace.QName;
 import javax.xml.stream.FactoryConfigurationError;
 import javax.xml.stream.XMLEventReader;
+import javax.xml.stream.XMLInputFactory;
 import javax.xml.stream.XMLStreamException;
 import javax.xml.stream.events.EndElement;
+import javax.xml.stream.events.StartDocument;
 import javax.xml.stream.events.StartElement;
 import javax.xml.stream.events.XMLEvent;
 import javax.xml.transform.Source;
@@ -57,10 +59,13 @@ import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
 
 /**
  * Tests for {@link StaxEventItemReader}.
- * 
+ *
  * @author Robert Kasanicky
  * @author Michael Minella
  * @author Mahmoud Ben Hassine
@@ -94,7 +99,7 @@ public class StaxEventItemReaderTests {
 	private Unmarshaller unmarshaller = new MockFragmentUnmarshaller();
 
 	private static final String FRAGMENT_ROOT_ELEMENT = "fragment";
-	
+
 	private static final String[] MULTI_FRAGMENT_ROOT_ELEMENTS = {"fragmentA", "fragmentB"};
 
 	private ExecutionContext executionContext;
@@ -170,6 +175,37 @@ public class StaxEventItemReaderTests {
 		source.close();
 	}
 
+	@Test
+	public void testNullEncoding() throws Exception {
+		// given
+		XMLEventReader eventReader = mock(XMLEventReader.class);
+		when(eventReader.peek()).thenReturn(mock(StartDocument.class));
+
+		Resource resource = mock(Resource.class);
+		InputStream inputStream = mock(InputStream.class);
+		when(resource.getInputStream()).thenReturn(inputStream);
+		when(resource.isReadable()).thenReturn(true);
+		when(resource.exists()).thenReturn(true);
+		XMLInputFactory xmlInputFactory = mock(XMLInputFactory.class);
+		when(xmlInputFactory.createXMLEventReader(inputStream)).thenReturn(eventReader);
+
+		StaxEventItemReader<Object> reader = new StaxEventItemReader<>();
+		reader.setUnmarshaller(new MockFragmentUnmarshaller());
+		reader.setFragmentRootElementName(FRAGMENT_ROOT_ELEMENT);
+		reader.setResource(resource);
+		reader.setEncoding(null);
+		reader.setStrict(false);
+		reader.setXmlInputFactory(xmlInputFactory);
+		reader.afterPropertiesSet();
+
+		// when
+		reader.open(new ExecutionContext());
+
+		// then
+		verify(xmlInputFactory).createXMLEventReader(inputStream);
+		reader.close();
+	}
+
 	@Test
 	public void testItemCountAwareFragment() throws Exception {
 		StaxEventItemReader<ItemCountAwareFragment> source = createNewItemCountAwareInputSource();
@@ -247,7 +283,7 @@ public class StaxEventItemReaderTests {
 
 		source.close();
 	}
-	
+
 	@Test
 	public void testMultiFragment() throws Exception {
 
@@ -262,7 +298,7 @@ public class StaxEventItemReaderTests {
 		assertNull(source.read()); // there are only three fragments
 
 		source.close();
-	}	
+	}
 
 	@Test
 	public void testMultiFragmentNameSpace() throws Exception {
@@ -277,7 +313,7 @@ public class StaxEventItemReaderTests {
 		assertNull(source.read()); // there are only two fragments (one has wrong namespace)
 
 		source.close();
-	}	
+	}
 
 	@Test
 	public void testMultiFragmentRestart() throws Exception {
@@ -289,23 +325,23 @@ public class StaxEventItemReaderTests {
 		// see asserts in the mock unmarshaller
 		assertNotNull(source.read());
 		assertNotNull(source.read());
-		
-		source.update(executionContext);		
+
+		source.update(executionContext);
 		assertEquals(2, executionContext.getInt(ClassUtils.getShortName(StaxEventItemReader.class) + ".read.count"));
-		
+
 		source.close();
-		
+
 		source = createNewInputSource();
 		source.setResource(new ByteArrayResource(xmlMultiFragment.getBytes()));
 		source.setFragmentRootElementNames(MULTI_FRAGMENT_ROOT_ELEMENTS);
 		source.afterPropertiesSet();
 		source.open(executionContext);
-		
+
 		assertNotNull(source.read());
 		assertNull(source.read()); // there are only three fragments
 
 		source.close();
-	}	
+	}
 
 	@Test
 	public void testMultiFragmentNested() throws Exception {
@@ -322,7 +358,7 @@ public class StaxEventItemReaderTests {
 
 		source.close();
 	}
-	
+
 	@Test
 	public void testMultiFragmentNestedRestart() throws Exception {
 
@@ -333,24 +369,24 @@ public class StaxEventItemReaderTests {
 		// see asserts in the mock unmarshaller
 		assertNotNull(source.read());
 		assertNotNull(source.read());
-		
-		source.update(executionContext);		
+
+		source.update(executionContext);
 		assertEquals(2, executionContext.getInt(ClassUtils.getShortName(StaxEventItemReader.class) + ".read.count"));
-		
+
 		source.close();
-		
+
 		source = createNewInputSource();
 		source.setResource(new ByteArrayResource(xmlMultiFragment.getBytes()));
 		source.setFragmentRootElementNames(MULTI_FRAGMENT_ROOT_ELEMENTS);
 		source.afterPropertiesSet();
 		source.open(executionContext);
-		
+
 		assertNotNull(source.read());
 		assertNull(source.read()); // there are only three fragments
 
 		source.close();
-	}	
-	
+	}
+
 	/**
 	 * Cursor is moved before beginning of next fragment.
 	 */
@@ -714,7 +750,7 @@ public class StaxEventItemReaderTests {
 
 		/**
 		 * A simple mapFragment implementation checking the StaxEventReaderItemReader basic read functionality.
-		 * 
+		 *
 		 * @param source
 		 * @return list of the events from fragment body
 		 */
@@ -753,7 +789,7 @@ public class StaxEventItemReaderTests {
 			}
 			return fragmentContent;
 		}
-		
+
 		private boolean isFragmentRootElement(String name) {
 			return FRAGMENT_ROOT_ELEMENT.equals(name) || Arrays.asList(MULTI_FRAGMENT_ROOT_ELEMENTS).contains(name);
 		}