INT-950: turns out all supporting classes already had this property, so only changes in the namespace and the parser were needed.

org.springframework.integration.file/src/main/java/org/springframework/integration/file/config/FileWritingMessageHandlerBeanDefinitionBuilder.java

@@ -50,6 +50,7 @@ abstract class FileWritingMessageHandlerBeanDefinitionBuilder {
 		}
 		IntegrationNamespaceUtils.setValueIfAttributeDefined(builder, element, "auto-create-directory");
 		IntegrationNamespaceUtils.setValueIfAttributeDefined(builder, element, "delete-source-files");
+		IntegrationNamespaceUtils.setValueIfAttributeDefined(builder, element, "charset");
 		String fileNameGenerator = element.getAttribute("filename-generator");
 		if (StringUtils.hasText(fileNameGenerator)) {
 			builder.addPropertyReference("fileNameGenerator", fileNameGenerator);

org.springframework.integration.file/src/main/resources/org/springframework/integration/file/config/spring-integration-file-2.0.xsd

@@ -200,6 +200,7 @@
             </xsd:annotation>
         </xsd:attribute>
         <xsd:attribute name="auto-startup" type="xsd:string"/>
+        <xsd:attribute name="charset" type="xsd:string"/>
     </xsd:complexType>
 
     <xsd:element name="file-to-string-transformer">

org.springframework.integration.file/src/test/java/org/springframework/integration/file/config/FileOutboundChannelAdapterParserTests-context.xml

@@ -29,6 +29,11 @@
 								   delete-source-files="true"
 								   directory="${java.io.tmpdir}"/>
 
+    <file:outbound-channel-adapter id="adapterWithCharset"
+								   channel="testChannel"
+                                   charset="UTF-8"
+								   directory="${java.io.tmpdir}"/>
+
 	<file:outbound-channel-adapter id="adapterWithOrder"
 								   channel="testChannel"
 								   order="555"

org.springframework.integration.file/src/test/java/org/springframework/integration/file/config/FileOutboundChannelAdapterParserTests.java

@@ -16,14 +16,8 @@
 
 package org.springframework.integration.file.config;
 
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertTrue;
-
-import java.io.File;
-
 import org.junit.Test;
 import org.junit.runner.RunWith;
-
 import org.springframework.beans.DirectFieldAccessor;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.beans.factory.annotation.Qualifier;
@@ -33,6 +27,12 @@ import org.springframework.integration.file.FileWritingMessageHandler;
 import org.springframework.test.context.ContextConfiguration;
 import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
 
+import java.io.File;
+import java.nio.charset.Charset;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
 /**
  * @author Mark Fisher
  * @author Marius Bogoevici
@@ -41,70 +41,83 @@ import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
 @RunWith(SpringJUnit4ClassRunner.class)
 public class FileOutboundChannelAdapterParserTests {
 
-	@Autowired
-	@Qualifier("simpleAdapter")
-	EventDrivenConsumer simpleAdapter;
+    @Autowired
+    @Qualifier("simpleAdapter")
+    EventDrivenConsumer simpleAdapter;
 
-	@Autowired
-	@Qualifier("adapterWithCustomNameGenerator")
-	EventDrivenConsumer adapterWithCustomNameGenerator;
+    @Autowired
+    @Qualifier("adapterWithCustomNameGenerator")
+    EventDrivenConsumer adapterWithCustomNameGenerator;
 
-	@Autowired
-	@Qualifier("adapterWithDeleteFlag")
-	EventDrivenConsumer adapterWithDeleteFlag;
+    @Autowired
+    @Qualifier("adapterWithDeleteFlag")
+    EventDrivenConsumer adapterWithDeleteFlag;
 
-	@Autowired
-	@Qualifier("adapterWithOrder")
-	EventDrivenConsumer adapterWithOrder;
+    @Autowired
+    @Qualifier("adapterWithOrder")
+    EventDrivenConsumer adapterWithOrder;
+
+    @Autowired
+    @Qualifier("adapterWithCharset")
+    EventDrivenConsumer adapterWithCharset;
 
 
-	@Test
-	public void simpleAdapter() {
-		DirectFieldAccessor adapterAccessor = new DirectFieldAccessor(simpleAdapter);
-		FileWritingMessageHandler handler = (FileWritingMessageHandler)
-				adapterAccessor.getPropertyValue("handler");
-		DirectFieldAccessor handlerAccessor = new DirectFieldAccessor(handler);
-		File expected = new File(System.getProperty("java.io.tmpdir"));
-		File actual = (File) handlerAccessor.getPropertyValue("destinationDirectory");
-		assertEquals(expected, actual);
-		assertTrue(handlerAccessor.getPropertyValue("fileNameGenerator") instanceof DefaultFileNameGenerator);
-		assertEquals(Boolean.FALSE, handlerAccessor.getPropertyValue("deleteSourceFiles"));
-	}
+    @Test
+    public void simpleAdapter() {
+        DirectFieldAccessor adapterAccessor = new DirectFieldAccessor(simpleAdapter);
+        FileWritingMessageHandler handler = (FileWritingMessageHandler)
+                adapterAccessor.getPropertyValue("handler");
+        DirectFieldAccessor handlerAccessor = new DirectFieldAccessor(handler);
+        File expected = new File(System.getProperty("java.io.tmpdir"));
+        File actual = (File) handlerAccessor.getPropertyValue("destinationDirectory");
+        assertEquals(expected, actual);
+        assertTrue(handlerAccessor.getPropertyValue("fileNameGenerator") instanceof DefaultFileNameGenerator);
+        assertEquals(Boolean.FALSE, handlerAccessor.getPropertyValue("deleteSourceFiles"));
+    }
 
-	@Test
-	public void adapterWithCustomFileNameGenerator() {
-		DirectFieldAccessor adapterAccessor = new DirectFieldAccessor(adapterWithCustomNameGenerator);
-		FileWritingMessageHandler handler = (FileWritingMessageHandler)
-				adapterAccessor.getPropertyValue("handler");
-		DirectFieldAccessor handlerAccessor = new DirectFieldAccessor(handler);
-		File expected = new File(System.getProperty("java.io.tmpdir"));
-		File actual = (File) handlerAccessor.getPropertyValue("destinationDirectory");
-		assertEquals(expected, actual);
-		assertTrue(handlerAccessor.getPropertyValue("fileNameGenerator") instanceof CustomFileNameGenerator);
-	}
+    @Test
+    public void adapterWithCustomFileNameGenerator() {
+        DirectFieldAccessor adapterAccessor = new DirectFieldAccessor(adapterWithCustomNameGenerator);
+        FileWritingMessageHandler handler = (FileWritingMessageHandler)
+                adapterAccessor.getPropertyValue("handler");
+        DirectFieldAccessor handlerAccessor = new DirectFieldAccessor(handler);
+        File expected = new File(System.getProperty("java.io.tmpdir"));
+        File actual = (File) handlerAccessor.getPropertyValue("destinationDirectory");
+        assertEquals(expected, actual);
+        assertTrue(handlerAccessor.getPropertyValue("fileNameGenerator") instanceof CustomFileNameGenerator);
+    }
 
-	@Test
-	public void adapterWithDeleteFlag() {
-		DirectFieldAccessor adapterAccessor = new DirectFieldAccessor(adapterWithDeleteFlag);
-		FileWritingMessageHandler handler = (FileWritingMessageHandler)
-				adapterAccessor.getPropertyValue("handler");
-		DirectFieldAccessor handlerAccessor = new DirectFieldAccessor(handler);
-		assertEquals(Boolean.TRUE, handlerAccessor.getPropertyValue("deleteSourceFiles"));
-	}
+    @Test
+    public void adapterWithDeleteFlag() {
+        DirectFieldAccessor adapterAccessor = new DirectFieldAccessor(adapterWithDeleteFlag);
+        FileWritingMessageHandler handler = (FileWritingMessageHandler)
+                adapterAccessor.getPropertyValue("handler");
+        DirectFieldAccessor handlerAccessor = new DirectFieldAccessor(handler);
+        assertEquals(Boolean.TRUE, handlerAccessor.getPropertyValue("deleteSourceFiles"));
+    }
 
-	@Test
-	public void adapterWithOrder() {
-		DirectFieldAccessor adapterAccessor = new DirectFieldAccessor(adapterWithOrder);
-		FileWritingMessageHandler handler = (FileWritingMessageHandler)
-				adapterAccessor.getPropertyValue("handler");
-		DirectFieldAccessor handlerAccessor = new DirectFieldAccessor(handler);
-		assertEquals(555, handlerAccessor.getPropertyValue("order"));
-	}
+    @Test
+    public void adapterWithOrder() {
+        DirectFieldAccessor adapterAccessor = new DirectFieldAccessor(adapterWithOrder);
+        FileWritingMessageHandler handler = (FileWritingMessageHandler)
+                adapterAccessor.getPropertyValue("handler");
+        DirectFieldAccessor handlerAccessor = new DirectFieldAccessor(handler);
+        assertEquals(555, handlerAccessor.getPropertyValue("order"));
+    }
 
-	@Test
-	public void adapterWithAutoStartupFalse() {
-		DirectFieldAccessor adapterAccessor = new DirectFieldAccessor(adapterWithOrder);
-		assertEquals(Boolean.FALSE, adapterAccessor.getPropertyValue("autoStartup"));
-	}
+    @Test
+    public void adapterWithAutoStartupFalse() {
+        DirectFieldAccessor adapterAccessor = new DirectFieldAccessor(adapterWithOrder);
+        assertEquals(Boolean.FALSE, adapterAccessor.getPropertyValue("autoStartup"));
+    }
+
+    @Test
+    public void adapterWithCharset() {
+        DirectFieldAccessor adapterAccessor = new DirectFieldAccessor(adapterWithCharset);
+             FileWritingMessageHandler handler = (FileWritingMessageHandler)
+                adapterAccessor.getPropertyValue("handler");
+        DirectFieldAccessor handlerAccessor = new DirectFieldAccessor(handler);
+        assertEquals(Charset.forName("UTF-8"), handlerAccessor.getPropertyValue("charset"));
+    }
 
 }