INT-3494: Resolve dir for writing as a Resource (#3109)

* INT-3494: Resolve dir for writing as a Resource

JIRA: https://jira.spring.io/browse/INT-3494

The expression for local directory can be resolved into a `Resource`
or resource location.
* Fix `ExpressionUtils.expressionToFile()` to support `Resource` and
also use `ResourceUtils.getFile(path)` when expression result is a string
* Modify tests to ensure that resource is resolved properly
* Upgrade affected tests to JUnit 5
* Mention an new functionality in docs

* * Improve Java doc for `ExpressionUtils.expressionToFile()`
* Finish the sentence in the `file.adoc`

Author: artembilan

spring-integration-core/src/main/java/org/springframework/integration/expression/ExpressionUtils.java

@@ -17,6 +17,8 @@
 package org.springframework.integration.expression;
 
 import java.io.File;
+import java.io.FileNotFoundException;
+import java.io.IOException;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
@@ -25,6 +27,7 @@
 import org.springframework.context.expression.BeanFactoryResolver;
 import org.springframework.context.expression.MapAccessor;
 import org.springframework.core.convert.ConversionService;
+import org.springframework.core.io.Resource;
 import org.springframework.expression.EvaluationContext;
 import org.springframework.expression.Expression;
 import org.springframework.expression.ExpressionParser;
@@ -39,6 +42,7 @@
 import org.springframework.lang.Nullable;
 import org.springframework.messaging.Message;
 import org.springframework.util.Assert;
+import org.springframework.util.ResourceUtils;
 
 /**
  * Utility class with static methods for helping with evaluation of SpEL expressions.
@@ -53,7 +57,7 @@ public final class ExpressionUtils {
 
 	private static final ExpressionParser EXPRESSION_PARSER = new SpelExpressionParser();
 
-	private static final Log logger = LogFactory.getLog(ExpressionUtils.class);
+	private static final Log LOGGER = LogFactory.getLog(ExpressionUtils.class);
 
 	private ExpressionUtils() {
 		super();
@@ -84,7 +88,7 @@ public static SimpleEvaluationContext createSimpleEvaluationContext() {
 	 */
 	public static StandardEvaluationContext createStandardEvaluationContext(@Nullable BeanFactory beanFactory) {
 		if (beanFactory == null) {
-			logger.warn("Creating EvaluationContext with no beanFactory", new RuntimeException("No beanFactory"));
+			LOGGER.warn("Creating EvaluationContext with no beanFactory", new RuntimeException("No beanFactory"));
 		}
 		return (StandardEvaluationContext) doCreateContext(beanFactory, false);
 	}
@@ -98,7 +102,7 @@ public static StandardEvaluationContext createStandardEvaluationContext(@Nullabl
 	 */
 	public static SimpleEvaluationContext createSimpleEvaluationContext(@Nullable BeanFactory beanFactory) {
 		if (beanFactory == null) {
-			logger.warn("Creating EvaluationContext with no beanFactory", new RuntimeException("No beanFactory"));
+			LOGGER.warn("Creating EvaluationContext with no beanFactory", new RuntimeException("No beanFactory"));
 		}
 		return (SimpleEvaluationContext) doCreateContext(beanFactory, true);
 	}
@@ -161,36 +165,56 @@ private static EvaluationContext createEvaluationContext(@Nullable ConversionSer
 	 * @param expression the expression.
 	 * @param evaluationContext the evaluation context.
 	 * @param message the message (if available).
-	 * @param name the name of the result of the evaluation.
+	 * @param propertyName the property name the expression is evaluated for.
 	 * @return the File.
 	 * @since 5.0
 	 */
 	public static File expressionToFile(Expression expression, EvaluationContext evaluationContext,
-			@Nullable Message<?> message, String name) {
-
-		File file;
-		Object value = message == null
-				? expression.getValue(evaluationContext)
-				: expression.getValue(evaluationContext, message);
-		if (value == null) {
-			throw new IllegalStateException(String.format("The provided %s expression (%s) must not evaluate to null.",
-					name, expression.getExpressionString()));
-		}
-		else if (value instanceof File) {
-			file = (File) value;
+			@Nullable Message<?> message, String propertyName) {
+
+		Object value =
+				message == null
+						? expression.getValue(evaluationContext)
+						: expression.getValue(evaluationContext, message);
+
+		Assert.state(value != null, () ->
+				String.format("The provided %s expression (%s) must not evaluate to null.",
+						propertyName, expression.getExpressionString()));
+
+		if (value instanceof File) {
+			return (File) value;
 		}
 		else if (value instanceof String) {
 			String path = (String) value;
-			Assert.hasText(path, String.format("Unable to resolve %s for the provided Expression '%s'.", name,
+			Assert.hasText(path, String.format("Unable to resolve %s for the provided Expression '%s'.", propertyName,
 					expression.getExpressionString()));
-			file = new File(path);
+			try {
+				return ResourceUtils.getFile(path);
+			}
+			catch (FileNotFoundException ex) {
+				throw new IllegalStateException(
+						String.format("Unable to resolve %s for the provided Expression '%s'.",
+								propertyName, expression.getExpressionString()),
+						ex);
+			}
+		}
+		else if (value instanceof Resource) {
+			try {
+				return ((Resource) value).getFile();
+			}
+			catch (IOException ex) {
+				throw new IllegalStateException(
+						String.format("Unable to resolve %s for the provided Expression '%s'.",
+								propertyName, expression.getExpressionString()),
+						ex);
+			}
 		}
 		else {
 			throw new IllegalStateException(String.format(
-					"The provided %s expression (%s) must evaluate to type java.io.File or String, not %s.", name,
+					"The provided %s expression (%s) must evaluate to type java.io.File, String " +
+							"or org.springframework.core.io.Resource, not %s.", propertyName,
 					expression.getExpressionString(), value.getClass().getName()));
 		}
-		return file;
 	}
 
 	/**

spring-integration-file/src/test/java/org/springframework/integration/file/FileOutboundChannelAdapterInsideChainTests-context.xml

@@ -18,7 +18,7 @@
 		<si:header-enricher>
 			<si:header name="#{T(org.springframework.integration.file.FileHeaders).FILENAME}" value="${test.file}"/>
 		</si:header-enricher>
-		<file:outbound-channel-adapter id="file-outbound-channel-adapter-within-chain" directory="${work.dir}"/>
+		<file:outbound-channel-adapter id="file-outbound-channel-adapter-within-chain" directory-expression="${work.dir}"/>
 	</si:chain>
 
 	<bean id="placeholderProperties" class="org.springframework.beans.factory.config.PropertiesFactoryBean">

spring-integration-file/src/test/java/org/springframework/integration/file/FileOutboundChannelAdapterInsideChainTests.java

@@ -22,69 +22,47 @@
 import java.io.IOException;
 import java.util.Properties;
 
-import org.junit.AfterClass;
-import org.junit.BeforeClass;
-import org.junit.Test;
-import org.junit.runner.RunWith;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.integration.support.MessageBuilder;
 import org.springframework.messaging.Message;
 import org.springframework.messaging.MessageChannel;
-import org.springframework.test.context.ContextConfiguration;
-import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
+import org.springframework.test.context.junit.jupiter.SpringJUnitConfig;
 import org.springframework.util.FileCopyUtils;
 
 /**
- * //INT-2275
- *
  * @author Artem Bilan
  * @author Gary Russell
  */
-@ContextConfiguration
-@RunWith(SpringJUnit4ClassRunner.class)
+@SpringJUnitConfig
 public class FileOutboundChannelAdapterInsideChainTests {
 
-	public static final String TEST_FILE_NAME = FileOutboundChannelAdapterInsideChainTests.class.getSimpleName();
+	static final String TEST_FILE_NAME = FileOutboundChannelAdapterInsideChainTests.class.getSimpleName();
 
-	public static final String WORK_DIR_NAME = System.getProperty("java.io.tmpdir") + "/" + FileOutboundChannelAdapterInsideChainTests.class.getSimpleName() + "Dir";
+	static final String SAMPLE_CONTENT = "test";
 
-	public static final String SAMPLE_CONTENT = "test";
+	@TempDir
+	static File WORK_DIR;
 
 	public static Properties placeholderProperties = new Properties();
 
-	static {
-		placeholderProperties.put("test.file", TEST_FILE_NAME);
-		placeholderProperties.put("work.dir", WORK_DIR_NAME);
-	}
-
 	@Autowired
 	private MessageChannel outboundChainChannel;
 
-	private static File workDir;
-
-	@BeforeClass
-	public static void setupClass() {
-		workDir = new File(WORK_DIR_NAME);
-		workDir.mkdir();
-		workDir.deleteOnExit();
-	}
-
-	@AfterClass
-	public static void cleanUp() {
-		if (workDir != null && workDir.exists()) {
-			for (File file : workDir.listFiles()) {
-				file.delete();
-			}
-		}
-		workDir.delete();
+	@BeforeAll
+	static void setupClass() {
+		placeholderProperties.put("test.file", TEST_FILE_NAME);
+		placeholderProperties.put("work.dir", "'file://" + WORK_DIR.getAbsolutePath() + '\'');
 	}
 
-	@Test //INT-2275
-	public void testFileOutboundChannelAdapterWithinChain() throws IOException {
+	@Test
+	void testFileOutboundChannelAdapterWithinChain() throws IOException {
 		Message<String> message = MessageBuilder.withPayload(SAMPLE_CONTENT).build();
 		outboundChainChannel.send(message);
-		File testFile = new File(workDir, TEST_FILE_NAME);
+		File testFile = new File(WORK_DIR, TEST_FILE_NAME);
 		assertThat(testFile.exists()).isTrue();
 		byte[] testFileContent = FileCopyUtils.copyToByteArray(testFile);
 		assertThat(SAMPLE_CONTENT).isEqualTo(new String(testFileContent));