INT-4155: Port FTP DSL

JIRA: https://jira.spring.io/browse/INT-4155

- Add streaming support
- Rework tests to use dynamic flow registrations due to the test FTP server is now a test support class.

Javadoc fixes

Checkstyle fix

Polishing - PR Comments

Polishing and Port SFTP

spring-integration-file/src/main/java/org/springframework/integration/file/dsl/RemoteFileOutboundGatewaySpec.java

@@ -280,8 +280,22 @@ public abstract class RemoteFileOutboundGatewaySpec<F, S extends RemoteFileOutbo
 		return _this();
 	}
 
+	/**
+	 * Specify a simple pattern to match remote files (e.g. '*.txt').
+	 * @param pattern the pattern.
+	 * @return the spec.
+	 * @see org.springframework.integration.file.filters.AbstractSimplePatternFileListFilter
+	 * @see #filter(org.springframework.integration.file.filters.FileListFilter)
+	 */
 	public abstract S patternFileNameFilter(String pattern);
 
+	/**
+	 * Specify a simple pattern to match remote files (e.g. '[0-9].*.txt').
+	 * @param regex the regex pattern.
+	 * @return the spec.
+	 * @see org.springframework.integration.file.filters.AbstractRegexPatternFileListFilter
+	 * @see #filter(org.springframework.integration.file.filters.FileListFilter)
+	 */
 	public abstract S regexFileNameFilter(String regex);
 
 }

spring-integration-file/src/main/java/org/springframework/integration/file/dsl/RemoteFileStreamingInboundChannelAdapterSpec.java

@@ -0,0 +1,128 @@
+/*
+ * Copyright 2016 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.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.integration.file.dsl;
+
+import java.util.function.Function;
+
+import org.springframework.expression.Expression;
+import org.springframework.integration.dsl.MessageSourceSpec;
+import org.springframework.integration.expression.FunctionExpression;
+import org.springframework.integration.file.filters.CompositeFileListFilter;
+import org.springframework.integration.file.filters.FileListFilter;
+import org.springframework.integration.file.remote.AbstractRemoteFileStreamingMessageSource;
+import org.springframework.integration.file.remote.synchronizer.AbstractInboundFileSynchronizingMessageSource;
+import org.springframework.messaging.Message;
+
+/**
+ * A {@link MessageSourceSpec} for an {@link AbstractInboundFileSynchronizingMessageSource}.
+ *
+ * @param <F> the target file type.
+ * @param <S> the target {@link RemoteFileStreamingInboundChannelAdapterSpec} implementation type.
+ * @param <MS> the target {@link AbstractInboundFileSynchronizingMessageSource} implementation type.
+ *
+ * @author Gary Russell
+ *
+ * @since 5.0
+ */
+public abstract class
+	RemoteFileStreamingInboundChannelAdapterSpec<F, S extends RemoteFileStreamingInboundChannelAdapterSpec<F, S, MS>,
+		MS extends AbstractRemoteFileStreamingMessageSource<F>>
+		extends MessageSourceSpec<S, MS> {
+
+	private CompositeFileListFilter<F> filter;
+
+	/**
+	 * Configure the file name path separator used by the remote system. Defaults to '/'.
+	 * @param remoteFileSeparator the remoteFileSeparator.
+	 * @return the spec.
+	 */
+	public S remoteFileSeparator(String remoteFileSeparator) {
+		this.target.setRemoteFileSeparator(remoteFileSeparator);
+		return _this();
+	}
+
+	/**
+	 * Specify the full path to the remote directory.
+	 * @param remoteDirectory the remoteDirectory.
+	 * @return the spec.
+	 * @see AbstractRemoteFileStreamingMessageSource#setRemoteDirectory(String)
+	 */
+	public S remoteDirectory(String remoteDirectory) {
+		this.target.setRemoteDirectory(remoteDirectory);
+		return _this();
+	}
+
+	/**
+	 * Specify an expression that evaluates to the full path to the remote directory.
+	 * @param remoteDirectoryExpression The remote directory expression.
+	 * @return the spec.
+	 */
+	public S remoteDirectory(Expression remoteDirectoryExpression) {
+		this.target.setRemoteDirectoryExpression(remoteDirectoryExpression);
+		return _this();
+	}
+
+	/**
+	 * Specify a function that is invoked to determine the full path to the remote directory.
+	 * @param remoteDirectoryFunction The remote directory function.
+	 * @return the spec.
+	 */
+	public S remoteDirectory(Function<Message<?>, String> remoteDirectoryFunction) {
+		this.target.setRemoteDirectoryExpression(new FunctionExpression<>(remoteDirectoryFunction));
+		return _this();
+	}
+
+	/**
+	 * Configure a {@link FileListFilter} to be applied to the remote files before
+	 * copying them.
+	 * @param filter the filter.
+	 * @return the spec.
+	 */
+	public S filter(FileListFilter<F> filter) {
+		if (this.filter == null) {
+			if (filter instanceof CompositeFileListFilter) {
+				this.filter = (CompositeFileListFilter<F>) filter;
+			}
+			else {
+				this.filter = new CompositeFileListFilter<F>();
+				this.filter.addFilter(filter);
+			}
+			this.target.setFilter(this.filter);
+		}
+		else {
+			this.filter.addFilter(filter);
+		}
+		return _this();
+	}
+
+	/**
+	 * Configure a simple pattern filter (e.g. '*.txt').
+	 * @param pattern the pattern.
+	 * @return the spec.
+	 * @see #filter(FileListFilter)
+	 */
+	public abstract S patternFilter(String pattern);
+
+	/**
+	 * Configure a regex pattern filter (e.g. '[0-9].*.txt').
+	 * @param regex the regex.
+	 * @return the spec.
+	 * @see #filter(FileListFilter)
+	 */
+	public abstract S regexFilter(String regex);
+
+}

spring-integration-file/src/test/java/org/springframework/integration/file/remote/RemoteFileTestSupport.java

@@ -57,6 +57,10 @@ public abstract class RemoteFileTestSupport {
 		return targetRemoteDirectory;
 	}
 
+	public String getTargetRemoteDirectoryName() {
+		return targetRemoteDirectory.getAbsolutePath() + File.separator;
+	}
+
 	public File getSourceLocalDirectory() {
 		return sourceLocalDirectory;
 	}
@@ -65,6 +69,10 @@ public abstract class RemoteFileTestSupport {
 		return targetLocalDirectory;
 	}
 
+	public String getTargetLocalDirectoryName() {
+		return targetLocalDirectory.getAbsolutePath() + File.separator;
+	}
+
 	/**
 	 * Default implementation creates the following folder structures:
 	 *