OPEN - issue BATCH-371: FlatFileItemWriter no longer uses LineAggregator

http://jira.springframework.org/browse/BATCH-371

Moved existing default transformer out to a top level class, and introduce lineAggregatorItemTransformer as an option.  I still don't see a good way to get a String[] in to it reliably.

spring-batch-infrastructure/src/main/java/org/springframework/batch/io/file/FlatFileItemWriter.java

@@ -24,12 +24,11 @@ import java.io.IOException;
 import java.nio.channels.Channels;
 import java.nio.channels.FileChannel;
 import java.nio.charset.UnsupportedCharsetException;
-import java.util.Collection;
-import java.util.Iterator;
 import java.util.Properties;
 
 import org.springframework.batch.io.exception.BatchCriticalException;
 import org.springframework.batch.io.exception.BatchEnvironmentException;
+import org.springframework.batch.io.file.transform.RecursiveCollectionItemTransformer;
 import org.springframework.batch.io.support.AbstractTransactionalIoSource;
 import org.springframework.batch.item.ExecutionContext;
 import org.springframework.batch.item.ItemStream;
@@ -75,15 +74,7 @@ public class FlatFileItemWriter extends AbstractTransactionalIoSource implements
 
 	private OutputState state = null;
 
-	private ItemTransformer transformer = new ItemTransformer() {
-		public Object transform(Object input) {
-			return "" + input;
-		}
-	};
-
-	private static class BooleanHolder {
-		public boolean value;
-	}
+	private ItemTransformer transformer = new RecursiveCollectionItemTransformer();
 
 	/**
 	 * Assert that mandatory properties (resource) are set.
@@ -128,51 +119,7 @@ public class FlatFileItemWriter extends AbstractTransactionalIoSource implements
 	 * @throws Exception if the transformer or file output fail
 	 */
 	public void write(Object data) throws Exception {
-		transformAndWrite(data, new BooleanHolder());
-	}
-
-	/**
-	 * Convert the date to a format that can be output and then write it out.
-	 * @param data
-	 * @param converted
-	 * @throws Exception
-	 */
-	private void transformAndWrite(Object data, BooleanHolder converted) throws Exception {
-
-		if (data instanceof Collection) {
-			converted.value = false;
-			for (Iterator iterator = ((Collection) data).iterator(); iterator.hasNext();) {
-				Object value = (Object) iterator.next();
-				// (recursive)
-				write(value);
-			}
-			return;
-		}
-		if (data.getClass().isArray()) {
-			converted.value = false;
-			Object[] array = (Object[]) data;
-			for (int i = 0; i < array.length; i++) {
-				Object value = array[i];
-				// (recursive)
-				write(value);
-			}
-			return;
-		}
-		if (data instanceof String) {
-			// This is where the output stream is actually written to
-			getOutputState().write(data + LINE_SEPARATOR);
-		}
-		else if (!converted.value) {
-			// (recursive)
-			converted.value = true;
-			transformAndWrite(transformer.transform(data), converted);
-			return;
-		}
-		else {
-			// Should not happen...
-			throw new IllegalStateException(
-					"Infinite loop detected - converter did not convert to String or collection/array of objects convertible to String.");
-		}
+		getOutputState().write(transformer.transform(data) + LINE_SEPARATOR);
 	}
 
 	/**

spring-batch-infrastructure/src/main/java/org/springframework/batch/io/file/transform/LineAggregatorItemTransformer.java

@@ -0,0 +1,48 @@
+/*
+ * Copyright 2006-2007 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.batch.io.file.transform;
+
+import org.springframework.batch.item.writer.ItemTransformer;
+
+/**
+ * An {@link ItemTransformer} that expects a String[] as input and delegates to
+ * a {@link LineAggregator}.
+ * 
+ * @author Dave Syer
+ * 
+ */
+public class LineAggregatorItemTransformer implements ItemTransformer {
+
+	private LineAggregator aggregator = new DelimitedLineAggregator();
+
+	/**
+	 * Public setter for the {@link LineAggregator}.
+	 * @param aggregator the aggregator to set
+	 */
+	public void setAggregator(LineAggregator aggregator) {
+		this.aggregator = aggregator;
+	}
+
+	/**
+	 * Assume the item is an array of String (no check is made) and delegate to
+	 * the aggregator.
+	 * 
+	 * @see org.springframework.batch.item.writer.ItemTransformer#transform(java.lang.Object)
+	 */
+	public Object transform(Object item) throws Exception {
+		return aggregator.aggregate((String[]) item);
+	}
+}

spring-batch-infrastructure/src/main/java/org/springframework/batch/io/file/transform/RecursiveCollectionItemTransformer.java

@@ -0,0 +1,91 @@
+package org.springframework.batch.io.file.transform;
+
+import java.util.Collection;
+import java.util.Iterator;
+
+import org.springframework.batch.item.writer.ItemTransformer;
+
+/**
+ * An implementation of {@link ItemTransformer} that just calls toString() on
+ * its argument, unless it it an array or collection, in which case it loops
+ * though, calling itself on each member in turn, concatenating the result with
+ * line separators.
+ * 
+ * @author Dave Syer
+ * 
+ */
+public class RecursiveCollectionItemTransformer implements ItemTransformer {
+
+	private static final String LINE_SEPARATOR = System.getProperty("line.separator");
+
+	/* (non-Javadoc)
+	 * @see org.springframework.batch.item.writer.ItemTransformer#transform(java.lang.Object)
+	 */
+	public Object transform(Object input) {
+		TransformHolder holder = new TransformHolder();
+		transformRecursively(input, holder);
+		String result = holder.builder.toString();
+		return result.substring(0, result.lastIndexOf(LINE_SEPARATOR));
+	}
+
+	public String stringify(Object input) {
+		return "" + input;
+	}
+
+	/**
+	 * Convert the date to a format that can be output and then write it out.
+	 * @param data
+	 * @param converted
+	 * @throws Exception
+	 */
+	private void transformRecursively(Object data, TransformHolder converted) {
+
+		if (data instanceof Collection) {
+			converted.value = false;
+			for (Iterator iterator = ((Collection) data).iterator(); iterator.hasNext();) {
+				Object value = (Object) iterator.next();
+				// (recursive)
+				transformRecursively(value, new TransformHolder(converted.builder));
+			}
+			return;
+		}
+		if (data.getClass().isArray()) {
+			converted.value = false;
+			Object[] array = (Object[]) data;
+			for (int i = 0; i < array.length; i++) {
+				Object value = array[i];
+				// (recursive)
+				transformRecursively(value, new TransformHolder(converted.builder));
+			}
+			return;
+		}
+		if (data instanceof String) {
+			// This is where the output stream is actually written to
+			converted.builder.append(data + LINE_SEPARATOR);
+		}
+		else if (!converted.value) {
+			// (recursive)
+			converted.value = true;
+			transformRecursively(stringify(data), converted);
+			return;
+		}
+		else {
+			// Should not happen...
+			throw new IllegalStateException(
+					"Infinite loop detected - converter did not convert to String or collection/array of objects convertible to String.");
+		}
+	}
+
+	private static class TransformHolder {
+		boolean value;
+
+		StringBuilder builder = new StringBuilder();
+
+		TransformHolder() {
+		}
+
+		TransformHolder(StringBuilder builder) {
+			this.builder = builder;
+		}
+	}
+}