Add convenience methods in FlatFileItemWriterBuilder to generate delimited files

Resolves BATCH-2696

Author: fmbenhassine

spring-batch-infrastructure/src/main/java/org/springframework/batch/item/file/builder/FlatFileItemWriterBuilder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016 the original author or authors.
+ * Copyright 2016-2018 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.
@@ -15,18 +15,29 @@
  */
 package org.springframework.batch.item.file.builder;
 
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Locale;
+
 import org.springframework.batch.item.file.FlatFileFooterCallback;
 import org.springframework.batch.item.file.FlatFileHeaderCallback;
 import org.springframework.batch.item.file.FlatFileItemWriter;
+import org.springframework.batch.item.file.transform.BeanWrapperFieldExtractor;
+import org.springframework.batch.item.file.transform.DelimitedLineAggregator;
+import org.springframework.batch.item.file.transform.FieldExtractor;
+import org.springframework.batch.item.file.transform.FormatterLineAggregator;
 import org.springframework.batch.item.file.transform.LineAggregator;
 import org.springframework.core.io.Resource;
 import org.springframework.util.Assert;
+import org.springframework.util.StringUtils;
 
 /**
  * A builder implementation for the {@link FlatFileItemWriter}
  *
  * @author Michael Minella
  * @author Glenn Renfro
+ * @author Mahmoud Ben Hassine
  * @since 4.0
  * @see FlatFileItemWriter
  */
@@ -58,6 +69,10 @@ public class FlatFileItemWriterBuilder<T> {
 
 	private String name;
 
+	private DelimitedBuilder<T> delimitedBuilder;
+
+	private FormattedBuilder<T> formattedBuilder;
+
 	/**
 	 * Configure if the state of the {@link org.springframework.batch.item.ItemStreamSupport}
 	 * should be persisted within the {@link org.springframework.batch.item.ExecutionContext}
@@ -155,7 +170,7 @@ public FlatFileItemWriterBuilder<T> encoding(String encoding) {
 	}
 
 	/**
-	 * If set to true, once the step is complete, if the resource previously provdied is
+	 * If set to true, once the step is complete, if the resource previously provided is
 	 * empty, it will be deleted.
 	 *
 	 * @param shouldDelete defaults to false
@@ -234,14 +249,245 @@ public FlatFileItemWriterBuilder<T> transactional(boolean transactional) {
 		return this;
 	}
 
+	/**
+	 * Returns an instance of a {@link DelimitedBuilder} for building a
+	 * {@link DelimitedLineAggregator}. The {@link DelimitedLineAggregator} configured by
+	 * this builder will only be used if one is not explicitly configured via
+	 * {@link FlatFileItemWriterBuilder#lineAggregator}
+	 *
+	 * @return a {@link DelimitedBuilder}
+	 *
+	 */
+	public DelimitedBuilder<T> delimited() {
+		this.delimitedBuilder = new DelimitedBuilder<>(this);
+		return this.delimitedBuilder;
+	}
+
+	/**
+	 * Returns an instance of a {@link FormattedBuilder} for building a
+	 * {@link FormatterLineAggregator}. The {@link FormatterLineAggregator} configured by
+	 * this builder will only be used if one is not explicitly configured via
+	 * {@link FlatFileItemWriterBuilder#lineAggregator}
+	 *
+	 * @return a {@link FormattedBuilder}
+	 *
+	 */
+	public FormattedBuilder<T> formatted() {
+		this.formattedBuilder = new FormattedBuilder<>(this);
+		return this.formattedBuilder;
+	}
+
+	/**
+	 * A builder for constructing a {@link FormatterLineAggregator}.
+	 *
+	 * @param <T> the type of the parent {@link FlatFileItemWriterBuilder}
+	 */
+	public static class FormattedBuilder<T> {
+
+		private FlatFileItemWriterBuilder<T> parent;
+
+		private String format;
+
+		private Locale locale = Locale.getDefault();
+
+		private int maximumLength = 0;
+
+		private int minimumLength = 0;
+
+		private FieldExtractor<T> fieldExtractor;
+
+		private List<String> names = new ArrayList<>();
+
+		protected FormattedBuilder(FlatFileItemWriterBuilder<T> parent) {
+			this.parent = parent;
+		}
+
+		/**
+		 * Set the format string used to aggregate items
+		 * @param format used to aggregate items
+		 * @return The instance of the builder for chaining.
+		 */
+		public FormattedBuilder<T> format(String format) {
+			this.format = format;
+			return this;
+		}
+
+		/**
+		 * Set the locale.
+		 * @param locale to use
+		 * @return The instance of the builder for chaining.
+		 */
+		public FormattedBuilder<T> locale(Locale locale) {
+			this.locale = locale;
+			return this;
+		}
+
+		/**
+		 * Set the minimum length of the formatted string. If this is not set
+		 * the default is to allow any length.
+		 * @param minimumLength of the formatted string
+		 * @return The instance of the builder for chaining.
+		 */
+		public FormattedBuilder<T> minimumLength(int minimumLength) {
+			this.minimumLength = minimumLength;
+			return this;
+		}
+
+		/**
+		 * Set the maximum length of the formatted string. If this is not set
+		 * the default is to allow any length.
+		 * @param maximumLength of the formatted string
+		 * @return The instance of the builder for chaining.
+		 */
+		public FormattedBuilder<T> maximumLength(int maximumLength) {
+			this.maximumLength = maximumLength;
+			return this;
+		}
+
+		/**
+		 * Set the {@link FieldExtractor} to use to extract fields from each item.
+		 * @param fieldExtractor to use to extract fields from each item
+		 * @return The current instance of the builder
+		 */
+		public FlatFileItemWriterBuilder<T> fieldExtractor(FieldExtractor<T> fieldExtractor) {
+			this.fieldExtractor = fieldExtractor;
+			return this.parent;
+		}
+
+		/**
+		 * Names of each of the fields within the fields that are returned in the order
+		 * they occur within the formatted file. These names will be used to create
+		 * a {@link BeanWrapperFieldExtractor} only if no explicit field extractor
+		 * is set via {@link FormattedBuilder#fieldExtractor(FieldExtractor)}.
+		 *
+		 * @param names names of each field
+		 * @return The parent {@link FlatFileItemWriterBuilder}
+		 * @see BeanWrapperFieldExtractor#setNames(String[])
+		 */
+		public FlatFileItemWriterBuilder<T> names(String[] names) {
+			this.names.addAll(Arrays.asList(names));
+			return this.parent;
+		}
+
+		public FormatterLineAggregator<T> build() {
+			Assert.notNull(this.format, "A format is required");
+			Assert.isTrue((this.names != null && !this.names.isEmpty()) || this.fieldExtractor != null,
+					"A list of field names or a field extractor is required");
+
+			FormatterLineAggregator<T> formatterLineAggregator = new FormatterLineAggregator<>();
+			formatterLineAggregator.setFormat(this.format);
+			formatterLineAggregator.setLocale(this.locale);
+			formatterLineAggregator.setMinimumLength(this.minimumLength);
+			formatterLineAggregator.setMaximumLength(this.maximumLength);
+
+			if (this.fieldExtractor == null) {
+				BeanWrapperFieldExtractor<T> beanWrapperFieldExtractor = new BeanWrapperFieldExtractor<>();
+				beanWrapperFieldExtractor.setNames(this.names.toArray(new String[this.names.size()]));
+				try {
+					beanWrapperFieldExtractor.afterPropertiesSet();
+				}
+				catch (Exception e) {
+					throw new IllegalStateException("Unable to initialize FormatterLineAggregator", e);
+				}
+				this.fieldExtractor = beanWrapperFieldExtractor;
+			}
+
+			formatterLineAggregator.setFieldExtractor(this.fieldExtractor);
+			return formatterLineAggregator;
+		}
+	}
+
+	/**
+	 * A builder for constructing a {@link DelimitedLineAggregator}
+	 *
+	 * @param <T> the type of the parent {@link FlatFileItemWriterBuilder}
+	 */
+	public static class DelimitedBuilder<T> {
+
+		private FlatFileItemWriterBuilder<T> parent;
+
+		private List<String> names = new ArrayList<>();
+
+		private String delimiter = ",";
+
+		private FieldExtractor<T> fieldExtractor;
+
+		protected DelimitedBuilder(FlatFileItemWriterBuilder<T> parent) {
+			this.parent = parent;
+		}
+
+		/**
+		 * Define the delimiter for the file.
+		 *
+		 * @param delimiter String used as a delimiter between fields.
+		 * @return The instance of the builder for chaining.
+		 * @see DelimitedLineAggregator#setDelimiter(String)
+		 */
+		public DelimitedBuilder<T> delimiter(String delimiter) {
+			this.delimiter = delimiter;
+			return this;
+		}
+
+		/**
+		 * Names of each of the fields within the fields that are returned in the order
+		 * they occur within the delimited file. These names will be used to create
+		 * a {@link BeanWrapperFieldExtractor} only if no explicit field extractor
+		 * is set via {@link DelimitedBuilder#fieldExtractor(FieldExtractor)}.
+		 *
+		 * @param names names of each field
+		 * @return The parent {@link FlatFileItemWriterBuilder}
+		 * @see BeanWrapperFieldExtractor#setNames(String[])
+		 */
+		public FlatFileItemWriterBuilder<T> names(String[] names) {
+			this.names.addAll(Arrays.asList(names));
+			return this.parent;
+		}
+
+		/**
+		 * Set the {@link FieldExtractor} to use to extract fields from each item.
+		 * @param fieldExtractor to use to extract fields from each item
+		 * @return The parent {@link FlatFileItemWriterBuilder}
+		 */
+		public FlatFileItemWriterBuilder<T> fieldExtractor(FieldExtractor<T> fieldExtractor) {
+			this.fieldExtractor = fieldExtractor;
+			return this.parent;
+		}
+
+		public DelimitedLineAggregator<T> build() {
+			Assert.isTrue((this.names != null && !this.names.isEmpty()) || this.fieldExtractor != null,
+					"A list of field names or a field extractor is required");
+
+			DelimitedLineAggregator<T> delimitedLineAggregator = new DelimitedLineAggregator<>();
+			if (StringUtils.hasLength(this.delimiter)) {
+				delimitedLineAggregator.setDelimiter(this.delimiter);
+			}
+
+			if (this.fieldExtractor == null) {
+				BeanWrapperFieldExtractor<T> beanWrapperFieldExtractor = new BeanWrapperFieldExtractor<>();
+				beanWrapperFieldExtractor.setNames(this.names.toArray(new String[this.names.size()]));
+				try {
+					beanWrapperFieldExtractor.afterPropertiesSet();
+				}
+				catch (Exception e) {
+					throw new IllegalStateException("Unable to initialize DelimitedLineAggregator", e);
+				}
+				this.fieldExtractor = beanWrapperFieldExtractor;
+			}
+
+			delimitedLineAggregator.setFieldExtractor(this.fieldExtractor);
+			return delimitedLineAggregator;
+		}
+	}
+
 	/**
 	 * Validates and builds a {@link FlatFileItemWriter}.
 	 *
 	 * @return a {@link FlatFileItemWriter}
 	 */
 	public FlatFileItemWriter<T> build() {
 
-		Assert.notNull(this.lineAggregator, "A LineAggregator is required");
+		Assert.isTrue(this.lineAggregator != null || this.delimitedBuilder != null || this.formattedBuilder != null,
+				"A LineAggregator or a DelimitedBuilder or a FormattedBuilder is required");
 		Assert.notNull(this.resource, "A Resource is required");
 
 		if(this.saveState) {
@@ -256,6 +502,16 @@ public FlatFileItemWriter<T> build() {
 		writer.setFooterCallback(this.footerCallback);
 		writer.setForceSync(this.forceSync);
 		writer.setHeaderCallback(this.headerCallback);
+		if (this.lineAggregator == null) {
+			Assert.state(this.delimitedBuilder == null || this.formattedBuilder == null,
+					"Either a DelimitedLineAggregator or a FormatterLineAggregator should be provided, but not both");
+			if (this.delimitedBuilder != null) {
+				this.lineAggregator = this.delimitedBuilder.build();
+			}
+			else {
+				this.lineAggregator = this.formattedBuilder.build();
+			}
+		}
 		writer.setLineAggregator(this.lineAggregator);
 		writer.setLineSeparator(this.lineSeparator);
 		writer.setResource(this.resource);