Added a builder for the StaxEventItemReader

This commit adds a fluent builder for the StaxEventItemReader.

Resolves BATCH-2576

spring-batch-infrastructure/src/main/java/org/springframework/batch/item/xml/builder/StaxEventItemReaderBuilder.java

@@ -0,0 +1,208 @@
+/*
+ * Copyright 2017 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.item.xml.builder;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+import org.springframework.batch.item.xml.StaxEventItemReader;
+import org.springframework.core.io.Resource;
+import org.springframework.oxm.Unmarshaller;
+import org.springframework.util.Assert;
+import org.springframework.util.StringUtils;
+
+/**
+ * A fluent builder for the {@link StaxEventItemReader}
+ *
+ * @author Michael Minella
+ * @since 4.0
+ */
+public class StaxEventItemReaderBuilder<T> {
+
+	private boolean strict = true;
+
+	private Resource resource;
+
+	private Unmarshaller unmarshaller;
+
+	private List<String> fragmentRootElements = new ArrayList<>();
+
+	private int currentItemCount = 0;
+
+	private int maxItemCount = Integer.MAX_VALUE;
+
+	private boolean saveState = true;
+
+	private String name;
+
+	/**
+	 * The name used to calculate the key within the
+	 * {@link org.springframework.batch.item.ExecutionContext}.  Required if
+	 * {@link StaxEventItemReaderBuilder#saveState(boolean)} is set to true.
+	 *
+	 * @param name name of the reader instance
+	 * @return The current instance of the builder.
+	 * @see StaxEventItemReader#setName(String)
+	 */
+	public StaxEventItemReaderBuilder<T> name(String name) {
+		this.name = name;
+
+		return this;
+	}
+
+	/**
+	 * The {@link Resource} to be used as input.
+	 *
+	 * @param resource the input to the reader.
+	 * @return The current instance of the builder.
+	 * @see StaxEventItemReader#setResource(Resource)
+	 */
+	public StaxEventItemReaderBuilder<T> resource(Resource resource) {
+		this.resource = resource;
+
+		return this;
+	}
+
+	/**
+	 * An implementation of the {@link Unmarshaller} from Spring's OXM module.
+	 *
+	 * @param unmarshaller component responsible for unmarshalling XML chunks
+	 * @return The current instance of the builder.
+	 * @see StaxEventItemReader#setUnmarshaller
+	 */
+	public StaxEventItemReaderBuilder<T> unmarshaller(Unmarshaller unmarshaller) {
+		this.unmarshaller = unmarshaller;
+
+		return this;
+	}
+
+	/**
+	 * Adds the list of fragments to be used as the root of each chunk to the configuration.
+	 *
+	 * @param fragmentRootElements the XML root elements to be used to identify XML chunks.
+	 * @return The current instance of the builder.
+	 * @see StaxEventItemReader#setFragmentRootElementNames(String[])
+	 */
+	public StaxEventItemReaderBuilder<T> addFragmentRootElements(String... fragmentRootElements) {
+		this.fragmentRootElements.addAll(Arrays.asList(fragmentRootElements));
+
+		return this;
+	}
+
+	/**
+	 * Adds the list of fragments to be used as the root of each chunk to the configuration.
+	 *
+	 * @param fragmentRootElements the XML root elements to be used to identify XML chunks.
+	 * @return The current instance of the builder.
+	 * @see StaxEventItemReader#setFragmentRootElementNames(String[])
+	 */
+	public StaxEventItemReaderBuilder<T> addFragmentRootElements(List<String> fragmentRootElements) {
+		this.fragmentRootElements.addAll(fragmentRootElements);
+
+		return this;
+	}
+
+	/**
+	 * The starting point for reading (offset number of items).  This value is overriden
+	 * on restart if saveState is set to true.
+	 *
+	 * @param currentItemCount item number to begin at
+	 * @return The current instance of the builder.
+	 * @see StaxEventItemReader#setCurrentItemCount(int)
+	 */
+	public StaxEventItemReaderBuilder<T> currentItemCount(int currentItemCount) {
+		this.currentItemCount = currentItemCount;
+
+		return this;
+	}
+
+	/**
+	 * The maximum number of items to read.
+	 *
+	 * @param maxItemCount max number of items to be read
+	 * @return The current instance of the builder.
+	 * @see StaxEventItemReader#setMaxItemCount(int)
+	 */
+	public StaxEventItemReaderBuilder<T> maxItemCount(int maxItemCount) {
+		this.maxItemCount = maxItemCount;
+
+		return this;
+	}
+
+	/**
+	 * Indicates that the state of the reader should be saved in the
+	 * {@link org.springframework.batch.item.ExecutionContext} for restart.  True by
+	 * default.
+	 *
+	 * @param saveState indicates the state of the reader should be saved
+	 * @return The current instance of the builder.
+	 * @see StaxEventItemReader#setSaveState(boolean)
+	 */
+	public StaxEventItemReaderBuilder<T> saveState(boolean saveState) {
+		this.saveState = saveState;
+
+		return this;
+	}
+
+	/**
+	 * Setting this value to true indicates that it is an error if the input does not
+	 * exist and an exception will be thrown.  Defaults to true.
+	 *
+	 * @param strict indicates the input file must exist
+	 * @return The current instance of the builder
+	 * @see StaxEventItemReader#setStrict(boolean)
+	 */
+	public StaxEventItemReaderBuilder<T> strict(boolean strict) {
+		this.strict = strict;
+
+		return this;
+	}
+
+	/**
+	 * Validates the configuration and builds a new {@link StaxEventItemReader}
+	 *
+	 * @return a new instance of the {@link StaxEventItemReader}
+	 */
+	public StaxEventItemReader<T> build() {
+		Assert.notNull(this.resource, "A resource is required.");
+
+		StaxEventItemReader<T> reader = new StaxEventItemReader<>();
+
+		if(this.saveState) {
+			Assert.state(StringUtils.hasText(this.name),
+					"A name is required when saveState is set to true.");
+		}
+		else {
+			reader.setName(this.name);
+		}
+
+		Assert.notEmpty(this.fragmentRootElements,
+				"At least one fragment root element is required");
+
+		reader.setSaveState(this.saveState);
+		reader.setResource(this.resource);
+		reader.setFragmentRootElementNames(
+				this.fragmentRootElements.toArray(new String[this.fragmentRootElements.size()]));
+
+		reader.setStrict(this.strict);
+		reader.setUnmarshaller(this.unmarshaller);
+		reader.setCurrentItemCount(this.currentItemCount);
+		reader.setMaxItemCount(this.maxItemCount);
+
+		return reader;
+	}
+}