spring-batch MongoItemReader 源码

  • 2022-08-16
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spring-batch MongoItemReader 代码

文件路径:/spring-batch-infrastructure/src/main/java/org/springframework/batch/item/data/MongoItemReader.java

/*
 * Copyright 2012-2022 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
 *
 *      https://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.data;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Map;

import org.bson.Document;
import org.bson.codecs.DecoderContext;

import org.springframework.batch.item.ExecutionContext;
import org.springframework.batch.item.ItemReader;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.data.domain.PageRequest;
import org.springframework.data.domain.Pageable;
import org.springframework.data.domain.Sort;
import org.springframework.data.mongodb.core.MongoOperations;
import org.springframework.data.mongodb.core.query.BasicQuery;
import org.springframework.data.mongodb.core.query.Query;
import org.springframework.data.mongodb.util.json.ParameterBindingDocumentCodec;
import org.springframework.data.mongodb.util.json.ParameterBindingJsonReader;
import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;
import org.springframework.util.StringUtils;

/**
 * <p>
 * Restartable {@link ItemReader} that reads documents from MongoDB via a paging
 * technique.
 * </p>
 *
 * <p>
 * If you set JSON String query {@link #setQuery(String)} then it executes the JSON to
 * retrieve the requested documents.
 * </p>
 *
 * <p>
 * If you set Query object {@link #setQuery(Query)} then it executes the Query to retrieve
 * the requested documents.
 * </p>
 *
 * <p>
 * The query is executed using paged requests specified in the {@link #setPageSize(int)}.
 * Additional pages are requested as needed to provide data when the {@link #read()}
 * method is called.
 * </p>
 *
 * <p>
 * The JSON String query provided supports parameter substitution via ?&lt;index&gt;
 * placeholders where the &lt;index&gt; indicates the index of the parameterValue to
 * substitute.
 * </p>
 *
 * <p>
 * The implementation is thread-safe between calls to {@link #open(ExecutionContext)}, but
 * remember to use <code>saveState=false</code> if used in a multi-threaded client (no
 * restart available).
 * </p>
 *
 * @author Michael Minella
 * @author Takaaki Iida
 * @author Mahmoud Ben Hassine
 * @author Parikshit Dutta
 */
public class MongoItemReader<T> extends AbstractPaginatedDataItemReader<T> implements InitializingBean {

	private MongoOperations template;

	private Query query;

	private String queryString;

	private Class<? extends T> type;

	private Sort sort;

	private String hint;

	private String fields;

	private String collection;

	private List<Object> parameterValues = new ArrayList<>();

	public MongoItemReader() {
		super();
		setName(ClassUtils.getShortName(MongoItemReader.class));
	}

	/**
	 * A Mongo Query to be used.
	 * @param query Mongo Query to be used.
	 */
	public void setQuery(Query query) {
		this.query = query;
	}

	/**
	 * Used to perform operations against the MongoDB instance. Also handles the mapping
	 * of documents to objects.
	 * @param template the MongoOperations instance to use
	 * @see MongoOperations
	 */
	public void setTemplate(MongoOperations template) {
		this.template = template;
	}

	/**
	 * A JSON formatted MongoDB query. Parameterization of the provided query is allowed
	 * via ?&lt;index&gt; placeholders where the &lt;index&gt; indicates the index of the
	 * parameterValue to substitute.
	 * @param queryString JSON formatted Mongo query
	 */
	public void setQuery(String queryString) {
		this.queryString = queryString;
	}

	/**
	 * The type of object to be returned for each {@link #read()} call.
	 * @param type the type of object to return
	 */
	public void setTargetType(Class<? extends T> type) {
		this.type = type;
	}

	/**
	 * {@link List} of values to be substituted in for each of the parameters in the
	 * query.
	 * @param parameterValues values
	 */
	public void setParameterValues(List<Object> parameterValues) {
		Assert.notNull(parameterValues, "Parameter values must not be null");
		this.parameterValues = parameterValues;
	}

	/**
	 * JSON defining the fields to be returned from the matching documents by MongoDB.
	 * @param fields JSON string that identifies the fields to sort by.
	 */
	public void setFields(String fields) {
		this.fields = fields;
	}

	/**
	 * {@link Map} of property
	 * names/{@link org.springframework.data.domain.Sort.Direction} values to sort the
	 * input by.
	 * @param sorts map of properties and direction to sort each.
	 */
	public void setSort(Map<String, Sort.Direction> sorts) {
		Assert.notNull(sorts, "Sorts must not be null");
		this.sort = convertToSort(sorts);
	}

	/**
	 * @param collection Mongo collection to be queried.
	 */
	public void setCollection(String collection) {
		this.collection = collection;
	}

	/**
	 * JSON String telling MongoDB what index to use.
	 * @param hint string indicating what index to use.
	 */
	public void setHint(String hint) {
		this.hint = hint;
	}

	@Override
	@SuppressWarnings("unchecked")
	protected Iterator<T> doPageRead() {
		if (queryString != null) {
			Pageable pageRequest = PageRequest.of(page, pageSize, sort);

			String populatedQuery = replacePlaceholders(queryString, parameterValues);

			Query mongoQuery;

			if (StringUtils.hasText(fields)) {
				mongoQuery = new BasicQuery(populatedQuery, fields);
			}
			else {
				mongoQuery = new BasicQuery(populatedQuery);
			}

			mongoQuery.with(pageRequest);

			if (StringUtils.hasText(hint)) {
				mongoQuery.withHint(hint);
			}

			if (StringUtils.hasText(collection)) {
				return (Iterator<T>) template.find(mongoQuery, type, collection).iterator();
			}
			else {
				return (Iterator<T>) template.find(mongoQuery, type).iterator();
			}

		}
		else {
			Pageable pageRequest = PageRequest.of(page, pageSize);
			query.with(pageRequest);

			if (StringUtils.hasText(collection)) {
				return (Iterator<T>) template.find(query, type, collection).iterator();
			}
			else {
				return (Iterator<T>) template.find(query, type).iterator();
			}
		}
	}

	/**
	 * Checks mandatory properties
	 *
	 * @see InitializingBean#afterPropertiesSet()
	 */
	@Override
	public void afterPropertiesSet() throws Exception {
		Assert.state(template != null, "An implementation of MongoOperations is required.");
		Assert.state(type != null, "A type to convert the input into is required.");
		Assert.state(queryString != null || query != null, "A query is required.");

		if (queryString != null) {
			Assert.state(sort != null, "A sort is required.");
		}
	}

	private String replacePlaceholders(String input, List<Object> values) {
		ParameterBindingJsonReader reader = new ParameterBindingJsonReader(input, values.toArray());
		DecoderContext decoderContext = DecoderContext.builder().build();
		Document document = new ParameterBindingDocumentCodec().decode(reader, decoderContext);
		return document.toJson();
	}

	private Sort convertToSort(Map<String, Sort.Direction> sorts) {
		List<Sort.Order> sortValues = new ArrayList<>(sorts.size());

		for (Map.Entry<String, Sort.Direction> curSort : sorts.entrySet()) {
			sortValues.add(new Sort.Order(curSort.getValue(), curSort.getKey()));
		}

		return Sort.by(sortValues);
	}

}

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