Add cursor-based ItemReader for MongoDB

Issue #4323

Author: juchanei

spring-batch-infrastructure/src/main/java/org/springframework/batch/item/data/MongoCursorItemReader.java

@@ -0,0 +1,297 @@
+/*
+ * Copyright 2002-2023 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.time.Duration;
+import java.time.temporal.ChronoUnit;
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Stream;
+
+import org.bson.Document;
+import org.bson.codecs.DecoderContext;
+
+import org.springframework.batch.item.support.AbstractItemCountingItemStreamItemReader;
+import org.springframework.beans.factory.InitializingBean;
+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.data.util.CloseableIterator;
+import org.springframework.util.Assert;
+import org.springframework.util.ClassUtils;
+import org.springframework.util.StringUtils;
+
+/**
+ * @author LEE Juchan
+ * @since 5.0
+ */
+public class MongoCursorItemReader<T> extends AbstractItemCountingItemStreamItemReader<T> implements InitializingBean {
+
+    private MongoOperations template;
+
+    private Class<? extends T> targetType;
+
+    private String collection;
+
+    private Query query;
+
+    private String queryString;
+
+    private List<Object> parameterValues = new ArrayList<>();
+
+    private String fields;
+
+    private Sort sort;
+
+    private String hint;
+
+    private Integer batchSize;
+
+    private Integer limit;
+
+    private Integer maxTimeMs;
+
+    private CloseableIterator<? extends T> cursor;
+
+    public MongoCursorItemReader() {
+        super();
+        setName(ClassUtils.getShortName(MongoCursorItemReader.class));
+    }
+
+    /**
+     * 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;
+    }
+
+    /**
+     * The targetType of object to be returned for each {@link #read()} call.
+     * @param targetType the targetType of object to return
+     */
+    public void setTargetType(Class<? extends T> targetType) {
+        this.targetType = targetType;
+    }
+
+    /**
+     * @param collection Mongo collection to be queried.
+     */
+    public void setCollection(String collection) {
+        this.collection = collection;
+    }
+
+    /**
+     * A Mongo Query to be used.
+     * @param query Mongo Query to be used.
+     */
+    public void setQuery(Query query) {
+        this.query = query;
+    }
+
+    /**
+     * 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;
+    }
+
+    /**
+     * {@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);
+    }
+
+    /**
+     * JSON String telling MongoDB what index to use.
+     * @param hint string indicating what index to use.
+     */
+    public void setHint(String hint) {
+        this.hint = hint;
+    }
+
+    /**
+     * The size of batches to use when iterating over results.
+     * @param batchSize size the batch size to apply to the cursor
+     */
+    public void setBatchSize(Integer batchSize) {
+        this.batchSize = batchSize;
+    }
+
+    /**
+     * The query limit
+     * @param limit The limit
+     */
+    public void setLimit(Integer limit) {
+        this.limit = limit;
+    }
+
+    /**
+     * The maximum execution time for the aggregation command
+     * @param maxTimeMs The max time
+     */
+    public void setMaxTimeMs(Integer maxTimeMs) {
+        this.maxTimeMs = maxTimeMs;
+    }
+
+    /**
+     * Checks mandatory properties
+     *
+     * @see InitializingBean#afterPropertiesSet()
+     */
+    @Override
+    public void afterPropertiesSet() {
+        Assert.state(template != null, "An implementation of MongoOperations is required.");
+        Assert.state(targetType != null, "A targetType 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.");
+        }
+    }
+
+    @Override
+    protected void doOpen() throws Exception {
+        Query mongoQuery;
+        if (queryString != null) {
+            mongoQuery = createQuery();
+        } else {
+            mongoQuery = query;
+        }
+
+        Stream<? extends T> stream;
+        if (StringUtils.hasText(collection)) {
+            stream = template.stream(mongoQuery, targetType, collection);
+        } else {
+            stream = template.stream(mongoQuery, targetType);
+        }
+
+        this.cursor = streamToIterator(stream);
+    }
+
+    @Override
+    protected T doRead() throws Exception {
+        return cursor.hasNext() ? cursor.next() : null;
+    }
+
+    @Override
+    protected void doClose() throws Exception {
+        this.cursor.close();
+    }
+
+    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);
+    }
+
+    private Query createQuery() {
+        String populatedQuery = replacePlaceholders(queryString, parameterValues);
+
+        Query mongoQuery;
+        if (StringUtils.hasText(fields)) {
+            mongoQuery = new BasicQuery(populatedQuery, fields);
+        } else {
+            mongoQuery = new BasicQuery(populatedQuery);
+        }
+
+        if (sort != null) {
+            mongoQuery.with(sort);
+        }
+        if (StringUtils.hasText(hint)) {
+            mongoQuery.withHint(hint);
+        }
+        if (batchSize != null) {
+            mongoQuery.cursorBatchSize(batchSize);
+        }
+        if (limit != null) {
+            mongoQuery.limit(limit);
+        }
+        if (maxTimeMs != null) {
+            mongoQuery.maxTime(Duration.of(maxTimeMs, ChronoUnit.MILLIS));
+        } else {
+            mongoQuery.noCursorTimeout();
+        }
+
+        return mongoQuery;
+    }
+
+    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 CloseableIterator<? extends T> streamToIterator(Stream<? extends T> stream) {
+        return new CloseableIterator<>() {
+            final private Iterator<? extends T> delegate = stream.iterator();
+
+            @Override
+            public boolean hasNext() {
+                return delegate.hasNext();
+            }
+
+            @Override
+            public T next() {
+                return delegate.next();
+            }
+
+            @Override
+            public void close() {
+                stream.close();
+            }
+        };
+    }
+
+}