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Merge branch '67-generic-map-converter' into 'dev'
Java: base classes for generic map converter See merge request objectbox/objectbox-java!69
2 parents 8687cc0 + 218eaef commit 5ad9ba0

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‎objectbox-java/src/main/java/io/objectbox/converter/FlexMapConverter.java

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package io.objectbox.converter;
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import io.objectbox.flatbuffers.ArrayReadWriteBuf;
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import io.objectbox.flatbuffers.FlexBuffers;
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import io.objectbox.flatbuffers.FlexBuffersBuilder;
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import java.lang.reflect.Field;
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import java.nio.ByteBuffer;
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import java.util.ArrayList;
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import java.util.HashMap;
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import java.util.List;
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import java.util.Map;
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import java.util.Map.Entry;
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import java.util.concurrent.atomic.AtomicReference;
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/**
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* Converts between {@link Map} properties and byte arrays using FlexBuffers.
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* <p>
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* All keys must have the same type (see {@link #convertToKey(String)}),
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* value types are limited to those supported by FlexBuffers.
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* <p>
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* If any item requires 64 bits for storage in the FlexBuffers Map/Vector (a large Long, a Double)
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* all integers are restored as Long, otherwise Integer.
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*/
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public abstract class FlexMapConverter implements PropertyConverter<Map<Object, Object>, byte[]> {
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private static final AtomicReference<FlexBuffersBuilder> cachedBuilder = new AtomicReference<>();
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@Override
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public byte[] convertToDatabaseValue(Map<Object, Object> map) {
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if (map == null) return null;
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FlexBuffersBuilder builder = cachedBuilder.getAndSet(null);
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if (builder == null) {
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// Note: BUILDER_FLAG_SHARE_KEYS_AND_STRINGS is as fast as no flags for small maps/strings
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// and faster for larger maps/strings. BUILDER_FLAG_SHARE_STRINGS is always slower.
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builder = new FlexBuffersBuilder(
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new ArrayReadWriteBuf(512),
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FlexBuffersBuilder.BUILDER_FLAG_SHARE_KEYS_AND_STRINGS
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);
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}
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addMap(builder, null, map);
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ByteBuffer buffer = builder.finish();
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byte[] out = new byte[buffer.limit()];
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buffer.get(out);
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// Cache if builder does not consume too much memory
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if (buffer.limit() <= 256 * 1024) {
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builder.clear();
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cachedBuilder.getAndSet(builder);
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}
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return out;
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}
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private void addMap(FlexBuffersBuilder builder, String mapKey, Map<Object, Object> map) {
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int mapStart = builder.startMap();
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for (Entry<Object, Object> entry : map.entrySet()) {
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Object value = entry.getValue();
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if (entry.getKey() == null || value == null) {
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throw new IllegalArgumentException("Map keys or values must not be null");
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}
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String key = entry.getKey().toString();
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if (value instanceof Map) {
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//noinspection unchecked
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addMap(builder, key, (Map<Object, Object>) value);
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} else if (value instanceof List) {
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//noinspection unchecked
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addVector(builder, key, (List<Object>) value);
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} else if (value instanceof String) {
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builder.putString(key, (String) value);
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} else if (value instanceof Boolean) {
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builder.putBoolean(key, (Boolean) value);
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} else if (value instanceof Integer) {
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builder.putInt(key, (Integer) value);
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} else if (value instanceof Long) {
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builder.putInt(key, (Long) value);
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} else if (value instanceof Float) {
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builder.putFloat(key, (Float) value);
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} else if (value instanceof Double) {
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builder.putFloat(key, (Double) value);
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} else if (value instanceof byte[]) {
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builder.putBlob(key, (byte[]) value);
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} else {
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throw new IllegalArgumentException(
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"Map values of this type are not supported: " + value.getClass().getSimpleName());
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}
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}
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builder.endMap(mapKey, mapStart);
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}
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private void addVector(FlexBuffersBuilder builder, String vectorKey, List<Object> list) {
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int vectorStart = builder.startVector();
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for (Object item : list) {
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if (item instanceof Map) {
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//noinspection unchecked
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addMap(builder, null, (Map<Object, Object>) item);
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} else if (item instanceof List) {
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//noinspection unchecked
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addVector(builder, null, (List<Object>) item);
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} else if (item instanceof String) {
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builder.putString((String) item);
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} else if (item instanceof Boolean) {
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builder.putBoolean((Boolean) item);
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} else if (item instanceof Integer) {
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builder.putInt((Integer) item);
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} else if (item instanceof Long) {
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builder.putInt((Long) item);
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} else if (item instanceof Float) {
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builder.putFloat((Float) item);
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} else if (item instanceof Double) {
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builder.putFloat((Double) item);
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} else if (item instanceof byte[]) {
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builder.putBlob((byte[]) item);
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} else {
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throw new IllegalArgumentException(
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"List values of this type are not supported: " + item.getClass().getSimpleName());
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}
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}
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builder.endVector(vectorKey, vectorStart, false, false);
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}
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@Override
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public Map<Object, Object> convertToEntityProperty(byte[] databaseValue) {
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if (databaseValue == null) return null;
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FlexBuffers.Map map = FlexBuffers.getRoot(new ArrayReadWriteBuf(databaseValue, databaseValue.length)).asMap();
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return buildMap(map);
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}
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/**
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* Converts a FlexBuffers string map key to the Java map key (e.g. String to Integer).
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* <p>
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* This required conversion restricts all keys (root and embedded maps) to the same type.
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*/
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abstract Object convertToKey(String keyValue);
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/**
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* Returns true if the width in bytes stored in the private parentWidth field of FlexBuffers.Reference is 8.
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* Note: FlexBuffers stores all items in a map/vector using the size of the widest item. However,
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* an item's size is only as wide as needed, e.g. a 64-bit integer (Java Long, 8 bytes) will be
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* reduced to 1 byte if it does not exceed its value range.
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*/
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protected boolean shouldRestoreAsLong(FlexBuffers.Reference reference) {
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try {
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Field parentWidthF = reference.getClass().getDeclaredField("parentWidth");
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parentWidthF.setAccessible(true);
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return (int) parentWidthF.get(reference) == 8;
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} catch (Exception e) {
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// If thrown, it is likely the FlexBuffers API has changed and the above should be updated.
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throw new RuntimeException("FlexMapConverter could not determine FlexBuffers integer bit width.", e);
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}
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}
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private Map<Object, Object> buildMap(FlexBuffers.Map map) {
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// As recommended by docs, iterate keys and values vectors in parallel to avoid binary search of key vector.
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int entryCount = map.size();
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FlexBuffers.KeyVector keys = map.keys();
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FlexBuffers.Vector values = map.values();
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// Note: avoid HashMap re-hashing by choosing large enough initial capacity.
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// From docs: If the initial capacity is greater than the maximum number of entries divided by the load factor,
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// no rehash operations will ever occur.
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// So set initial capacity based on default load factor 0.75 accordingly.
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Map<Object, Object> resultMap = new HashMap<>((int) (entryCount / 0.75 + 1));
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for (int i = 0; i < entryCount; i++) {
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String rawKey = keys.get(i).toString();
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Object key = convertToKey(rawKey);
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FlexBuffers.Reference value = values.get(i);
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if (value.isMap()) {
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resultMap.put(key, buildMap(value.asMap()));
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} else if (value.isVector()) {
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resultMap.put(key, buildList(value.asVector()));
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} else if (value.isString()) {
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resultMap.put(key, value.asString());
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} else if (value.isBoolean()) {
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resultMap.put(key, value.asBoolean());
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} else if (value.isInt()) {
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if (shouldRestoreAsLong(value)) {
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resultMap.put(key, value.asLong());
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} else {
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resultMap.put(key, value.asInt());
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}
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} else if (value.isFloat()) {
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// Always return as double; if original was float casting will give original value.
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resultMap.put(key, value.asFloat());
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} else if (value.isBlob()) {
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resultMap.put(key, value.asBlob().getBytes());
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} else {
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throw new IllegalArgumentException(
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"Map values of this type are not supported: " + value.getClass().getSimpleName());
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}
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}
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return resultMap;
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}
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private List<Object> buildList(FlexBuffers.Vector vector) {
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int itemCount = vector.size();
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List<Object> list = new ArrayList<>(itemCount);
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// FlexBuffers uses the byte width of the biggest item to size all items, so only need to check the first.
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Boolean shouldRestoreAsLong = null;
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for (int i = 0; i < itemCount; i++) {
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FlexBuffers.Reference item = vector.get(i);
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if (item.isMap()) {
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list.add(buildMap(item.asMap()));
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} else if (item.isVector()) {
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list.add(buildList(item.asVector()));
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} else if (item.isString()) {
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list.add(item.asString());
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} else if (item.isBoolean()) {
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list.add(item.asBoolean());
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} else if (item.isInt()) {
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if (shouldRestoreAsLong == null) {
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shouldRestoreAsLong = shouldRestoreAsLong(item);
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}
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if (shouldRestoreAsLong) {
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list.add(item.asLong());
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} else {
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list.add(item.asInt());
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}
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} else if (item.isFloat()) {
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// Always return as double; if original was float casting will give original value.
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list.add(item.asFloat());
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} else if (item.isBlob()) {
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list.add(item.asBlob().getBytes());
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} else {
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throw new IllegalArgumentException(
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"List values of this type are not supported: " + item.getClass().getSimpleName());
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}
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}
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return list;
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}
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}

‎objectbox-java/src/main/java/io/objectbox/converter/IntegerFlexMapConverter.java

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package io.objectbox.converter;
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/**
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* Used to automatically convert {@code Map<Integer, V>}.
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*/
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public class IntegerFlexMapConverter extends FlexMapConverter {
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@Override
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Integer convertToKey(String keyValue) {
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return Integer.valueOf(keyValue);
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}
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}

‎objectbox-java/src/main/java/io/objectbox/converter/IntegerLongMapConverter.java

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package io.objectbox.converter;
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import io.objectbox.flatbuffers.FlexBuffers;
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/**
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* Used to automatically convert {@code Map<Integer, Long>}.
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*/
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public class IntegerLongMapConverter extends IntegerFlexMapConverter {
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@Override
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protected boolean shouldRestoreAsLong(FlexBuffers.Reference reference) {
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return true; // Restore all integers as java.lang.Long.
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}
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}

‎objectbox-java/src/main/java/io/objectbox/converter/LongFlexMapConverter.java

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package io.objectbox.converter;
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/**
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* Used to automatically convert {@code Map<Long, V>}.
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*/
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public class LongFlexMapConverter extends FlexMapConverter {
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@Override
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Object convertToKey(String keyValue) {
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return Long.valueOf(keyValue);
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}
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}

‎objectbox-java/src/main/java/io/objectbox/converter/LongLongMapConverter.java

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package io.objectbox.converter;
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import io.objectbox.flatbuffers.FlexBuffers;
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/**
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* Used to automatically convert {@code Map<Long, Long>}.
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*/
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public class LongLongMapConverter extends LongFlexMapConverter {
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@Override
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protected boolean shouldRestoreAsLong(FlexBuffers.Reference reference) {
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return true; // Restore all integers as java.lang.Long.
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}
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}

‎objectbox-java/src/main/java/io/objectbox/converter/StringFlexMapConverter.java

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package io.objectbox.converter;
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/**
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* Used to automatically convert {@code Map<String, V>}.
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*/
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public class StringFlexMapConverter extends FlexMapConverter {
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@Override
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Object convertToKey(String keyValue) {
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return keyValue;
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}
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}

‎objectbox-java/src/main/java/io/objectbox/converter/StringLongMapConverter.java

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package io.objectbox.converter;
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import io.objectbox.flatbuffers.FlexBuffers;
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/**
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* Used to automatically convert {@code Map<String, Long>}.
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*/
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public class StringLongMapConverter extends StringFlexMapConverter {
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@Override
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protected boolean shouldRestoreAsLong(FlexBuffers.Reference reference) {
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return true; // Restore all integers as java.lang.Long.
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}
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}

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