assertTrue(extraFieldNames.contains("custom_field"));
        assertFalse(extraFieldNames.contains("_id"), "Reserved field _id should be excluded");
        assertFalse(extraFieldNames.contains("_version"), "Reserved field _version should be excluded");
        assertFalse(extraFieldNames.contains("_seq_no"), "Reserved field _seq_no should be excluded");

                    return "doc_id";
                case FessConfig.INDEX_FIELD_ID:
                    return "id";
                case FessConfig.INDEX_FIELD_VERSION:
                    return "_version";
                case FessConfig.INDEX_FIELD_seq_no:
                    return "_seq_no";
                case FessConfig.INDEX_FIELD_primary_term:
                    return "_primary_term";

        }

        @Override
        public String getIndexFieldId() {
            return "_id";
        }

        @Override
        public String getIndexFieldVersion() {
            return "_version";
        }

        @Override
        public String getIndexFieldSeqNo() {
            return "_seq_no";
        }

        @Override
        public String getIndexFieldPrimaryTerm() {

index.field.url=url
# Field name for document ID in the index.
index.field.doc_id=doc_id
# Field name for internal ID in the index.
index.field.id=_id
# Field name for version in the index.
index.field.version=_version
# Field name for sequence number in the index.
index.field.seq_no=_seq_no
# Field name for primary term in the index.
index.field.primary_term=_primary_term
# Field name for language in the index.

     */
    String getIndexFieldId();

    /**
     * Get the value for the key 'index.field.version'. <br>
     * The value is, e.g. _version <br>
     * comment: Field name for version in the index.
     * @return The value of found property. (NotNull: if not found, exception but basically no way)
     */
    String getIndexFieldVersion();

    /**

        assertEquals(11, JvmUtil.getJavaVersion());

        System.setProperty("java.version", "17_0_2");
        assertEquals(17, JvmUtil.getJavaVersion());

        System.setProperty("java.version", "8.0.332");
        assertEquals(8, JvmUtil.getJavaVersion());

        // Edge case: version starts with 1 but not old format
        System.setProperty("java.version", "18.0.1");

        String id1 = event.getId();
        String id2 = event.getId();
        assertEquals(id1, id2);

        Long version1 = event.getVersionNo();
        Long version2 = event.getVersionNo();
        assertEquals(version1, version2);

        String type1 = event.getEventType();
        String type2 = event.getEventType();
        assertEquals(type1, type2);

                if (url.contains("maven-metadata.xml")) {
                    return "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n" + "<metadata>\n" + "  <versioning>\n" + "    <versions>\n"
                            + "      <version>1.0.0</version>\n" + "      <version>2.0.0</version>\n" + "    </versions>\n"
                            + "  </versioning>\n" + "</metadata>";
                }

/*
 * Copyright 2012-2025 CodeLibs Project and the Others.
 *
 * 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,

/*
 * Copyright 2012-2025 CodeLibs Project and the Others.
 *
 * 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,