JDBC execute batch only executing last query

Question

I'm trying to execute batch insert queries on MariaDB.

However, I am facing the problem that; I try to execute few insert queries, but only last one is executed.

Here is my code with Java:

private boolean fetchBatches(){
    long[] resultSequences = null;
    MkDbAccessor DA = new MkDbAccessor();

    String befQuery = ConnectionChecker.regularQuery(ftpAttributes.getSqlControlName(), sqlControl.get(1).getServiceName(), false);
    String query = ConnectionChecker.setQuery(befQuery);

    DA.setBatch(query);
    List<String[]> batches = new ArrayList<>();
    for(currentIndex = 0; currentIndex < fileNames.length; currentIndex++){
        if(fileNames[currentIndex] == null || fileNames[currentIndex].isEmpty()){
            continue;
        }

        String[] reqValues = {ftpService.getControlName(), ftpService.getServiceName(), filePath, extension};
        batches.add(reqValues);
    }

    try{
        resultSequences = DA.executeBatch(batches);
    } catch (SQLException e){
        responseCode = 500;
        responseMsg = new StringBuilder("Fail to fetch Database.");
        return false;
    }
    return true;
}

// MkDatabaseAccessor.class
public void setBatch(String query){
    try {
        if (preparedStatement == null) {
            preparedStatement = dbCon.prepareStatement(query, PreparedStatement.RETURN_GENERATED_KEYS);
        }
    } catch (SQLException se){
        se.printStackTrace();
    }
}

public long[] executeBatch(List<String[]> batches) throws SQLException{
    ArrayList<Long> result = new ArrayList<>();
    if(dbCon != null)
    {
        if(this.preparedStatement != null)
        {
            if(this.preparedStatement == null){
                return null;
            }
            if(batches == null || batches.size() == 0){
                return null;
            }

            try {
                for (String[] values : batches) {
                    for (int i = 0; i < values.length; i++) {
                        preparedStatement.setString((i + 1), values[i]);
                    }
                    preparedStatement.addBatch();
                }
            } catch (SQLException se){
                se.printStackTrace();
                return null;
            }

            preparedStatement.executeBatch();

            try(ResultSet generated = preparedStatement.getGeneratedKeys()){
                if(generated.next()) {
                    result.add(generated.getLong(1));
                }
            }
            if(preparedStatement != null)
                preparedStatement.close();

            if(dbCon != null)
                dbCon.close();
            }
    }

    return result.stream().mapToLong(l -> l).toArray();
}

And I'm trying to:

INSERT INTO STR_FILES (controller, service, directory, format) VALUES(?, ?, ?, ?);

And Values are:

set 1: 'free', 'text', 'board/1', 'jpg'

...

set 5: 'anonymous', 'comments', 'comment/1', 'jpg'

But I only query for set 5 is executed, whereas the others are not.

How can I execute batch queries? I read a lot of articles in Stack Overflow, and most problems are creating PreparedStatement inside of loop that I am creating in outside of the loop.

And here is my SQL URI String url = "jdbc:mysql://192.168.0.13:3306/Study?characterEncoding=UTF-8&serverTimezone=UTC&rewriteBatchedStatements=true&useBulkCopyForBatchInsert=true&autoReconnect=true&validationQuery=select 1;";