FileEngine.java

/**
 * H2GIS is a library that brings spatial support to the H2 Database Engine
 * <http://www.h2database.com>. H2GIS is developed by CNRS
 * <http://www.cnrs.fr/>.
 *
 * This code is part of the H2GIS project. H2GIS is free software; 
 * you can redistribute it and/or modify it under the terms of the GNU
 * Lesser General Public License as published by the Free Software Foundation;
 * version 3.0 of the License.
 *
 * H2GIS is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License
 * for more details <http://www.gnu.org/licenses/>.
 *
 *
 * For more information, please consult: <http://www.h2gis.org/>
 * or contact directly: info_at_h2gis.org
 */

package org.h2gis.functions.io.file_table;

import org.h2.api.TableEngine;
import org.h2.command.ddl.CreateTableData;
import org.h2.api.ErrorCode;
import org.h2.message.DbException;
import org.h2.table.Column;
import org.h2.table.Table;
import org.h2.util.StringUtils;
import org.h2.value.Value;
import org.h2gis.functions.io.FileDriver;
import org.h2gis.utilities.URIUtilities;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.File;
import java.io.IOException;
import java.util.List;

/**
 * Implement theses abstract methods in order to define a file engine.
 * @author Nicolas Fortin
 * @param <Driver> file driver
 */
public abstract class FileEngine<Driver extends FileDriver> implements TableEngine {
    private Logger LOGGER = LoggerFactory.getLogger(FileEngine.class);

    @Override
    public Table createTable(CreateTableData data) {
        if(data.tableEngineParams.isEmpty()) {
            throw DbException.get(ErrorCode.FILE_NOT_FOUND_1);
        }
        File filePath = URIUtilities.fileFromString(StringUtils.javaDecode(data.tableEngineParams.get(0)));
        if(!filePath.exists()) {
            // Do not throw an exception as it will prevent the user from opening the database
            LOGGER.error("File not found:\n"+filePath.getAbsolutePath()+"\nThe table "+data.tableName+" will be empty.");
            return new DummyTable(data);
        }
        try {
            Driver driver = createDriver(filePath, data.tableEngineParams);
            if(data.columns.isEmpty()) {
                feedCreateTableData(driver, data);
                // Add primary key column
                String pkColumnName = getUniqueColumnName(H2TableIndex.PK_COLUMN_NAME, data.columns);
                Column pk = new Column(pkColumnName, Value.LONG);
                pk.setPrimaryKey(true);
                pk.setNullable(false);
                data.columns.add(0, pk);
            }
            H2Table shpTable = new H2Table(driver, data);
            shpTable.init(data.session);
            return shpTable;
        } catch (IOException ex) {
            throw DbException.get(ErrorCode.IO_EXCEPTION_1,ex);
        }
    }

    /**
     * Compute unique column name among the other columns
     * @param base Returned name if there is no duplicate
     * @param columns Other existing columns
     * @return Unique column name
     */
    public static String getUniqueColumnName(String base, List<Column> columns) {
        String cursor = base;
        int cpt = 2;
        boolean findDuplicate= true;
        while(findDuplicate) {
            findDuplicate = false;
            for (Column column : columns) {
                if (column.getName().equalsIgnoreCase(cursor)) {
                    findDuplicate = true;
                    break;
                }
            }
            if(findDuplicate) {
                cursor = base + Integer.toString(cpt);
            }
        }
        return cursor;
    }
    /**
     * Create the driver instance using the file name and additional arguments provided in SQL create table request.
     * @param filePath First argument, file name
     * @param args Additional argument, contains the file name as first argument
     * @return Instance of FileDriver
     * @throws IOException
     */
    protected  abstract Driver createDriver(File filePath, List<String> args) throws IOException;


    /**
     * Add columns definition of the file into the CreateTableData instance.
     * @param driver driver object
     * @param data Data to initialise
     * @throws java.io.IOException
     */
    protected abstract void feedCreateTableData(Driver driver,CreateTableData data) throws IOException;
}