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Apache Commons BeanUtils provides an easy-to-use but flexible wrapper around reflection and introspection.
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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.apache.commons.beanutils2.sql;

import java.sql.Date;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.sql.Time;
import java.sql.Timestamp;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Objects;

import org.apache.commons.beanutils2.DynaBean;
import org.apache.commons.beanutils2.DynaClass;
import org.apache.commons.beanutils2.DynaProperty;

/**
 * 
 * Provides common logic for JDBC implementations of {@link DynaClass}.
 * 
 */
abstract class AbstractJdbcDynaClass implements DynaClass {

    /**
     * Cross Reference for column name --> dyna property name (needed when lowerCase option is true)
     */
    private Map columnNameXref;

    /**
     * 
     * Flag defining whether column names should be lower cased when converted to property names.
     * 
     */
    protected boolean lowerCase = true;

    /**
     * 
     * The set of dynamic properties that are part of this {@link DynaClass}.
     * 
     */
    protected DynaProperty[] properties;

    /**
     * 
     * The set of dynamic properties that are part of this {@link DynaClass}, keyed by the property name. Individual descriptor instances will be the same
     * instances as those in the {@code properties} list.
     * 
     */
    protected Map propertiesMap = new HashMap<>();

    /**
     * 
     * Flag defining whether column names or labels should be used.
     */
    private boolean useColumnLabel;

    /**
     * 

     * Factory method to create a new DynaProperty for the given index into the result set metadata.
     * 
     *
     * @param metadata is the result set metadata
     * @param i        is the column index in the metadata
     * @return the newly created DynaProperty instance
     * @throws SQLException If an error occurs accessing the SQL metadata
     */
    protected DynaProperty createDynaProperty(final ResultSetMetaData metadata, final int i) throws SQLException {
        String columnName = null;
        if (useColumnLabel) {
            columnName = metadata.getColumnLabel(i);
        }
        if (columnName == null || columnName.trim().isEmpty()) {
            columnName = metadata.getColumnName(i);
        }
        final String name = lowerCase ? columnName.toLowerCase() : columnName;
        if (!name.equals(columnName)) {
            if (columnNameXref == null) {
                columnNameXref = new HashMap<>();
            }
            columnNameXref.put(name, columnName);
        }
        String className = null;
        try {
            final int sqlType = metadata.getColumnType(i);
            switch (sqlType) {
            case java.sql.Types.DATE:
                return new DynaProperty(name, java.sql.Date.class);
            case java.sql.Types.TIMESTAMP:
                return new DynaProperty(name, java.sql.Timestamp.class);
            case java.sql.Types.TIME:
                return new DynaProperty(name, java.sql.Time.class);
            default:
                className = metadata.getColumnClassName(i);
            }
        } catch (final SQLException e) {
            // this is a patch for HsqlDb to ignore exceptions
            // thrown by its metadata implementation
        }

        // Default to Object type if no class name could be retrieved
        // from the metadata
        Class clazz = Object.class;
        if (className != null) {
            clazz = loadClass(className);
        }
        return new DynaProperty(name, clazz);
    }

    /**
     * Gets the table column name for the specified property name.
     *
     * @param name The property name
     * @return The column name (which can be different if the lowerCase option is used).
     */
    protected String getColumnName(final String name) {
        if (columnNameXref != null && columnNameXref.containsKey(name)) {
            return columnNameXref.get(name);
        }
        return name;
    }

    /**
     * 
     * Gets an array of {@code PropertyDescriptor} for the properties currently defined in this DynaClass. If no properties are defined, a zero-length array
     * will be returned.
     * 
     */
    @Override
    public DynaProperty[] getDynaProperties() {
        return properties;
    }

    /**
     * 
     * Gets a property descriptor for the specified property, if it exists; otherwise, return {@code null}.
     * 
     *
     * @param name Name of the dynamic property for which a descriptor is requested
     * @throws IllegalArgumentException if no property name is specified
     */
    @Override
    public DynaProperty getDynaProperty(final String name) {
        return propertiesMap.get(Objects.requireNonNull(name, "name"));

    }

    /**
     * 
     * Gets the name of this DynaClass (analogous to the {@code getName() method of java.lang.Class}, which allows the same {@code DynaClass}
     * implementation class to support different dynamic classes, with different sets of properties.
     * 

     */
    @Override
    public String getName() {
        return this.getClass().getName();

    }

    /**
     * Gets a column value from a {@link ResultSet} for the specified name.
     *
     * @param resultSet The result set
     * @param name      The property name
     * @return The value
     * @throws SQLException if an error occurs
     */
    protected Object getObject(final ResultSet resultSet, final String name) throws SQLException {
        final DynaProperty property = getDynaProperty(name);
        if (property == null) {
            throw new IllegalArgumentException("Invalid name '" + name + "'");
        }
        final String columnName = getColumnName(name);
        final Class type = property.getType();

        // java.sql.Date
        if (type.equals(Date.class)) {
            return resultSet.getDate(columnName);
        }

        // java.sql.Timestamp
        if (type.equals(Timestamp.class)) {
            return resultSet.getTimestamp(columnName);
        }

        // java.sql.Time
        if (type.equals(Time.class)) {
            return resultSet.getTime(columnName);
        }

        return resultSet.getObject(columnName);
    }

    /**
     * 
     * Introspect the metadata associated with our result set, and populate the {@code properties and propertiesMap} instance variables.
     * 

     *
     * @param resultSet The {@code resultSet} whose metadata is to be introspected
     * @throws SQLException if an error is encountered processing the result set metadata
     */
    protected void introspect(final ResultSet resultSet) throws SQLException {
        // Accumulate an ordered list of DynaProperties
        final List list = new ArrayList<>();
        final ResultSetMetaData metadata = resultSet.getMetaData();
        final int n = metadata.getColumnCount();
        for (int i = 1; i <= n; i++) { // JDBC is one-relative!
            final DynaProperty dynaProperty = createDynaProperty(metadata, i);
            if (dynaProperty != null) {
                list.add(dynaProperty);
            }
        }

        // Convert this list into the internal data structures we need
        properties = list.toArray(DynaProperty.EMPTY_ARRAY);
        for (final DynaProperty property : properties) {
            propertiesMap.put(property.getName(), property);
        }
    }

    /**
     * 
     * Loads and returns the {@code Class} of the given name. By default, a load from the thread context class loader is attempted. If there is no such class
     * loader, the class loader used to load this class will be utilized.
     * 
     *
     * @param className The name of the class to load
     * @return The loaded class
     * @throws SQLException if an exception was thrown trying to load the specified class
     */
    protected Class loadClass(final String className) throws SQLException {
        try {
            ClassLoader cl = Thread.currentThread().getContextClassLoader();
            if (cl == null) {
                cl = this.getClass().getClassLoader();
            }
            // use Class.forName() - see BEANUTILS-327
            return Class.forName(className, false, cl);
        } catch (final Exception e) {
            throw new SQLException("Cannot load column class '" + className + "': " + e);
        }
    }

    /**
     * 
     * Instantiate and return a new DynaBean instance, associated with this DynaClass. NOTE - This operation is not supported, and throws an
     * exception.
     * 
     *
     * @throws IllegalAccessException if the Class or the appropriate constructor is not accessible
     * @throws InstantiationException if this Class represents an abstract class, an array class, a primitive type, or void; or if instantiation fails for some
     *                                other reason
     */
    @Override
    public DynaBean newInstance() throws IllegalAccessException, InstantiationException {
        throw new UnsupportedOperationException("newInstance() not supported");
    }

    /**
     * Sets whether the column label or name should be used for the property name.
     *
     * @param useColumnLabel true if the column label should be used, otherwise false
     */
    public void setUseColumnLabel(final boolean useColumnLabel) {
        this.useColumnLabel = useColumnLabel;
    }

}