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The MyBatis SQL mapper framework makes it easier to use a relational database with object-oriented applications. MyBatis couples objects with stored procedures or SQL statements using a XML descriptor or annotations. Simplicity is the biggest advantage of the MyBatis data mapper over object relational mapping tools.
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/**
 *    Copyright 2009-2016 the original author or authors.
 *
 *    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,
 *    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.ibatis.executor.resultset;

import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.Set;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.mapping.ResultMap;
import org.apache.ibatis.session.Configuration;
import org.apache.ibatis.type.JdbcType;
import org.apache.ibatis.type.ObjectTypeHandler;
import org.apache.ibatis.type.TypeHandler;
import org.apache.ibatis.type.TypeHandlerRegistry;
import org.apache.ibatis.type.UnknownTypeHandler;

/**
 * @author Iwao AVE!
 */
public class ResultSetWrapper {

  private final ResultSet resultSet;
  private final TypeHandlerRegistry typeHandlerRegistry;
  private final List columnNames = new ArrayList();
  private final List classNames = new ArrayList();
  private final List jdbcTypes = new ArrayList();
  private final Map, TypeHandler>> typeHandlerMap = new HashMap, TypeHandler>>();
  private Map> mappedColumnNamesMap = new HashMap>();
  private Map> unMappedColumnNamesMap = new HashMap>();

  public ResultSetWrapper(ResultSet rs, Configuration configuration) throws SQLException {
    super();
    this.typeHandlerRegistry = configuration.getTypeHandlerRegistry();
    this.resultSet = rs;
    final ResultSetMetaData metaData = rs.getMetaData();
    final int columnCount = metaData.getColumnCount();
    for (int i = 1; i <= columnCount; i++) {
      columnNames.add(configuration.isUseColumnLabel() ? metaData.getColumnLabel(i) : metaData.getColumnName(i));
      jdbcTypes.add(JdbcType.forCode(metaData.getColumnType(i)));
      classNames.add(metaData.getColumnClassName(i));
    }
  }

  public ResultSet getResultSet() {
    return resultSet;
  }

  public List getColumnNames() {
    return this.columnNames;
  }

  public List getClassNames() {
    return Collections.unmodifiableList(classNames);
  }

  public JdbcType getJdbcType(String columnName) {
    for (int i = 0 ; i < columnNames.size(); i++) {
      if (columnNames.get(i).equalsIgnoreCase(columnName)) {
        return jdbcTypes.get(i);
      }
    }
    return null;
  }

  /**
   * Gets the type handler to use when reading the result set.
   * Tries to get from the TypeHandlerRegistry by searching for the property type.
   * If not found it gets the column JDBC type and tries to get a handler for it.
   * 
   * @param propertyType
   * @param columnName
   * @return
   */
  public TypeHandler getTypeHandler(Class propertyType, String columnName) {
    TypeHandler handler = null;
    Map, TypeHandler> columnHandlers = typeHandlerMap.get(columnName);
    if (columnHandlers == null) {
      columnHandlers = new HashMap, TypeHandler>();
      typeHandlerMap.put(columnName, columnHandlers);
    } else {
      handler = columnHandlers.get(propertyType);
    }
    if (handler == null) {
      JdbcType jdbcType = getJdbcType(columnName);
      handler = typeHandlerRegistry.getTypeHandler(propertyType, jdbcType);
      // Replicate logic of UnknownTypeHandler#resolveTypeHandler
      // See issue #59 comment 10
      if (handler == null || handler instanceof UnknownTypeHandler) {
        final int index = columnNames.indexOf(columnName);
        final Class javaType = resolveClass(classNames.get(index));
        if (javaType != null && jdbcType != null) {
          handler = typeHandlerRegistry.getTypeHandler(javaType, jdbcType);
        } else if (javaType != null) {
          handler = typeHandlerRegistry.getTypeHandler(javaType);
        } else if (jdbcType != null) {
          handler = typeHandlerRegistry.getTypeHandler(jdbcType);
        }
      }
      if (handler == null || handler instanceof UnknownTypeHandler) {
        handler = new ObjectTypeHandler();
      }
      columnHandlers.put(propertyType, handler);
    }
    return handler;
  }

  private Class resolveClass(String className) {
    try {
      return Resources.classForName(className);
    } catch (ClassNotFoundException e) {
      return null;
    }
  }

  private void loadMappedAndUnmappedColumnNames(ResultMap resultMap, String columnPrefix) throws SQLException {
    List mappedColumnNames = new ArrayList();
    List unmappedColumnNames = new ArrayList();
    final String upperColumnPrefix = columnPrefix == null ? null : columnPrefix.toUpperCase(Locale.ENGLISH);
    final Set mappedColumns = prependPrefixes(resultMap.getMappedColumns(), upperColumnPrefix);
    for (String columnName : columnNames) {
      final String upperColumnName = columnName.toUpperCase(Locale.ENGLISH);
      if (mappedColumns.contains(upperColumnName)) {
        mappedColumnNames.add(upperColumnName);
      } else {
        unmappedColumnNames.add(columnName);
      }
    }
    mappedColumnNamesMap.put(getMapKey(resultMap, columnPrefix), mappedColumnNames);
    unMappedColumnNamesMap.put(getMapKey(resultMap, columnPrefix), unmappedColumnNames);
  }

  public List getMappedColumnNames(ResultMap resultMap, String columnPrefix) throws SQLException {
    List mappedColumnNames = mappedColumnNamesMap.get(getMapKey(resultMap, columnPrefix));
    if (mappedColumnNames == null) {
      loadMappedAndUnmappedColumnNames(resultMap, columnPrefix);
      mappedColumnNames = mappedColumnNamesMap.get(getMapKey(resultMap, columnPrefix));
    }
    return mappedColumnNames;
  }

  public List getUnmappedColumnNames(ResultMap resultMap, String columnPrefix) throws SQLException {
    List unMappedColumnNames = unMappedColumnNamesMap.get(getMapKey(resultMap, columnPrefix));
    if (unMappedColumnNames == null) {
      loadMappedAndUnmappedColumnNames(resultMap, columnPrefix);
      unMappedColumnNames = unMappedColumnNamesMap.get(getMapKey(resultMap, columnPrefix));
    }
    return unMappedColumnNames;
  }

  private String getMapKey(ResultMap resultMap, String columnPrefix) {
    return resultMap.getId() + ":" + columnPrefix;
  }

  private Set prependPrefixes(Set columnNames, String prefix) {
    if (columnNames == null || columnNames.isEmpty() || prefix == null || prefix.length() == 0) {
      return columnNames;
    }
    final Set prefixed = new HashSet();
    for (String columnName : columnNames) {
      prefixed.add(prefix + columnName);
    }
    return prefixed;
  }
  
}