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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 2004 Clinton Begin
 *
 *  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 com.ibatis.sqlmap.engine.mapping.result.loader;

import java.sql.SQLException;
import java.util.Collection;
import java.util.List;
import java.util.Set;

import net.sf.cglib.proxy.Enhancer;
import net.sf.cglib.proxy.LazyLoader;
import net.sf.cglib.proxy.NoOp;

import com.ibatis.common.beans.ClassInfo;
import com.ibatis.sqlmap.engine.impl.SqlMapClientImpl;
import com.ibatis.sqlmap.engine.type.DomTypeMarker;

/**
 * Class to lazily load results into objects (uses CGLib to improve performance)
 */
public class EnhancedLazyResultLoader {

  private static final Class[] SET_INTERFACES = new Class[]{Set.class};
  private static final Class[] LIST_INTERFACES = new Class[]{List.class};
  private Object loader;


  /**
   * Constructor for an enhanced lazy list loader
   *
   * @param client - the client that is creating the lazy list
   * @param statementName - the statement to be used to build the list
   * @param parameterObject - the parameter object to be used to build the list
   * @param targetType - the type we are putting data into
   */
  public EnhancedLazyResultLoader(SqlMapClientImpl client, String statementName, Object parameterObject, Class targetType) {
    loader = new EnhancedLazyResultLoaderImpl(client, statementName, parameterObject, targetType);
  }

  /**
   * Loads the result
   *
   * @return the results - a list or object
   *
   * @throws SQLException if there is a problem
   */
  public Object loadResult() throws SQLException {
    return ((EnhancedLazyResultLoaderImpl) loader).loadResult();
  }


  private static class EnhancedLazyResultLoaderImpl implements LazyLoader {


    protected SqlMapClientImpl client;
    protected String statementName;
    protected Object parameterObject;
    protected Class targetType;

    protected boolean loaded;
    protected Object resultObject;

    /**
     * Constructor for an enhanced lazy list loader implementation
     *
     * @param client - the client that is creating the lazy list
     * @param statementName - the statement to be used to build the list
     * @param parameterObject - the parameter object to be used to build the list
     * @param targetType - the type we are putting data into
     */
    public EnhancedLazyResultLoaderImpl(SqlMapClientImpl client, String statementName, Object parameterObject, Class targetType) {
      this.client = client;
      this.statementName = statementName;
      this.parameterObject = parameterObject;
      this.targetType = targetType;
    }

    /**
     * Loads the result
     *
     * @return the results - a list or object
     *
     * @throws SQLException if there is a problem
     */
    public Object loadResult() throws SQLException {
      if (DomTypeMarker.class.isAssignableFrom(targetType)) {
        return ResultLoader.getResult(client, statementName, parameterObject, targetType);
      } else if (Collection.class.isAssignableFrom(targetType)) {
        if (Set.class.isAssignableFrom(targetType)) {
          return Enhancer.create(Object.class, SET_INTERFACES, this);
        } else {
          return Enhancer.create(Object.class, LIST_INTERFACES, this);
        }
      } else if (targetType.isArray() || ClassInfo.isKnownType(targetType)) {
        return ResultLoader.getResult(client, statementName, parameterObject, targetType);
      } else {
        return Enhancer.create(targetType, this);
      }
    }

	public Object loadObject() throws Exception {
		try {
			Object result = ResultLoader.getResult(client, statementName, parameterObject, targetType);
			if (result == null) {
				// if no result is available return a proxy with a default object is returned
				// because the loadObject() method must not return null
				result = Enhancer.create(targetType, NoOp.INSTANCE);
			}
			return result;
		} catch (SQLException e) {
			throw new RuntimeException("Error lazy loading result. Cause: " + e, e);
		}
	}
  }


}