LazyResultLoader.java

/**
 * Copyright 2004-2017 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 com.ibatis.sqlmap.engine.mapping.result.loader;

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

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.sql.SQLException;
import java.util.Collection;
import java.util.List;
import java.util.Set;

/**
 * Class to lazily load results into objects
 */
public class LazyResultLoader implements InvocationHandler {

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

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

  protected boolean loaded;
  protected Object resultObject;

  /**
   * Constructor for a 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 LazyResultLoader(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 (Collection.class.isAssignableFrom(targetType)) {
      InvocationHandler handler = new LazyResultLoader(client, statementName, parameterObject, targetType);
      ClassLoader cl = targetType.getClassLoader();
      if (Set.class.isAssignableFrom(targetType)) {
        return Proxy.newProxyInstance(cl, SET_INTERFACES, handler);
      } else {
        return Proxy.newProxyInstance(cl, LIST_INTERFACES, handler);
      }
    } else {
      return ResultLoader.getResult(client, statementName, parameterObject, targetType);
    }
  }

  public Object invoke(Object o, Method method, Object[] objects) throws Throwable {
    if ("finalize".hashCode() == method.getName().hashCode() && "finalize".equals(method.getName())) {
      return null;
    } else {
      loadObject();
      if (resultObject != null) {
        try {
          return method.invoke(resultObject, objects);
        } catch (Throwable t) {
          throw ClassInfo.unwrapThrowable(t);
        }
      } else {
        return null;
      }
    }
  }

  private synchronized void loadObject() {
    if (!loaded) {
      try {
        loaded = true;
        resultObject = ResultLoader.getResult(client, statementName, parameterObject, targetType);
      } catch (SQLException e) {
        throw new RuntimeException("Error lazy loading result. Cause: " + e, e);
      }
    }
  }

}