Android Open Source - lightbox-android-webservices Retrieve Operation

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License

The source code is released under:

Apache License

Java Source Code

/**
 * Copyright (c) 2012 Lightbox//from w w  w. j  ava  2 s.  com
 *
 * 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.lightbox.android.operations;

import java.sql.SQLException;
import java.util.Collections;
import java.util.List;

import android.util.Log;

import com.j256.ormlite.stmt.PreparedQuery;
import com.j256.ormlite.stmt.QueryBuilder;
import com.lightbox.android.data.SaveBatchTask;
import com.lightbox.android.utils.debug.DebugLog;
import com.lightbox.android.webservices.requests.ApiRequest;
import com.lightbox.android.webservices.responses.ApiResponse;

/** 
 * RetrieveOperation 
 * @author Fabien Devos
 */
public class RetrieveOperation<T> extends AbstractOperation<T> {
  /** Used to tag logs */
  // @SuppressWarnings("unused")
  private static final String TAG = "RetrieveOperation";
  
  /** Cache duration for the retrieve operations, should be short since we always fall back on old data if no network
   *  connection is available. */
  public static final long CACHE_DURATION = 5 * 60 * 1000; // 5min

  private QueryBuilder<T, String> mQueryBuilder = null;
  private PreparedQuery<T> mPreparedQuery;
  private List<T> mResultList = null;
  private boolean mRetrieveFromLocalDataOnly = false;
  
  //----------------------------------------------
  // Constructor
  
  /**
   * Constructor. Note that you <strong>must</strong> call {@link #buildQuery()}, and optionally set some statements,
   * before any attempt to execute this RetrieveOperation.
   * @param dataOperation
   * @param apiRequest
   */
  public RetrieveOperation(Class<T> dataClass, ApiRequest apiRequest, boolean retrieveFromLocalDataOnly) {
    super(dataClass, apiRequest);
    mRetrieveFromLocalDataOnly = retrieveFromLocalDataOnly;
  }
  
  //----------------------------------------------
  // Query
  
  /**
   * Use this method to build the query for this RetrieveOperation. You <strong>must</strong> call this method before
   * executing the Operation. If you don't set anything on the returned {@link QueryBuilder}, it will simply returns
   * every objects of the type T present in the database.
   * @return a {@link QueryBuilder} that you can modify to set any constraint on the retrieve operation.
   * @throws SQLException
   */
  public QueryBuilder<T, String> buildQuery() throws SQLException {
    if (mQueryBuilder == null) {
      mQueryBuilder = getDao().queryBuilder();
    }
    return mQueryBuilder;
  }

  private PreparedQuery<T> getPreparedQuery() throws SQLException {
    if (mQueryBuilder == null) { throw new IllegalStateException("You must call buildQuery, and optionally set some statements, before executing RetrieveOperation."); }
    if (mPreparedQuery == null) { mPreparedQuery = mQueryBuilder.prepare(); }
    return mPreparedQuery;
  }
    
  //----------------------------------------------
  // Hooks for subclasses

  protected void onRetrieveDataFromDatabase(List<T> result) throws Exception {
    // Nothing by default
  }

  protected void onRetrieveDataFromServer(List<T> result) throws Exception {
    // Nothing by default
  }
  
  //----------------------------------------------
  // Operation

  // Override the default executeAsync to add support for caching on the main thread.
  @Override
  public final void executeAsync(OperationListener<T> listener) {
    mResultList = null;
    try {
      // Try to get data locally first
      mResultList = executeLocalOperationSync();
    } catch (Exception e) {
      Log.w(TAG, "Failed to retrieve data from db: %s", e);
    }
    
    if (mResultList != null) {
      // Call back on main thread
      if (listener != null) {
        listener.onSuccess(this, mResultList);
      }
    }

    if ( ! mRetrieveFromLocalDataOnly ) {
      // Proceed with normal operation execution
      super.executeAsync(listener);
    }
  }

  @Override
  public List<T> executeLocalOperationSync() throws Exception {
    
    // Query database
    PreparedQuery<T> preparedQuery = getPreparedQuery();     
    List<T> resultList = getDao().query(preparedQuery);
        
    // Hook
    if (resultList != null) { onRetrieveDataFromDatabase(resultList); }
    
    // Remove locally deleted data from the result list
    removeLocallyDeletedData(resultList);

    return resultList;
  }

  @Override
  public List<T> executeServerOperationSync() throws Exception {
    List<T> resultList = null;
    
    // Query server
    ApiResponse<?> apiResponse = getApiRequest().execute();        
    Object result = apiResponse.getContent();
    if (result == null) { throw new NullPointerException("Result was null"); }
    resultList = wrapInList(result);
    
    // Hook
    if (resultList != null) { onRetrieveDataFromServer(resultList); }

    // Save in database
    saveDataFromServer(resultList);
    
    return resultList;
  }
  
  @Override
  public final List<T> executeSync() throws Exception {
    List<T> resultList = mResultList;

    // If (there is no result OR the data are too old) AND there is no local update 
    if ( (resultList == null || isDataTooOld(resultList)) && ! hasLocalUpdate(resultList) ) {
      DebugLog.d(TAG, "(No result from database OR data is too old) AND no local updates: retrieving from network.");
      
      // Try to retrieve data from web services
      resultList = executeServerOperationSync();
      
      // No need to send back result from cache because it's already done
    }
    
    return resultList;
  }
  
  private static <T> boolean isDataTooOld(List<T> list) {
    boolean isDataTooOld = true;
    
    // in the empty case, we consider the data as too old, thus we will always check the network
    if (list.size() > 0) {
      try {
        // Take the oldest item and test if it is too old, if so, we consider the whole list as too old
        @SuppressWarnings("unchecked")
        List<Retrievable> retrievableList = (List<Retrievable>) list; 
        Retrievable oldest = Collections.min(retrievableList, Retrievable.BY_RETRIEVED_TIME);        
        isDataTooOld = (System.currentTimeMillis() - oldest.getRetrievedTime()) > CACHE_DURATION;
      } catch (ClassCastException e) {
        // Ignore
      }
    }

    return isDataTooOld;
  }
    
    private static <T> boolean hasLocalUpdate(List<T> list) {
    boolean hasLocalUpdate = false;
    if (list != null) {
      for (T object : list) {
        if (object instanceof Updatable) {
          Updatable updatable = (Updatable) object;
          if (updatable.getLocallyUpdatedFields().size() > 0) {
            hasLocalUpdate = true;
            break;
          }
        }
      }
    }
    return hasLocalUpdate;
  }
  
  private void saveDataFromServer(List<T> list) {
    try {
      for (T object : list) {
        // Since this comes from the server, we can set the retrieved time to now
        if (object instanceof Retrievable) {
          Retrievable retrievable = (Retrievable) object;
          retrievable.setRetrievedTime(System.currentTimeMillis());
        }
      }
      // Save in batch
      getDao().callBatchTasks(new SaveBatchTask<T>(list, getDataClass()));

    } catch (Exception e) {
      Log.w(TAG, "Failed to save data after retrieving from network.", e);
    }
  }
}

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