Android example source code file (DictionaryDatabase.java)

This example Android source code file (DictionaryDatabase.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Android by Example" ^TM.

Java - Android tags/keywords

android, bufferedreader, content, cursor, database, database_name, database_version, dictionarydatabase, dictionaryopenhelper, fts_virtual_table, hashmap, io, ioexception, key_definition, key_word, override, provider, sqlitequerybuilder, string, util

The DictionaryDatabase.java Android example source code

/*
 * Copyright (C) 2010 The Android Open Source Project
 *
 * 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.example.android.searchabledict;

import android.app.SearchManager;
import android.content.ContentValues;
import android.content.Context;
import android.content.res.Resources;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.database.sqlite.SQLiteQueryBuilder;
import android.provider.BaseColumns;
import android.text.TextUtils;
import android.util.Log;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.HashMap;

/**
 * Contains logic to return specific words from the dictionary, and
 * load the dictionary table when it needs to be created.
 */
public class DictionaryDatabase {
    private static final String TAG = "DictionaryDatabase";

    //The columns we'll include in the dictionary table
    public static final String KEY_WORD = SearchManager.SUGGEST_COLUMN_TEXT_1;
    public static final String KEY_DEFINITION = SearchManager.SUGGEST_COLUMN_TEXT_2;

    private static final String DATABASE_NAME = "dictionary";
    private static final String FTS_VIRTUAL_TABLE = "FTSdictionary";
    private static final int DATABASE_VERSION = 2;

    private final DictionaryOpenHelper mDatabaseOpenHelper;
    private static final HashMap<String,String> mColumnMap = buildColumnMap();

    /**
     * Constructor
     * @param context The Context within which to work, used to create the DB
     */
    public DictionaryDatabase(Context context) {
        mDatabaseOpenHelper = new DictionaryOpenHelper(context);
    }

    /**
     * Builds a map for all columns that may be requested, which will be given to the 
     * SQLiteQueryBuilder. This is a good way to define aliases for column names, but must include 
     * all columns, even if the value is the key. This allows the ContentProvider to request
     * columns w/o the need to know real column names and create the alias itself.
     */
    private static HashMap<String,String> buildColumnMap() {
        HashMap<String,String> map = new HashMap();
        map.put(KEY_WORD, KEY_WORD);
        map.put(KEY_DEFINITION, KEY_DEFINITION);
        map.put(BaseColumns._ID, "rowid AS " +
                BaseColumns._ID);
        map.put(SearchManager.SUGGEST_COLUMN_INTENT_DATA_ID, "rowid AS " +
                SearchManager.SUGGEST_COLUMN_INTENT_DATA_ID);
        map.put(SearchManager.SUGGEST_COLUMN_SHORTCUT_ID, "rowid AS " +
                SearchManager.SUGGEST_COLUMN_SHORTCUT_ID);
        return map;
    }

    /**
     * Returns a Cursor positioned at the word specified by rowId
     *
     * @param rowId id of word to retrieve
     * @param columns The columns to include, if null then all are included
     * @return Cursor positioned to matching word, or null if not found.
     */
    public Cursor getWord(String rowId, String[] columns) {
        String selection = "rowid = ?";
        String[] selectionArgs = new String[] {rowId};

        return query(selection, selectionArgs, columns);

        /* This builds a query that looks like:
         *     SELECT <columns> FROM  WHERE rowid = 
         */
    }

    /**
     * Returns a Cursor over all words that match the given query
     *
     * @param query The string to search for
     * @param columns The columns to include, if null then all are included
     * @return Cursor over all words that match, or null if none found.
     */
    public Cursor getWordMatches(String query, String[] columns) {
        String selection = KEY_WORD + " MATCH ?";
        String[] selectionArgs = new String[] {query+"*"};

        return query(selection, selectionArgs, columns);

        /* This builds a query that looks like:
         *     SELECT <columns> FROM  WHERE  MATCH 'query*'
         * which is an FTS3 search for the query text (plus a wildcard) inside the word column.
         *
         * - "rowid" is the unique id for all rows but we need this value for the "_id" column in
         *    order for the Adapters to work, so the columns need to make "_id" an alias for "rowid"
         * - "rowid" also needs to be used by the SUGGEST_COLUMN_INTENT_DATA alias in order
         *   for suggestions to carry the proper intent data.
         *   These aliases are defined in the DictionaryProvider when queries are made.
         * - This can be revised to also search the definition text with FTS3 by changing
         *   the selection clause to use FTS_VIRTUAL_TABLE instead of KEY_WORD (to search across
         *   the entire table, but sorting the relevance could be difficult.
         */
    }

    /**
     * Performs a database query.
     * @param selection The selection clause
     * @param selectionArgs Selection arguments for "?" components in the selection
     * @param columns The columns to return
     * @return A Cursor over all rows matching the query
     */
    private Cursor query(String selection, String[] selectionArgs, String[] columns) {
        /* The SQLiteBuilder provides a map for all possible columns requested to
         * actual columns in the database, creating a simple column alias mechanism
         * by which the ContentProvider does not need to know the real column names
         */
        SQLiteQueryBuilder builder = new SQLiteQueryBuilder();
        builder.setTables(FTS_VIRTUAL_TABLE);
        builder.setProjectionMap(mColumnMap);

        Cursor cursor = builder.query(mDatabaseOpenHelper.getReadableDatabase(),
                columns, selection, selectionArgs, null, null, null);

        if (cursor == null) {
            return null;
        } else if (!cursor.moveToFirst()) {
            cursor.close();
            return null;
        }
        return cursor;
    }


    /**
     * This creates/opens the database.
     */
    private static class DictionaryOpenHelper extends SQLiteOpenHelper {

        private final Context mHelperContext;
        private SQLiteDatabase mDatabase;

        /* Note that FTS3 does not support column constraints and thus, you cannot
         * declare a primary key. However, "rowid" is automatically used as a unique
         * identifier, so when making requests, we will use "_id" as an alias for "rowid"
         */
        private static final String FTS_TABLE_CREATE =
                    "CREATE VIRTUAL TABLE " + FTS_VIRTUAL_TABLE +
                    " USING fts3 (" +
                    KEY_WORD + ", " +
                    KEY_DEFINITION + ");";

        DictionaryOpenHelper(Context context) {
            super(context, DATABASE_NAME, null, DATABASE_VERSION);
            mHelperContext = context;
        }

        @Override
        public void onCreate(SQLiteDatabase db) {
            mDatabase = db;
            mDatabase.execSQL(FTS_TABLE_CREATE);
            loadDictionary();
        }

        /**
         * Starts a thread to load the database table with words
         */
        private void loadDictionary() {
            new Thread(new Runnable() {
                public void run() {
                    try {
                        loadWords();
                    } catch (IOException e) {
                        throw new RuntimeException(e);
                    }
                }
            }).start();
        }

        private void loadWords() throws IOException {
            Log.d(TAG, "Loading words...");
            final Resources resources = mHelperContext.getResources();
            InputStream inputStream = resources.openRawResource(R.raw.definitions);
            BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));

            try {
                String line;
                while ((line = reader.readLine()) != null) {
                    String[] strings = TextUtils.split(line, "-");
                    if (strings.length < 2) continue;
                    long id = addWord(strings[0].trim(), strings[1].trim());
                    if (id < 0) {
                        Log.e(TAG, "unable to add word: " + strings[0].trim());
                    }
                }
            } finally {
                reader.close();
            }
            Log.d(TAG, "DONE loading words.");
        }

        /**
         * Add a word to the dictionary.
         * @return rowId or -1 if failed
         */
        public long addWord(String word, String definition) {
            ContentValues initialValues = new ContentValues();
            initialValues.put(KEY_WORD, word);
            initialValues.put(KEY_DEFINITION, definition);

            return mDatabase.insert(FTS_VIRTUAL_TABLE, null, initialValues);
        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
            Log.w(TAG, "Upgrading database from version " + oldVersion + " to "
                    + newVersion + ", which will destroy all old data");
            db.execSQL("DROP TABLE IF EXISTS " + FTS_VIRTUAL_TABLE);
            onCreate(db);
        }
    }

}


Other Android examples (source code examples)
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