com.google.gwt.gears.sample.gwtnote.client.local.GearsHelper.java Source code

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Here is the source code for com.google.gwt.gears.sample.gwtnote.client.local.GearsHelper.java

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/*
 * Copyright 2008 Google Inc.
 * 
 * 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.google.gwt.gears.sample.gwtnote.client.local;

import com.google.gwt.core.client.GWT;
import com.google.gwt.gears.client.Factory;
import com.google.gwt.gears.client.GearsException;
import com.google.gwt.gears.client.database.Database;
import com.google.gwt.gears.client.database.DatabaseException;
import com.google.gwt.gears.client.database.ResultSet;
import com.google.gwt.gears.client.localserver.LocalServer;
import com.google.gwt.gears.client.localserver.ManagedResourceStore;
import com.google.gwt.gears.sample.gwtnote.client.rpc.Note;
import com.google.gwt.user.client.Timer;

import java.util.ArrayList;

/**
 * Provides helper functions for accessing the Gears database. Used to
 * encapsulate all DB-related operations.
 */
public class GearsHelper {
    private static final String DB_UPDATE = "update notes set version=?, content=? where noteid=?";

    private static final String DB_INSERT = "insert into notes values (?, ?, ?)";

    private static final String DB_FETCH_TEXT = "select * from notes";

    private static final String DB_FETCH_NAMES = "select noteid from notes";

    private static final String DB_EXISTS = "select noteid from notes where noteid = ?";

    private static final String DB_CREATE = "create table notes ("
            + "noteid text not null primary key, version text not null, " + "content text not null)";

    protected boolean gearsReady;

    private Database db = null;

    private LocalServer localServer;

    private ManagedResourceStore store;

    /**
     * Creates a new GearsHelper.
     */
    public GearsHelper() {
        try {
            db = Factory.getInstance().createDatabase();
            try {
                db.execute(DB_FETCH_NAMES);
            } catch (GearsException ex) {
                db.execute(DB_CREATE);
            }

            // initialize the localstore and have it update the manifest
            localServer = Factory.getInstance().createLocalServer();
            store = localServer.createManagedStore("GWTGearsNote");
            store.setManifestUrl(GWT.getModuleBaseURL() + "manifest");
            store.checkForUpdate();
            Timer t = new Timer() {
                @Override
                public void run() {
                    int status = store.getUpdateStatus();
                    if (status == ManagedResourceStore.UPDATE_OK) {
                        this.cancel();
                    } else if (status == ManagedResourceStore.UPDATE_FAILED) {
                        this.cancel();
                    }
                }
            };
            t.scheduleRepeating(100);
        } catch (Throwable t) { // not just GearsException b/c we can also have NPEs
            localServer = null;
            store = null;
            db = null;
        }
    }

    /**
     * Checks whether Gears is present and enabled on the current browser.
     * 
     * @return true if Gears is present and enabled, false otherwise
     */
    public boolean gearsEnabled() {
        return (db != null);
    }

    /**
     * Unmarshals all rows in the database into an array of {@link Note}
     * instances.
     * 
     * @return a list of all notes in the DB
     */
    public Note[] getNotes() {
        if (db == null) {
            return null;
        }

        ResultSet rs = null;
        ArrayList<Note> al = new ArrayList<Note>();
        try {
            rs = db.execute(DB_FETCH_TEXT);
            while (rs.isValidRow()) {
                Note nd = new Note(rs.getFieldAsString(0), rs.getFieldAsString(1), rs.getFieldAsString(2));
                al.add(nd);
                rs.next();
            }
        } catch (DatabaseException e) {
            return null;
        }

        Note[] notes = new Note[al.size()];
        for (int i = 0; i < al.size(); ++i) {
            notes[i] = al.get(i);
        }
        return notes;
    }

    /**
     * Marshals the indicated note to the database. This amounts to updating the
     * row with the data as provided.
     * 
     * If <code>dirty</code> is true, the row will be marked as dirty. Note that
     * even if the argument is NOT true, the row may still be dirty -- that is,
     * <code>dirty</code> specifies whether the current operation makes the row
     * dirty, not the absolute state of the row.
     * 
     * @param n the note to update
     */
    public void updateNote(Note n) {
        if (db == null) {
            return;
        }

        String name = n.getName();
        String data = n.getText();
        String vers = n.getVersion();
        String[] args = null;

        ResultSet rs = null;
        try {
            // test whether the row exists or not -- controls behavior below
            args = new String[] { name };
            rs = db.execute(DB_EXISTS, args);
        } catch (DatabaseException e1) {
            return;
        }

        // if row exists update it; if not, create a new one
        if (rs.isValidRow()) {
            args = new String[] { vers, data, name };
            try {
                db.execute(DB_UPDATE, args);
            } catch (DatabaseException e) {
                return;
            }
        } else {
            args = new String[] { name, vers, data };
            try {
                db.execute(DB_INSERT, args);
            } catch (DatabaseException e) {
                return;
            }
        }
    }
}