com.ovrhere.android.currencyconverter.model.parsers.AbstractJsonParser.java Source code

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Here is the source code for com.ovrhere.android.currencyconverter.model.parsers.AbstractJsonParser.java

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/*
 * Copyright 2014 Jason J.
 * 
 * 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.ovrhere.android.currencyconverter.model.parsers;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;

import com.google.gson.stream.JsonReader;
import com.google.gson.stream.JsonToken;

/** The basic outline to a JSON parser. Provides pause/resume features.
 * Requires GSON library. Compatible 2.3.3 and up.
 * @author Jason J.
 * @version 0.1.0-20140929
 * @param <R1>
 */
abstract public class AbstractJsonParser<R1> {
    /** The tag for debugging purposes. */
    @SuppressWarnings("unused")
    final static private String LOGTAG = AbstractJsonParser.class.getSimpleName();

    /////////////////////////////////////////////////////////////////////////////////////////////////
    /// End contants
    ////////////////////////////////////////////////////////////////////////////////////////////////
    /** The boolean for determining if paused. */
    volatile boolean paused = false;

    /** The pull parser for this object. */
    protected JsonReader jsonReader = null;

    /** Pauses the thread based on value. */
    public void pause() {
        paused = true;
    }

    /** Resumes the thread based on value. */
    public void resume() {
        paused = false;
    }

    /** Parses the JSON stream and returns it described return type.
     * Note that this method initializes and closes the reader.
     * @param reader The input reading
     * @return R1, the parsed data.
     * @throws IOException Re-thrown exception from reader
     */
    public R1 parseJsonStream(Reader reader) throws IOException {

        checkPause();
        jsonReader = new JsonReader(reader);
        checkPause();

        try {
            return parseJsonToReturnData();
        } finally {
            try {
                jsonReader.close();
            } catch (IOException e) {
            }
        }
    }

    /** Parses the JSON stream and returns it described return type.
     * Note that this method initializes and closes the reader.
     * @param in The input stream
     * @return R1, the parsed data. 
     * @throws IOException Re-thrown exception from reader 
     */
    public R1 parseJsonStream(InputStream in) throws IOException {
        checkPause();
        InputStreamReader reader = new InputStreamReader(in);
        jsonReader = new JsonReader(reader);
        checkPause();

        try {
            return parseJsonToReturnData();
        } finally {
            try {
                jsonReader.close();
            } catch (IOException e) {
            }
        }
    }

    /////////////////////////////////////////////////////////////////////////////////////////////////
    /// Abstract methods
    ////////////////////////////////////////////////////////////////////////////////////////////////

    /** Parses the JSON to a R1 using the prepared JsonReader  {@link #jsonReader}.
     * Remember to use {@link #checkPause()} for proper thread control.
     * Additionally, consider the use of {@link Thread#yield()} for throttling.
     * @return The parsed group of values 
     * @throws IOException Re-thrown exception
     * */
    abstract protected R1 parseJsonToReturnData() throws IOException;

    /////////////////////////////////////////////////////////////////////////////////////////////////
    /// Helper methods
    ////////////////////////////////////////////////////////////////////////////////////////////////

    /** Checks to see if to yield the thread based on
     * If so, it:
     * <ol><li>Sets priority to lowest</li>
     * <li>Sleeps for 50 milliseconds</li>
     * <li>Rechecks</li>
     * <li>Repeats step 2.</li></ul>
     * After exiting this loop it is restored to its former priority. */
    protected void checkPause() {
        final Thread t = Thread.currentThread();
        final int priority = t.getPriority();
        if (paused) {
            t.setPriority(Thread.MIN_PRIORITY);
        }
        while (paused) {
            try {
                Thread.sleep(50);
            } catch (InterruptedException e) {
            }
        }
        t.setPriority(priority);
    }

    /** Checks to see if the next element of the reader is {@link JsonToken#NULL}.
     * @return <code>true</code> if not NULL, <code>false</code> if 
     * if null.
     * @throws IOException Re-thrown exception from peek    */
    final protected boolean nextNotNull() throws IOException {
        return jsonReader.peek() != JsonToken.NULL;
    }

}