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Android example source code file (UEventObserver.java)

This example Android source code file (UEventObserver.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

arraylist, hashmap, string, tag, throwable, uevent, ueventobserver, ueventthread, util

The UEventObserver.java Android example source code

/*
 * Copyright (C) 2008 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 android.os;

import java.util.ArrayList;
import java.util.HashMap;

/**
 * UEventObserver is an abstract class that receives UEvent's from the kernel.<p>
 *
 * Subclass UEventObserver, implementing onUEvent(UEvent event), then call
 * startObserving() with a match string. The UEvent thread will then call your
 * onUEvent() method when a UEvent occurs that contains your match string.<p>
 *
 * Call stopObserving() to stop receiving UEvent's.<p>
 *
 * There is only one UEvent thread per process, even if that process has
 * multiple UEventObserver subclass instances. The UEvent thread starts when
 * the startObserving() is called for the first time in that process. Once
 * started the UEvent thread will not stop (although it can stop notifying
 * UEventObserver's via stopObserving()).<p>
 *
 * @hide
*/
public abstract class UEventObserver {
    private static final String TAG = UEventObserver.class.getSimpleName();

    /**
     * Representation of a UEvent.
     */
    static public class UEvent {
        // collection of key=value pairs parsed from the uevent message
        public HashMap<String,String> mMap = new HashMap();

        public UEvent(String message) {
            int offset = 0;
            int length = message.length();

            while (offset < length) {
                int equals = message.indexOf('=', offset);
                int at = message.indexOf(0, offset);
                if (at < 0) break;

                if (equals > offset && equals < at) {
                    // key is before the equals sign, and value is after
                    mMap.put(message.substring(offset, equals),
                            message.substring(equals + 1, at));
                }

                offset = at + 1;
            }
        }

        public String get(String key) {
            return mMap.get(key);
        }

        public String get(String key, String defaultValue) {
            String result = mMap.get(key);
            return (result == null ? defaultValue : result);
        }

        public String toString() {
            return mMap.toString();
        }
    }

    private static UEventThread sThread;
    private static boolean sThreadStarted = false;

    private static class UEventThread extends Thread {
        /** Many to many mapping of string match to observer.
         *  Multimap would be better, but not available in android, so use
         *  an ArrayList where even elements are the String match and odd
         *  elements the corresponding UEventObserver observer */
        private ArrayList<Object> mObservers = new ArrayList();
        
        UEventThread() {
            super("UEventObserver");
        }
        
        public void run() {
            native_setup();

            byte[] buffer = new byte[1024];
            int len;
            while (true) {
                len = next_event(buffer);
                if (len > 0) {
                    String bufferStr = new String(buffer, 0, len);  // easier to search a String
                    synchronized (mObservers) {
                        for (int i = 0; i < mObservers.size(); i += 2) {
                            if (bufferStr.indexOf((String)mObservers.get(i)) != -1) {
                                ((UEventObserver)mObservers.get(i+1))
                                        .onUEvent(new UEvent(bufferStr));
                            }
                        }
                    }
                }
            }
        }
        public void addObserver(String match, UEventObserver observer) {
            synchronized(mObservers) {
                mObservers.add(match);
                mObservers.add(observer);
            }
        }
        /** Removes every key/value pair where value=observer from mObservers */
        public void removeObserver(UEventObserver observer) {
            synchronized(mObservers) {
                boolean found = true;
                while (found) {
                    found = false;
                    for (int i = 0; i < mObservers.size(); i += 2) {
                        if (mObservers.get(i+1) == observer) {
                            mObservers.remove(i+1);
                            mObservers.remove(i);
                            found = true;
                            break;
                        }
                    }
                }
            }
        }
    }

    private static native void native_setup();
    private static native int next_event(byte[] buffer);

    private static final synchronized void ensureThreadStarted() {
        if (sThreadStarted == false) {
            sThread = new UEventThread();
            sThread.start();
            sThreadStarted = true;
        }
    }

    /**
     * Begin observation of UEvent's.<p>
     * This method will cause the UEvent thread to start if this is the first
     * invocation of startObserving in this process.<p>
     * Once called, the UEvent thread will call onUEvent() when an incoming
     * UEvent matches the specified string.<p>
     * This method can be called multiple times to register multiple matches.
     * Only one call to stopObserving is required even with multiple registered
     * matches.
     * @param match A substring of the UEvent to match. Use "" to match all
     *              UEvent's
     */
    public final synchronized void startObserving(String match) {
        ensureThreadStarted();
        sThread.addObserver(match, this);
    }

    /**
     * End observation of UEvent's.<p>
     * This process's UEvent thread will never call onUEvent() on this
     * UEventObserver after this call. Repeated calls have no effect.
     */
    public final synchronized void stopObserving() {
        sThread.removeObserver(this);
    }

    /**
     * Subclasses of UEventObserver should override this method to handle
     * UEvents.
     */
    public abstract void onUEvent(UEvent event);

    protected void finalize() throws Throwable {
        try {
            stopObserving();
        } finally {
            super.finalize();
        }
    }
}




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