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Android example source code file (EventLog.java)

This example Android source code file (EventLog.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

bufferedreader, error, hashmap, illegalargumentexception, int_type, integer, io, ioexception, long_type, nio, object, pattern, regex, string, string_type, tags_file, utf-8, util

The EventLog.java Android example source code

 * Copyright (C) 2007 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,
 * See the License for the specific language governing permissions and
 * limitations under the License.

package android.util;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.nio.BufferUnderflowException;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.util.Collection;
import java.util.HashMap;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

 * Access to the system diagnostic event record.  System diagnostic events are
 * used to record certain system-level events (such as garbage collection,
 * activity manager state, system watchdogs, and other low level activity),
 * which may be automatically collected and analyzed during system development.
 * <p>This is not the main "logcat" debugging log ({@link android.util.Log})!
 * These diagnostic events are for system integrators, not application authors.
 * <p>Events use integer tag codes corresponding to /system/etc/event-log-tags.
 * They carry a payload of one or more int, long, or String values.  The
 * event-log-tags file defines the payload contents for each type code.
public class EventLog {
    private static final String TAG = "EventLog";

    private static final String TAGS_FILE = "/system/etc/event-log-tags";
    private static final String COMMENT_PATTERN = "^\\s*(#.*)?$";
    private static final String TAG_PATTERN = "^\\s*(\\d+)\\s+(\\w+)\\s*(\\(.*\\))?\\s*$";
    private static HashMap<String, Integer> sTagCodes = null;
    private static HashMap<Integer, String> sTagNames = null;

    /** A previously logged event read from the logs. */
    public static final class Event {
        private final ByteBuffer mBuffer;

        // Layout of event log entry received from kernel.
        private static final int LENGTH_OFFSET = 0;
        private static final int PROCESS_OFFSET = 4;
        private static final int THREAD_OFFSET = 8;
        private static final int SECONDS_OFFSET = 12;
        private static final int NANOSECONDS_OFFSET = 16;

        private static final int PAYLOAD_START = 20;
        private static final int TAG_OFFSET = 20;
        private static final int DATA_START = 24;

        // Value types
        private static final byte INT_TYPE    = 0;
        private static final byte LONG_TYPE   = 1;
        private static final byte STRING_TYPE = 2;
        private static final byte LIST_TYPE   = 3;

        /** @param data containing event, read from the system */
        /*package*/ Event(byte[] data) {
            mBuffer = ByteBuffer.wrap(data);

        /** @return the process ID which wrote the log entry */
        public int getProcessId() {
            return mBuffer.getInt(PROCESS_OFFSET);

        /** @return the thread ID which wrote the log entry */
        public int getThreadId() {
            return mBuffer.getInt(THREAD_OFFSET);

        /** @return the wall clock time when the entry was written */
        public long getTimeNanos() {
            return mBuffer.getInt(SECONDS_OFFSET) * 1000000000l
                    + mBuffer.getInt(NANOSECONDS_OFFSET);

        /** @return the type tag code of the entry */
        public int getTag() {
            return mBuffer.getInt(TAG_OFFSET);

        /** @return one of Integer, Long, String, null, or Object[] of same. */
        public synchronized Object getData() {
            try {
                mBuffer.limit(PAYLOAD_START + mBuffer.getShort(LENGTH_OFFSET));
                mBuffer.position(DATA_START);  // Just after the tag.
                return decodeObject();
            } catch (IllegalArgumentException e) {
                Log.wtf(TAG, "Illegal entry payload: tag=" + getTag(), e);
                return null;
            } catch (BufferUnderflowException e) {
                Log.wtf(TAG, "Truncated entry payload: tag=" + getTag(), e);
                return null;

        /** @return the loggable item at the current position in mBuffer. */
        private Object decodeObject() {
            byte type = mBuffer.get();
            switch (type) {
            case INT_TYPE:
                return (Integer) mBuffer.getInt();

            case LONG_TYPE:
                return (Long) mBuffer.getLong();

            case STRING_TYPE:
                try {
                    int length = mBuffer.getInt();
                    int start = mBuffer.position();
                    mBuffer.position(start + length);
                    return new String(mBuffer.array(), start, length, "UTF-8");
                } catch (UnsupportedEncodingException e) {
                    Log.wtf(TAG, "UTF-8 is not supported", e);
                    return null;

            case LIST_TYPE:
                int length = mBuffer.get();
                if (length < 0) length += 256;  // treat as signed byte
                Object[] array = new Object[length];
                for (int i = 0; i < length; ++i) array[i] = decodeObject();
                return array;

                throw new IllegalArgumentException("Unknown entry type: " + type);

    // We assume that the native methods deal with any concurrency issues.

     * Record an event log message.
     * @param tag The event type tag code
     * @param value A value to log
     * @return The number of bytes written
    public static native int writeEvent(int tag, int value);

     * Record an event log message.
     * @param tag The event type tag code
     * @param value A value to log
     * @return The number of bytes written
    public static native int writeEvent(int tag, long value);

     * Record an event log message.
     * @param tag The event type tag code
     * @param str A value to log
     * @return The number of bytes written
    public static native int writeEvent(int tag, String str);

     * Record an event log message.
     * @param tag The event type tag code
     * @param list A list of values to log
     * @return The number of bytes written
    public static native int writeEvent(int tag, Object... list);

     * Read events from the log, filtered by type.
     * @param tags to search for
     * @param output container to add events into
     * @throws IOException if something goes wrong reading events
    public static native void readEvents(int[] tags, Collection<Event> output)
            throws IOException;

     * Get the name associated with an event type tag code.
     * @param tag code to look up
     * @return the name of the tag, or null if no tag has that number
    public static String getTagName(int tag) {
        return sTagNames.get(tag);

     * Get the event type tag code associated with an event name.
     * @param name of event to look up
     * @return the tag code, or -1 if no tag has that name
    public static int getTagCode(String name) {
        Integer code = sTagCodes.get(name);
        return code != null ? code : -1;

     * Read TAGS_FILE, populating sTagCodes and sTagNames, if not already done.
    private static synchronized void readTagsFile() {
        if (sTagCodes != null && sTagNames != null) return;

        sTagCodes = new HashMap<String, Integer>();
        sTagNames = new HashMap<Integer, String>();

        Pattern comment = Pattern.compile(COMMENT_PATTERN);
        Pattern tag = Pattern.compile(TAG_PATTERN);
        BufferedReader reader = null;
        String line;

        try {
            reader = new BufferedReader(new FileReader(TAGS_FILE), 256);
            while ((line = reader.readLine()) != null) {
                if (comment.matcher(line).matches()) continue;

                Matcher m = tag.matcher(line);
                if (!m.matches()) {
                    Log.wtf(TAG, "Bad entry in " + TAGS_FILE + ": " + line);

                try {
                    int num = Integer.parseInt(m.group(1));
                    String name = m.group(2);
                    sTagCodes.put(name, num);
                    sTagNames.put(num, name);
                } catch (NumberFormatException e) {
                    Log.wtf(TAG, "Error in " + TAGS_FILE + ": " + line, e);
        } catch (IOException e) {
            Log.wtf(TAG, "Error reading " + TAGS_FILE, e);
            // Leave the maps existing but unpopulated
        } finally {
            try { if (reader != null) reader.close(); } catch (IOException e) {}

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