Volley源码简读

接下来，我将一点一滴地记录自己对Android第三方框架Volley的阅读理解，以便后用。

/* * Copyright (C) 2011 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.android.volley;import android.os.SystemClock;import android.util.Log;import java.util.ArrayList;import java.util.List;import java.util.Locale;/** * Logging helper class. * <p/> * to see Volley logs call:<br/> * {@code <android-sdk>/platform-tools/adb shell setprop log.tag.Volley VERBOSE} */public class VolleyLog {//一个用来简化打印日志的日志类    public static String TAG = "Volley";    public static boolean DEBUG = Log.isLoggable(TAG, Log.VERBOSE);    /**     * Customize the log tag for your application, so that other apps     * using Volley don't mix their logs with yours.     * <br />     * Enable the log property for your tag before starting your app:     * <br />     * {@code adb shell setprop log.tag.<tag>}     */    public static void setTag(String tag) {        d("Changing log tag to %s", tag);        TAG = tag;        // Reinitialize the DEBUG "constant"        DEBUG = Log.isLoggable(TAG, Log.VERBOSE);    }    public static void v(String format, Object... args) {        if (DEBUG) {            Log.v(TAG, buildMessage(format, args));        }    }    public static void d(String format, Object... args) {        Log.d(TAG, buildMessage(format, args));    }    public static void e(String format, Object... args) {        Log.e(TAG, buildMessage(format, args));    }    public static void e(Throwable tr, String format, Object... args) {        Log.e(TAG, buildMessage(format, args), tr);    }    public static void wtf(String format, Object... args) {        Log.wtf(TAG, buildMessage(format, args));    }    public static void wtf(Throwable tr, String format, Object... args) {        Log.wtf(TAG, buildMessage(format, args), tr);    }    /**     * Formats the caller's provided message and prepends useful info like     * calling thread ID and method name.     */    private static String buildMessage(String format, Object... args) {        String msg = (args == null) ? format : String.format(Locale.US, format, args);        StackTraceElement[] trace = new Throwable().fillInStackTrace().getStackTrace();        String caller = "<unknown>";        // Walk up the stack looking for the first caller outside of VolleyLog.        // It will be at least two frames up, so start there.        for (int i = 2; i < trace.length; i++) {            Class<?> clazz = trace[i].getClass();            if (!clazz.equals(VolleyLog.class)) {                String callingClass = trace[i].getClassName();                callingClass = callingClass.substring(callingClass.lastIndexOf('.') + 1);                callingClass = callingClass.substring(callingClass.lastIndexOf('$') + 1);                caller = callingClass + "." + trace[i].getMethodName();                break;            }        }        return String.format(Locale.US, "[%d] %s: %s",                Thread.currentThread().getId(), caller, msg);    }    /**     * A simple event log with records containing a name, thread ID, and timestamp.     */    static class MarkerLog {        public static final boolean ENABLED = VolleyLog.DEBUG;        /** Minimum duration from first marker to last in an marker log to warrant logging. */        private static final long MIN_DURATION_FOR_LOGGING_MS = 0;        private static class Marker {            public final String name;            public final long thread;            public final long time;            public Marker(String name, long thread, long time) {                this.name = name;                this.thread = thread;                this.time = time;            }        }        private final List<Marker> mMarkers = new ArrayList<Marker>();        private boolean mFinished = false;        /** Adds a marker to this log with the specified name. */        public synchronized void add(String name, long threadId) {            if (mFinished) {                throw new IllegalStateException("Marker added to finished log");            }            mMarkers.add(new Marker(name, threadId, SystemClock.elapsedRealtime()));        }        /**         * Closes the log, dumping it to logcat if the time difference between         * the first and last markers is greater than {@link #MIN_DURATION_FOR_LOGGING_MS}.         * @param header Header string to print above the marker log.         */        public synchronized void finish(String header) {            mFinished = true;            long duration = getTotalDuration();            if (duration <= MIN_DURATION_FOR_LOGGING_MS) {                return;            }            long prevTime = mMarkers.get(0).time;            d("(%-4d ms) %s", duration, header);            for (Marker marker : mMarkers) {                long thisTime = marker.time;                d("(+%-4d) [%2d] %s", (thisTime - prevTime), marker.thread, marker.name);                prevTime = thisTime;            }        }        @Override        protected void finalize() throws Throwable {            // Catch requests that have been collected (and hence end-of-lifed)            // but had no debugging output printed for them.            if (!mFinished) {                finish("Request on the loose");                e("Marker log finalized without finish() - uncaught exit point for request");            }        }        /** Returns the time difference between the first and last events in this log. */        private long getTotalDuration() {            if (mMarkers.size() == 0) {                return 0;            }            long first = mMarkers.get(0).time;            long last = mMarkers.get(mMarkers.size() - 1).time;            return last - first;        }    }

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