MessageUtils.java revision b5c09b5487699bfde612f4833641cc57aaa4a0c8 
1/*
2 * Copyright (C) 2016 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package com.android.internal.util;
18
19import android.os.Message;
20import android.util.Log;
21import android.util.SparseArray;
22
23import java.lang.reflect.Field;
24import java.lang.reflect.Modifier;
25
26/**
27 * Static utility class for dealing with {@link Message} objects.
28 */
29public class MessageUtils {
30
31    private static final String TAG = MessageUtils.class.getSimpleName();
32    private static final boolean DBG = false;
33
34    /** Thrown when two different constants have the same value. */
35    public static class DuplicateConstantError extends Error {
36        private DuplicateConstantError() {}
37        public DuplicateConstantError(String name1, String name2, int value) {
38            super(String.format("Duplicate constant value: both %s and %s = %d",
39                name1, name2, value));
40        }
41    }
42
43    /**
44     * Finds the names of integer constants. Searches the specified {@code classes}, looking for
45     * accessible static integer fields whose names begin with one of the specified
46     * {@code prefixes}.
47     *
48     * @param classes the classes to examine.
49     * @param prefixes only consider fields names starting with one of these prefixes.
50     * @return a {@link SparseArray} mapping integer constants to their names.
51     */
52    public static SparseArray<String> findMessageNames(Class[] classes, String[] prefixes) {
53        SparseArray<String> messageNames = new SparseArray<>();
54        for (Class c : classes) {
55            String className = c.getName();
56            if (DBG) Log.d(TAG, "Examining class " + className);
57
58            Field[] fields;
59            try {
60                fields = c.getDeclaredFields();
61            } catch (SecurityException e) {
62                Log.e(TAG, "Can't list fields of class " + className);
63                continue;
64            }
65
66            for (Field field : fields) {
67                int modifiers = field.getModifiers();
68                if (!Modifier.isStatic(modifiers) | !Modifier.isFinal(modifiers)) {
69                    continue;
70                }
71
72                String name = field.getName();
73                for (String prefix : prefixes) {
74                    // Does this look like a constant?
75                    if (!name.startsWith(prefix)) {
76                        continue;
77                    }
78
79                    try {
80                        // TODO: can we have the caller try to access the field instead, so we don't
81                        // expose constants it does not have access to?
82                        field.setAccessible(true);
83
84                        // Fetch the constant's value.
85                        int value;
86                        try {
87                            value = field.getInt(null);
88                        } catch (IllegalArgumentException | ExceptionInInitializerError e) {
89                            // The field is not an integer (or short or byte), or c's static
90                            // initializer failed and we have no idea what its value is.
91                            // Either way, give up on this field.
92                            break;
93                        }
94
95                        // Check for duplicate values.
96                        String previousName = messageNames.get(value);
97                        if (previousName != null && !previousName.equals(name)) {
98                            throw new DuplicateConstantError(name, previousName, value);
99                        }
100
101                        messageNames.put(value, name);
102                        if (DBG) {
103                            Log.d(TAG, String.format("Found constant: %s.%s = %d",
104                                    className, name, value));
105                        }
106                    } catch (SecurityException | IllegalAccessException e) {
107                        // Not allowed to make the field accessible, or no access. Ignore.
108                        continue;
109                    }
110                }
111            }
112        }
113        return messageNames;
114    }
115
116    /**
117     * Default prefixes for constants.
118     */
119    public static final String[] DEFAULT_PREFIXES = {"CMD_", "EVENT_"};
120
121    /**
122     * Finds the names of integer constants. Searches the specified {@code classes}, looking for
123     * accessible static integer values whose names begin with {@link #DEFAULT_PREFIXES}.
124     *
125     * @param classNames the classes to examine.
126     * @return a {@link SparseArray} mapping integer constants to their names.
127     */
128    public static SparseArray<String> findMessageNames(Class[] classNames) {
129        return findMessageNames(classNames, DEFAULT_PREFIXES);
130    }
131}
132
133