MessageUtils.java revision d2457a3ee39ea55ed8e302bd93feede793cb5055 
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;
24
25/**
26 * Static utility class for dealing with {@link Message} objects.
27 */
28public class MessageUtils {
29
30    private static final String TAG = MessageUtils.class.getSimpleName();
31    private static final boolean DBG = false;
32
33    /** Thrown when two different constants have the same value. */
34    public static class DuplicateConstantError extends Error {
35        private DuplicateConstantError() {}
36        public DuplicateConstantError(String name1, String name2, int value) {
37            super(String.format("Duplicate constant value: both %s and %s = %d",
38                name1, name2, value));
39        }
40    }
41
42    /**
43     * Finds the names of integer constants. Searches the specified {@code classes}, looking for
44     * accessible static integer fields whose names begin with one of the specified {@prefixes}.
45     *
46     * @param classes the classes to examine.
47     * @prefixes only consider fields names starting with one of these prefixes.
48     * @return a {@link SparseArray} mapping integer constants to their names.
49     */
50    public static SparseArray<String> findMessageNames(Class[] classes, String[] prefixes) {
51        SparseArray<String> messageNames = new SparseArray<>();
52        for (Class c : classes) {
53            String className = c.getName();
54            if (DBG) Log.d(TAG, "Examining class " + className);
55
56            Field[] fields;
57            try {
58                fields = c.getDeclaredFields();
59            } catch (SecurityException e) {
60                Log.e(TAG, "Can't list fields of class " + className);
61                continue;
62            }
63
64            for (Field field : fields) {
65                String name = field.getName();
66
67                for (String prefix : prefixes) {
68                    // Does this look like a constant?
69                    if (!name.startsWith(prefix)) {
70                        continue;
71                    }
72
73                    try {
74                        // TODO: can we have the caller try to access the field instead, so we don't
75                        // expose constants it does not have access to?
76                        field.setAccessible(true);
77
78                        // Fetch the constant's value.
79                        int value;
80                        try {
81                            value = field.getInt(null);
82                        } catch (IllegalArgumentException | ExceptionInInitializerError e) {
83                            // The field is not an integer (or short or byte), or c's static
84                            // initializer failed and we have no idea what its value is.
85                            // Either way, give up on this field.
86                            break;
87                        }
88
89                        // Check for duplicate values.
90                        String previousName = messageNames.get(value);
91                        if (previousName != null && !previousName.equals(name)) {
92                            throw new DuplicateConstantError(name, previousName, value);
93                        }
94
95                        messageNames.put(value, name);
96                        if (DBG) {
97                            Log.d(TAG, String.format("Found constant: %s.%s = %d",
98                                    className, name, value));
99                        }
100                    } catch (SecurityException | IllegalAccessException e) {
101                        // Not allowed to make the field accessible, or no access. Ignore.
102                        continue;
103                    }
104                }
105            }
106        }
107        return messageNames;
108    }
109
110    /**
111     * Default prefixes for constants.
112     */
113    public static final String[] DEFAULT_PREFIXES = {"CMD_", "EVENT_"};
114
115    /**
116     * Finds the names of integer constants. Searches the specified {@code classes}, looking for
117     * accessible static integer values whose names begin with {@link #DEFAULT_PREFIXES}.
118     *
119     * @param classNames the classes to examine.
120     * @prefixes only consider fields names starting with one of these prefixes.
121     * @return a {@link SparseArray} mapping integer constants to their names.
122     */
123    public static SparseArray<String> findMessageNames(Class[] classNames) {
124        return findMessageNames(classNames, DEFAULT_PREFIXES);
125    }
126}
127
128