Android通过SystemProperties获取build.prop中配置的信息
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前言
我们知道system.prop文件中存储着系统运行的很多配置信息（具体特定平台或产品的修改信息），system.prop文件中的内容最终会被编译到build.prop文件中，当程序运行时需要某种系统状态时，会到build.prop中进行读取。Android中提供了一个android.os.SystemProperties类来负责读取其中的内容，并且提供了几个Static的方法，可以让应用很方便地使用。
系统源码展示
/* * Copyright (C) 2006 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;/** * Gives access to the system properties store. The system properties * store contains a list of string key-value pairs. * * {@hide} */public class SystemProperties{ public static final int PROP_NAME_MAX = 31; public static final int PROP_VALUE_MAX = 91; private static final ArrayList<Runnable> sChangeCallbacks = new ArrayList<Runnable>(); private static native String native_get(String key); private static native String native_get(String key, String def); private static native int native_get_int(String key, int def); private static native long native_get_long(String key, long def); private static native boolean native_get_boolean(String key, boolean def); private static native void native_set(String key, String def); private static native void native_add_change_callback(); /** * Get the value for the given key. * @return an empty string if the key isn't found * @throws IllegalArgumentException if the key exceeds 32 characters */ public static String get(String key) { if (key.length() > PROP_NAME_MAX) { throw new IllegalArgumentException("key.length > " + PROP_NAME_MAX); } return native_get(key); } /** * Get the value for the given key. * @return if the key isn't found, return def if it isn't null, or an empty string otherwise * @throws IllegalArgumentException if the key exceeds 32 characters */ public static String get(String key, String def) { if (key.length() > PROP_NAME_MAX) { throw new IllegalArgumentException("key.length > " + PROP_NAME_MAX); } return native_get(key, def); } /** * Get the value for the given key, and return as an integer. * @param key the key to lookup * @param def a default value to return * @return the key parsed as an integer, or def if the key isn't found or * cannot be parsed * @throws IllegalArgumentException if the key exceeds 32 characters */ public static int getInt(String key, int def) { if (key.length() > PROP_NAME_MAX) { throw new IllegalArgumentException("key.length > " + PROP_NAME_MAX); } return native_get_int(key, def); } /** * Get the value for the given key, and return as a long. * @param key the key to lookup * @param def a default value to return * @return the key parsed as a long, or def if the key isn't found or * cannot be parsed * @throws IllegalArgumentException if the key exceeds 32 characters */ public static long getLong(String key, long def) { if (key.length() > PROP_NAME_MAX) { throw new IllegalArgumentException("key.length > " + PROP_NAME_MAX); } return native_get_long(key, def); } /** * Get the value for the given key, returned as a boolean. * Values 'n', 'no', '0', 'false' or 'off' are considered false. * Values 'y', 'yes', '1', 'true' or 'on' are considered true. * (case sensitive). * If the key does not exist, or has any other value, then the default * result is returned. * @param key the key to lookup * @param def a default value to return * @return the key parsed as a boolean, or def if the key isn't found or is * not able to be parsed as a boolean. * @throws IllegalArgumentException if the key exceeds 32 characters */ public static boolean getBoolean(String key, boolean def) { if (key.length() > PROP_NAME_MAX) { throw new IllegalArgumentException("key.length > " + PROP_NAME_MAX); } return native_get_boolean(key, def); } /** * Set the value for the given key. * @throws IllegalArgumentException if the key exceeds 32 characters * @throws IllegalArgumentException if the value exceeds 92 characters */ public static void set(String key, String val) { if (key.length() > PROP_NAME_MAX) { throw new IllegalArgumentException("key.length > " + PROP_NAME_MAX); } if (val != null && val.length() > PROP_VALUE_MAX) { throw new IllegalArgumentException("val.length > " + PROP_VALUE_MAX); } native_set(key, val); } public static void addChangeCallback(Runnable callback) { synchronized (sChangeCallbacks) { if (sChangeCallbacks.size() == 0) { native_add_change_callback(); } sChangeCallbacks.add(callback); } } static void callChangeCallbacks() { synchronized (sChangeCallbacks) { //Log.i("foo", "Calling " + sChangeCallbacks.size() + " change callbacks!"); if (sChangeCallbacks.size() == 0) { return; } ArrayList<Runnable> callbacks = new ArrayList<Runnable>(sChangeCallbacks); for (int i=0; i<callbacks.size(); i++) { callbacks.get(i).run(); } } }}工具类源码展示
因为SystemProperties.java类已被系统隐藏，因此我们通过Java反射机制获取该类内容，通过get和set方法来读取、设置build.prop里面的内容。
package com.mufeng.testproject.tools;import android.content.Context;import android.util.Log;import java.io.File;import java.io.IOException;import java.lang.reflect.Method;import dalvik.system.DexFile;/** * Created by zhangqing on 2017/3/1. */public class SystemPropertiesProxy { public static final String TAG = "SystemPropertiesProxy"; /** * 根据给定的Key返回String类型的值 * * @param context 上下文 * @param key 获取指定信息所需的key * @return 返回一个String类型的值，如果不存在该key则返回空字符串 */ public static String getString(Context context, String key) { String result = ""; try { ClassLoader classLoader = context.getClassLoader(); @SuppressWarnings("rawtypes") Class SystemProperties = classLoader.loadClass("android.os.SystemProperties"); //参数类型 @SuppressWarnings("rawtypes") Class[] paramTypes = new Class[1]; paramTypes[0] = String.class; Method getString = SystemProperties.getMethod("get", paramTypes); //参数 Object[] params = new Object[1]; params[0] = new String(key); result = (String) getString.invoke(SystemProperties, params); } catch (IllegalArgumentException e) { //e.printStackTrace(); //如果key超过32个字符则抛出该异常 Log.w(TAG, "key超过32个字符"); } catch (Exception e) { result = ""; } return result; } /** * 根据给定的Key返回String类型的值 * * @param context 上下文 * @param key 获取指定信息所需的key * @param def key不存在时的默认值 * @return 返回一个String类型的值，如果key不存在, 并且如果def不为null则返回def,否则返回空字符串 */ public static String getString(Context context, String key, String def) { String result = def; try { ClassLoader classLoader = context.getClassLoader(); @SuppressWarnings("rawtypes") Class SystemProperties = classLoader.loadClass("android.os.SystemProperties"); //参数类型 @SuppressWarnings("rawtypes") Class[] paramTypes = new Class[2]; paramTypes[0] = String.class; paramTypes[1] = String.class; Method getString = SystemProperties.getMethod("get", paramTypes); //参数 Object[] params = new Object[2]; params[0] = new String(key); params[1] = new String(def); result = (String) getString.invoke(SystemProperties, params); } catch (IllegalArgumentException e) { //e.printStackTrace(); //如果key超过32个字符则抛出该异常 Log.w(TAG, "key超过32个字符"); } catch (Exception e) { result = def; } return result; } /** * 根据给定的key返回int类型的值 * * @param context 上下文 * @param key 要查询的key * @param def 默认返回值 * @return 返回一个int类型的值，如果没有发现则返回默认值 def */ public static Integer getInt(Context context, String key, int def) { Integer result = def; try { ClassLoader classLoader = context.getClassLoader(); @SuppressWarnings("rawtypes") Class SystemProperties = classLoader.loadClass("android.os.SystemProperties"); //参数类型 @SuppressWarnings("rawtypes") Class[] paramTypes = new Class[2]; paramTypes[0] = String.class; paramTypes[1] = int.class; Method getInt = SystemProperties.getMethod("getInt", paramTypes); //参数 Object[] params = new Object[2]; params[0] = new String(key); params[1] = new Integer(def); result = (Integer) getInt.invoke(SystemProperties, params); } catch (IllegalArgumentException e) { //e.printStackTrace(); //如果key超过32个字符则抛出该异常 Log.w(TAG, "key超过32个字符"); } catch (Exception e) { result = def; } return result; } /** * 根据给定的key返回long类型的值 * * @param context 上下文 * @param key 要查询的key * @param def 默认返回值 * @return 返回一个long类型的值，如果没有发现则返回默认值def */ public static Long getLong(Context context, String key, long def) { Long result = def; try { ClassLoader classLoader = context.getClassLoader(); @SuppressWarnings("rawtypes") Class SystemProperties = classLoader.loadClass("android.os.SystemProperties"); //参数类型 @SuppressWarnings("rawtypes") Class[] paramTypes = new Class[2]; paramTypes[0] = String.class; paramTypes[1] = long.class; Method getLong = SystemProperties.getMethod("getLong", paramTypes); //参数 Object[] params = new Object[2]; params[0] = new String(key); params[1] = new Long(def); result = (Long) getLong.invoke(SystemProperties, params); } catch (IllegalArgumentException e) { //e.printStackTrace(); //如果key超过32个字符则抛出该异常 Log.w(TAG, "key超过32个字符"); } catch (Exception e) { result = def; } return result; } /** * 根据给定的key返回boolean类型的值 * 如果值为'n','no','0','false' or 'off'返回false * 如果值为'y','yes','1','true' or 'on'返回true * 如果key不存在, 或者是其它的值, 则返回默认值 * * @param context 上下文 * @param key 要查询的key * @param def 默认返回值 * @return 返回一个boolean类型的值，如果没有发现则返回默认值def */ public static Boolean getBoolean(Context context, String key, boolean def) { Boolean result = def; try { ClassLoader classLoader = context.getClassLoader(); @SuppressWarnings("rawtypes") Class SystemProperties = classLoader.loadClass("android.os.SystemProperties"); //参数类型 @SuppressWarnings("rawtypes") Class[] paramTypes = new Class[2]; paramTypes[0] = String.class; paramTypes[1] = boolean.class; Method getBoolean = SystemProperties.getMethod("getBoolean", paramTypes); //参数 Object[] params = new Object[2]; params[0] = new String(key); params[1] = new Boolean(def); result = (Boolean) getBoolean.invoke(SystemProperties, params); } catch (IllegalArgumentException e) { //e.printStackTrace(); //如果key超过32个字符则抛出该异常 Log.w(TAG, "key超过32个字符"); } catch (Exception e) { result = def; } return result; } /** * 根据给定的key和值设置属性, 该方法需要特定的权限才能操作. * * @param context 上下文 * @param key 设置属性的key * @param val 设置属性的value */ public static void set(Context context, String key, String val) { try { @SuppressWarnings("rawtypes") DexFile df = new DexFile(new File("/system/app/Settings.apk")); ClassLoader classLoader = context.getClassLoader(); @SuppressWarnings("rawtypes") Class SystemProperties = Class.forName("android.os.SystemProperties"); //参数类型 @SuppressWarnings("rawtypes") Class[] paramTypes = new Class[2]; paramTypes[0] = String.class; paramTypes[1] = String.class; Method set = SystemProperties.getMethod("set", paramTypes); //参数 Object[] params = new Object[2]; params[0] = new String(key); params[1] = new String(val); set.invoke(SystemProperties, params); } catch (IllegalArgumentException e) { //e.printStackTrace(); //如果key超过32个字符或者value超过92个字符则抛出该异常 Log.w(TAG, "key超过32个字符或者value超过92个字符"); } catch (Exception e) { e.printStackTrace(); } }} 1 0
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