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();
- }
- }
- }
- }
/* * 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();
- }
- }
- }
转载于: https://blog.csdn.net/u013693649/article/details/60143634
反射技术在安卓中的应用:https://blog.csdn.net/tiefeng0606/article/details/51700866