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 sChangeCallbacks = new ArrayList();
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 callbacks = new ArrayList(sChangeCallbacks);
for (int i=0; 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();
}
}
}

Android通过SystemProperties获取build.prop中配置的信息

前言

系统源码展示

工具类源码展示

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