Android通过反射获取build.prop中的值（代码实例）

前言

我们知道system.prop文件中存储着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。

/* 
 * 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 
 * 
 *      https://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();  
            }  
        }  
    }  
}  

系统展示

/* 
 * 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 
 * 
 *      https://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();  
        }  
    }  
}