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在apk中，有时候需要root权限，例如通过apk更新系统库等system的文件等，避免升级固件，或者在apk中需要直接访问某些设备等。下面是在apk中获取root权限的方法，前提是设备已经root过了。
关键点在于下面这句，通过执行su产生一个具有root权限的进程：
Process p = Runtime.getRuntime().exec("su");
然后，在向这个进程的写入要执行的命令，即可达到以root权限执行命令：
dos = new DataOutputStream(p.getOutputStream());
dos.writeBytes(cmd + "\n");
dos.flush();
或者用下面的方式：
Runtime.getRuntime().exec(new String[]{"/system/bin/su","-c", cmd});
经过测试，以root权限执行命令，只在真机上测试成功，在模拟器上没有成功过。
第一次运行时，会出现请求root权限的界面，选中记住，并允许：
测试程序界面，如果已经root，界面中可以显示出/system分区对应的设备节点：
主要文件：RootCmd.java
[java]
package org.ckl.root;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import android.util.Log;
public final class RootCmd {
private static final String TAG = "RootCmd";
private static boolean mHaveRoot = false;
// 判断机器Android是否已经root，即是否获取root权限
public static boolean haveRoot() {
if (!mHaveRoot) {
int ret = execRootCmdSilent("echo test"); // 通过执行测试命令来检测
if (ret != -1) {
Log.i(TAG, "have root!");
mHaveRoot = true;
} else {
Log.i(TAG, "not root!");
}
} else {
Log.i(TAG, "mHaveRoot = true, have root!");
}
return mHaveRoot;
}
// 执行命令并且输出结果
public static String execRootCmd(String cmd) {
String result = "";
DataOutputStream dos = null;
DataInputStream dis = null;
try {
Process p = Runtime.getRuntime().exec("su");// 经过Root处理的android系统即有su命令
dos = new DataOutputStream(p.getOutputStream());
dis = new DataInputStream(p.getInputStream());
Log.i(TAG, cmd);
dos.writeBytes(cmd + "\n");
dos.flush();
dos.writeBytes("exit\n");
dos.flush();
String line = null;
while ((line = dis.readLine()) != null) {
Log.d("result", line);
result += line;
}
p.waitFor();
} catch (Exception e) {
e.printStackTrace();
} finally {
if (dos != null) {
try {
dos.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if (dis != null) {
try {
dis.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
return result;
}
// 执行命令但不关注结果输出
public static int execRootCmdSilent(String cmd) {
int result = -1;
DataOutputStream dos = null;
try {
Process p = Runtime.getRuntime().exec("su");
dos = new DataOutputStream(p.getOutputStream());
Log.i(TAG, cmd);
dos.writeBytes(cmd + "\n");
dos.flush();
dos.writeBytes("exit\n");
dos.flush();
p.waitFor();
result = p.exitValue();
} catch (Exception e) {
e.printStackTrace();
} finally {
if (dos != null) {
try {
dos.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
return result;
}
}
相关文件：SystemPartition.java，获取/system分区设备节点，并支持重新mount /system为可读写：
[java]
package org.ckl.root;
import java.io.DataInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import android.util.Log;
public class SystemPartition {
private static final String TAG = "SystemMount";
private static String TMP_PATH = "/sdcard/mount.txt";
private static String mMountPiont = null;
private static boolean mWriteable = false;
private SystemPartition() {
Log.i(TAG, "new SystemMount()");
}
private static class SystemPartitionHolder {
private static SystemPartition instance = new SystemPartition();
}
public SystemPartition getInstance() {
return SystemPartitionHolder.instance;
}
public static String getSystemMountPiont() {
DataInputStream dis = null;
if (mMountPiont == null) {
try {
RootCmd.execRootCmd("mount > " + TMP_PATH);
// Runtime.getRuntime().exec("mount > " + TMP_PATH);
dis = new DataInputStream(new FileInputStream(TMP_PATH));
String line = null;
int index = -1;
while ( (line = dis.readLine()) != null ) {
index = line.indexOf(" /system ");
if (index > 0) {
mMountPiont = line.substring(0, index);
if (line.indexOf(" rw") > 0) {
mWriteable = true;
Log.i(TAG, "/system is writeable !");
} else {
mWriteable = false;
Log.i(TAG, "/system is readonly !");
}
break;
}
}
} catch (Exception e) {
e.printStackTrace();
} finally {
if (dis != null) {
try {
dis.close();
} catch (IOException e1) {
e1.printStackTrace();
}
dis = null;
}
File f = new File(TMP_PATH);
if (f.exists()) {
f.delete();
}
}
}
if (mMountPiont != null) {
Log.i(TAG, "/system mount piont: " + mMountPiont);
} else {
Log.i(TAG, "get /system mount piont failed !!!");
}
return mMountPiont;
}
public static boolean isWriteable() {
mMountPiont = null;
getSystemMountPiont();
return mWriteable;
}
public static void remountSystem(boolean writeable) {
String cmd = null;
getSystemMountPiont();
if (mMountPiont != null && RootCmd.haveRoot()) {
if (writeable) {
cmd = "mount -o remount,rw " + mMountPiont + " /system";
} else {
cmd = "mount -o remount,ro " + mMountPiont + " /system";
}
RootCmd.execRootCmdSilent(cmd);
isWriteable();
}
}
}
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