原文地址：https://www.2cto.com/kf/201210/159834.html

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();          }      }  }