在android上运行native可执行程序

最近做了一些关于Android Native 编程相关的东西，在这篇文章中我将介绍如何在Android application中调用Native executable。至于如何编写Native executable和如何打包native到apk中，之前我都有文章介绍这里就不再重复了。

我写了一个Demo程序，演示如何在Android Application中调用Native executable。该示例中：

    * 可以调用系统自带的executable，例如“/system/bin/ls”；
    * 可以调用自己编写的Native executable，放置在apk的assets目录下；
    * 可以调用从远程服务器下载的Native executable；

接下来详细介绍代码的实现，在这里我们主要用到了android.os.Exec，但是android.os.Exec不被包含在android.jar中，因此只能通过java反射机制来实现。

以下代码实现了一个通用的exec函数：
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   1. private String exec(String arg0, String arg1, String arg2) { 
   2.         try { 
   3.             // android.os.Exec is not included in android.jar so we need to use reflection. 
   4.             Class execClass = Class.forName("android.os.Exec"); 
   5.             Method createSubprocess = execClass.getMethod("createSubprocess", 
   6.                     String.class, String.class, String.class, int[].class); 
   7.             Method waitFor = execClass.getMethod("waitFor", int.class); 
   8.  
   9.             // Executes the command. 
  10.             // NOTE: createSubprocess() is asynchronous. 
  11.             int[] pid = new int[1]; 
  12.             FileDescriptor fd = (FileDescriptor)createSubprocess.invoke( 
  13.                     null, arg0, arg1, arg2, pid); 
  14.  
  15.             // Reads stdout. 
  16.             // NOTE: You can write to stdin of the command using new FileOutputStream(fd). 
  17.             FileInputStream in = new FileInputStream(fd); 
  18.             BufferedReader reader = new BufferedReader(new InputStreamReader(in)); 
  19.             String output = ""; 
  20.             try { 
  21.                 String line; 
  22.                 while ((line = reader.readLine()) != null) { 
  23.                     output += line + "\n"; 
  24.                 } 
  25.             } catch (IOException e) { 
  26.                 // It seems IOException is thrown when it reaches EOF. 
  27.             } 
  28.  
  29.             // Waits for the command to finish. 
  30.             waitFor.invoke(null, pid[0]); 
  31.  
  32.             return output; 
  33.         } catch (ClassNotFoundException e) { 
  34.             throw new RuntimeException(e.getMessage()); 
  35.         } catch (SecurityException e) { 
  36.             throw new RuntimeException(e.getMessage()); 
  37.         } catch (NoSuchMethodException e) { 
  38.             throw new RuntimeException(e.getMessage()); 
  39.         } catch (IllegalArgumentException e) { 
  40.             throw new RuntimeException(e.getMessage()); 
  41.         } catch (IllegalAccessException e) { 
  42.             throw new RuntimeException(e.getMessage()); 
  43.         } catch (InvocationTargetException e) { 
  44.             throw new RuntimeException(e.getMessage()); 
  45.         } 
  46.     } 

private String exec(String arg0, String arg1, String arg2) {
try {
// android.os.Exec is not included in android.jar so we need to use reflection.
Class execClass = Class.forName("android.os.Exec");
        Method createSubprocess = execClass.getMethod("createSubprocess",
        String.class, String.class, String.class, int[].class);
        Method waitFor = execClass.getMethod("waitFor", int.class);

        // Executes the command.
        // NOTE: createSubprocess() is asynchronous.
        int[] pid = new int[1];
        FileDescriptor fd = (FileDescriptor)createSubprocess.invoke(
        null, arg0, arg1, arg2, pid);

        // Reads stdout.
        // NOTE: You can write to stdin of the command using new FileOutputStream(fd).
        FileInputStream in = new FileInputStream(fd);
        BufferedReader reader = new BufferedReader(new InputStreamReader(in));
        String output = "";
        try {
        String line;
while ((line = reader.readLine()) != null) {
output += line + "\n";
}
} catch (IOException e) {
// It seems IOException is thrown when it reaches EOF.
}

// Waits for the command to finish.
waitFor.invoke(null, pid[0]);

return output;
} catch (ClassNotFoundException e) {
throw new RuntimeException(e.getMessage());
} catch (SecurityException e) {
throw new RuntimeException(e.getMessage());
} catch (NoSuchMethodException e) {
throw new RuntimeException(e.getMessage());
} catch (IllegalArgumentException e) {
throw new RuntimeException(e.getMessage());
} catch (IllegalAccessException e) {
throw new RuntimeException(e.getMessage());
} catch (InvocationTargetException e) {
throw new RuntimeException(e.getMessage());
}
    }

以下代码实现如何执行assets中的Native executable程序：
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   1. private int getassetsfile(String fileName, String tagFile) { 
   2.         int retVal = 0; 
   3.         try { 
   4.  
   5.             File dir = new File(tagFile); 
   6.             if (dir.exists()) { 
   7.                 dir.delete(); 
   8.             } 
   9.  
  10.             InputStream in = this.getAssets().open(fileName); 
  11.             if(in.available() == 0) { 
  12.                 return retVal; 
  13.             } 
  14.  
  15.             FileOutputStream out = new FileOutputStream(tagFile); 
  16.             int read; 
  17.             byte[] buffer = new byte[4096]; 
  18.             while ((read = in.read(buffer)) > 0) { 
  19.                 out.write(buffer, 0, read); 
  20.             } 
  21.             out.close(); 
  22.             in.close(); 
  23.  
  24.             retVal = 1; 
  25.             return retVal; 
  26.         } catch (IOException e) { 
  27.             throw new RuntimeException(e.getMessage()); 
  28.         } 
  29.     } 

private int getassetsfile(String fileName, String tagFile) {
    int retVal = 0;
    try {

    File dir = new File(tagFile);
if (dir.exists()) {
dir.delete();
}

    InputStream in = this.getAssets().open(fileName);
    if(in.available() == 0) {
    return retVal;
    }

    FileOutputStream out = new FileOutputStream(tagFile);
int read;
byte[] buffer = new byte[4096];
while ((read = in.read(buffer)) > 0) {
out.write(buffer, 0, read);
}
out.close();
in.close();

retVal = 1;
return retVal;
} catch (IOException e) {
throw new RuntimeException(e.getMessage());
}
    }

以下代码实现如何执行远程服务器上的Native executable程序：
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   1. private void download(String urlStr, String localPath) { 
   2.         try { 
   3.             URL url = new URL(urlStr); 
   4.             HttpURLConnection urlconn = (HttpURLConnection)url.openConnection(); 
   5.             urlconn.setRequestMethod("GET"); 
   6.             urlconn.setInstanceFollowRedirects(true); 
   7.             urlconn.connect(); 
   8.             InputStream in = urlconn.getInputStream(); 
   9.             FileOutputStream out = new FileOutputStream(localPath); 
  10.             int read; 
  11.             byte[] buffer = new byte[4096]; 
  12.             while ((read = in.read(buffer)) > 0) { 
  13.                 out.write(buffer, 0, read); 
  14.             } 
  15.             out.close(); 
  16.             in.close(); 
  17.             urlconn.disconnect(); 
  18.         } catch (MalformedURLException e) { 
  19.             throw new RuntimeException(e.getMessage()); 
  20.         } catch (IOException e) { 
  21.             throw new RuntimeException(e.getMessage()); 
  22.         } 
  23.     } 

private void download(String urlStr, String localPath) {
    try {
URL url = new URL(urlStr);
HttpURLConnection urlconn = (HttpURLConnection)url.openConnection();
urlconn.setRequestMethod("GET");
urlconn.setInstanceFollowRedirects(true);
urlconn.connect();
InputStream in = urlconn.getInputStream();
FileOutputStream out = new FileOutputStream(localPath);
int read;
byte[] buffer = new byte[4096];
while ((read = in.read(buffer)) > 0) {
out.write(buffer, 0, read);
}
out.close();
in.close();
urlconn.disconnect();
} catch (MalformedURLException e) {
throw new RuntimeException(e.getMessage());
} catch (IOException e) {
throw new RuntimeException(e.getMessage());
}
    }

总结下：

通常有三种方法把Native executable放置到手机上：1.assets；2.via network；3.via pc use adb。在本例子中前两种方法都有实现，至于第三种我相信地球人都知道。

http://www.theiter.com/2010/05/%E5%9C%A8android%E4%B8%8A%E8%BF%90%E8%A1%8Cnative%E5%8F%AF%E6%89%A7%E8%A1%8C%E7%A8%8B%E5%BA%8F.html