1.read value:

 public String readRegister(String path){
		 try {
 
				Process process = Runtime.getRuntime().exec("/system/bin/cat  "+path);
 
			    BufferedReader reader = new BufferedReader(
			            new InputStreamReader(process.getInputStream()));
			    int read;
			    char[] buffer = new char[4096];
			    StringBuffer output = new StringBuffer();
			    while ((read = reader.read(buffer)) > 0) {
			        output.append(buffer, 0, read);
			    }
			    reader.close();
			    
			    // Waits for the command to finish.
			    process.waitFor();			    
			    
			    System.out.println(output.toString());
			    valRegister = output.toString();
			    return valRegister;
			    
			} catch (IOException e) {
			    throw new RuntimeException(e);
			} catch (InterruptedException e) {
			    throw new RuntimeException(e);
			}		
     }
 

Runtime.getRuntime().exec("su -c chmod 777 /data/glad.txt");

3.write value:

Runtime.getRuntime().exec("/system/bin/sh /data/test.sh");

test.sh:
echo 777 > /data/glad.txt

ps:

   寫操作需要設定apk為系統應用。