關於Java中Process類和Runtime.exec()的一些使用
阿新 • • 發佈:2019-02-02
在Android中有一個需求,有幾個二進位制可執行檔案要執行,並作為單獨的程序跑在後臺,需要監聽它們的狀態,如果意外終止,要重啟它們。
啟動程式碼大致如下所示:
Runtime.getRuntime().exec("chmod 777 " + mContext.getApplicationContext(). getApplicationContext().getFilesDir().getAbsolutePath() + "/" + copyFileNameList.get(i)); Process process = Runtime.getRuntime().exec(mContext.getApplicationContext(). getFilesDir().getAbsolutePath() + "/" + copyFileNameList.get(i) + " " + copyFileExArgs.get(i));
Runtime.getRuntime().exec()相當於你可以在Java程式中執行Linux終端中的命令,chmod給許可權,這裡不展開說,然後我們就可以得到一個Process物件。
想拿到程序PID,檢視API:http://docs.oracle.com/javase/7/docs/api/java/lang/Process.html ,發現沒有獲得PID的方法,不過通過:
System.out.println(process.toString())
的輸出結果:
Process[pid=2869]
稍微解析下就OK,程式碼如下:
public int getPIDFromProcessToString(String s) { StringBuilder stringBuilder = new StringBuilder(); for (int i = 0; i < s.length(); i++) { if (s.charAt(i) >= '0' && s.charAt(i) <= '9') { stringBuilder.append(s.charAt(i)); } } return Integer.valueOf(stringBuilder.toString()); }
那麼如何在程序意外終止,重啟它們。
方法一是輪詢,從proc目錄中我們可以獲得正在執行程序的PID,程式碼如下:
public HashMap<Integer, Integer> getRunningPIDFromProc() { HashMap<Integer, Integer> hashMap = new HashMap<>(); File file = new File("/proc"); File[] files = file.listFiles(); for (File temp : files) { if (stringIsDigit(temp.getName())) { hashMap.put(Integer.valueOf(temp.getName()), 0); } } return hashMap; }
將程序PID作為HashMap的key值,通過下面程式碼每個一段時間判斷下即可:
!hashMap.containsKey(zSXSharedPreferences.getInt(copyFileNameList.get(i) + "_pid", -1))
如果掛掉了,重啟即可。具體實現的時候開個執行緒即可,具體程式碼大概如下:
// polling thread
new Thread(new Runnable() {
@Override
public void run() {
while (true) {
try {
Thread.sleep(15*60000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("polling thread");
HashMap<Integer, Integer> hashMap = getRunningPIDFromProc();
for (int i = 0; i < copyFileNameList.size(); i++) {
System.out.println("PID in SharedPreferences:" + zSXSharedPreferences.getInt(copyFileNameList.get(i) + "_pid", -1));
if (!hashMap.containsKey(zSXSharedPreferences.getInt(copyFileNameList.get(i) + "_pid", -1))) {
System.out.println(mContext.getApplicationContext().
getApplicationContext().getFilesDir().getAbsolutePath() + "/" +
copyFileNameList.get(i) + " " + copyFileExArgs.get(i));
Process process = null;
try {
process = Runtime.getRuntime().exec(mContext.getApplicationContext().
getApplicationContext().getFilesDir().getAbsolutePath() + "/" +
copyFileNameList.get(i) + " " + copyFileExArgs.get(i));
System.out.println(process.toString() + "***");
zSXEditor.putInt(copyFileNameList.get(i) + "_pid",
getPIDFromProcessToString(process.toString()));
zSXEditor.commit();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
}).start();
方法二可以藉助Process.waitFor()方法。具體就是開個執行緒來啟動我們要啟動的程序,然後在Process.waitFor()後再遞迴呼叫這個過程,這樣當我們的程序被殺死後,就又可以被啟動了,如果覺得馬上就啟動太明顯的話,還可以做個延時,過段時間再啟動,具體見下面的程式碼:
public void startThreadForProcess(final int finalI,final List<String> copyFileNameList,
final List<String> copyFileExArgs,
final SharedPreferences.Editor zSXEditor) {
new Thread(new Runnable() {
@Override
public void run() {
Process process = null;
try {
process = Runtime.getRuntime().exec(mContext.getApplicationContext().
getApplicationContext().getFilesDir().getAbsolutePath() + "/" +
copyFileNameList.get(finalI) + " " + copyFileExArgs.get(finalI));
System.out.println(process.toString() + "**");
zSXEditor.putInt(copyFileNameList.get(finalI) + "_pid", getPIDFromProcessToString(process.toString()));
try {
System.out.println("process.waitFor()");
process.waitFor();
System.out.println("process.waitFor() stop");
startThreadForProcess(finalI,copyFileNameList,copyFileExArgs,zSXEditor);
} catch (InterruptedException e) {
System.out.println("process.waitFor() InterruptedException");
e.printStackTrace();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}).start();
}