用Java執行命令行程序時只收到null

好的，所以我一直在試驗Process和Runtime類，並且遇到了問題。當我嘗試執行此命令時：cmd /c dir，輸出爲空。這裏是我的代碼片段：用Java執行命令行程序時只收到null

try { 
    Runtime runtime = Runtime.getRuntime(); 
    Process process = runtime.exec("cmd /c dir"); 

    BufferedReader output = new BufferedReader(new InputStreamReader(process.getInputStream())); 

    //BufferedReader serverOutputError = new BufferedReader(new InputStreamReader(serverStart.getErrorStream())); 

    String line = null; 

    while ((output.readLine()) != null) { 
     System.out.println(line); 
    } 

    int exitValue = process.waitFor(); 
    System.out.println("Command exited with exit value: " + exitValue); 

    process.destroy(); 
    System.out.println("destroyed"); 
} catch (IOException e) { 
    e.printStackTrace(); 
} catch (InterruptedException e) { 
    e.printStackTrace(); 
}

而且我得到這個對於輸出：

(18 lines of just "null") 
Command exited with exit value: 0 
destroyed

任何想法？

來源

2012-08-03 mattbdean

您從未設置您用於寫入控制檯的變量line。

更換

while ((output.readLine()) != null) {

與

while ((line = output.readLine()) != null) {

來源

2012-08-03 14:26:21

哦，謝謝。我甚至沒有意識到XD – mattbdean 2012-08-03 14:54:35

嘗試這樣的：

String line = output.readLine(); 

while (line != null) { 
    System.out.println(line); 
    line = output.readLine(); 
}

來源

2012-08-03 14:27:05 Tom

String line = null; 
while ((output.readLine()) != null) { 
     System.out.println(line); 
    }

這是你的問題。你永遠不會在你的循環中設置任何東西。它仍然是空的。您需要將行設置爲output.readLine（）的值。

while((line = output.readLine()) != null)

來源

2012-08-03 14:28:30 nook

然後你知道它一定是對的。 – nook 2012-08-03 15:35:16

while ((output.readLine()) != null) { 
    System.out.println(line); 
}

應該

while ((line = output.readLine()) != null) { 
    System.out.println(line); 
}

來源

2012-08-03 14:30:47 chead23

用Java執行命令行程序時只收到null

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