的Java：啓動過程中的一個線索，並得到一個參考所創建的進程

Question

我有以下的集成測試代碼，我開始各種服務，然後測試才能運行：

@BeforeClass 
public static void setup() throws Exception { 

    // Set some vars like javaBin location 

    ProcessBuilder builder = new ProcessBuilder(javaBin, "-jar", "app.jar"); 
    Process process = launchProcess(builder); 

} 

private static Process launchProcess(ProcessBuilder builder) throws IOException { 

    AtomicReference<Process> process = new AtomicReference<>(); 
    new Thread(() -> { 
    try { 
     process.set(builder.start()); 

     BufferedReader processStd = new BufferedReader(new InputStreamReader(process.get().getInputStream());  
     BufferedReader processErr = new BufferedReader(new InputStreamReader(process.get().getErrorStream())); 

     // To prevent deadlocks due to limited buffer size 
     String s = ""; 
     while(processStd .readLine() != null) {} 
     while((s = processErr .readLine()) != null) { 
      System.err.println(s); 
     } 
    } 
    catch (IOException e) { 
     e.printStackTrace(); 
    } 
    }).start(); 

    return process.get(); 
} 

過程開始OK，但我process.get()總是返回null。我究竟做錯了什麼？如何使用上述方法獲得對已啓動流程的引用？如果我在setup()函數本身設置了進程，即process = builder.start()，那麼它可以正常工作。但是，這也導致了很多重複，因爲我需要在單獨的JVM中啓動許多單獨的服務。

Answer 1

問題很可能是線程在launchProcess的末尾以process.get()返回時實際未啓動。

您需要等待線程在您的方法返回之前實際啓動並執行process.set(builder.start())的調用。

這可以用一個簡單的東西來完成，如CountDownLatch。

private static Process launchProcess(ProcessBuilder builder) throws IOException { 
    final CountDownLatch latch = new CountDownLatch(1); 
    // ... 
    new Thread(() -> { 
    try { 
     process.set(builder.start()); 
     latch.countDown(); 
     //... 
    } catch (IOException e) { 
     //... 
    } 
    }).start(); 

    latch.await(); 
    return process.get(); 
}