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在Windows下，當我的程序從命令行啓動時，無法可靠地操作子進程的I/O。這很令人沮喪，因爲它是服務器使用控制檯進行I/O的標準。圖形用戶界面很好，但我更喜歡堅持命令行並保持簡單。我注意到當我從Eclipse IDE執行我的服務器時，子進程I/O就沒有問題，但是從命令行運行完全不同的故事。我無法讀取或寫入子進程，但該進程仍將運行。我在下面寫了一些測試代碼來證明這個問題，我希望這個問題可以在另一臺機器上覆制，然後希望能夠從中解決問題。從Eclipse執行時，繼承的I/O按預期工作。但是，從Windows命令提示符處執行時，無法讀取或寫入子進程。在這兩種情況下，將子進程輸出重定向到文件總是成功，但輸入仍然不能傳遞給子進程。如果已經有解決這個問題的方法，請鏈接頁面。當設置爲父級的標準IO（命令提示符）時，Windows Java子進程不會輸入或輸出
JRE/JDK實現：
>java -version
java version "1.7.0_01"
Java(TM) SE Runtime Environment (build 1.7.0_01-b08)
Java HotSpot(TM) 64-Bit Server VM (build 21.1-b02, mixed mode)
考慮下面的代碼：
package com.comp8nerd4u2.io.test;
/*
* These tests attempt to confirm what I'm experiencing under my build environment
*/
import java.io.File;
import java.io.IOException;
public final class PIOTest {
/** The command to run as a child process. The command itself isn't the test, but what you use to run this Java program is the test. */
private static final String[] COMMAND = {"cmd.exe", "/c", "echo This is a test. Feel free to change this."}; // Change this to just {"cmd.exe"} or some other program that accepts input and you'll see how frustrating this is
/** Controls how the test process is built */
private static final ProcessBuilder PB = new ProcessBuilder(COMMAND);
/** How long to allow the process to run before forcibly terminating it. */
private static final long PROCESS_TIMEOUT = 10000L;
private static final Runnable R = new TimedInterruptWorker(PROCESS_TIMEOUT);
private static int n = 0;
static {
PB.redirectErrorStream(true);
}
private PIOTest() {}
public static void main(String[] args) {
// ----- Begin Tests -----
/*
* Test #1: Let's test putting our command's output onto our standard I/O streams
* Goal condition: Child process outputs expected output, and exits before the timeout. If child process expects input, it should accept entered input.
* Known success factors: Parent process' standard I/O is piped to Eclipse. Tests would probably succeed with Netbeans as well
* Known fail factors: Parent process' standard I/O is piped to Windows Command Prompt
* Result under fail condition: Child process hangs if it fills up its output buffer or requests input, but exits on its own otherwise, unless it took longer than the timeout.
*/
PB.inheritIO();
doTest();
// Test #2: Let's test putting our command's output into a file
PB.redirectOutput(new File("piotest.txt"));
doTest();
}
/**
* Performs the I/O test.
*/
private static void doTest() {
n++;
Process p = null;
try {
p = PB.start();
} catch (IOException e) {
e.printStackTrace();
return;
}
try {
Thread t = new Thread(R);
t.setDaemon(true);
t.start();
System.out.format("[Test #%d] Child exited with status code %d\n", n, p.waitFor());
t.interrupt();
} catch (InterruptedException e) {
p.destroy();
System.out.format("[Test #%d] Child took longer than the timeout.\n", n);
}
}
/**
* Useful for sending interrupts after a certain amount of time has passed.
*
* @author comp8nerd4u2
*/
private static final class TimedInterruptWorker implements Runnable {
private long timeout = 0;
private Thread target = null;
public TimedInterruptWorker(long timeout) {
this(timeout, Thread.currentThread());
}
public TimedInterruptWorker(long timeout, Thread target) {
this.timeout = timeout;
this.target = target;
}
@Override
public void run() {
try {
Thread.sleep(timeout);
} catch (InterruptedException e) {
return;
}
target.interrupt();
}
}
}
更新：我修改了測試，以接受在運行任何命令，並將其上傳到我的Linux VPS服務器。我從ssh會話中運行它，並且所有子進程的I/O都可以輕鬆讀取和寫入。有一件事我注意到了。當我作爲一個子進程打開一個交互式bash shell，然後將其輸出重定向到一個文件時，我想，CentOS停止了我的程序。那或我的程序崩潰了。
[[email protected] piotest]$ java -jar piotest.jar
Enter command to run : bash
[[email protected] piotest]$ [Test #1] Child took longer than the timeout.
[1]+ Stopped java -jar piotest.jar
[[email protected] piotest]$
第一行是我輸入的命令。第二行是產生的bash shell，但我從來沒有輸入任何東西，所以我的程序在超時後殺死它。它準備好進行第二次測試，創建「piotest.txt」文件，然後崩潰或被OS停止。實際的測試本身並沒有改變，只是測試現在允許你輸入在運行時運行的命令。這在linux中正常工作，但不在Windows中。我希望知道Win32 API的人能夠以某種方式解釋爲什麼這個測試在Windows中失敗。
沒有什麼內在的原因，這不應該工作在Windows上，它看起來就像Java 7運行時中的一個bug一樣。 –
你還在爲此工作嗎？我可能會有一個建議。 –
解決方法是手動流式I/O。我認爲JVM實現只是針對繼承的I/O而被竊聽。我想里程會因不同的實施而有所不同。 – comp8nerd4u2