[英]java: how to both read and write to & from process thru pipe (stdin/stdout)
(i'm new to java) I need to start a process and receive 2 or 3 handles: for STDIN, STDOUT, (and STDERR), so I can write input to the process and receive its output, the same way command line pipes behave (eg "grep") (我是java新手)我需要启动一个进程并接收2个或3个句柄:对于STDIN,STDOUT,(和STDERR),所以我可以向进程写入输入并接收其输出,命令行管道的方式相同表现(例如“grep”)
in Python this is acheived with the following code: 在Python中,这是通过以下代码实现的:
from subprocess import Popen, PIPE
p = Popen(cmd, shell=True, stdin=PIPE, stdout=PIPE)
(child_stdin, child_stdout) = (p.stdin, p.stdout)
child_stdin.write('Yoram Opposum\n')
child_stdin.flush()
child_stdout.readlines()
What's the Java equivalent?? 什么是Java等价物?
I've tried so far 到目前为止我已经尝试过了
Process p = Runtime.getRuntime().exec(cmd);
BufferedReader inp = new BufferedReader( new InputStreamReader(p.getInputStream()) );
BufferedWriter out = new BufferedWriter( new OutputStreamWriter(p.getOutputStream()) );
out.write( "Some Text!\n\n" );
out.flush();
line = inp.readLine();
print("response1: " + line ); // that's ok
out.write( "Second Line...\n" );
out.flush();
line = inp.readLine();
print("response2: " + line ); // returns an empty string, if it returns,,,
inp.close();
out.close();
BTW the first try works only with \\n\\n, but doesn't work with single \\n (why?) BTW第一次尝试仅适用于\\ n \\ n,但不适用于单\\ n(为什么?)
the following code works, but all input is given in advance, not the behavior i'm looking for: 以下代码有效,但所有输入都是事先给出的,而不是我正在寻找的行为:
out.write( "Aaaaa\nBbbbbb\nCcccc\n" );
out.flush();
line = inp.readLine();
print("response1: " + line );
line = inp.readLine();
print("response2: " + line );
line = inp.readLine();
print("response3: " + line );
line = inp.readLine();
print("response4: " + line );
output: 输出:
response1: AAAAA
response2:
response3: bbbbbb
response4:
the process being run looks like that: 正在运行的进程看起来像这样:
s = sys.stdin.readline()
print s.upper()
s = sys.stdin.readline()
print s.lower()
ok, it was also my python's code fault, but opposite to @Jon's answer, there was an EXTRA newline (0xA0 to be exact, which isn't Windows' standard). 好吧,这也是我的python的代码错误,但与@ Jon的答案相反,有一个EXTRA换行符(确切地说是0xA0,这不是Windows的标准)。
once i'm strip()ing the extra 0xA0 from the line i get from Java, python adds a single "normal" \\n to Java on the way back, and things run smoothly. 一旦我从Java中获取了额外的0xA0,python就会在回来的路上为Java添加一个“正常”的\\ n,并且事情顺利进行。
for the completeness of the question and answer, here's a working Java code: 为了问题和答案的完整性,这是一个有效的Java代码:
import java.io.*;
import java.util.*;
public class Main {
public static BufferedReader inp;
public static BufferedWriter out;
public static void print(String s) {
System.out.println(s);
}
public static String pipe(String msg) {
String ret;
try {
out.write( msg + "\n" );
out.flush();
ret = inp.readLine();
return ret;
}
catch (Exception err) {
}
return "";
}
public static void main(String[] args) {
String s;
String cmd = "c:\\programs\\python\\python.exe d:\\a.py";
try {
print(cmd);
print(System.getProperty("user.dir"));
Process p = Runtime.getRuntime().exec(cmd);
inp = new BufferedReader( new InputStreamReader(p.getInputStream()) );
out = new BufferedWriter( new OutputStreamWriter(p.getOutputStream()) );
print( pipe("AAAaaa") );
print( pipe("RoteM") );
pipe("quit")
inp.close();
out.close();
}
catch (Exception err) {
err.printStackTrace();
}
}
}
and this is the python code 这是python代码
import sys
s = sys.stdin.readline().strip()
while s not in ['break', 'quit']:
sys.stdout.write(s.upper() + '\n')
sys.stdout.flush()
s = sys.stdin.readline().strip()
I believe the problem is in the process you're calling: 我相信问题出在你正在调用的过程中:
s = sys.stdin.readline()
print s.upper()
s = sys.stdin.readline()
print s.lower()
I suspect that readline
is going to read the line but s
will not include the line terminator. 我怀疑readline
将读取该行,但s
将不包括行终止符。 You're then printing that line, but without a line terminator ... Java is then blocking until it reads a line terminator, which will block forever as the process isn't giving one. 然后你打印那行,但是没有行终止符 ......然后Java会阻塞,直到它读取一个行终止符,它将永远阻塞,因为进程没有给出。
This is all a bit of a guess as it's not exactly clear to me what language your called process is in - if print
actually does output a line terminator, then it's an incorrect guess. 这是一个猜测,因为我不清楚你所调用的语言是什么语言 - 如果print
确实输出了行终止符,那么这是一个不正确的猜测。 However, if not, you may need to change it to something like: 但是,如果没有,您可能需要将其更改为:
s = sys.stdin.readline()
println s.upper()
s = sys.stdin.readline()
println s.lower()
EDIT: That doesn't explain the blank lines in sample output... no idea what's going on, really, but unfortunately I can't look into it now. 编辑:这并没有解释样本输出中的空白行...不知道发生了什么,真的,但不幸的是我现在无法调查。
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