Mixing
InheritIO and redirecting stdout
I'm trying to write a test for a class that uses ProcessBuilder.inheritIO and I can't seem to get it to work. I've stripped the code down to the core and came up with the following example that I think should write all the output of the child process to a ByteArrayOutputStream but doesn't.
Environment: Java 9.0.4 on Windows 7
import java.io.*;
public class ProcessTest {
public static void main(String args) throws Throwable {
PrintStream original = System.out;
ByteArrayOutputStream baos = new ByteArrayOutputStream();
PrintStream ps = new PrintStream(baos);
System.setOut(ps);
System.out.println("BEGIN");
Process process = new ProcessBuilder().command("where", "where")
.inheritIO().start();
process.waitFor();
System.out.println("END");
String output = new String(baos.toByteArray());
original.println("output = " + output);
}
}
The output is:
C:WindowsSystem32where.exe
output = BEGIN
END
And when I look in the debugger, the output stream does not contain the path to where.
I'm thinking System.setOut isn't doing what I'm thinking but I'm not sure. I found other SO questions suggest a StreamGrabber but I thought that was for Java 6 and earlier and inheritIO would work for me. Any help would be appreciated. Thanks.
Edit
I've come to realize that calling System.setOut() isn't really doing what I hope. It is not changing the underlying file descriptor of 1. If I was doing this in C, I would be working with the low level file descriptors. But that's not what setOut() is doing. That's just changing pointers.
java io processbuilder
asked Nov 21 '18 at 13:48
Mike BrazinskiMike Brazinski
11
add a comment |
I'm trying to write a test for a class that uses ProcessBuilder.inheritIO and I can't seem to get it to work. I've stripped the code down to the core and came up with the following example that I think should write all the output of the child process to a ByteArrayOutputStream but doesn't.
Environment: Java 9.0.4 on Windows 7
import java.io.*;
public class ProcessTest {
public static void main(String args) throws Throwable {
PrintStream original = System.out;
ByteArrayOutputStream baos = new ByteArrayOutputStream();
PrintStream ps = new PrintStream(baos);
System.setOut(ps);
System.out.println("BEGIN");
Process process = new ProcessBuilder().command("where", "where")
.inheritIO().start();
process.waitFor();
System.out.println("END");
String output = new String(baos.toByteArray());
original.println("output = " + output);
}
}
The output is:
C:WindowsSystem32where.exe
output = BEGIN
END
And when I look in the debugger, the output stream does not contain the path to where.
I'm thinking System.setOut isn't doing what I'm thinking but I'm not sure. I found other SO questions suggest a StreamGrabber but I thought that was for Java 6 and earlier and inheritIO would work for me. Any help would be appreciated. Thanks.
Edit
I've come to realize that calling System.setOut() isn't really doing what I hope. It is not changing the underlying file descriptor of 1. If I was doing this in C, I would be working with the low level file descriptors. But that's not what setOut() is doing. That's just changing pointers.
java io processbuilder
asked Nov 21 '18 at 13:48
Mike BrazinskiMike Brazinski
11
I have just verified I'm seeing the same behavior under CentOS, changing "where" to "which".
– Mike Brazinski
Nov 21 '18 at 14:46
add a comment |
I'm trying to write a test for a class that uses ProcessBuilder.inheritIO and I can't seem to get it to work. I've stripped the code down to the core and came up with the following example that I think should write all the output of the child process to a ByteArrayOutputStream but doesn't.
Environment: Java 9.0.4 on Windows 7
import java.io.*;
public class ProcessTest {
public static void main(String args) throws Throwable {
PrintStream original = System.out;
ByteArrayOutputStream baos = new ByteArrayOutputStream();
PrintStream ps = new PrintStream(baos);
System.setOut(ps);
System.out.println("BEGIN");
Process process = new ProcessBuilder().command("where", "where")
.inheritIO().start();
process.waitFor();
System.out.println("END");
String output = new String(baos.toByteArray());
original.println("output = " + output);
}
}
The output is:
C:WindowsSystem32where.exe
output = BEGIN
END
And when I look in the debugger, the output stream does not contain the path to where.
I'm thinking System.setOut isn't doing what I'm thinking but I'm not sure. I found other SO questions suggest a StreamGrabber but I thought that was for Java 6 and earlier and inheritIO would work for me. Any help would be appreciated. Thanks.
Edit
I've come to realize that calling System.setOut() isn't really doing what I hope. It is not changing the underlying file descriptor of 1. If I was doing this in C, I would be working with the low level file descriptors. But that's not what setOut() is doing. That's just changing pointers.
java io processbuilder
asked Nov 21 '18 at 13:48
Mike BrazinskiMike Brazinski
11
I'm trying to write a test for a class that uses ProcessBuilder.inheritIO and I can't seem to get it to work. I've stripped the code down to the core and came up with the following example that I think should write all the output of the child process to a ByteArrayOutputStream but doesn't.
Environment: Java 9.0.4 on Windows 7
import java.io.*;
public class ProcessTest {
public static void main(String args) throws Throwable {
PrintStream original = System.out;
ByteArrayOutputStream baos = new ByteArrayOutputStream();
PrintStream ps = new PrintStream(baos);
System.setOut(ps);
System.out.println("BEGIN");
Process process = new ProcessBuilder().command("where", "where")
.inheritIO().start();
process.waitFor();
System.out.println("END");
String output = new String(baos.toByteArray());
original.println("output = " + output);
}
}
The output is:
C:WindowsSystem32where.exe
output = BEGIN
END
And when I look in the debugger, the output stream does not contain the path to where.
I'm thinking System.setOut isn't doing what I'm thinking but I'm not sure. I found other SO questions suggest a StreamGrabber but I thought that was for Java 6 and earlier and inheritIO would work for me. Any help would be appreciated. Thanks.
Edit
I've come to realize that calling System.setOut() isn't really doing what I hope. It is not changing the underlying file descriptor of 1. If I was doing this in C, I would be working with the low level file descriptors. But that's not what setOut() is doing. That's just changing pointers.
java io processbuilder
java io processbuilder
asked Nov 21 '18 at 13:48
Mike BrazinskiMike Brazinski
11
asked Nov 21 '18 at 13:48
Mike BrazinskiMike Brazinski
11
edited Nov 23 '18 at 14:12
Mike Brazinski
asked Nov 21 '18 at 13:48
Mike BrazinskiMike Brazinski
11
asked Nov 21 '18 at 13:48
Mike BrazinskiMike Brazinski
11
asked Nov 21 '18 at 13:48
Mike BrazinskiMike Brazinski
11
11
I have just verified I'm seeing the same behavior under CentOS, changing "where" to "which".
– Mike Brazinski
Nov 21 '18 at 14:46
add a comment |
I have just verified I'm seeing the same behavior under CentOS, changing "where" to "which".
– Mike Brazinski
Nov 21 '18 at 14:46
I have just verified I'm seeing the same behavior under CentOS, changing "where" to "which".
– Mike Brazinski
Nov 21 '18 at 14:46
I have just verified I'm seeing the same behavior under CentOS, changing "where" to "which".
– Mike Brazinski
Nov 21 '18 at 14:46
add a comment |
1 Answer
1
active
oldest
votes
System.setOut changes the Java process’s standard output. There’s no guarantee it will affect child processes.
Regardless, it’s probably not a good idea to alter a global setting just to capture the output of a single process, especially if you expect your code to run amidst other other code (libraries, appications, etc.).
Solution: Don’t try to hack System.out. Read from the Process’s stdout InputStream:
ProcessBuilder builder = new ProcessBuilder().command("where", "where").inheritIO();
builder.redirectOutput(ProcessBuilder.Redirect.PIPE);
Process process = builder.start();
String output;
try (InputStream processStdOut = process.getInputStream()) {
output = new String(processStdOut.readAllBytes());
}
process.waitFor();
answered Nov 21 '18 at 15:41
VGRVGR
22.8k42840
I'm trying to avoid opening new streams as the real world version of this starts 16 processes. The legacy code (pre-Java 5) I'm updating uses 64 threads to monitor the processes (1 each for stdin, out and err and a watchdog thread) and merge the pipes. I was hopinginheritIOwould take care of a lot of that for me.
– Mike Brazinski
Nov 23 '18 at 13:58
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
System.setOut changes the Java process’s standard output. There’s no guarantee it will affect child processes.
Regardless, it’s probably not a good idea to alter a global setting just to capture the output of a single process, especially if you expect your code to run amidst other other code (libraries, appications, etc.).
Solution: Don’t try to hack System.out. Read from the Process’s stdout InputStream:
ProcessBuilder builder = new ProcessBuilder().command("where", "where").inheritIO();
builder.redirectOutput(ProcessBuilder.Redirect.PIPE);
Process process = builder.start();
String output;
try (InputStream processStdOut = process.getInputStream()) {
output = new String(processStdOut.readAllBytes());
}
process.waitFor();
answered Nov 21 '18 at 15:41
VGRVGR
22.8k42840
I'm trying to avoid opening new streams as the real world version of this starts 16 processes. The legacy code (pre-Java 5) I'm updating uses 64 threads to monitor the processes (1 each for stdin, out and err and a watchdog thread) and merge the pipes. I was hopinginheritIOwould take care of a lot of that for me.
– Mike Brazinski
Nov 23 '18 at 13:58
add a comment |
System.setOut changes the Java process’s standard output. There’s no guarantee it will affect child processes.
Regardless, it’s probably not a good idea to alter a global setting just to capture the output of a single process, especially if you expect your code to run amidst other other code (libraries, appications, etc.).
Solution: Don’t try to hack System.out. Read from the Process’s stdout InputStream:
ProcessBuilder builder = new ProcessBuilder().command("where", "where").inheritIO();
builder.redirectOutput(ProcessBuilder.Redirect.PIPE);
Process process = builder.start();
String output;
try (InputStream processStdOut = process.getInputStream()) {
output = new String(processStdOut.readAllBytes());
}
process.waitFor();
answered Nov 21 '18 at 15:41
VGRVGR
22.8k42840
I'm trying to avoid opening new streams as the real world version of this starts 16 processes. The legacy code (pre-Java 5) I'm updating uses 64 threads to monitor the processes (1 each for stdin, out and err and a watchdog thread) and merge the pipes. I was hopinginheritIOwould take care of a lot of that for me.
– Mike Brazinski
Nov 23 '18 at 13:58
add a comment |
System.setOut changes the Java process’s standard output. There’s no guarantee it will affect child processes.
Regardless, it’s probably not a good idea to alter a global setting just to capture the output of a single process, especially if you expect your code to run amidst other other code (libraries, appications, etc.).
Solution: Don’t try to hack System.out. Read from the Process’s stdout InputStream:
ProcessBuilder builder = new ProcessBuilder().command("where", "where").inheritIO();
builder.redirectOutput(ProcessBuilder.Redirect.PIPE);
Process process = builder.start();
String output;
try (InputStream processStdOut = process.getInputStream()) {
output = new String(processStdOut.readAllBytes());
}
process.waitFor();
answered Nov 21 '18 at 15:41
VGRVGR
22.8k42840
System.setOut changes the Java process’s standard output. There’s no guarantee it will affect child processes.
Regardless, it’s probably not a good idea to alter a global setting just to capture the output of a single process, especially if you expect your code to run amidst other other code (libraries, appications, etc.).
Solution: Don’t try to hack System.out. Read from the Process’s stdout InputStream:
ProcessBuilder builder = new ProcessBuilder().command("where", "where").inheritIO();
builder.redirectOutput(ProcessBuilder.Redirect.PIPE);
Process process = builder.start();
String output;
try (InputStream processStdOut = process.getInputStream()) {
output = new String(processStdOut.readAllBytes());
}
process.waitFor();
answered Nov 21 '18 at 15:41
VGRVGR
22.8k42840
answered Nov 21 '18 at 15:41
VGRVGR
22.8k42840
answered Nov 21 '18 at 15:41
VGRVGR
22.8k42840
answered Nov 21 '18 at 15:41
VGRVGR
22.8k42840
22.8k42840
I'm trying to avoid opening new streams as the real world version of this starts 16 processes. The legacy code (pre-Java 5) I'm updating uses 64 threads to monitor the processes (1 each for stdin, out and err and a watchdog thread) and merge the pipes. I was hopinginheritIOwould take care of a lot of that for me.
– Mike Brazinski
Nov 23 '18 at 13:58
add a comment |
I'm trying to avoid opening new streams as the real world version of this starts 16 processes. The legacy code (pre-Java 5) I'm updating uses 64 threads to monitor the processes (1 each for stdin, out and err and a watchdog thread) and merge the pipes. I was hopinginheritIOwould take care of a lot of that for me.
– Mike Brazinski
Nov 23 '18 at 13:58
I'm trying to avoid opening new streams as the real world version of this starts 16 processes. The legacy code (pre-Java 5) I'm updating uses 64 threads to monitor the processes (1 each for stdin, out and err and a watchdog thread) and merge the pipes. I was hoping
inheritIO would take care of a lot of that for me.– Mike Brazinski
Nov 23 '18 at 13:58
I'm trying to avoid opening new streams as the real world version of this starts 16 processes. The legacy code (pre-Java 5) I'm updating uses 64 threads to monitor the processes (1 each for stdin, out and err and a watchdog thread) and merge the pipes. I was hoping
inheritIO would take care of a lot of that for me.– Mike Brazinski
Nov 23 '18 at 13:58
add a comment |
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I have just verified I'm seeing the same behavior under CentOS, changing "where" to "which".
– Mike Brazinski
Nov 21 '18 at 14:46