问题
I'm moving our servlets (pure Java, running in Tomcat 6) from CentOS to Debian, and faced the problem with executing commands with Runtime.exec().
(The command should be ImageMagick's convert in production, but I have simplified the calls to find the source of problems, so all the following code with echo is tested and not working as well).
String command = "echo test123 > /tmp/tomcat6-tmp/1";
Runtime runtime = Runtime.getRuntime();
Process process = runtime.exec(command);
int exitVal = process.waitFor();
Seems to be pretty common way to call an external program. It does run, returns 0 in exitVal, but fails to create file and put text in it.
So does low-level approach:
ProcessBuilder pb = new ProcessBuilder("echo", "test123 > /tmp/tomcat6-tmp/3");
Process process = pb.start();
int resInt = process.waitFor();
But it is possible to create a file and put some text in it using Java code placed in the same method:
String fname = "/tmp/tomcat6-tmp/2";
File file = new File(fname);
file.createNewFile();
FileWriter fileWriter = new FileWriter(file);
fileWriter.write("test123");
fileWriter.close();
Runtime.exec("whoami") successfully returns tomcat6, the folder /tmp/tomcat6-tmp/ does exist, all permissions are set correctly.
$ ls -al /tmp/tomcat6-tmp/
total 60
drwxr-xr-x 2 tomcat6 root 4096 Mar 2 15:26 .
drwxrwxrwt 6 root root 4096 Mar 2 15:25 ..
-rw-r--r-- 1 tomcat6 tomcat6 7 Mar 2 15:26 2
All commands without need to access files in system are seem to execute normally with Runtime.exec() in the same context.
I use fresh install of debian squeeze with tomcat6 installed from packages, without any modifications in configuration:
$ aptitude show tomcat6
Package: tomcat6
State: installed
Version: 6.0.28-9+squeeze1
.....
$ cat /etc/issue
Debian GNU/Linux 6.0 \n \l
How can I solve the issue? Or at least where should I look? I've googled every imaginable reason for Java to misbehave this way, but failed to find a clue.
P.S. As this is default installation, Java security manager is disabled in /etc/init.d/tomcat6
# Use the Java security manager? (yes/no)
TOMCAT6_SECURITY=no
回答1:
Put the action you want into a single executable shell script, then exec the shell script.
Java's Runtime.exec() is a wrapper around the exec system call, which will run the process directly, rather than under a sub-shell. The > redirection is carried out by the shell, and will not work as an argument to a directly execed process.
回答2:
Don't know if this "echo test123 > /tmp/tomcat6-tmp/1" can be run as one command. I remember that I had similar problem and I had to split it, so try to run "echo test123" and then obtain an input stream with the output of the command. If you have a stream you can easily write to file.
Moreover, you execute command with args so try to use method that takes array as a parameter.
来源：https://stackoverflow.com/questions/5168806/runtime-exec-from-tomcat6-succeeds-but-cannot-access-any-files