我是不是正确地向exec()发送了一系列命令“hello world”？
正确的输出，你好世界：
thufir@mordor:~$
thufir@mordor:~$ java -jar NetBeansProjects/HelloExec/dist/HelloExec.jar
Apr 05, 2016 7:11:23 AM net.bounceme.mordor.telnet.Main run
INFO: starting..
Apr 05, 2016 7:11:23 AM net.bounceme.mordor.telnet.Telnet <init>
INFO: connecting..
Apr 05, 2016 7:11:23 AM net.bounceme.mordor.telnet.Telnet connect
INFO: connect..
Apr 05, 2016 7:11:23 AM net.bounceme.mordor.telnet.Telnet connect
INFO: [echo hello 1, echo hello 2, echo hello 3]
Apr 05, 2016 7:11:24 AM net.bounceme.mordor.telnet.Telnet connect
INFO: did process..
Apr 05, 2016 7:11:24 AM net.bounceme.mordor.telnet.Telnet connect
INFO: trying..
hello 1
Apr 05, 2016 7:11:24 AM net.bounceme.mordor.telnet.Telnet read
SEVERE: exiting.. 0
thufir@mordor:~$
代码：
package net.bounceme.mordor.telnet;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;
import java.util.Properties;
import java.util.logging.Level;
import java.util.logging.Logger;
import static java.lang.System.out;
public class Telnet {
private final static Logger LOG = Logger.getLogger(Telnet.class.getName());
public Telnet() {
LOG.info("connecting..");
}
private List<String> getCommand() {
List<String> commands = new ArrayList<>();
commands.add("echo hello 1");
commands.add("echo hello 2");
commands.add("echo hello 3");
return commands;
}
private void read(Process process) throws IOException, InterruptedException {
BufferedReader input = new BufferedReader(new InputStreamReader(process.getInputStream()));
String line = null;
while ((line = input.readLine()) != null) {
out.println(line);
}
int exitVal = process.waitFor();
LOG.log(Level.SEVERE, "exiting.. {0}", exitVal);
}
private void connect() {
LOG.info("connect..");
Runtime runtime = Runtime.getRuntime();
List<String> cmds = getCommand();
String[] cmdArray = cmds.toArray(new String[cmds.size()]);
String command = cmdArray[0];
LOG.info(cmds.toString());
Process process = null;
try {
process = runtime.exec(command);
} catch (IOException ex) {
LOG.severe("process wrong");
Logger.getLogger(Telnet.class.getName()).log(Level.SEVERE, null, ex);
}
LOG.info("did process..");
LOG.info("trying..");
try {
read(process);
} catch (IOException | InterruptedException ex) {
LOG.severe("read wrong");
Logger.getLogger(Telnet.class.getName()).log(Level.SEVERE, null, ex);
}
}
public void tryConnect() {
connect();
}
}
碰撞：
thufir@mordor:~$
thufir@mordor:~$ java -jar NetBeansProjects/HelloExec/dist/HelloExec.jar
Apr 05, 2016 7:12:32 AM net.bounceme.mordor.telnet.Main run
INFO: starting..
Apr 05, 2016 7:12:32 AM net.bounceme.mordor.telnet.Telnet <init>
INFO: connecting..
Apr 05, 2016 7:12:32 AM net.bounceme.mordor.telnet.Telnet connect
INFO: connect..
Apr 05, 2016 7:12:32 AM net.bounceme.mordor.telnet.Telnet connect
INFO: [echo hello 1, echo hello 2, echo hello 3]
Apr 05, 2016 7:12:32 AM net.bounceme.mordor.telnet.Telnet connect
SEVERE: process wrong
Apr 05, 2016 7:12:32 AM net.bounceme.mordor.telnet.Telnet connect
SEVERE: null
java.io.IOException: Cannot run program "echo hello 1": error=2, No such file or directory
at java.lang.ProcessBuilder.start(ProcessBuilder.java:1048)
at java.lang.Runtime.exec(Runtime.java:620)
at java.lang.Runtime.exec(Runtime.java:485)
at net.bounceme.mordor.telnet.Telnet.connect(Telnet.java:48)
at net.bounceme.mordor.telnet.Telnet.tryConnect(Telnet.java:66)
at net.bounceme.mordor.telnet.Main.run(Main.java:17)
at net.bounceme.mordor.telnet.Main.main(Main.java:11)
Caused by: java.io.IOException: error=2, No such file or directory
at java.lang.UNIXProcess.forkAndExec(Native Method)
at java.lang.UNIXProcess.<init>(UNIXProcess.java:248)
at java.lang.ProcessImpl.start(ProcessImpl.java:134)
at java.lang.ProcessBuilder.start(ProcessBuilder.java:1029)
... 6 more
Apr 05, 2016 7:12:32 AM net.bounceme.mordor.telnet.Telnet connect
INFO: did process..
Apr 05, 2016 7:12:32 AM net.bounceme.mordor.telnet.Telnet connect
INFO: trying..
Exception in thread "main" java.lang.NullPointerException
at net.bounceme.mordor.telnet.Telnet.read(Telnet.java:30)
at net.bounceme.mordor.telnet.Telnet.connect(Telnet.java:57)
at net.bounceme.mordor.telnet.Telnet.tryConnect(Telnet.java:66)
at net.bounceme.mordor.telnet.Main.run(Main.java:17)
at net.bounceme.mordor.telnet.Main.main(Main.java:11)
thufir@mordor:~$
尝试使用cmdArray时：
process = runtime.exec(cmdArray);
推理：
...这是因为当exec被赋予一个字符串时，它首先解析它 （以某种我们不喜欢的方式）。相反，当给予exec时 字符串数组，它只是将它传递给操作系统而不用 解析它。