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import java.io.*;
// This appears in Core Web Programming from
// Prentice Hall Publishers, and may be freely used
// or adapted. 1997 Marty Hall, hall@apl.jhu.edu.
/** A class that eases the pain of running external
* processes from applications.
* Lets you run a program three ways:
* <OL>
* <LI><B>exec</B>: Execute the command, returning
* immediately even if the command is still
* running. This would be appropriate
* for printing a file.
* <LI><B>execWait</B>: Execute the command, but
* don't return until the command finishes.
* This would be appropriate for
* sequential commands where the first depends
* on the second having finished (e.g.
* <CODE>javac</CODE> followed by
* <CODE>java</CODE>).
* <LI><B>execPrint</B>: Execute the command and
* print the output. This would be appropriate
* for the UNIX command <CODE>ls</CODE>.
* </OL>
* Note that the PATH is not taken into account,
* so you must specify the <B>full</B> pathname to
* the command, and shell builtin commands
* will not work. For instance, on Unix the above
* three examples might look like:
* <OL>
* <LI><PRE>Exec.exec("/usr/ucb/lpr Some-File");</PRE>
* <LI><PRE>
* Exec.execWait("/usr/local/bin/javac Foo.java");
* Exec.execWait("/usr/local/bin/java Foo");
* </PRE>
* <LI><PRE>Exec.execPrint("/usr/bin/ls -al");</PRE>
* </OL>
*
* @author Marty Hall
* (<A HREF="mailto:hall@apl.jhu.edu">
* hall@apl.jhu.edu</A>)
* @version 1.0 1997
*/
public class Exec {
//----------------------------------------------------
private static boolean verbose = true;
/** Determines if the Exec class should print which
* commands are being executed, and print error
* messages if a problem is found. Default is true.
*
* @param verboseFlag true: print messages.
* false: don't.
*/
public static void setVerbose(boolean verboseFlag) {
verbose = verboseFlag;
}
/** Will Exec print status messages? */
public static boolean getVerbose() {
return(verbose);
}
//----------------------------------------------------
/** Starts a process to execute the command. Returns
* immediately, even if the new process is still
* running.
*
* @param command The <B>full</B> pathname of the
* command to be executed. No shell builtins
* (e.g. "cd") or shell meta-chars (e.g. ">")
* allowed.
* @return false if a problem is known to occur, but
* since this returns immediately, problems
* aren't usually found in time.
* Returns true otherwise.
*/
public static boolean exec(String command) {
return(exec(command, false, false));
}
//----------------------------------------------------
/** Starts a process to execute the command. Waits
* for the process to finish before returning.
*
* @param command The <B>full</B> pathname of the
* command to be executed. No shell builtins
* or shell meta-chars allowed.
* @return false if a problem is known to occur,
* either due to an exception or from the
* subprocess returning a non-zero value.
* Returns true otherwise.
*/
public static boolean execWait(String command) {
return(exec(command, false, true));
}
//----------------------------------------------------
/** Starts a process to execute the command. Prints
* all output the command gives.
*
* @param command The <B>full</B> pathname of the
* command to be executed. No shell builtins
* or shell meta-chars allowed.
* @return false if a problem is known to occur,
* either due to an exception or from the
* subprocess returning a non-zero value.
* Returns true otherwise.
*/
public static boolean execPrint(String command) {
return(exec(command, true, false));
}
//----------------------------------------------------
// This creates a Process object via
// Runtime.getRuntime.exec(). Depending on the
// flags, it may call waitFor on the process
// to avoid continuing until the process terminates,
// or open an input stream from the process to read
// the results.
private static boolean exec(String command,
boolean printResults,
boolean wait) {
if (verbose) {
printSeparator();
System.out.println("Executing '" + command + "'.");
}
try {
// Start running command, returning immediately.
Process p = Runtime.getRuntime().exec(command);
// Print the output. Since we read until
// there is no more input, this causes us
// to wait until the process is completed
if(printResults) {
BufferedInputStream buffer =
new BufferedInputStream(p.getInputStream());
DataInputStream commandResult =
new DataInputStream(buffer);
String s = null;
try {
while ((s = commandResult.readLine()) != null)
System.out.println("Output: " + s);
commandResult.close();
if (p.exitValue() != 0) {
if (verbose)
printError(command +
" -- p.exitValue() != 0");
return(false);
}
// Ignore read errors; they mean process is done
} catch (Exception e) {}
// If you don't print the results, then you
// need to call waitFor to stop until the process
// is completed
} else if (wait) {
try {
System.out.println(" ");
int returnVal = p.waitFor();
if (returnVal != 0) {
if (verbose)
printError(command);
return(false);
}
} catch (Exception e) {
if (verbose)
printError(command, e);
return(false);
}
}
} catch (Exception e) {
if (verbose)
printError(command, e);
return(false);
}
return(true);
}
//----------------------------------------------------
private static void printError(String command,
Exception e) {
System.out.println("Error doing exec(" +
command + "): " + e.getMessage());
System.out.println("Did you specify the full " +
"pathname?");
}
private static void printError(String command) {
System.out.println("Error executing '" +
command + "'.");
}
//----------------------------------------------------
private static void printSeparator() {
System.out.println
("==============================================");
}
//----------------------------------------------------
}
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