使用 ProcessBuilder 执行外部程序并提供输入

Question

I'm trying to execute an external program with Java using ProcessBuilder , but it expects input from the user.

To be more specific, the program is PGSQL (Postgres SQL), when it's executed the program prompts the user for a password. The only way to bypass that is to save a file in the user home containing the passwords, I'm trying to avoid that, so I want to execute the program from Java and send the password using the process' output stream.

The code works fine when the program doesn't expect any user input, but when I delete the password file from the user home, the program hangs. I see that it's being executed, but nothing happens. If I debug it, it reaches the while and then nothing happens until I kill the process.

This is the code, any help will be greatly appreciated.

@Test
public void testSQLExecution() throws Exception {
String path = "C:/tmp";
List<String> commandList = new ArrayList<String>();
commandList.add("psql");
commandList.add("-f");
commandList.add("test.sql");
commandList.add("-h");
commandList.add(HOST);
commandList.add("-p");
commandList.add(PORT);
commandList.add("-U");
commandList.add(DATABASE);
commandList.add(SCHEMA);

ProcessBuilder processBuilder = new ProcessBuilder(commandList);
processBuilder.directory(new File(path));
processBuilder.redirectErrorStream(true);

Process p = processBuilder.start();

String line;
BufferedReader input = new BufferedReader(new InputStreamReader(p
    .getInputStream()));
BufferedWriter out = new BufferedWriter(new OutputStreamWriter(p
    .getOutputStream()));

out.write("password");
out.newLine();
out.flush();
out.close();

    // When this line is reached, the execution halts.
while (input.ready() && (line = input.readLine()) != null) {
    System.out.println(line);
}

if (p.waitFor() != 0) {
    Assert.fail("The process did not run succesfully.");
}

input.close();
}

Thanks a lot.

Answer 1

Been a long time, but got exactly the same problem. Here is a SSCCE that should work:

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.util.ArrayList;
import java.util.List;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class Toto
{

    private static Logger logger = LoggerFactory.getLogger(Toto.class);

    static class Params 
    {
        public String getUserName() {
            return "PUT USERNAME HERE";
        }
        public String getHost() {
            return "PUT HOST HERE";
        }
        public String getDbName() {
            return "PUT DBNAME HERE";
        }
        public char[] getPassword() {
            return new char[]{'p','a','s','s','w','o','r','d'};
        }
        public String getSqlFile() {
            return "PUT SQL COMMAND FILE HERE";
        }
    }

    public static void main(String[] args)
    {
        Params params = new Params();

        try {
            final String userName   = params.getUserName();
            final String host       = params.getHost();
            final String dbName     = params.getDbName();
            final char[] pass       = params.getPassword();
            if (userName == null || host == null || dbName == null || pass == null) {
                logger.error("Missing the following info to execute the SQL command file: {} {} {} {}"  , userName  == null ? "username": ""
                    , host      == null ? "host"    : ""
                        , dbName    == null ? "database": ""
                            , pass      == null ? "password": "");
                return;
            }
            List<String> sb = new ArrayList<String>();
            sb.add("psql");
            sb.add("-h");
            sb.add(host);
            sb.add("-U");
            sb.add(userName);
            sb.add("-d");
            sb.add(dbName);
            sb.add("-f");
            sb.add(params.getSqlFile());
            //              sb.add("-W"); // force password prompt
            logger.debug("Executing the following command: {}", sb.toString());
            ProcessBuilder pb = new ProcessBuilder(sb);
            final Process p = pb.start();
            final BufferedReader stdinReader = new BufferedReader(new InputStreamReader(p.getInputStream()));
            final BufferedReader stderrReader = new BufferedReader(new InputStreamReader(p.getErrorStream()));
            new Thread(new Runnable()
            {
                @Override
                public void run()
                {
                    try
                    {

                        OutputStreamWriter s = new OutputStreamWriter(p.getOutputStream());
                        s.write(pass);
                        s.write(System.getProperty("line.separator"));
                        s.flush();
                        System.out.println("Pass written");
                    }
                    catch(IOException e)
                    {
                        logger.error("Exception raised in the thread writting password to psql", e);
                    }
                }
            }).start();

            new Thread(new Runnable()
            {

                @Override
                public void run()
                {
                    try
                    {
                        String s;
                        while (( s=stdinReader.readLine()) != null) {
                            logger.debug("psql [STDOUT]: {}", s);
                        }
                    }
                    catch(IOException e)
                    {
                        logger.error("Exception raised in thread displaying stdout of psql", e);
                    }
                }
            }).start();
            new Thread(new Runnable()
            {

                @Override
                public void run()
                {
                    try
                    {
                        String s;
                        while (( s=stderrReader.readLine()) != null) {
                            logger.error("psql [STDERR]: {}", s);
                        }
                    }
                    catch(IOException e)
                    {
                        logger.error("Exception raised in thread displaying stderr of psql", e);
                    }
                }
            }).start();
            int returnVal = p.waitFor();
            logger.debug("Process ended with return val {} ", returnVal);

        }
        catch (Exception e) {
            logger.error("Exception raised while executing the results on server", e);
        }

    }

}

Answer 2

I believe the prompt is going to STDERR, not STDOUT, so you'll have to open a stream connected to that and read there. When you try to read from STDOUT your code hangs waiting for output that will never arrive.

EDIT: I see you have redirected the error stream in the ProcessBuilder.

One other possibility is that the BufferedReader is waiting for a newline to finish reading, and the prompt does not end with a newline.