I installed mysql in a docker container, and tried to run this Java code to get some variable value:

String[] cmd = new String[] {"docker", "exec", "my", "mysql", "-p123456", "-e", "select @@report_host\\G"};
Pair<Integer, String> result = this.execForExitCode(cmd);
String[] lines = result.getRight().split("\n");
log.info("getDbReportHost:");
for (String line : lines) {
    log.info(line);
}

    private Pair<Integer, String> execForExitCode(String[] command) {
        try {
            Process process = new ProcessBuilder(command).inheritIO().start();
            String rst = new String(process.getInputStream().readAllBytes(), StandardCharsets.UTF_8);
            return Pair.of(process.waitFor(), rst);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

But got nothing.

Instead, if I run the command directly on the console:

docker exec -it my mysql -uroot -p123456 -e "select @@report_host\G"

I get this output:

*************************** 1. row ***************************
@@report_host: 10.15.100.95

And this is what I want.

So what's wrong with my Java code?

I installed mysql in a docker container, and tried to run this Java code to get some variable value:

String[] cmd = new String[] {"docker", "exec", "my", "mysql", "-p123456", "-e", "select @@report_host\\G"};
Pair<Integer, String> result = this.execForExitCode(cmd);
String[] lines = result.getRight().split("\n");
log.info("getDbReportHost:");
for (String line : lines) {
    log.info(line);
}

    private Pair<Integer, String> execForExitCode(String[] command) {
        try {
            Process process = new ProcessBuilder(command).inheritIO().start();
            String rst = new String(process.getInputStream().readAllBytes(), StandardCharsets.UTF_8);
            return Pair.of(process.waitFor(), rst);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

But got nothing.

Instead, if I run the command directly on the console:

docker exec -it my mysql -uroot -p123456 -e "select @@report_host\G"

I get this output:

*************************** 1. row ***************************
@@report_host: 10.15.100.95

And this is what I want.

So what's wrong with my Java code?

• java
• mysql

• Are you sure that this output comes at the output channel, not the error channel? You might want to try getErrorStream() instead of getInputStream() to see if this is the case. – Erich Kitzmueller Commented Apr 2 at 7:56
• 1 You don't want inheritIO() if you want to capture the command output. Notice that the answer does not use that. – Abra Commented Apr 2 at 8:02
• @Abra You are right. inheritIO() redirects the output to my Java console. – Calvin_Z Commented Apr 2 at 8:14
• It's important to consum all streams/chanels, for further details have a look on my blog post: thilosdevblog.wordpress/2022/09/18/… – Thilo Schwarz Commented Apr 2 at 10:13

1 Answer 1

maybe missing -uroot and \G is used interactive mode, so try this

String[] cmd = new String[] {
    "docker", "exec", "my", "mysql", "-uroot", "-p123456", "-e", "SELECT @@report_host;"
};

Pair<Integer, String> result = this.execForExitCode(cmd);
log.info("getDbReportHost: {}", result.getRight());




private Pair<Integer, String> execForExitCode(String[] command) {
    try {
        ProcessBuilder pb = new ProcessBuilder(command);
        pb.redirectErrorStream(true); // adovid thread  blocked
        Process process = pb.start();

        // read line by line advoid , thread  blocked
        StringBuilder result = new StringBuilder();
        try (BufferedReader reader = new BufferedReader(new InputStreamReader(process.getInputStream(), StandardCharsets.UTF_8))) {
            String line;
            while ((line = reader.readLine()) != null) {
                result.append(line).append("\n");
            }
        }

        int exitCode = process.waitFor();
        return Pair.of(exitCode, result.toString().trim()); 
    } catch (Exception e) {
        throw new RuntimeException(e);
    }
}