CODEWITHSUNDEEP
javabashruntime.exec
DevilCode
DevilCode

Reputation: 1100

Slow System Commands From Java

I am calling a bash scrip script from Java. The script does the following:

cat /home/user/Downloads/bigtextfile.txt | grep 'hello'

This particular command when run command line takes about 1 second to complete on the text file which is 150MB.

When calling the bash script via Java using the following call:

command = "sh /home/user/bashfiletocall"
p = Runtime.getRuntime().exec(command);

The time to complete takes so long I don't wait.

Am I doing something very wrong and if not can you explain the reason for the huge lack in performance?

NOTE: I was running it in Netbeans and this seems to be the problem .. when I ran the file command line it was quick. The performance between execution in netbeans and command line is huge.

Many thanks.

private String executeCommand(String command) {     
    StringBuilder output = new StringBuilder();
    BufferedReader reader = null;
    Process p;
   try {
    p = Runtime.getRuntime().exec(command);
    p.waitFor();

  reader = new BufferedReader(new InputStreamReader(p.getInputStream()));

    String line = "";           
    while ((line = reader.readLine())!= null) {
        output.append(line + "\n");
    }                    

} catch (Exception e) {
    e.printStackTrace();
}             
return output.toString();
}

Upvotes: 2

Views: 2014

Answers (1)

Uli
Uli

Reputation: 1500

After starting your process you need start reading from the input stream. Otherwise the buffers are running full and p.waitFor() waits forever.

Javadoc of the Process class:

Because some native platforms only provide limited buffer size for standard input and output streams, failure to promptly write the input stream or read the output stream of the subprocess may cause the subprocess to block, or even deadlock.

Upvotes: 2

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