Thread: Java runtime get result output from prompt problem with a larger output in type

I am using java process to start a system command in windows

Runtime r = Runtime.getRuntime();
Process pr = r.exec(cmdString);

I want to get the prompt out put from cmdString = "cmd /c type fileSmallSize"->>>> It is ok the have the content of the file when file is small.
However, for a large file java process will hang and no Exception occurred, what is the problem?

The easiest testing you can try on the logging.properties file in java.

Need help to find out

public static String executeCmdAndReturnPromptResult(String cmdString)
throws Exception {
LOGGER.entering(CLASSNAME,
"Entering executeCmdAndReturnPromptResult()", cmdString);

String cmd = cmdString;
LOGGER.info("The system command: " + cmd);
Runtime r = Runtime.getRuntime();
Process pr = r.exec(cmd);
LOGGER.info("Error: " +getStringFromInputStream(pr.getErrorStream()));
int exitVal = pr.waitFor();
// System.out.println("ExitCode cmd return = " + exitVal);
LOGGER.info("ExitCode cmd return = " + exitVal);

// String s = "";
java.io.InputStream input = pr.getInputStream();
BufferedInputStream buffer = new BufferedInputStream(input);
BufferedReader commandResult = new BufferedReader(
new InputStreamReader(buffer));
StringBuilder sb = new StringBuilder();
String line = "";
try {
while ((line = commandResult.readLine()) != null) {
sb.append(line+ "\n") ;
System.out.println("Emcli info: "+ sb.toString());
}
} catch (Exception e) {
e.printStackTrace();
}finally{
if (commandResult!=null){
commandResult.close();
}
}
System.out.println("The prompt from the cmd -> " + sb.toString());

LOGGER.exiting(CLASSNAME, "Exiting executeCmdAndReturnPromptResult()",
sb.toString());

return sb.toString().trim();

}

It seemed to me that the bufferSize is limited so that I can only have it less than a default one, how to increase it?

My question now is how to increase the size of buffer in order to read a larger InputStream ?
BufferedInputStream() default size is
private static int defaultCharBufferSize = 8192;
private static int defaultExpectedLineLength = 80;

How to make it larger and working? I tried to increase the defaultCharBufferSize to 500000000 but it did not help!

First, please wrap all code in the code tags to preserve formatting as explained here: Forum Guidelines

Second, I would recommend reading When Runtime.exec() won't | JavaWorld

Lastly, it seems your exec command simply reads and prints the contents of a file. Why use Runtime exec rather than reading the file using java IO (which is platform independent)?

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