How to set Java ProcessBuilder parameter to run external .java file?

Question

I'm trying to run other java file using ProcessBuilder class.

I would like to get input of entire path of java file + file name + .java and compile it.

Example, input: C:\Windows\test.java

And then, I store input into String variable FILE_LOCATION and call processbuilder to compile input .java file.

Here is my code:

 static String JAVA_FILE_LOCATION;
 static String command[] = {"javac", JAVA_FILE_LOCATION};
 ProcessBuilder processBuilder = new ProcessBuilder(command);
 Process process = processBuilder.start();
 process = new ProcessBuilder(new String[]{"java","-cp",A,B}).start();

But I don't know how to set the parameters.

process = new ProcessBuilder(new String[]{
"java","-cp",A,B}).start();

How should I set that parameter (A, B)?

You can call java compiler without necessarily relying on running an external process, by using a javax.tools.ToolProvider.getSystemJavaCompiler(). — M. Prokhorov
– M. Prokhorov, Commented Nov 24, 2017 at 15:59

DodgyCodeException · Accepted Answer · 2017-11-24 15:25:01Z

1

To answer your exact question, let's say, for instance, your class is in package com.yourcompany.yourproduct and your class file is in /dir/to/your/classes/com/yourcompany/yourproduct/Yourclass.c‌lass.

Then A = "/dir/to/your/classes" and B = "com.yourcompany.yourproduct.Yourclass".

However, there's a few things to be aware of. Looking at your code:

static String JAVA_FILE_LOCATION;
static String command[] = {"javac", JAVA_FILE_LOCATION};
ProcessBuilder processBuilder = new ProcessBuilder(command);

No. You need to CD to the directory and then run javac. The easiest way to do that is by calling processBuilder.directory(new File("/dir/to/your/classes")). Then you need to give javac a relative path to your source file ("com/yourcompany/yourproduct/Yourclass.java").

Process process = processBuilder.start();
process = new ProcessBuilder(new String[]{"java","-cp",A,B}).start();

Wait until the first process has finished compiling before you try to run it! Between the two lines above, insert process.waitFor();. You might also want to check for any errors and only run the second process if the first has succeeded.

By the way, there's no need for all that long-hand creation of string arrays. Just use varargs: process = new ProcessBuilder("java", "-cp", A, B).start();.

answered Nov 24, 2017 at 15:25

DodgyCodeException

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1 Comment

SongDoHou Over a year ago

I really appreciate your help.

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