ProcessBuilder Java launch successfully But Tomcat launch failed

Question

I run this method in normal java program (eclipse and cmd) successfully, but when I run this method in Tomcat 8.5.9, it shows error(Error: Could not find or load main class Main). Why that happened? Thanks for help.

public synchronized static String run(SourceCode sourceCode) {
    try {
        ProcessBuilder java = new ProcessBuilder("java", "Main");
        File file = new File("C:\\apache-tomcat-8.5.9\\webapps\\onlineJudge\\data\\Piers\\1\\1483703529849");
        java = java.directory(file);
        java = java.redirectErrorStream(true);
        Process process = java.start();
        List<String> list = java.command();
        try (Scanner in = new Scanner(process.getInputStream())) {
            System.out.println(in.nextLine());
        }
    } catch (IOException e) {
        e.printStackTrace();
    }
    return null;
}

Dir: C:\apache-tomcat-8.5.9\webapps\onlineJudge\data\Piers\1\148370352984

File in Dir: Main.class, Main.java(code below)

public class Main{

    public static void main(String args[]){
        System.out.println("Hello World.");
    }
}

PS:

How I test:

Copy this method to another normal Java Project and test. It shows (Hello World.).

Something Wired

After I post this question, I run Tomcat in Eclipse. Before, I run Tomcat in cmd(use startup command). When load the method(public synchronized static String run(SourceCode sourceCode)) it runs successfully! What happened?

Thanks!

Answer 1

I am the author. I find that Tomcat changed my classpath for compling java! It uses its own classpath for security.