Runtime class in java

Question

How to execute a java program with the help of Runtime.getRuntime().exec(). For example we shall have the java file path as c:/java/abc.java. Please help me with the code.

Dicta

Answer 1

Assuming that abc.java contains a main method that you want to execute:

Runtime.getRuntime().exec("javac c:\java\abc.java -d c:\java\")
Runtime.getRuntime().exec("java c:\java\abc")

Wallywalnut

CreateProcess: c:\j2sdk1.4.0\bin\helloworld error=2 This is the runtime exception message – Dicta

That doesn't really give a whole lot to go off of. Can you edit your question to include a simple helloworld file and the whole stack trace? – Wallywalnut

Answer 2

Do not forget that:

• you may need to read stdout/stderr of a java program

• you may have to set/update environment variable and PATH before executing your java command

  CreateProcess: c:\j2sdk1.4.0\bin\helloworld error=2

means Win32's CreateProcess returns a 2 as error code when it cannot find the command you specify; more specifically, when the command does not refer to an executable file on its lookup path.

Look at this SO question for a more complete "Runtime.getRuntime().exec()" code, and also to this snippet.

This code creates a shell (as in Runtime.getRuntime().exec("cmd /K")), in which you write on sdtin whatever command you want to execute.

The interest of this approach is to reuse the shell process to benefit from a previous command: it you execute a 'cd', then execute a 'dir', the latter command would display the content of the directory referenced by the cd command.

The same would be true for PATH settings, just before using javac or java.

Assignor

Answer 3

You should use ProcessBuilder instead of Runtime. Basic usage is like:

Process process = new ProcessBuilder(command).start();

You will find more code under the link above. Also see this question.

Bensen

Answer 4

You mean you want a Java program to run another Java program. This SO thread might be helpful, in that case.

Ardenardency

Answer 5

String path1 = "f://" + File.separator+username+File.separator+progName; 
Runtime runtime = Runtime.getRuntime();
String command = "javac -classpath " + path + " " + path1;
System.out.println(command);
Process process = runtime.exec(command);
InputStream error = process.getErrorStream();

Copper

Answer 6

Please see the excellent resource which used to be called javaalmanac.

http://www.exampledepot.com/egs/java.lang/Exec.html

try {
    // Execute a command with an argument that contains a space
    String[] commands = new String[]{"grep", "hello world", "/tmp/f.txt"};
    commands = new String[]{"grep", "hello world", "c:\\Documents and Settings\\f.txt"};
    Process child = Runtime.getRuntime().exec(commands);
 } catch (IOException e) {
 }

Brower