java-process-call.adoc

방법

http://blog.art-of-coding.eu/executing-operating-system-commands-from-java/

import java.io.IOException;

import java.io.InputStream;

import org.apache.commons.io.IOUtils;

import org.junit.Test;

public class ShellTest {

String[] command = new String[]{"ls","-al"};

@Test

public void withProcessBuilder() throws IOException, InterruptedException {

ProcessBuilder builder = new ProcessBuilder(command);

Process process = builder.start();

printStream(process);

}

@Test

public void withRunetime() throws IOException, InterruptedException {

Runtime runtime = Runtime.getRuntime();

Process process = runtime.exec(command);

printStream(process);

}

private void printStream(Process process) throws IOException, InterruptedException {

process.waitFor();

InputStream stream = process.getInputStream();

IOUtils.copy(stream, System.out);

IOUtils.closeQuietly(stream);

}

}

무한 대기 문제

public static void main(String[] args) throws IOException, InterruptedException{
       Process pc = Runtime.getRuntime().exec("java");
       InputStream input = pc.getInputStream();
       IOUtils.copy(input, System.out);
       int exitCode = pc.waitFor();
       System.out.println(exitCode);
}

waitFor는 무한대기 될 수도 있다…​

그런데 위의 코드를 Runtime.exec("javac")를 실행시키는 코드로 바꾸어보면, 이 호출은 영원히 끝나지 않게 됩니다.

When Runtime.exec() won’t : : javaworld에 올라온 고전이자 최고의 글

• You cannot obtain an exit status from an external process until it has exited

• You must immediately handle the input, output, and error streams from your spawned external process

• You must use Runtime.exec() to execute programs

• You cannot use Runtime.exec() like a command line Alvin Alexander의 글

• Running system commands in Java applications : 스트림 처리 제대로 암함

• http://alvinalexander.com/java/java-exec-processbuilder-process-1 : 개선판

• http://alvinalexander.com/java/java-exec-processbuilder-process-2

• http://alvinalexander.com/java/java-exec-processbuilder-process-3

참고할만한 구현체

• 분산처리 프레임워크 JPPF의 ProcessWrapper

• Alvin Alexander가 Java exec - execute system processes with Java ProcessBuilder and Process 글에 공유한 소스

• SystemCommandExecutor : shell 실행 전담 클래스

• ThreadedStreamHandler : 스트림처리 클래스

• ProcessBuilderExample : SystemCommandExecutor를 사용하는 예제

• Ant Exec Task의 PumpStreamHandler

• Apache-commons-exec의 PumpStreamHandler (Ant의 것과 패키지는 다르나 같은 코드)

• Exec-maven-plugin의 ExecMojo (Apache-commons-exec를 활용) public class StreamConverter implements Runnable {

  private StringBuilder message =null;
  private InputStream input = null;
  public StreamConverter(InputStream input){
   this.input = input;
   this.message = new StringBuilder();
  }

  public void run() {
     BufferedReader reader = new BufferedReader(new InputStreamReader(input));
     String line= null;
     try {
    while( (line = reader.readLine())!=null){
       message.append(line);
      }
     } catch (IOException e) {
     throw new IllegalStateException("cann not read stream",e);
     }
  }

   public StringBuilder getMessage() {
    return message;
   }
  }

부모 프로세스의 메모리 복제

외부 프로그램을 실행할 때 JVM에서는 무슨 일이?

Apache Exec

http://commons.apache.org/exec

<dependency> <groupId>org.apache.commons</groupId> <artifactId>commons-exec</artifactId> <version>1.1</version> </dependency>