Maven Problem (Id can not be null)

Samad — Tue, 13 Jul 2010 20:08:01 +0000

Working with Maven I came across a very weird issue. I attempted to build a new project, and received a Fatal Error: ID Can Not Be Null. Basically a Java.Lang.NullPointerException. I work in a corporate environment so I had an idea of which parent POM was having issues, but it didn’t quite click in my mind until about 5 minutes ago. After researching the net for the past few hours, I finally had my AHA! moment and decided to try it out. The solution to this problem is as follows:

Inside the POM.XML file for the project you are currently working with, you should have something like the following:

com.mycompany.or.something

parent

1.0

../../parent/

The groupId tag is very important, as in my case this is where the problem existed. I navigated to the local maven repo (~.m2/repositories) and through the directories til I came to the following dir:

~m2/repositories/com/mycompany/or/something/parent/1.0/

Inside this directory was a parent pom file. I opened it up in Notepad++ and looked through the tags. Sure enough, the repositories tag did not contain an ID element. I simply added one in ( ) and voila, problem solved.

Hope this helps someone in the future, because it had me banging my head against everything I could possibly find – from walls to staplers to windows (oh my!)

Unix Lucas Fork Program

Samad — Sat, 05 Apr 2008 18:05:43 +0000

I wrote this program for a class a few semesters ago. It is a Lucas Number calculator that uses forks/pipes (a requirement of the project). Works great, hopefully it will help someone out there! It is also available for download below.

/* Lucas Fork & Pipe*/ #include #include // to print the time


float    fib(int); // fibonacci function, recursive

int    fork(void);

void   sleep(unsigned);
int main(void)

{

   int n; // input variable

   int i; // for the loop

   int start = time(NULL); // get the time the process started

        char buf[100]; /* store the characters read */
   // pipe needs an integer array of size 2

		int fd[2];

		printf("Create the pipe\n\n");

		pipe(fd); /* fd[0] read; fd[1] write */
	printf("Enter a number: ");

	if (scanf("%d", &n) != 1) { // check to make sure there is input

		printf("Input error.\n");

		return 1;

	}

		printf("Create the child process using fork\n");

   if (fork() == 0) {    // child process

		close(fd[1]); /* close write end */

		printf("child is running...\n");

        printf("about to read from the pipe\n");

		n = read( fd[0], buf, 100); /* child reads from pipe */

		printf("after reading from the pipe\n");

        printf("the value of n is: %d\n",n);

        printf("the value in the buffer is: %s\n\n", buf);

      for (i = 0; i <= n; ++i) {

         printf("fib(%2d) = %d\n", i, fib(i));

		 sleep(1);

		}

	}

   else    {            // parent process

		close(fd[0]); /* close read end - not needed for this example */

		printf("parent is running...\n");

        printf("about to write to the pipe\n");

        write( fd[1], "Writing to pipe\n", n); /* parent writes to pipe */

        printf("after writing to the pipe\n\n");

	 for (i = 0; i < n; ++i) {

         sleep(1);

         printf("Calculating...elapsed time = %d\n", time(NULL) - start);

      }

	}

   return 0; // exits program

}

float fib(int n) // fibonacci function, recursive { if (n <= 1) return n; else return (fib(n - 1) + fib(n - 2)); }

Lucas Fork Source File (zipped)

Samad's Blog » Coding

Maven Problem (Id can not be null)

Unix Lucas Fork Program