Java – way to release a saturated connection pool

Since Java 5 you can use Arrays.toString(arr) or Arrays.deepToString(arr) for arrays within arrays. Note that the Object[] version calls .toString() on each object in the array. The output is even decorated in the exact way you're asking.

Examples:

• Simple Array:

  String[] array = new String[] {"John", "Mary", "Bob"};
  System.out.println(Arrays.toString(array));
  

  Output:

  [John, Mary, Bob]
  

• Nested Array:

  String[][] deepArray = new String[][] {{"John", "Mary"}, {"Alice", "Bob"}};
  System.out.println(Arrays.toString(deepArray));
  //output: [[Ljava.lang.String;@106d69c, [Ljava.lang.String;@52e922]
  System.out.println(Arrays.deepToString(deepArray));
  

  Output:

  [[John, Mary], [Alice, Bob]]
  

• double Array:

  double[] doubleArray = { 7.0, 9.0, 5.0, 1.0, 3.0 };
  System.out.println(Arrays.toString(doubleArray));
  

  Output:

  [7.0, 9.0, 5.0, 1.0, 3.0 ]
  

• int Array:

  int[] intArray = { 7, 9, 5, 1, 3 };
  System.out.println(Arrays.toString(intArray));
  

  Output:

  [7, 9, 5, 1, 3 ]
  

How to know how much connection the application is currently using

You don't give enough information to answer that. Most appservers will have some sort of JMX reporting on things like this. Alternatively, depending on the database, you could find the number of currently open connections.

what should be the optimal connection pool settings for a heavily traffic applicaiton

Higher than what you've got?

The above of course assumes that you're not mishandling connections. By that I mean if you're using them directly in code you should always use this idiom:

Connection conn = null;
try {
  conn = ... ; // get connection
  // do stuff
} finally {
  if (conn != null) try { conn.close(); } catch (Exception e) { }
}

If you're not released connections back to the pool and are waiting for the garbage collector to clean them up and release them you're going to use way more connections that you actually need.