Genius-Field » Java Technology

Genius-Field Database Connection Pool API 0.2(RC) Release

Icyfish — Mon, 19 Oct 2009 13:41:41 +0000

0.2-rc (2009-10-19)
New features:
Add a new method which can load properties from a variable instead of from a file

Download dbcp-0.2-rc

Genius-Field Database Connection Pool API 0.2(beta) Release

Icyfish — Thu, 08 Oct 2009 13:11:13 +0000

0.2-beta (2009-10-08)
Bugfixes and minor changes:
Fix an error which may throw IllegalMonitorStateException

Download dbcp-0.2-beta

Genius-Field Database Connection Pool API 0.2(alpha) Release

Icyfish — Mon, 07 Sep 2009 03:25:32 +0000

We are glad to inform you that our new version of Genius-Field Database Connection Pool is released. From now on, we will post the change logs here as well as the jar distribution and put other stuff on Google Code. You may visit here.

0.2-dev (2009-09-03)

New features:

Initial release

0.2-alpha (2009-09-07)

Bugfixes and minor changes:

Compatible with JDK 1.5

0.2-dev (2009-09-03)

New features:

Initial release

Download dbcp-0.2-dev

0.2-alpha (2009-09-07)

Bugfixes and minor changes:

Compatible with JDK 1.5

Download dbcp-0.2-alpha

New Genius-Field Database Connection Pool API Coming Soon

Icyfish — Sat, 01 Aug 2009 10:29:00 +0000

We are developing new version of Genius-Field Database Connection Pool in order to make it more stable and efficient. In the new version, the entire structure will be changed and it hopefully will be easy to use and easy to control.

We are not going to make any updates for the old API and the new version will be open-source and hosted on Google Code under GNU General Public License v3. We have already created the project home on Google Code, but nothing in it. You may visit here if you like. There is no ETA for the new version release. We will make announcement when it arrives.

Genius-Field Database Connection Pool API 0.1 Release

Icyfish — Tue, 28 Apr 2009 05:04:45 +0000

New features:
Allow user to release all conns at one time
Allow user to watch some basic status of the connection pool
Allow user to manually drop a conn if it works abnormally

Bugfixes and minor changes:
Fix the number of conns may be less than the minimum requirement

Download sql-01

Further study on duplicate elements of HashSet

Icyfish — Wed, 22 Apr 2009 13:30:50 +0000

In mathematics, it is trivial to check duplicate elements because the properties of an element are simple. It may just contain numbers, letters, and colors and so on. However, it is complicated to check whether two elements (objects) are the “same” in computer programming.
In Java language, the Set interface is defined as “A collection that contains no duplicate elements. More formally, sets contain no pair of elements e1 and e2 such that e1.equals(e2), and at most one null element”. The HashSet class implements the Set interface. How does it check? Does it really use equals method? Let’s have a look.
We may first think there’re two ways to check the equality of two objects: using “=” operation or using equals method. The former is checked by the addresses of two objects. If they refer to the same address, they are equal. The latter usually returns the same result as “=” operation, but many classes override this method so that we may get different result. To be mentioned, hashCode method is also used here. Let’s see what actually happens.
We write a class and override both equals method and hashCode method. The equals method can return true or false and the hashCode method may return the same or two different integers on two objects. So, there’re four combinations:
1. true same
2. true different
3. false same
4. false different
We create two instances of the class and put them into a HashSet. Then change the combination one by one to see how they influence the result of HashSet, and the corresponding results are listed below:
1. one element
2. two elements
3. two elements
4. two elements
Hence, we may conclude that two objects are the “same” if and only if hashCodes are equal and equals method return true.

Actually, this is part of the right answer.
Now, we look into the source of JDK to see the truth.

The add method in HashSet:

private transient HashMap<E,Object> map;
 
public boolean add(E e) {
    return map.put(e, PRESENT)==null;
}

We know from documentation that “This class(HashSet) implements the Set interface, backed by a hash table (actually a HashMap instance)”. So, it invokes the put method in HashMap. We trace into it and find:

The put method in HashMap:

public V put(K key, V value) {
    if (key == null)
        return putForNullKey(value);
    int hash = hash(key.hashCode());
    int i = indexFor(hash, table.length);
    for (Entry<K,V> e = table[i]; e != null; e = e.next) {
        Object k;
        if (e.hash == hash && ((k = e.key) == key || key.equals(k))) {
            V oldValue = e.value;
            e.value = value;
            e.recordAccess(this);
            return oldValue;
        }
    }
 
    modCount++;
    addEntry(hash, key, value, i);
    return null;
}

Pay attention to the key statement “if (e.hash == hash && ((k = e.key) == key || key.equals(k)))”. From this sentence, we can know the truth:
Two objects are the “same” when they satisfy both of the following conditions:
1. hashCode are the same
2. They refer to the same address or equals method returns true

You may look up the source of TreeSet or other sets to see how they check duplicate elements. They differ from each other.

Genius-Field Database Connection Pool API 0.1(RC) Release

Icyfish — Wed, 15 Apr 2009 10:13:39 +0000

New features:
Allow user to specify when the Conn will be recycled automatically if one does NOT explicitly invoke freeCon()
Throw general java exceptions and Genius-Field exceptions for easy debug

Bugfixes and minor changes:
Provide default values for the properties file
Fix getConn() may return null

Download sql-01-rc

Genius-Field Database Connection Pool API 0.1(beta) Release

Icyfish — Sun, 12 Apr 2009 10:47:10 +0000

New features:
Initial beta release
Allow user to specify the path of properties file
Allow user to specify the class name of jdbc connector
Change package name gaccount.sql to com.geniusfield.sql
Change method name Conn.getConn() to Conn.getCon() to avoid confusion

Bugfixes and minor changes:
Properties file isn’t closed after being used
Call Class.forName() method in case of old JDKs

Download sql-01-beta