如果一個B/S的應用，并發量在2000以上時，新建的對象累積會占用大量內存，當超過一定數量的時候，會報內存不夠，使用享元模式就可以解決這一問題，也就是建立對象池。現在的方案可以使用
Apache Commons Pool。
一、基本String對象測試
import org.apache.commons.pool.impl.GenericKeyedObjectPool;
import org.apache.commons.pool.BaseKeyedPoolableObjectFactory;
/** *//**
* Created by IntelliJ IDEA.
*
* @author leizhimin 2009-10-27 17:46:18
*/
public class Test 
{
public static void main(String[] args) throws Exception {
//創建一個對象池
GenericKeyedObjectPool pool = new GenericKeyedObjectPool(new BaseKeyedPoolableObjectFactory() {
@Override
public Object makeObject(Object o) throws Exception {
return o;
}
});
//添加對象到池，重復的不會重復入池
pool.addObject("a");
pool.addObject("a");
pool.addObject("b");
pool.addObject("x");
//清除最早的對象
pool.clearOldest();
//獲取并輸出對象
System.out.println(pool.borrowObject("a"));
System.out.println(pool.borrowObject("b"));
System.out.println(pool.borrowObject("c"));
System.out.println(pool.borrowObject("c"));
System.out.println(pool.borrowObject("a"));
//輸出池狀態
System.out.println(pool.getMaxIdle());
System.out.println(pool.getMaxActive());
}
}輸出結果：
a
b
c
c
a
8
8
Process finished with exit code 0
二、自定義復雜對象測試
import org.apache.commons.pool.impl.GenericKeyedObjectPool;
import org.apache.commons.pool.BaseKeyedPoolableObjectFactory;
/** *//**
* Created by IntelliJ IDEA.
*
* @author leizhimin 2009-10-27 17:46:18
*/
public class Test {
public static void main(String[] args) throws Exception {
//創建一個對象池
GenericKeyedObjectPool pool = new GenericKeyedObjectPool(new BaseKeyedPoolableObjectFactory() {
@Override
public Object makeObject(Object o) throws Exception {
if (o != null && o instanceof User)
return o;
else
return null;
}
});
//添加對象到池，重復的不會重復入池
pool.addObject("a");
pool.addObject("b");
pool.addObject("x");
pool.addObject(null);
pool.addObject(null);
pool.addObject(null);
pool.addObject(new User("zhangsan", "123"));
pool.addObject(new User("lisi", "112"));
pool.addObject(new User("lisi", "112", 32));
pool.addObject(new User("lisi", "112", 32, "一個爛人！"));
//清除最早的對象
pool.clearOldest();
//獲取并輸出對象
User u1 = new User("lisi", "112", 32, "一個爛人！");
System.out.println(pool.borrowObject(u1));
pool.returnObject(u1,u1);
//獲取并輸出對象
User u2 = new User("lisi", "112", 32, "一個爛人！");
System.out.println(pool.borrowObject(u2));
pool.returnObject(u2,u2);
//獲取并輸出對象
User u3 = new User("lisi", "112", 32);
System.out.println(pool.borrowObject(u3));
pool.returnObject(u3,u3);
//獲取并輸出對象
User u4 = new User("lisi", "112");
System.out.println(pool.borrowObject(u4));
pool.returnObject(u4,u4);
System.out.println(pool.borrowObject(u4));
pool.returnObject(u4,u4);
System.out.println(pool.borrowObject(u4));
pool.returnObject(u4,u4);
System.out.println(pool.borrowObject(u4));
pool.returnObject(u4,u4);
System.out.println(pool.borrowObject(u4));
pool.returnObject(u4,u4);
System.out.println(pool.borrowObject(u4));
pool.returnObject(u4,u4);
System.out.println(pool.borrowObject(u4));
pool.returnObject(u4,u4);
System.out.println(pool.borrowObject(u4));
pool.returnObject(u4,u4);
System.out.println(pool.borrowObject(new User("lisi", "112")));
// System.out.println(pool.borrowObject(new User("lisi", "112")));
//輸出池狀態
System.out.println(pool.getMaxIdle());
System.out.println(pool.getMaxActive());
pool.clearOldest();
pool.close();
}
}
class User {
private String name;
private String pswd;
private int age;
private String reamark;
User() {
}
User(String name, String pswd) {
this.name = name;
this.pswd = pswd;
}
User(String name, String pswd, int age) {
this.name = name;
this.pswd = pswd;
this.age = age;
}
User(String name, String pswd, int age, String reamark) {
this.name = name;
this.pswd = pswd;
this.age = age;
this.reamark = reamark;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getPswd() {
return pswd;
}
public void setPswd(String pswd) {
this.pswd = pswd;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getReamark() {
return reamark;
}
public void setReamark(String reamark) {
this.reamark = reamark;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
User user = (User) o;
if (!name.equals(user.name)) return false;
if (!pswd.equals(user.pswd)) return false;
return true;
}
@Override
public int hashCode() {
int result = name.hashCode();
result = 31 * result + pswd.hashCode();
return result;
}
@Override
public String toString() {
return "User{" +
"name='" + name + '\'' +
", pswd='" + pswd + '\'' +
", age=" + age +
", reamark='" + reamark + '\'' +
'}';
}
} 測試結果：
User{name='lisi', pswd='112', age=32, reamark='
null'}
User{name='lisi', pswd='112', age=32, reamark='一個爛人！'}
User{name='lisi', pswd='112', age=32, reamark='一個爛人！'}
User{name='lisi', pswd='112', age=32, reamark='
null'}
User{name='lisi', pswd='112', age=0, reamark='
null'}
User{name='lisi', pswd='112', age=0, reamark='
null'}
User{name='lisi', pswd='112', age=0, reamark='
null'}
User{name='lisi', pswd='112', age=0, reamark='
null'}
User{name='lisi', pswd='112', age=0, reamark='
null'}
User{name='lisi', pswd='112', age=0, reamark='
null'}
User{name='lisi', pswd='112', age=0, reamark='
null'}
User{name='lisi', pswd='112', age=0, reamark='
null'}
8
8
Process finished with exit code 0
這次測試得出一些有用的結論：
1、復雜對象應該實現equals() 、hashCode()方法，以便不重復入池。
2、對于非入池的目標對象，比如a、b、x字符串，目前沒有有效的辦法過濾掉，不讓其入池，雖然在工廠方法里做了努力。
3、試圖將null入池，不會成功的，但也不拋異常。
4、對于池對象，使用應該遵循“接而有還，再借不難”-----從池中獲取，不用時候歸池，否則當池中沒有空閑可用的對象時候，程序會處于等待狀態，如果沒有顯式的調用歸還方法，則造成程序死鎖。
池的大小是初始化配置的，在沒有顯式配置指定的情況下，池大小默認為8.可以通過
GenericKeyedObjectPool.Config來配置。