如果一个B/S的应用，并发量在2000以上时，新建的对象累积会占用大量内存，当超过一定数量的时候，会报内存不够，使用享元模式就可以解决这一问题，也就是建立对象池。现在的方案可以使用
Apache Commons Pool。
一、基本String对象测试
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 {
//创建一个对象池
GenericKeyedObjectPool pool = new GenericKeyedObjectPool(new BaseKeyedPoolableObjectFactory() {
@Override
public Object makeObject(Object o) throws Exception {
return o;
}
});
//添加对象到池，重复的不会重复入池
pool.addObject("a");
pool.addObject("a");
pool.addObject("b");
pool.addObject("x");
//清除最早的对象
pool.clearOldest();
//获取并输出对象
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"));
//输出池状态
System.out.println(pool.getMaxIdle());
System.out.println(pool.getMaxActive());
}
}输出结果：
a
b
c
c
a
8
8
Process finished with exit code 0
二、自定义复杂对象测试
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 {
//创建一个对象池
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;
}
});
//添加对象到池，重复的不会重复入池
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, "一个烂人！"));
//清除最早的对象
pool.clearOldest();
//获取并输出对象
User u1 = new User("lisi", "112", 32, "一个烂人！");
System.out.println(pool.borrowObject(u1));
pool.returnObject(u1,u1);
//获取并输出对象
User u2 = new User("lisi", "112", 32, "一个烂人！");
System.out.println(pool.borrowObject(u2));
pool.returnObject(u2,u2);
//获取并输出对象
User u3 = new User("lisi", "112", 32);
System.out.println(pool.borrowObject(u3));
pool.returnObject(u3,u3);
//获取并输出对象
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")));
//输出池状态
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 + '\'' +
'}';
}
} 测试结果：
User{name='lisi', pswd='112', age=32, reamark='
null'}
User{name='lisi', pswd='112', age=32, reamark='一个烂人！'}
User{name='lisi', pswd='112', age=32, reamark='一个烂人！'}
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
这次测试得出一些有用的结论：
1、复杂对象应该实现equals() 、hashCode()方法，以便不重复入池。
2、对于非入池的目标对象，比如a、b、x字符串，目前没有有效的办法过滤掉，不让其入池，虽然在工厂方法里做了努力。
3、试图将null入池，不会成功的，但也不抛异常。
4、对于池对象，使用应该遵循“接而有还，再借不难”-----从池中获取，不用时候归池，否则当池中没有空闲可用的对象时候，程序会处于等待状态，如果没有显式的调用归还方法，则造成程序死锁。
池的大小是初始化配置的，在没有显式配置指定的情况下，池大小默认为8.可以通过
GenericKeyedObjectPool.Config来配置。