23种设计模式-Object Pool

在对象池中，你可能会面对一些共享对象的问题。你肯能需要创建一个方案包括共享对象的迁出或者迁入。

package design;

import java.util.ArrayList;

/**
 * Created by Administrator on 2018/4/18.
 */
public class PoolManager {
    private static class PoolItem{
        boolean inUse=false;
        Object item;
        PoolItem(Object item){
            this.item=item;
        }
    }
    private ArrayList items=new ArrayList();

    public void add(Object item){
        items.add(new PoolItem(item));
    }

    static class EmptyPoolException extends Exception{}
    public Object get() throws EmptyPoolException{
        for(int i=0;i<items.size();i++){
            PoolItem poolItem=(PoolItem) items.get(i);
            if(poolItem.inUse==false)
                poolItem.inUse=true;
            return poolItem.item;
        }
        throw new EmptyPoolException();
    }
    public void release(Object item){
        for(int i=0;i<items.size();i++){
            PoolItem poolItem=(PoolItem) items.get(i);
            if(item==poolItem.item){
                poolItem.inUse=false;
                return;
            }
        }
        throw new RuntimeException(item+"not found");
    }
}

public interface Connection {
    Object get();
    void set(Object x);
}

public class ConnectionImplementation implements Connection {
    public Object get() {
        return null;
    }

    public void set(Object x) {

    }
}

public class ConnectionPool {
    private static PoolManager poolManager=new PoolManager();
    public static void addConnection(int number){
        for(int i=0;i<number;i++)
            poolManager.add(new ConnectionImplementation());

    }
    public static Connection getConnection()
            throws PoolManager.EmptyPoolException {
        return (Connection)poolManager.get();
    }
    public static void releaseConnection(Connection c) {
        poolManager.release(c);
    }
}

public class ConnectionPoolDemo  extends TestCase {
    static {
        ConnectionPool.addConnection(5);
    }
    public void test() {
        Connection c = null;
        try {
            c = ConnectionPool.getConnection();
        } catch (PoolManager.EmptyPoolException e) {
            throw new RuntimeException(e);
        }
        c.set(new Object());
        c.get();
        ConnectionPool.releaseConnection(c);
    }
    public void test2() {
        Connection c = null;
        try {
            c = ConnectionPool.getConnection();
        } catch (PoolManager.EmptyPoolException e) {
            throw new RuntimeException(e);
        }
        c.set(new Object());
        c.get();
        ConnectionPool.releaseConnection(c);
    }
    public static void main(String args[]) {
        junit.textui.TestRunner.run(ConnectionPoolDemo.class);
    }
}