Java design pattern implementation object pool pattern sample sharing
- 2020-04-01 02:56:47
- OfStack
ObjectPool abstracts the parent class
import java.util.Iterator;
import java.util.Vector;
public abstract class ObjectPool<T> {
private Vector<T> locked, unlocked; //Locked is already takes up the collection of objects, unlocked a collection of objects is available
public ObjectPool() {
locked = new Vector<T>();
unlocked = new Vector<T>();
}
//Create an object
protected abstract T create();
//Validate the object
public abstract boolean validate(T o);
//Invalidate an object
public abstract void expire(T o);
//Checkout: gets an object from an object pool
public synchronized T checkOut() {
T t;
if (unlocked.size() > 0) {
Iterator<T> iter = unlocked.iterator();
while(iter.hasNext()) {
t = iter.next();
if(validate(t)) { //Object effectively
unlocked.remove(t);
locked.add(t);
return t;
}
else { //Object is invalid
unlocked.remove(t);
expire(t);
}
}
}
//Object pool has no available objects. Create new objects
t = create();
locked.add(t);
return (t);
}
//Check in: releases the object back to the object pool
public synchronized void checkIn(T t) {
locked.remove(t);
if(validate(t)) { //If the object is still valid, it is returned to the collection of available objects
unlocked.add(t);
}
else { //Otherwise invalidate the object
expire(t);
}
}
}
JDBCConnectionPool subclass
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
public class JDBCConnectionPool extends ObjectPool<Connection> {
private String url, usr, pwd;
public JDBCConnectionPool(String driver, String url, String usr, String pwd) {
super();
//Load the corresponding database driver
try {
Class.forName(driver).newInstance();
}
catch(Exception e) {
e.printStackTrace();
}
this.url = url;
this.usr = usr;
this.pwd = pwd;
}
@Override
protected Connection create() {
try {
return DriverManager.getConnection(url, usr, pwd);
}
catch(SQLException e) {
e.printStackTrace();
}
return null;
}
@Override
public boolean validate(Connection o) {
try {
return o.isClosed();
}
catch(SQLException e) {
e.printStackTrace();
}
return false;
}
@Override
public void expire(Connection o) {
try {
o.close();
}
catch(SQLException e) {
e.printStackTrace();
}
finally {
o = null;
}
}
public static void main(String[] args) {
JDBCConnectionPool dbConnPool = new JDBCConnectionPool("com.mysql.jdbc.Driver", "jdbc:mysql://127.0.0.1:3306/test", "root", "123");
//Gets the database connection object
Connection conn = dbConnPool.checkOut();
//Use the database connection object
// ...
//Release the database connection object
dbConnPool.checkIn(conn);
}
}
class Pool {
private static final MAX_AVAILABLE = 100;
private final Semaphore available = new Semaphore(MAX_AVAILABLE, true);
public Object getItem() throws InterruptedException {
available.acquire();
return getNextAvailableItem();
}
public void putItem(Object x) {
if (markAsUnused(x))
available.release();
}
// Not a particularly efficient data structure; just for demo
protected Object[] items = ... whatever kinds of items being managed
protected boolean[] used = new boolean[MAX_AVAILABLE];
protected synchronized Object getNextAvailableItem() {
for (int i = 0; i < MAX_AVAILABLE; ++i) {
if (!used[i]) {
used[i] = true;
return items[i];
}
}
return null; // not reached
}
protected synchronized boolean markAsUnused(Object item) {
for (int i = 0; i < MAX_AVAILABLE; ++i) {
if (item == items[i]) {
if (used[i]) {
used[i] = false;
return true;
} else
return false;
}
}
return false;
}
}