http://blog.csdn.net/xilangyuyun/article/details/52800380
写JDBC connection pool 的注意事项有：1. 有一个简单的函数从连接池中得到一个 Connection。
2. close 函数必须将connection 放回 数据库连接池。
3. 当数据库连接池中没有空闲的connection，数据库连接池必须能够自动增加connection 个数。
4. 当数据库连接池中的connection 个数在某一个特别的时间变得很大，但是以后很长时间只用其中一小部分，应该可以自动将多余的connection 关闭掉。
5. 如果可能，应该提供debug 信息报告没有关闭的new Connection 。
如果要new Connection 就可以直接从数据库连接池中返回Connection， 可以这样写( Mediator pattern ) (以下代码中使用了中文全角空格)：
public class EasyConnection implements java.sql.Connection{
private Connection m_delegate = null
public EasyConnection(){
m_delegate = getConnectionFromPool()
}
public void close(){
putConnectionBackToPool(m_delegate)
}
public PreparedStatement prepareStatement(String sql) throws SQLException{
m_delegate.prepareStatement(sql)
}
//...... other method
}
看来并不难。不过不建议这种写法，因为应该尽量避免使用Java Interface, 关于Java Interface 的缺点我另外再写文章讨论。大家关注的是Connection Pool 的实现方法。下面给出一种实现方法。
import java.sql.*
import java.lang.reflect.*
import java.util.*
import java.io.*
public class SimpleConnetionPool {
private static LinkedList m_notUsedConnection = new LinkedList()
private static HashSet m_usedUsedConnection = new HashSet()
private static String m_url = ""
private static String m_user = ""
private static String m_password = ""
static final boolean DEBUG = true
static private long m_lastClearClosedConnection = System.currentTimeMillis()
public static long CHECK_CLOSED_CONNECTION_TIME = 4 * 60 * 60 * 1000//4 hours
static {
initDriver()
}
private SimpleConnetionPool() {
}
private static void initDriver() {
Driver driver = null
//load mysql driver
try {
driver = (Driver) Class.forName("com.mysql.jdbc.Driver").newInstance()
installDriver(driver)
} catch (Exception e) {
}
//load postgresql driver
try {
driver = (Driver) Class.forName("org.postgresql.Driver").newInstance()
installDriver(driver)
} catch (Exception e) {
}
}
public static void installDriver(Driver driver) {
try {
DriverManager.registerDriver(driver)
} catch (Exception e) {
e.printStackTrace()
}
}
public static synchronized Connection getConnection() {
clearClosedConnection()
while (m_notUsedConnection.size() >0) {
try {
ConnectionWrapper wrapper = (ConnectionWrapper) m_notUsedConnection.removeFirst()
if (wrapper.connection.isClosed()) {
continue
}
m_usedUsedConnection.add(wrapper)
if (DEBUG) {
wrapper.debugInfo = new Throwable("Connection initial statement")
}
return wrapper.connection
} catch (Exception e) {
}
}
int newCount = getIncreasingConnectionCount()
LinkedList list = new LinkedList()
ConnectionWrapper wrapper = null
for (int i = 0i <newCounti++) {
wrapper = getNewConnection()
if (wrapper != null) {
list.add(wrapper)
}
}
if (list.size() == 0) {
return null
}
wrapper = (ConnectionWrapper) list.removeFirst()
m_usedUsedConnection.add(wrapper)
m_notUsedConnection.addAll(list)
list.clear()
return wrapper.connection
}
private static ConnectionWrapper getNewConnection() {
try {
Connection con = DriverManager.getConnection(m_url, m_user, m_password)
ConnectionWrapper wrapper = new ConnectionWrapper(con)
return wrapper
} catch (Exception e) {
e.printStackTrace()
}
return null
}
static synchronized void pushConnectionBackToPool(ConnectionWrapper con) {
boolean exist = m_usedUsedConnection.remove(con)
if (exist) {
m_notUsedConnection.addLast(con)
}
}
public static int close() {
int count = 0
Iterator iterator = m_notUsedConnection.iterator()
while (iterator.hasNext()) {
try {
( (ConnectionWrapper) iterator.next()).close()
count++
} catch (Exception e) {
}
}
m_notUsedConnection.clear()
iterator = m_usedUsedConnection.iterator()
while (iterator.hasNext()) {
try {
ConnectionWrapper wrapper = (ConnectionWrapper) iterator.next()
wrapper.close()
if (DEBUG) {
wrapper.debugInfo.printStackTrace()
}
count++
} catch (Exception e) {
}
}
m_usedUsedConnection.clear()
return count
}
private static void clearClosedConnection() {
long time = System.currentTimeMillis()
//sometimes user change system time,just return
if (time <m_lastClearClosedConnection) {
time = m_lastClearClosedConnection
return
}
//no need check very often
if (time - m_lastClearClosedConnection <CHECK_CLOSED_CONNECTION_TIME) {
return
}
m_lastClearClosedConnection = time
//begin check
Iterator iterator = m_notUsedConnection.iterator()
while (iterator.hasNext()) {
ConnectionWrapper wrapper = (ConnectionWrapper) iterator.next()
try {
if (wrapper.connection.isClosed()) {
iterator.remove()
}
} catch (Exception e) {
iterator.remove()
if (DEBUG) {
System.out.println("connection is closed, this connection initial StackTrace")
wrapper.debugInfo.printStackTrace()
}
}
}
//make connection pool size smaller if too big
int decrease = getDecreasingConnectionCount()
if (m_notUsedConnection.size() <decrease) {
return
}
while (decrease-- >0) {
ConnectionWrapper wrapper = (ConnectionWrapper) m_notUsedConnection.removeFirst()
try {
wrapper.connection.close()
} catch (Exception e) {
}
}
}
public static int getIncreasingConnectionCount() {
int count = 1
int current = getConnectionCount()
count = current / 4
if (count <1) {
count = 1
}
return count
}
public static int getDecreasingConnectionCount() {
int count = 0
int current = getConnectionCount()
if (current <10) {
return 0
}
return current / 3
}
public synchronized static void printDebugMsg() {
printDebugMsg(System.out)
}
public synchronized static void printDebugMsg(PrintStream out) {
if (DEBUG == false) {
return
}
StringBuffer msg = new StringBuffer()
msg.append("debug message in " + SimpleConnetionPool.class.getName())
msg.append("\r\n")
msg.append("total count is connection pool: " + getConnectionCount())
msg.append("\r\n")
msg.append("not used connection count: " + getNotUsedConnectionCount())
msg.append("\r\n")
msg.append("used connection, count: " + getUsedConnectionCount())
out.println(msg)
Iterator iterator = m_usedUsedConnection.iterator()
while (iterator.hasNext()) {
ConnectionWrapper wrapper = (ConnectionWrapper) iterator.next()
wrapper.debugInfo.printStackTrace(out)
}
out.println()
}
public static synchronized int getNotUsedConnectionCount() {
return m_notUsedConnection.size()
}
public static synchronized int getUsedConnectionCount() {
return m_usedUsedConnection.size()
}
public static synchronized int getConnectionCount() {
return m_notUsedConnection.size() + m_usedUsedConnection.size()
}
public static String getUrl() {
return m_url
}
public static void setUrl(String url) {
if (url == null) {
return
}
m_url = url.trim()
}
public static String getUser() {
return m_user
}
public static void setUser(String user) {
if (user == null) {
return
}
m_user = user.trim()
}
public static String getPassword() {
return m_password
}
public static void setPassword(String password) {
if (password == null) {
return
}
m_password = password.trim()
}
}
class ConnectionWrapper implements InvocationHandler {
private final static String CLOSE_METHOD_NAME = "close"
public Connection connection = null
private Connection m_originConnection = null
public long lastAccessTime = System.currentTimeMillis()
Throwable debugInfo = new Throwable("Connection initial statement")
ConnectionWrapper(Connection con) {
this.connection = (Connection) Proxy.newProxyInstance(
con.getClass().getClassLoader(),
new Class[]{Connection.class}, this)
m_originConnection = con
}
void close() throws SQLException {
m_originConnection.close()
}
public Object invoke(Object proxy, Method m, Object[] args) throws Throwable {
Object obj = null
if (CLOSE_METHOD_NAME.equals(m.getName())) {
SimpleConnetionPool.pushConnectionBackToPool(this)
}
else {
obj = m.invoke(m_originConnection, args)
}
lastAccessTime = System.currentTimeMillis()
return obj
}
}
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