连接池代码：
public class MyDataSource2{
private static String url = "jdbc:mysql://localhost:3306/jdbc";
private static String user = "root";
private static String password = "";
private static int initCount = 1;
private static int maxCount = 1;
int currentCount = 0;
LinkedList<Connection> connectionsPool = new LinkedList<Connection>();
public MyDataSource2() {
try {
for (int i = 0; i < initCount; i++) {
this.connectionsPool.addLast(this.createConnection());
this.currentCount++;
}
} catch (SQLException e) {
throw new ExceptionInInitializerError(e);
}
}
public Connection getConnection() throws SQLException {
synchronized (connectionsPool) {
if (this.connectionsPool.size() > 0)
return this.connectionsPool.removeFirst();
if (this.currentCount < maxCount) {
this.currentCount++;
return this.createConnection();
}
throw new SQLException("已没有链接");
}
}
public void free(Connection conn) {
this.connectionsPool.addLast(conn);
}
private Connection createConnection() throws SQLException {
Connection realConn = DriverManager.getConnection(url, user, password);
MyConnection myConnection = new MyConnection(realConn, this);
return myConnection;
}
//自建Connection类，重写了close方法，并且限定了同一个Connection的最大使用次数，其它的都使用realConnection的方法
public class MyConnection implements Connection {
private Connection realConnection;
private MyDataSource2 dataSource;
private int maxUseCount = 5;
private int currentUserCount = 0;
MyConnection(Connection connection, MyDataSource2 dataSource) {
this.realConnection = connection;
this.dataSource = dataSource;
}
public void close() throws SQLException {
this.currentUserCount++;
if (this.currentUserCount < this.maxUseCount)
this.dataSource.connectionsPool.addLast(this);
else {
this.realConnection.close();
this.dataSource.currentCount--;//这段是限定同一个链接的使用次数，如果这个MyConnection对象被重复使用过好多次了，就释放了它。
//但是这么做有什么意义？同一个链接使用了很多次会造成什么严重后果吗？这块我真是百思不得其解
}
}
……
}
public final class JdbcUtils {
private static MyDataSource2 myDataSource = null;
private JdbcUtils() {
}
static {
try {
Class.forName("com.mysql.jdbc.Driver");
myDataSource = new MyDataSource2();//放在这个地方，要加载后才能初始化
} catch (Exception e) {
throw new ExceptionInInitializerError(e);
}
}
public static DataSource getDataSource() {
return myDataSource;
}
public static Connection getConnection() throws SQLException {
return myDataSource.getConnection();
}
public static void free(ResultSet rs, Statement st, Connection conn) {
try {
if (rs != null)
rs.close();
} catch (SQLException e) {
e.printStackTrace();
} finally {
try {
if (st != null)
st.close();
} catch (SQLException e) {
e.printStackTrace();
} finally {
if (conn != null)
try {
conn.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
}
