典型:各种连接池

public class ConnectionPool {                    private Vector
     
       pool;                    /*公有属性*/          private String url = "jdbc:mysql://localhost:3306/test";          private String username = "root";          private String password = "root";          private String driverClassName = "com.mysql.jdbc.Driver";                private int poolSize = 100;          private static ConnectionPool instance = null;          Connection conn = null;                /*构造方法，做一些初始化工作*/          private ConnectionPool() {              pool = new Vector
      
       (poolSize);                    for (int i = 0; i < poolSize; i++) {                  try {                      Class.forName(driverClassName);                      conn = DriverManager.getConnection(url, username, password);                      pool.add(conn);                  } catch (ClassNotFoundException e) {                      e.printStackTrace();                  } catch (SQLException e) {                      e.printStackTrace();                  }              }          }                /* 返回连接到连接池 */          public synchronized void release() {              pool.add(conn);          }                /* 返回连接池中的一个数据库连接 */          public synchronized Connection getConnection() {              if (pool.size() > 0) {                  Connection conn = pool.get(0);                  pool.remove(conn);                  return conn;              } else {                  return null;              }          }      }