自定义一个简单的JDBC连接池实现方法

public static Connection getConn(){
  Connection conn = null;
  String url = "jdbc:mysql://localhost:3306/test";
  String user = "root";
  String password = "root";
  try {
   Class.forName("com.mysql.jdbc.Driver");
   conn = DriverManager.getConnection(url, user, password);
  } catch (ClassNotFoundException e) {
   e.printStackTrace();
  } catch (SQLException e) {
   e.printStackTrace();
  }
  return conn;
 }

private static List<Connection> connectionList = new LinkedList<>();

public Connection getOneConnection(){
  Connection conn = null;
  try{
   //此处通过外部的properties文件来获取的数据，这样更加灵活。
   InputStream in = MyDataSource.class.getClassLoader().
     getResourceAsStream("jdbc/jdbc.properties");
   Properties pro = new Properties();
   pro.load(in);
   driver = pro.getProperty("driver");
   url = pro.getProperty("url");
   username = pro.getProperty("user");
   password = pro.getProperty("password");
   Class.forName(driver);
   conn = DriverManager.getConnection(url,username,password);
  }catch (Exception e){
   e.getStackTrace();
  }
  return conn;
 }

public MyDataSource() {
  for (int i = 0; i < 5; i++) {
   Connection conn = getOneConnection();//调用创建连接的方法
   connectionList.add(conn);
  }
 }

@Override
 public Connection getConnection() throws SQLException {
  Connection conn = null;
  if(connectionList == null || connectionList.size() <= 0){
   Connection connection = getConnection();
   connectionList.add(connection);
  }
  conn = connectionList.remove(0);
  return conn;
 }

public void backConnection(Connection conn){
  connectionList.add(conn);
 }

public static void main( String[] args ) throws SQLException
 {
  MyDataSource dataSource = new MyDataSource();
  Connection conn = dataSource.getConnection();
  String sql = "select * from user where u_id = ?";
  PreparedStatement ps = null;
  ResultSet rs = null;
  try {
   ps = conn.prepareStatement(sql);
   ps.setInt(1, 1);
   rs = ps.executeQuery();
   while (rs.next()) {
    System.out.println("id="+rs.getInt(1));
    System.out.println("username="+rs.getString(2));
    System.out.println("password="+rs.getString(3));
   }
  } catch (SQLException e) {
   e.printStackTrace();
  } finally {
   dataSource.backConnection(conn);
  }
 }

private Connection conn;
 private List<Connection> pool;
 
 public MyConnection(Connection conn, List<Connection> pool) {
  this.conn = conn;
  this.pool = pool;
 }

 @Override
 public void close() throws SQLException {
  System.out.println("回收连接");
  pool.add(conn);
 }

@Override
 public PreparedStatement prepareStatement(String sql) throws SQLException {
  System.out.println("获得Statement");
  return conn.prepareStatement(sql);
 }

public MyDataSource2() {
  for (int i = 0; i < 5; i++) {
   Connection conn = getOneConnection();
   MyConnection myConn = new MyConnection(conn, connectionList);
   connectionList.add(myConn);
  }
 }

@Override
 public Connection getConnection() throws SQLException {
  Connection conn = null;
  if(connectionList == null || connectionList.size() <= 0){
   Connection connection = getConnection();
   MyConnection myConn = new MyConnection(connection, connectionList);
   connectionList.add(myConn);
  }
  conn = connectionList.remove(0);
  return conn;
 }