编写一个基本的连接池来实现连接的复用&一些工程细节上的优化

 package it.cast.jdbc;

 import java.sql.Connection;
 import java.sql.DriverManager;
 import java.sql.SQLException;
 import java.util.LinkedList;

 public class MyDataSource {

     private static String url = "jdbc:mysql://localhost:3306/jdbc";
     private static String username = "root";
     private static String password = "123";

     private static int initCount = 5;
     private static int maxCount = 10;
     private int currentCount = 0;

     private LinkedList<Connection> connectionPool = new LinkedList<Connection>();

     public MyDataSource() {
         try {
             for (int i = 0; i < initCount; i++) {

                 this.connectionPool.addLast(this.createConnection());

                 this.currentCount++;
             }
         } catch (SQLException e) {
             throw new ExceptionInInitializerError(e);
         }

     }

     public Connection getConnection() throws SQLException {
         synchronized (connectionPool) {
             if (this.connectionPool.size() > 0) {
                 return this.connectionPool.removeFirst();
             }
             if (this.currentCount < maxCount) {
                 this.currentCount++;
                 return this.createConnection();
             }
             throw new SQLException("NO Connection!!");
         }

     }

     public void free(Connection conn) {
         this.connectionPool.addLast(conn);
     }

     private Connection createConnection() throws SQLException {
         return DriverManager.getConnection(url, username, password);
     }
 }

MyDataSource

 package it.cast.jdbc;

 import java.sql.CallableStatement;
 import java.sql.Connection;
 import java.sql.DriverManager;
 import java.sql.PreparedStatement;
 import java.sql.ResultSet;
 import java.sql.SQLException;
 import java.sql.Statement;

 public class jdbcUtils {

     private static String url = "jdbc:mysql://localhost:3306/jdbc?generateSimpleParameterMetadata=true";
     private static String user = "root";
     private static String password = "123";

     private static MyDataSource myDataSource = null;

     private jdbcUtils() {

     }

     static {
         try {
             Class.forName("com.mysql.jdbc.Driver");
             myDataSource =new MyDataSource();
         } catch (ClassNotFoundException e) {
             e.printStackTrace();
         }
     }

     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 {

                 try {
                     if (conn != null)
                         //conn.close();
                         myDataSource.free(conn);
                 } catch (Exception e) {
                     e.printStackTrace();
                 }
             }

         }

     }

     public static void free(ResultSet rs, PreparedStatement ps, Connection conn) {

         try {
             if (rs != null)
                 rs.close();
         } catch (SQLException e) {
             e.printStackTrace();
         } finally {

             try {
                 if (ps != null)
                     ps.close();
             } catch (SQLException e) {
                 e.printStackTrace();
             } finally {

                 try {
                     if (conn != null)
                         //conn.close();
                         myDataSource.free(conn);
                 } catch (Exception e) {
                     e.printStackTrace();
                 }
             }

         }

     }
     public static void free(ResultSet rs, CallableStatement cs, Connection conn) {

         try {
             if (rs != null)
                 rs.close();
         } catch (SQLException e) {
             e.printStackTrace();
         } finally {

             try {
                 if (cs != null)
                     cs.close();
             } catch (SQLException e) {
                 e.printStackTrace();
             } finally {

                 try {
                     if (conn != null)
                         //conn.close();
                         myDataSource.free(conn);
                 } catch (Exception e) {
                     e.printStackTrace();
                 }
             }

         }

     }
 }

jdbcUtils

 package it.cast.jdbc;

 import java.sql.Connection;
 import java.sql.ResultSet;
 import java.sql.SQLException;
 import java.sql.Statement;

 public class Base {

     static Connection conn = null;

     public static void main(String[] args) throws SQLException, ClassNotFoundException {
         for (int i = 0; i < 20; i++) {
             Connection conn = jdbcUtils.getConnection();
             System.out.println(conn);
             //jdbcUtils.free(null, null, conn);
         }
     }

     static void test() throws SQLException, ClassNotFoundException {

         // 2.建立连接
         conn = jdbcUtils.getConnection();

         // 3.创建语句
         Statement st = conn.createStatement();

         // 4.执行语句
         ResultSet rs = st.executeQuery("select * from user");

         // 5.处理结果
         while (rs.next()) {
             System.out.println(rs.getObject(1) + "\t" + rs.getObject(2) + "\t"
                     + rs.getObject(3)+"\t" + rs.getObject(4));
         }

         //6.释放资源
         jdbcUtils.free(rs, st, conn);
     }

 }

Base