十四 数据库连接池&DBUtils

关于数据库连接池：

1 数据库的连接对象创建工作，比较消耗性能。

2 一开始在内存中开辟一块空间，往池子里放置多个连接对象，需要连接的时候从连接池里面调用，

使用完毕归还连接，确保连接对象能够循环利用。解决jdbc中连接部分的工作

自定义数据库连接池：

/**
 *
 * 这是一个数据库连接池
 * 1 一开始先往池子里放10个连接
 * 2 通过getConnection获取连接
 * 3 用完之后用addback归还连接
 * 4 扩容
 *
 * 问题：
 *    1 sun公司针对数据库连接池定义的一套规范
 *      需要额外记住addBack的方法
 *    2 需要做成单例
 *    3 无法面向接口编程，因为接口里面没有定义addBack方法
 */
public class MyDataSource implements DataSource{

    List<Connection> list = new ArrayList<>();
    public MyDataSource(){
    for(int i = 0; i<10 ; i++){
        Connection conn =  JDBCUtil.getConn();
        list.add(conn);
        }
    }

    @Override
    //该连接池对外公布的获取连接的方法
    public Connection getConnection() throws SQLException{
        //看看池子还有没有连接
        if(list.size()==0){
            for(int i = 0; i<10 ; i++){
                Connection conn =  JDBCUtil.getConn();
                list.add(conn);
                }
        }
        Connection conn = list.remove(0);
        return conn;
    }
    //归还
    public void addBack(Connection conn){
        list.add(conn);
    }

    @Override

解决自定义数据库连接池出现的问题

修改接口的close方法，Connection调用close,归还对象，而非关闭连接

如何扩展？

1. 修改源码

2. 继承，必须得知道这个接口的具体实现是谁

3. 使用装饰者模式

4. 动态代理

开源连接池：DBCP，C3P0

DBCP：Apache开发

DBCP开发的两种方式：

public class DBCPDemo {

  static String driverClassName  = "com.mysql.jdbc.Driver";
  //jdbc主协议，mysql子协议，所以类名倒着写driverClassName为com.mysql,url为jdbc协议下mysql
  //主协议：子协议：//本地:数据库
  static String url  = "jdbc:mysql://localhost/bank";
  static String username  = "root";
  static String password  = "fungsumyuet";

  @Test
  //手动设置的方式
  public void testDBCP01(){

      Connection conn = null;
      PreparedStatement ps  = null;
      try {
        //构建数据源对象
        BasicDataSource dataSource = new BasicDataSource();
        //数据库连接参数
        dataSource.setDriverClassName(driverClassName);
        dataSource.setUrl(url);
        dataSource.setUsername(username);
        dataSource.setPassword(password);
        conn  = dataSource.getConnection();
        String sql = "insert into account values(null,?,?)";
        ps  = conn.prepareStatement(sql);
        ps.setString(1, "bushi");
        ps.setInt(2, 1000);
        ps.executeUpdate();
    } catch (SQLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }finally {
        JDBCUtil.release(conn, ps);
    }
  }

  @Test
  //配置文件的方式，因为是Java工程而非web工程，所以可以用IO流FileInputStream加载文件，web工程用类加载形式
  public void testDBCP02(){
      Connection conn = null;
      PreparedStatement ps  = null;
      try {
          BasicDataSourceFactory factory = new BasicDataSourceFactory();
          Properties properties = new Properties();
          InputStream is = new FileInputStream("src//dbcpconfig.properties");
          properties.load(is);;
          DataSource dataSource = factory.createDataSource(properties);

          conn = dataSource.getConnection();
          String sql = "insert into account values(null,?,?)";
          ps  = conn.prepareStatement(sql);
          ps.setString(1, "liangchaowei");
          ps.setInt(2, 1000);
          ps.executeUpdate();
    } catch (Exception e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }finally {
        JDBCUtil.release(conn, ps);
    }
  }
}

C3P0（重点掌握）：

public class C3P0Demo01 {

    @Test
    //c3p0代码方式
    public void testC3P0(){
        //1 .创建dataSource
        ComboPooledDataSource dataSource = new ComboPooledDataSource();
        Connection conn = null;
        PreparedStatement ps  = null;
        try {
            //设置参数
            dataSource.setDriverClass("com.mysql.jdbc.Driver");
            dataSource.setJdbcUrl("jdbc:mysql://localhost/bank");
            dataSource.setUser("root");
            dataSource.setPassword("fungsumyuet");
            conn = dataSource.getConnection();
            String sql = "insert into account values(null,?,?)";
            ps = conn.prepareStatement(sql);
            ps.setString(1, "zhourunfa");
            ps.setInt(2,1000);
            ps.executeUpdate();
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally {
            JDBCUtil.release(conn, ps);
        }
    }

    @Test
    //C3P0配置文件方式
    public void testC3P02(){

        Connection conn = null;
        PreparedStatement ps  = null;
        try {
            //1 .创建dataSource,源码里面类加载形式加载配置文件
            ComboPooledDataSource dataSource = new ComboPooledDataSource();
            //设置参数
            conn = dataSource.getConnection();
            String sql = "insert into account values(null,?,?)";
            ps = conn.prepareStatement(sql);
            ps.setString(1, "wuqilong");
            ps.setInt(2,1000);
            ps.executeUpdate();
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally {
            JDBCUtil.release(conn, ps);
        }
    }
}

DBUtils:联合连接池，简化CRUD操作

1.导包，引入配置文件

2.创建连接池对象，dataSource

3.将连接池对象传进QueryRunner()

4.处理业务实现功能

public class TestDBUtils {

   @Test
   public void demo01() throws SQLException{
       //C3P0连接池
       ComboPooledDataSource dataSource = new ComboPooledDataSource();
       //dbUtils简化CRUD代码
       QueryRunner queryRunner = new QueryRunner(dataSource);
       //增加
//       queryRunner.update("insert into account values(null,?,?)", "panfeng",1000);
       //删除
//       queryRunner.update("delete from account where id = ?", 12);
       //更新
//       queryRunner.update("update account set money = ? where id = ? ", 999,9);

       //查询,查询到的数据还是在ResultSet里面，然后调用下面的handle方法，由用户手动去封装
/*       Account account =  queryRunner.query("select * from account where id = ?",
       new ResultSetHandler<Account>(){
        @Override
        public Account handle(ResultSet rs) throws SQLException {
            Account account = new Account();
            while(rs.next()){
                int id = rs.getInt("id");
                String name = rs.getString("name");
                int money = rs.getInt("money");

                account.setId(id);
                account.setName(name);
                account.setMoney(money);
            }
            return account;
        }

       }, 9);

       System.out.println(account.toString());*/

       //查询单个对象,通过类的字节码得到该类的实例： A1 a  = new A1.class.newInstance();
      /*Account account =  queryRunner.query("select * from account where id = ?",
              new BeanHandler<Account>(Account.class),8);
      System.out.println(account.toString());*/

      //查询多个对象
       List<Account> list =  queryRunner.query("select * from account", new BeanListHandler<Account>(Account.class));
       for(Account account : list){
           System.out.println(account.toString());
       }
  }
}

DBUtil通用模版：

元数据：描述数据的数据。比如String sql , 描述sql的数据叫做元数据

public class CommonCRUDUtil {

    @Test
    //sql 可变参数
    public void testUpdate(){
//        update("insert into account values(null,?,?)","aa" , 10);
//        update("delete from account where id = ?", 12);
        //按照问号个数
//        update02("update account set money = ?  where id = ?", 800 , 7);

    }

    @Test
    public void testQuery(){
        Account account = query("select * from account where id = ?", new ResultSetHandler<Account>(){

            @Override
            public Account handle(ResultSet rs) {
                Account account = new Account();
                try {
                    if(rs.next()){
                        int id = rs.getInt("id");
                        String name = rs.getString("name");
                        int money = rs.getInt("money");

                        account.setId(id);
                        account.setName(name);
                        account.setMoney(money);
                        return account;
                    }
                } catch (SQLException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                return null;
            }}, 9 );
            System.out.println(account.toString());
    }

    //通用的增删改查功能
    /**
     * @param sql
     * @param args 可变参数，有几个占位符，就写几个参数进来
     */
    public void update(String sql , Object ... args){
      Connection conn = null;
      PreparedStatement ps = null;
      try {
        conn = JDBCUtil02.getConn();
        ps = conn.prepareStatement(sql);
        //因为不知道是什么类型的数组，所以都用Object来对待
        for(int i = 0 ; i<args.length ; i++){
          ps.setObject(i+1, args[i]);
        }
        ps.executeUpdate();
      } catch (SQLException e) {
        e.printStackTrace();
     }finally {
        JDBCUtil.release(conn, ps);
    }
  }

    public void update02(String sql , Object ... args){
        Connection conn = null;
        PreparedStatement ps = null;
        try {
            conn = JDBCUtil02.getConn();
            ps = conn.prepareStatement(sql);
            //元数据，获取到有几个问号，占位符
            ParameterMetaData metaData = ps.getParameterMetaData();
            int count = metaData.getParameterCount();
            for(int i = 0; i<count ; i++){
                ps.setObject(i+1, args[i]);
            }
                ps.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            JDBCUtil.release(conn, ps);
        }
    }

    //通用查询
    public <T> T query(String sql ,ResultSetHandler<T> handler, Object ... args){
        Connection conn = null;
        PreparedStatement ps = null;
        try {
            conn = JDBCUtil02.getConn();
            ps = conn.prepareStatement(sql);
            //元数据，获取到有几个问号，占位符
            ParameterMetaData metaData = ps.getParameterMetaData();
            int count = metaData.getParameterCount();
            for(int i = 0; i<count ; i++){
                ps.setObject(i+1, args[i]);
            }
            //问题1：数据获取封装成什么对象返回？
            ResultSet rs = ps.executeQuery();
            T t = (T) handler.handle(rs);
            return t;
        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            JDBCUtil.release(conn, ps);
        }
        return null;
    }
}