「MySQL」自定义数据库连接池和开源数据库连接池的使用

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原创最新推荐文章于 2026-03-04 02:57:36 发布 262 阅读 AI 写同款· GEO 优化 ›

Mysql-数据库优化-连接参数这个参数是管理连接池数量的，和线程池的思想一样，spring.datasource.druid.min-idle这个相当于核心线程数，无论怎样连接池始终保持这么多的连接数量。数据库连接池化的思想也就是提前将连接创建好并保存用的时候直接拿来用，同时要进行管理，也就有了上面这些相关的参数，如果不适用池化的思想，数据库会有一个最大的连接数，如果超过这个最大连接数，数据库直接无法处客户端的查询请求。可以看到一旦达到最大连接数就会报错，异常比例是相当高的，但是使用连接池就不会有这种大量报错的现象。阅读详情

数据库连接池的概念

数据库连接背景数据库连接是一种关键的、有限的、昂贵的资源，这一点在多用户的网页应用程序中体现得尤为突出。对数据库连接的管理能显著影响到整个应用程序的伸缩性和健壮性，影响到程序的性能指标。数据库连接池正是针对这个问题提出来的。
数据库连接池数据库连接池负责分配、管理和释放数据库连接，它允许应用程序重复使用一个现有的数据库连接，而不是再重新建立一个。这项技术能明显提高对数据库操作的性能。
数据库连接池的原理没有使用数据库连接池：一个访问创建一个连接，使用完关闭连接。而频繁的创建和关闭连接非常耗时

使用数据库连接池之后：提前准备一些数据库连接，使用时从池中取出，用完归还连接池

自定义连接池

初探连接池

自定义JDBC工具类

配置文件 config.properties

driverClass=com.mysql.jdbc.Driver
url=jdbc:mysql://主机名:3306/数据库名
username=用户名
password=密码

JDBCUtils工具类

public class JDBCUtils {
    private JDBCUtils() {}  //构造函数私有化

    private static String driverClass;
    private static String url;
    private static String username;
    private static String password;
    private static Connection con;

    static {
        try {
            InputStream is = JDBCUtils.class.getClassLoader().getResourceAsStream("config.properties");
            Properties properties = new Properties();
            properties.load(is);
            driverClass = properties.getProperty("driverClass");
            url = properties.getProperty("url");
            username = properties.getProperty("username");
            password = properties.getProperty("password");
            Class.forName(driverClass);

        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }

    public static Connection getConnection() {  //获取连接对象
        try {
            con = DriverManager.getConnection(url, username, password);
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return con;
    }
    //关闭连接（有查询结果集）
    public static void close(Connection con, Statement stat, ResultSet res) {
        if (con != null) {
            try {
                con.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if (stat != null) {
            try {
                stat.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if (res != null) {
            try {
                res.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
    //关闭连接（无查询结果集）
    public static void close(Connection con, Statement stat) {
        close(con, stat, null);
    }
}

实现连接池类

定义一个连接池类并实现 java.sql.DataSource 接口。

Connection getConnection();  //获取数据库连接对象

public class MyDataSource implements DataSource{
    //定义集合容器，用于保存多个数据库连接对象
    //使用Collections 工具类实现集合的线程同步
    private static List<Connection> pool = Collections.synchronizedList(new ArrayList<Connection>());

    //静态代码块，生成10个数据库连接保存到集合中
    static {
        for (int i = 0; i < 10; i++) {
            Connection con = JDBCUtils.getConnection();
            pool.add(con);
        }
    }

    //返回连接池的大小
    public int getSize() {
        return pool.size();
    }

    //从池中返回一个数据库连接
    @Override
    public Connection getConnection() {
        if(pool.size() > 0) {
            //从池中获取数据库连接
            return pool.remove(0);
        }else {
            throw new RuntimeException("连接数量已用尽");
        }
    }

    @Override
    public Connection getConnection(String username, String password) throws SQLException {
        return null;
    }

    @Override
    public <T> T unwrap(Class<T> iface) throws SQLException {
        return null;
    }

    @Override
    public boolean isWrapperFor(Class<?> iface) throws SQLException {
        return false;
    }

    @Override
    public PrintWriter getLogWriter() throws SQLException {
        return null;
    }

    @Override
    public void setLogWriter(PrintWriter out) throws SQLException {

    }

    @Override
    public void setLoginTimeout(int seconds) throws SQLException {

    }

    @Override
    public int getLoginTimeout() throws SQLException {
        return 0;
    }

    @Override
    public Logger getParentLogger() throws SQLFeatureNotSupportedException {
        return null;
    }
}

自定义连接池的测试

public class MyDataSourceTest {
    public static void main(String[] args) throws SQLException {
        MyDataSource dataSource = new MyDataSource();
        System.out.println("使用前连接池数量：" + dataSource.getSize());

        Connection con = dataSource.getConnection();

        String sql = "select * from emp";

        PreparedStatement pst = con.prepareStatement(sql);

        ResultSet res = pst.executeQuery();
        while (res.next()) {
            String ename = res.getString("ename");
            String job = res.getString("job");
            String hiredate = res.getString("hiredate");
            System.out.println("ename:" + ename + "\t job:" + job + "\t hiredate:" + hiredate);
        }

        res.close();
        pst.close();
        con.close();
        System.out.println("使用后连接池数量：" + dataSource.getSize());
    }
}

输出：

使用前连接池数量：10
ename:SMITH	 job:CLERK	 hiredate:1980-12-17
ename:ALLEN	 job:SALESMAN	 hiredate:1981-02-20
ename:WARD	 job:SALESMAN	 hiredate:1981-02-22
ename:JONES	 job:MANAGER	 hiredate:1981-04-02
ename:MARTIN	 job:SALESMAN	 hiredate:1981-09-28
ename:BLAKE	 job:MANAGER	 hiredate:1981-05-01
ename:CLARK	 job:MANAGER	 hiredate:1981-06-09
ename:SCOTT	 job:ANALYST	 hiredate:1987-04-19
ename:KING	 job:PRESIDENT	 hiredate:1981-11-17
ename:TURNER	 job:SALESMAN	 hiredate:1981-09-08
ename:ADAMS	 job:CLERK	 hiredate:1987-05-23
ename:JAMES	 job:CLERK	 hiredate:1981-12-03
ename:FORD	 job:ANALYST	 hiredate:1981-12-03
ename:MILLER	 job:CLERK	 hiredate:1982-01-23
使用后连接池数量：9

问题：虽然我们自定义了数据库连接池，但是连接关闭以后并没有归还给数据库连接池，还需要改进归还连接的问题

继承方式改进连接池

System.out.println(JDBCUtils.getConnection());
//com.mysql.jdbc.JDBC4Connection@470e2030

通过输出 Connection 的地址发现 Connection 类的实现类是 JDBC4Connection ，是否能够通过编写一个类继承 JDBC4Connection ，然后重写 close() 方法，在关闭连接的同时归还连接？

/*
      自定义Connection类
   */
  public class MyConnection1 extends JDBC4Connection {
      //声明连接对象和连接池集合对象
      private Connection con;
      private List<Connection> pool;
  
      //通过构造方法给成员变量赋值
      public MyConnection1(String hostToConnectTo, int portToConnectTo, Properties info, String databaseToConnectTo, String url,Connection con,List<Connection> pool) throws SQLException {
          super(hostToConnectTo, portToConnectTo, info, databaseToConnectTo, url);
          this.con = con;
          this.pool = pool;
      }
  
      //重写close()方法，将连接归还给池中
      @Override
      public void close() throws SQLException {
          pool.add(con);
      }
  }

但是这种方式行不通，通过查看JDBC工具类获取连接的方法我们发现：我们虽然自定义了一个子类，完成了归还连接的操作。但是 DriverManager 获取的还是 JDBC4Connection 这个对象，并不是我们的子类对象。而我们又不能整体去修改驱动包中类的功能！

//将之前的连接对象换成自定义的子类对象
  private static MyConnection1 con;
  
  public static Connection getConnection() {
      try {
          //等效于：MyConnection1 con = new JDBC4Connection();  子类引用指向父类对象，语法错误！
          con = DriverManager.getConnection(url,username,password);
      } catch (SQLException e) {
          e.printStackTrace();
      }
  
      return con;
  }

装饰设计模式改进连接池

自定义Connection类。通过装饰设计模式，实现和mysql驱动包中的Connection实现类相同的功能！

实现步骤：

定义一个类，实现Connection接口
定义Connection连接对象和连接池容器对象的变量
提供有参构造方法，接收连接对象和连接池对象，对变量赋值
在close()方法中，完成连接的归还
剩余方法，只需要调用mysql驱动包的连接对象完成即可

public class MyConnection2 implements Connection {
  
      //2.定义Connection连接对象和连接池容器对象的变量
      private Connection con;
      private List<Connection> pool;
  
      //3.提供有参构造方法，接收连接对象和连接池对象，对变量赋值
      public MyConnection2(Connection con,List<Connection> pool) {
          this.con = con;
          this.pool = pool;
      }
  
      //4.在close()方法中，完成连接的归还
      @Override
      public void close() throws SQLException {
          pool.add(con);
      }
  
  
      @Override
      public Statement createStatement() throws SQLException {
          return con.createStatement();
      }
  
      @Override
      public PreparedStatement prepareStatement(String sql) throws SQLException {
          return con.prepareStatement(sql);
      }
  
      @Override
      public CallableStatement prepareCall(String sql) throws SQLException {
          return con.prepareCall(sql);
      }
  
      @Override
      public String nativeSQL(String sql) throws SQLException {
          return con.nativeSQL(sql);
      }
  
      @Override
      public void setAutoCommit(boolean autoCommit) throws SQLException {
          con.setAutoCommit(autoCommit);
      }
  
      @Override
      public boolean getAutoCommit() throws SQLException {
          return con.getAutoCommit();
      }
  
      @Override
      public void commit() throws SQLException {
          con.commit();
      }
  
      @Override
      public void rollback() throws SQLException {
          con.rollback();
      }
  
      @Override
      public boolean isClosed() throws SQLException {
          return con.isClosed();
      }
  
      @Override
      public DatabaseMetaData getMetaData() throws SQLException {
          return con.getMetaData();
      }
  
      @Override
      public void setReadOnly(boolean readOnly) throws SQLException {
          con.setReadOnly(readOnly);
      }
  
      @Override
      public boolean isReadOnly() throws SQLException {
          return con.isReadOnly();
      }
  
      @Override
      public void setCatalog(String catalog) throws SQLException {
          con.setCatalog(catalog);
      }
  
      @Override
      public String getCatalog() throws SQLException {
          return con.getCatalog();
      }
  
      @Override
      public void setTransactionIsolation(int level) throws SQLException {
          con.setTransactionIsolation(level);
      }
  
      @Override
      public int getTransactionIsolation() throws SQLException {
          return con.getTransactionIsolation();
      }
  
      @Override
      public SQLWarning getWarnings() throws SQLException {
          return con.getWarnings();
      }
  
      @Override
      public void clearWarnings() throws SQLException {
          con.clearWarnings();
      }
  
      @Override
      public Statement createStatement(int resultSetType, int resultSetConcurrency) throws SQLException {
          return con.createStatement(resultSetType,resultSetConcurrency);
      }
  
      @Override
      public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {
          return con.prepareStatement(sql,resultSetType,resultSetConcurrency);
      }
  
      @Override
      public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {
          return con.prepareCall(sql,resultSetType,resultSetConcurrency);
      }
  
      @Override
      public Map<String, Class<?>> getTypeMap() throws SQLException {
          return con.getTypeMap();
      }
  
      @Override
      public void setTypeMap(Map<String, Class<?>> map) throws SQLException {
          con.setTypeMap(map);
      }
  
      @Override
      public void setHoldability(int holdability) throws SQLException {
          con.setHoldability(holdability);
      }
  
      @Override
      public int getHoldability() throws SQLException {
          return con.getHoldability();
      }
  
      @Override
      public Savepoint setSavepoint() throws SQLException {
          return con.setSavepoint();
      }
  
      @Override
      public Savepoint setSavepoint(String name) throws SQLException {
          return con.setSavepoint(name);
      }
  
      @Override
      public void rollback(Savepoint savepoint) throws SQLException {
          con.rollback(savepoint);
      }
  
      @Override
      public void releaseSavepoint(Savepoint savepoint) throws SQLException {
          con.releaseSavepoint(savepoint);
      }
  
      @Override
      public Statement createStatement(int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {
          return con.createStatement(resultSetType,resultSetConcurrency,resultSetHoldability);
      }
  
      @Override
      public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {
          return con.prepareStatement(sql,resultSetType,resultSetConcurrency,resultSetHoldability);
      }
  
      @Override
      public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {
          return con.prepareCall(sql,resultSetType,resultSetConcurrency,resultSetHoldability);
      }
  
      @Override
      public PreparedStatement prepareStatement(String sql, int autoGeneratedKeys) throws SQLException {
          return con.prepareStatement(sql,autoGeneratedKeys);
      }
  
      @Override
      public PreparedStatement prepareStatement(String sql, int[] columnIndexes) throws SQLException {
          return con.prepareStatement(sql,columnIndexes);
      }
  
      @Override
      public PreparedStatement prepareStatement(String sql, String[] columnNames) throws SQLException {
          return con.prepareStatement(sql,columnNames);
      }
  
      @Override
      public Clob createClob() throws SQLException {
          return con.createClob();
      }
  
      @Override
      public Blob createBlob() throws SQLException {
          return con.createBlob();
      }
  
      @Override
      public NClob createNClob() throws SQLException {
          return con.createNClob();
      }
  
      @Override
      public SQLXML createSQLXML() throws SQLException {
          return con.createSQLXML();
      }
  
      @Override
      public boolean isValid(int timeout) throws SQLException {
          return con.isValid(timeout);
      }
  
      @Override
      public void setClientInfo(String name, String value) throws SQLClientInfoException {
          con.setClientInfo(name,value);
      }
  
      @Override
      public void setClientInfo(Properties properties) throws SQLClientInfoException {
          con.setClientInfo(properties);
      }
  
      @Override
      public String getClientInfo(String name) throws SQLException {
          return con.getClientInfo(name);
      }
  
      @Override
      public Properties getClientInfo() throws SQLException {
          return con.getClientInfo();
      }
  
      @Override
      public Array createArrayOf(String typeName, Object[] elements) throws SQLException {
          return con.createArrayOf(typeName,elements);
      }
  
      @Override
      public Struct createStruct(String typeName, Object[] attributes) throws SQLException {
          return con.createStruct(typeName,attributes);
      }
  
      @Override
      public void setSchema(String schema) throws SQLException {
          con.setSchema(schema);
      }
  
      @Override
      public String getSchema() throws SQLException {
          return con.getSchema();
      }
  
      @Override
      public void abort(Executor executor) throws SQLException {
          con.abort(executor);
      }
  
      @Override
      public void setNetworkTimeout(Executor executor, int milliseconds) throws SQLException {
          con.setNetworkTimeout(executor,milliseconds);
      }
  
      @Override
      public int getNetworkTimeout() throws SQLException {
          return con.getNetworkTimeout();
      }
  
      @Override
      public <T> T unwrap(Class<T> iface) throws SQLException {
          return con.unwrap(iface);
      }
  
      @Override
      public boolean isWrapperFor(Class<?> iface) throws SQLException {
          return con.isWrapperFor(iface);
      }
  }

自定义连接池类

public class MyDataSource implements DataSource{
      //定义集合容器，用于保存多个数据库连接对象
      private static List<Connection> pool = Collections.synchronizedList(new ArrayList<Connection>());
  
      //静态代码块，生成10个数据库连接保存到集合中
      static {
          for (int i = 0; i < 10; i++) {
              Connection con = JDBCUtils.getConnection();
              pool.add(con);
          }
      }
  
      //返回连接池的大小
      public int getSize() {
          return pool.size();
      }
  
      //从池中返回一个数据库连接
      @Override
      public Connection getConnection() {
          if(pool.size() > 0) {
              //从池中获取数据库连接
              Connection con = pool.remove(0);
              //通过自定义连接对象进行包装
              MyConnection2 mycon = new MyConnection2(con,pool);
              //返回包装后的连接对象
              return mycon;
          }else {
              throw new RuntimeException("连接数量已用尽");
          }
      }
  }

缺点： Connection 接口中要实现的方法太多了，代码繁杂

适配器设计模式改进连接池

提供一个适配器类，实现 Connection 接口，将所有功能进行实现(除了 close()方法)，作为中间类。自定义连接类只需要继承这个适配器类，重写需要改进的 close() 方法即可！

适配器类不需要实现 close() 方法，所以定义为抽象类

public abstract class MyAdapter implements Connection {
  
      // 定义数据库连接对象的变量
      private Connection con;
  
      // 通过构造方法赋值
      public MyAdapter(Connection con) {
          this.con = con;
      }
  
      // 所有的方法，均调用mysql的连接对象实现
      @Override
      public Statement createStatement() throws SQLException {
          return con.createStatement();
      }
  
      @Override
      public PreparedStatement prepareStatement(String sql) throws SQLException {
          return con.prepareStatement(sql);
      }
  
      @Override
      public CallableStatement prepareCall(String sql) throws SQLException {
          return con.prepareCall(sql);
      }
  
      @Override
      public String nativeSQL(String sql) throws SQLException {
          return con.nativeSQL(sql);
      }
  
      @Override
      public void setAutoCommit(boolean autoCommit) throws SQLException {
          con.setAutoCommit(autoCommit);
      }
  
      @Override
      public boolean getAutoCommit() throws SQLException {
          return con.getAutoCommit();
      }
  
      @Override
      public void commit() throws SQLException {
          con.commit();
      }
  
      @Override
      public void rollback() throws SQLException {
          con.rollback();
      }
  
      @Override
      public boolean isClosed() throws SQLException {
          return con.isClosed();
      }
  
      @Override
      public DatabaseMetaData getMetaData() throws SQLException {
          return con.getMetaData();
      }
  
      @Override
      public void setReadOnly(boolean readOnly) throws SQLException {
          con.setReadOnly(readOnly);
      }
  
      @Override
      public boolean isReadOnly() throws SQLException {
          return con.isReadOnly();
      }
  
      @Override
      public void setCatalog(String catalog) throws SQLException {
          con.setCatalog(catalog);
      }
  
      @Override
      public String getCatalog() throws SQLException {
          return con.getCatalog();
      }
  
      @Override
      public void setTransactionIsolation(int level) throws SQLException {
          con.setTransactionIsolation(level);
      }
  
      @Override
      public int getTransactionIsolation() throws SQLException {
          return con.getTransactionIsolation();
      }
  
      @Override
      public SQLWarning getWarnings() throws SQLException {
          return con.getWarnings();
      }
  
      @Override
      public void clearWarnings() throws SQLException {
          con.clearWarnings();
      }
  
      @Override
      public Statement createStatement(int resultSetType, int resultSetConcurrency) throws SQLException {
          return con.createStatement(resultSetType,resultSetConcurrency);
      }
  
      @Override
      public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {
          return con.prepareStatement(sql,resultSetType,resultSetConcurrency);
      }
  
      @Override
      public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {
          return con.prepareCall(sql,resultSetType,resultSetConcurrency);
      }
  
      @Override
      public Map<String, Class<?>> getTypeMap() throws SQLException {
          return con.getTypeMap();
      }
  
      @Override
      public void setTypeMap(Map<String, Class<?>> map) throws SQLException {
          con.setTypeMap(map);
      }
  
      @Override
      public void setHoldability(int holdability) throws SQLException {
          con.setHoldability(holdability);
      }
  
      @Override
      public int getHoldability() throws SQLException {
          return con.getHoldability();
      }
  
      @Override
      public Savepoint setSavepoint() throws SQLException {
          return con.setSavepoint();
      }
  
      @Override
      public Savepoint setSavepoint(String name) throws SQLException {
          return con.setSavepoint(name);
      }
  
      @Override
      public void rollback(Savepoint savepoint) throws SQLException {
          con.rollback(savepoint);
      }
  
      @Override
      public void releaseSavepoint(Savepoint savepoint) throws SQLException {
          con.releaseSavepoint(savepoint);
      }
  
      @Override
      public Statement createStatement(int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {
          return con.createStatement(resultSetType,resultSetConcurrency,resultSetHoldability);
      }
  
      @Override
      public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {
          return con.prepareStatement(sql,resultSetType,resultSetConcurrency,resultSetHoldability);
      }
  
      @Override
      public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {
          return con.prepareCall(sql,resultSetType,resultSetConcurrency,resultSetHoldability);
      }
  
      @Override
      public PreparedStatement prepareStatement(String sql, int autoGeneratedKeys) throws SQLException {
          return con.prepareStatement(sql,autoGeneratedKeys);
      }
  
      @Override
      public PreparedStatement prepareStatement(String sql, int[] columnIndexes) throws SQLException {
          return con.prepareStatement(sql,columnIndexes);
      }
  
      @Override
      public PreparedStatement prepareStatement(String sql, String[] columnNames) throws SQLException {
          return con.prepareStatement(sql,columnNames);
      }
  
      @Override
      public Clob createClob() throws SQLException {
          return con.createClob();
      }
  
      @Override
      public Blob createBlob() throws SQLException {
          return con.createBlob();
      }
  
      @Override
      public NClob createNClob() throws SQLException {
          return con.createNClob();
      }
  
      @Override
      public SQLXML createSQLXML() throws SQLException {
          return con.createSQLXML();
      }
  
      @Override
      public boolean isValid(int timeout) throws SQLException {
          return con.isValid(timeout);
      }
  
      @Override
      public void setClientInfo(String name, String value) throws SQLClientInfoException {
          con.setClientInfo(name,value);
      }
  
      @Override
      public void setClientInfo(Properties properties) throws SQLClientInfoException {
          con.setClientInfo(properties);
      }
  
      @Override
      public String getClientInfo(String name) throws SQLException {
          return con.getClientInfo(name);
      }
  
      @Override
      public Properties getClientInfo() throws SQLException {
          return con.getClientInfo();
      }
  
      @Override
      public Array createArrayOf(String typeName, Object[] elements) throws SQLException {
          return con.createArrayOf(typeName,elements);
      }
  
      @Override
      public Struct createStruct(String typeName, Object[] attributes) throws SQLException {
          return con.createStruct(typeName,attributes);
      }
  
      @Override
      public void setSchema(String schema) throws SQLException {
          con.setSchema(schema);
      }
  
      @Override
      public String getSchema() throws SQLException {
          return con.getSchema();
      }
  
      @Override
      public void abort(Executor executor) throws SQLException {
          con.abort(executor);
      }
  
      @Override
      public void setNetworkTimeout(Executor executor, int milliseconds) throws SQLException {
          con.setNetworkTimeout(executor,milliseconds);
      }
  
      @Override
      public int getNetworkTimeout() throws SQLException {
          return con.getNetworkTimeout();
      }
  
      @Override
      public <T> T unwrap(Class<T> iface) throws SQLException {
          return con.unwrap(iface);
      }
  
      @Override
      public boolean isWrapperFor(Class<?> iface) throws SQLException {
          return con.isWrapperFor(iface);
      }
  }

自定义连接类

通过适配器设计模式。完成close()方法的重写

定义一个类，继承适配器父类
定义 Connection 连接对象和连接池容器对象的变量
提供有参构造方法，接收连接对象和连接池对象，对变量赋值
在 close() 方法中，完成连接的归还

public class MyConnection3 extends MyAdapter {
      //2.定义Connection连接对象和连接池容器对象的变量
      private Connection con;
      private List<Connection> pool;
  
      //3.提供有参构造方法，接收连接对象和连接池对象，对变量赋值
      public MyConnection3(Connection con,List<Connection> pool) {
          super(con);    // 将接收的数据库连接对象给适配器父类传递
          this.con = con;
          this.pool = pool;
      }
  
      //4.在close()方法中，完成连接的归还
      @Override
      public void close() throws SQLException {
          pool.add(con);
      }
  }

自定义连接池类

public class MyDataSource implements DataSource{
      //定义集合容器，用于保存多个数据库连接对象
      private static List<Connection> pool = Collections.synchronizedList(new ArrayList<Connection>());
  
      //静态代码块，生成10个数据库连接保存到集合中
      static {
          for (int i = 0; i < 10; i++) {
              Connection con = JDBCUtils.getConnection();
              pool.add(con);
          }
      }
  
      //返回连接池的大小
      public int getSize() {
          return pool.size();
      }
  
      //从池中返回一个数据库连接
      @Override
      public Connection getConnection() {
          if(pool.size() > 0) {
              //从池中获取数据库连接
              Connection con = pool.remove(0);
  
              //通过自定义连接对象进行包装
              MyConnection3 mycon = new MyConnection3(con,pool);
  
              //返回包装后的连接对象
              return mycon;
          }else {
              throw new RuntimeException("连接数量已用尽");
          }
      }
  }

缺点：自定义连接类中的方法已经很简洁了。剩余所有的方法已经抽取到了适配器类中。但是适配器这个类还是我们自己编写的，也比较麻烦！所以可以使用动态代理的方式来改进。

动态代理

public class MyDataSource implements DataSource{
      //定义集合容器，用于保存多个数据库连接对象
      private static List<Connection> pool = Collections.synchronizedList(new ArrayList<Connection>());
  
      //静态代码块，生成10个数据库连接保存到集合中
      static {
          for (int i = 0; i < 10; i++) {
              Connection con = JDBCUtils.getConnection();
              pool.add(con);
          }
      }
  
      //返回连接池的大小
      public int getSize() {
          return pool.size();
      }
  
      //动态代理方式
      @Override
      public Connection getConnection() {
          if(pool.size() > 0) {
              //从池中获取数据库连接
              Connection con = pool.remove(0);
  
              Connection proxyCon = (Connection)Proxy.newProxyInstance(con.getClass().getClassLoader(), new Class[]{Connection.class}, new InvocationHandler() {
                  /*
                      执行Connection实现类所有方法都会经过invoke
                      如果是close方法，则将连接还回池中
                      如果不是，直接执行实现类的原有方法
                   */
                  @Override
                  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                      if(method.getName().equals("close")) {
                          pool.add(con);
                          return null;
                      }else {
                          return method.invoke(con,args);
                      }
                  }
              });
  
              return proxyCon;
          }else {
              throw new RuntimeException("连接数量已用尽");
          }
      }
  
  
      //从池中返回一个数据库连接
      /*@Override
      public Connection getConnection() {
          if(pool.size() > 0) {
              //从池中获取数据库连接
              Connection con = pool.remove(0);
  
              //通过自定义连接对象进行包装
              //MyConnection2 mycon = new MyConnection2(con,pool);
              MyConnection3 mycon = new MyConnection3(con,pool);
  
              //返回包装后的连接对象
              return mycon;
          }else {
              throw new RuntimeException("连接数量已用尽");
          }
      }*/
  }

开源连接池的使用

C3P0连接池

导入jar包
导入配置文件到src目录下
创建c3p0连接池对象
获取数据库连接进行使用

配置文件 c3p0-config.xml 注意该配置文件的名字是固定的不要改，否则无法识别

initialPoolSize ：初始化连接数量
maxPoolSize ：最大连接数量，当连接数量超过初始化连接数量时，会在连接池内继续创建连接，直到达到数据库连接池所能容纳的最大连接数量
checkoutTimeout ：超过时间。如果使用的连接数量超过最大连接数量，编译器会在 checkoutTimeout 时间以后报错并终止程序。

<c3p0-config>
  <!-- 使用默认的配置读取连接池对象 -->
  <default-config>
  	<!--  连接参数 -->
    <property name="driverClass">com.mysql.jdbc.Driver</property>
    <property name="jdbcUrl">jdbc:mysql://主机名:3306/数据库名</property>
    <property name="user">用户名</property>
    <property name="password">密码</property>
    
    <!-- 连接池参数 -->
    <!-- 初始化连接数量 -->
    <property name="initialPoolSize">5</property>
    <!--  最大连接数量  -->
    <property name="maxPoolSize">10</property>
    <!--  超时时间  -->
    <property name="checkoutTimeout">3000</property>
  </default-config>


  <!--  创建数据库连接池时指定名称-->
  <named-config name="otherc3p0"> 
    <!--  连接参数 -->
    <property name="driverClass">com.mysql.jdbc.Driver</property>
    <property name="jdbcUrl">jdbc:mysql://主机名:3306/数据库名</property>
    <property name="user">用户名</property>
    <property name="password">密码</property>
    
    <!-- 连接池参数 -->
    <property name="initialPoolSize">5</property>
    <property name="maxPoolSize">8</property>
    <property name="checkoutTimeout">1000</property>
  </named-config>
</c3p0-config>

C3P0数据库连接池的使用

public static void main(String[] args) throws SQLException {
        //创建c3p0连接池对象
        DataSource dataSource = new ComboPooledDataSource();
        //获取数据库连接进行使用
        Connection con = dataSource.getConnection();
        String s = "select *from emp";
        PreparedStatement pst = con.prepareStatement(s);
        ResultSet rs = pst.executeQuery();
        while (rs.next()) {
            String ename = rs.getString("ename");
            String job = rs.getString("job");
            String hiredate = rs.getString("hiredate");
            System.out.println("ename:" + ename + " job:" + job + " hiredate:" + hiredate);
        }
        rs.close();
        pst.close();
        con.close(); // 将连接对象归还池中
    }

Druid连接池

导入jar包
编写配置文件，放在src目录下
通过Properties集合加载配置文件
通过Druid连接池工厂类获取数据库连接池对象
获取数据库连接，进行使用

配置文件 druid.properties

driverClassName=com.mysql.jdbc.Driver
url=jdbc:mysql://主机名:3306/数据库名
username:用户名
password:密码
# 初始连接数量
initialSize=5
# 最大连接数量
maxActive=10
# 最长等待时间
maxWait=3000

Druid数据库的使用

public static void main(String[] args) throws Exception {
        //通过Properties集合加载配置文件
        InputStream is = demo01.class.getClassLoader().getResourceAsStream("druid.properties");
        Properties prop = new Properties();
        prop.load(is);
        //通过Druid连接池工厂类获取数据库连接池对象
        DataSource dataSource = DruidDataSourceFactory.createDataSource(prop);
        //获取数据库连接，进行使用
        Connection con = dataSource.getConnection();
        PreparedStatement pst = con.prepareStatement("select *from emp");
        ResultSet rs = pst.executeQuery();
        while (rs.next()) {
            String ename = rs.getString("ename");
            String job = rs.getString("job");
            String hiredate = rs.getString("hiredate");
            System.out.println("ename:" + ename + " job:" + job + " hiredate:" + hiredate);
        }
        rs.close();
        pst.close();
        con.close();
    }

抽取工具类

/*
      数据库连接池工具类
   */
  public class DataSourceUtils {
      //1.私有构造方法
      private DataSourceUtils(){}
  
      //2.定义DataSource数据源变量
      private static DataSource dataSource;
  
      //3.提供静态代码块，完成配置文件的加载和获取连接池对象
      static {
          try{
              //加载配置文件
              InputStream is = DruidDemo1.class.getClassLoader().getResourceAsStream("druid.properties");
              Properties prop = new Properties();
              prop.load(is);
  
              //获取数据库连接池对象
              dataSource = DruidDataSourceFactory.createDataSource(prop);
  
          } catch(Exception e) {
              e.printStackTrace();
          }
      }
  
      //4.提供获取数据库连接的方法
      public static Connection getConnection() {
          Connection con = null;
          try {
              con = dataSource.getConnection();
          } catch (SQLException e) {
              e.printStackTrace();
          }
          return con;
      }
  
      //5.提供获取数据库连接池的方法
      public static DataSource getDataSource() {
          return dataSource;
      }
  
      //6.提供释放资源的方法
      public static void close(Connection con, Statement stat, ResultSet rs) {
          if(con != null) {
              try {
                  con.close();
              } catch (SQLException e) {
                  e.printStackTrace();
              }
          }
  
          if(stat != null) {
              try {
                  stat.close();
              } catch (SQLException e) {
                  e.printStackTrace();
              }
          }
  
          if(rs != null) {
              try {
                  rs.close();
              } catch (SQLException e) {
                  e.printStackTrace();
              }
          }
      }
  
      public static void close(Connection con, Statement stat) {
          close(con,stat,null);
      }
  
  }

工具类的使用

public static void main(String[] args) throws SQLException {
        //利用工具类获取DataSoure
        DataSource dataSource = DataSourceUtils.getDataSource();
        //获取连接，并使用
        Connection con = dataSource.getConnection();
        String s = "select *from emp";
        PreparedStatement pst = con.prepareStatement(s);
        ResultSet rs = pst.executeQuery();
        while (rs.next()) {
            String ename = rs.getString("ename");
            String job = rs.getString("job");
            String hiredate = rs.getString("hiredate");
            System.out.println("ename:" + ename + " job:" + job + " hiredate:" + hiredate);
        }
        DataSourceUtils.close(con, pst, rs);
    }

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