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);

    }

巴特西

【MySQL】自定义数据库连接池和开源数据库连接池的使用